U.S. patent application number 10/026732 was filed with the patent office on 2002-06-27 for processes for producing b-halogeno-a-amino-carboxylic acids and phenylcysteine derivatives and intermediates thereof.
Invention is credited to Inoue, Kenji, Kinoshita, Koichi, Murao, Hiroshi, Ueda, Yasuyoshi, Yamashita, Koki.
Application Number | 20020082450 10/026732 |
Document ID | / |
Family ID | 27325723 |
Filed Date | 2002-06-27 |
United States Patent
Application |
20020082450 |
Kind Code |
A1 |
Yamashita, Koki ; et
al. |
June 27, 2002 |
Processes for producing B-halogeno-a-amino-carboxylic acids and
phenylcysteine derivatives and intermediates thereof
Abstract
An industrially advantageous method of producing
.beta.-halogeno-.alpha.-a- minocarboxylic acids is provided.
Methods are also provided of producing optically active
N-protected-S-phenylcysteines having high optical purity and of
intermediates thereof, respectively, in which the above production
method is utilized. A method of producing
.beta.-halogeno-.alpha.-aminocarboxylic acids or salts thereof is
disclosed which comprises halogenating the hydroxyl group of a
.beta.-hydroxy-.alpha.-aminocarboxylic acid (in which the basicity
of the amino group in .alpha.-position is not masked by the
presence of a substituent on said amino group) or a salt thereof
with an acid with a halogenating agent. A method of producing
optically active N-protected-S-phenylcysteines represented by the
general formula (3) or salts thereof is further disclosed which
comprises applying the above production method to optically active
serine or a salt thereof and then carrying out treatment with an
amino-protecting agent and reaction with thiophenol under a basic
condition. 1
Inventors: |
Yamashita, Koki; (Kobe-shi,
JP) ; Inoue, Kenji; (Kakogawa-shi, JP) ;
Kinoshita, Koichi; (Takasago-shi, JP) ; Ueda,
Yasuyoshi; (Himeji-shi, JP) ; Murao, Hiroshi;
(Takasago-shi, JP) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ LLP
SUITE 800
1990 M STREET NW
WASHINGTON
DC
20036-3425
US
|
Family ID: |
27325723 |
Appl. No.: |
10/026732 |
Filed: |
December 27, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10026732 |
Dec 27, 2001 |
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09582461 |
Aug 16, 1999 |
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09582461 |
Aug 16, 1999 |
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PCT/JP98/05983 |
Dec 28, 1998 |
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Current U.S.
Class: |
562/574 |
Current CPC
Class: |
C07C 319/14 20130101;
Y02P 20/55 20151101; C07C 227/16 20130101; C07C 319/14 20130101;
C07C 323/58 20130101; C07C 319/14 20130101; C07C 323/59 20130101;
C07C 227/16 20130101; C07C 229/20 20130101 |
Class at
Publication: |
562/574 |
International
Class: |
C07C 229/06 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 1997 |
JP |
9/367814 |
Jul 1, 1998 |
JP |
10/186314 |
Sep 18, 1998 |
JP |
10/264397 |
Claims
1. A method of producing a .beta.-halogeno-.alpha.-aminocarboxylic
acid or a salt thereof which comprises halogenating the hydroxyl
group of a .beta.-hydroxy-.alpha.-aminocarboxylic acid, in which
the basicity of the amino group in .alpha.-position is not masked
by the presence of a substituent on said amino group, or a salt
thereof with an acid by treating the same with a halogenating
agent.
2. The method of producing according to claim 1, wherein the
halogenating agent is a thionyl halide.
3. The method of producing according to claim 2, wherein the
thionyl halide is thionyl chloride.
4. The method of producing according to claim 1, 2 or 3, wherein
the halogenating agent is used in an amount of 1 to 10 moles per
mole of the .beta.-hydroxy-.alpha.-aminocarboxylic acid
5. The method of producing according to any of claims 1 to 4,
wherein the treatment with the halogenating agent is carried out
using a solvent containing an ether type solvent.
6. The method of producing according to claim 5, wherein the ether
type solvent is miscible with water.
7. The method of producing according to claim 6, wherein the
water-miscible ether type solvent comprises at least one species
from the group consisting of 1,2-dimethoxyethane, 1,4-dioxane,
tetrahydrofuran, diethylene glycol dimethyl ether, triethylene
glycol dimethyl ether, tetraethylene glycol dimethyl ether and
polyethylene glycol dimethyl ether.
8. The method of producing according to any of claims 1 to 7,
wherein the treatment with the halogenating agent is carried out in
the presence of a hydrogen halide.
9. The method of producing according to claim 8, wherein the
hydrogen halide is used in an amount exceeding 2.0 molar
equivalents relative to the .beta.-hydroxy-.alpha.-aminocarboxylic
acid.
10. The method of producing according to claim 8 or 9, wherein the
treatment with the halogenating agent is carried out in a state
completely saturated or almost saturated with the hydrogen halide
gas.
11. The method of producing according to claim 8, 9 or 10, wherein
the hydrogen halide is hydrogen chloride.
12. The method of producing according to any of claims 1 to 11,
wherein the treatment with the chlorinating agent is carried out in
the presence of an amine or a salt thereof.
13. The method of producing according to claim 12, wherein the
amine is a tertiary amine.
14. The method of producing according to any of claims 1 to 13,
wherein the coexisting acid after treatment with the halogenating
agent is converted to a salt form by means of a basic lithium
compound, and dissolved in a medium composed of a water-miscible
organic solvent and water while the
.beta.-halogeno-.alpha.-aminocarboxylic acid is caused to
precipitate out in its free form.
15. The method of producing according to claim 14, wherein the
water-miscible ether type solvent comprises at least one species
selected from the group consisting of 1,2-dimethoxyethane,
1,4-dioxane, tetrahydrofuran, diethylene glycol dimethyl ether,
triethylene glycol dimethyl ether, tetraethylene glycol dimethyl
ether, polyethylene glycol dimethyl ether, acetonitrile, methanol,
ethanol, n-propanol, isopropanol, tert-butanol and acetone.
16. The method of producing according to claim 15, wherein the
water-miscible organic solvent is acetone.
17. The method of producing according to claim 14, 15 or 16,
wherein the volume ratio of the water-miscible organic solvent to
water is not less than 1.
18. The method of producing according to any of claims 14 to 17,
wherein the final cooling temperature in the step of precipitation
is not higher than 10.degree. C.
19. The method of producing according to any of claims 14 to 18,
wherein the low-boiling components occurring in the reaction
mixture are reduced or removed beforehand after treatment with the
halogenating agent but before precipitation of the desired
product.
20. The method of producing according to any of claims 1 to 13,
wherein, after treatment with the halogenating agent, the
.beta.-halogeno-.alpha.-- aminocarboxylic acid in hydrohalogenic
acid salt form that has precipitated from the reaction mixture as
such or after concentration thereof is recovered.
21. The method of producing according to any of claims 1 to 13,
wherein, after treatment with the halogenating agent, the reaction
solvent is replaced with water to give an aqueous solution
containing the .beta.-halogeno-.alpha.-aminocarboxylic acid.
22. The method of producing according to any of claims 1 to 21,
wherein the .beta.-hydroxy-.alpha.-aminocarboxylic acid is serine,
threonine, allothreonine or .beta.-phenylserine.
23. The method of producing according to claim 22, wherein the
.beta.-hydroxy-.alpha.-aminocarboxylic acid is serine.
24. The method of producing according to any of claims 1 to 23,
wherein the .beta.-hydroxy-.alpha.-aminocarboxylic acid is
optically active.
25. The method of producing according to claim 23 or 24, wherein
the .beta.-hydroxy-.alpha.-aminocarboxylic acid is L-serine.
26. A method of purifying and isolating a
.beta.-halogeno-.alpha.-aminocar- boxylic acid which comprises
causing a .beta.-halogeno-.alpha.-aminocarbox- ylic acid, in which
the basicity of the amino group in .alpha.-position is not masked
by the presence of a substituent on said amino group, to
crystallize out using water as a good solvent and a water-miscible
organic solvent as a poor solvent.
27. The method of purifying and isolating a
.beta.-halogeno-.alpha.-aminoc- arboxylic acid according to claim
26, wherein the water-miscible organic solvent is acetone.
28. The method of purifying and isolating a
.beta.-halogeno-.alpha.-aminoc- arboxylic acid according to claim
27, wherein acetone is used as a poor solvent for causing the
.beta.-halogeno-.alpha.-aminocarboxylic acid to crystallize and
precipitate out in its free form from an aqueous solution resulting
from treatment of an aqueous solution containing the
.beta.-halogeno-.alpha.-aminocarboxylic acid and hydrohalogenic
acid with a basic lithium compound for converting said
hydrohalogenic acid to the salt thereof.
29. The method of purifying and isolating a
.beta.-halogeno-.alpha.-aminoc- arboxylic acid according to claim
26, 27 or 28, wherein the volume ratio of the water-miscible
organic solvent to water in the step of crystallization is not less
than
30. The method of purifying and isolating a
.beta.-halogeno-.alpha.-aminoc- arboxylic acid according to any of
claims 26 to 29, wherein the final cooling temperature in the step
of crystallization is not higher than 10.degree. C.
31. The method of purifying and isolating a
.beta.-halogeno-.alpha.-aminoc- arboxylic acid according to any of
claims 26 to 30, wherein the
.beta.-halogeno-.alpha.-aminocarboxylic acid is
.beta.-chloroalanine, .beta.-chloro-.alpha.-aminobutyric acid or
.beta.-chloro-.beta.-phenyl-.a- lpha.-aminopropionic acid.
32. The method of purifying and isolating a
.beta.-halogeno-.alpha.-aminoc- arboxylic acid according to claim
31, wherein the -halogeno-.alpha.-aminoc- arboxylic acid is
.beta.-chloroalanine.
33. The method of purifying and isolating a
.beta.-halogeno-.alpha.-aminoc- arboxylic acid according to any of
claims 26 to 32, wherein the
.beta.-halogeno-.alpha.-aminocarboxylic acid is optically
active.
34. The method of purifying and isolating a
.beta.-halogeno-.alpha.-aminoc- arboxylic acid according to claim
32 or 33, wherein the .beta.-halogeno-.alpha.-aminocarboxylic acid
is .beta.-chloro-L-alanine.
35. A method of producing an optically active
N-protected-.beta.-chloroala- nine of the general formula (2) or a
salt thereof: 5wherein R.sup.1 represents an amino-protecting group
and R.sup.0 represents a hydrogen atom or, taken together with
R.sup.1, an amino-protecting group, which comprises preparing an
optically active .beta.-chloroalanine of the following formula (1)
or a salt thereof: 6from an optically active serine or a salt
thereof with an acid by the method of producing according to claim
1 and then treating the same with an amino-protecting agent.
36. The method of producing according to claim 35, wherein the
optically active .beta.-chloroalanine is obtainable by the method
of producing according to any of claims 2 to 25,
37. The method of producing according to claim 35 or 36, wherein
the amino-protecting agent is benzyl chloroformate and the
optically active N-protected-.beta.-chloroalanine is represented by
the general formula (2) in which R.sup.0 is a hydrogen atom and
R.sup.1 is a carbobenzyloxy group.
38. A method of producing an optically active
N-protected-S-phenylcysteine of the general formula (3) or a salt
thereof: 7wherein R.sup.1 represents an amino-protecting group and
R.sup.0 represents a hydrogen atom or, taken together with R.sup.1,
an amino-protecting group, which comprises preparing an optically
active N-protected-.beta.-chloroalanine or a salt thereof by the
method of producing according to claim 35, and then reacting the
same with thiophenol under a basic condition.
39. The method of producing according to claim 38, wherein the
optically active N-protected-.beta.-chloroalanine is obtainable by
the method of producing according to claim 36.
40. The method of producing according to claim 38 or 39, wherein
the amino-protecting agent is benzyl chloroformate and the
optically active N-protected-S-phenylcysteine is represented by the
general formula (3) in which R.sup.0 is a hydrogen atom and R.sup.1
is a carbobenzyloxy group.
41. The method of producing according to any of claims 38 to 40,
wherein the treatment of optically active serine or a salt of
optically active serine with an acid with the chlorinating agent,
the treatment with the amino-protecting agent and the
thiophenylation are carried out without isolating the respective
intermediates.
42. A method of producing an optically active
N-protected-S-phenylcysteine of the general formula (3) or a salt
thereof, 8wherein R.sup.1 represents an amino-protecting group and
R.sup.0 represents a hydrogen atom or, taken together with R.sup.1,
an amino-protecting group, which comprises treating an optically
active .beta.-chloroalanine or a salt thereof with an
amino-protecting agent and then reacting the thus-prepared
optically active N-protected-.beta.-chloroalanine of the general
formula (2) or a salt thereof with thiophenol under a basic
condition, 9wherein R.sup.1 represents an amino-protecting group
and R.sup.0 represents a hydrogen atom or, taken together with
R.sup.1, an amino-protecting group.
43. The method of producing according to claim 42, wherein the
amino-protecting agent is benzyl chloroformate and the optically
active N-protected-.beta.-chloroalanine and optically active
N-protected-S-phenylcysteine are represented by the general formula
(2) and the general formula (3), respectively, in which R.sup.0 is
a hydrogen atom and R.sup.1 is a carbobenzyloxy group.
44. The method of producing according to claim 42 or 43, wherein
the treatment with amino-protecting agent and the thiophenylation
are carried out without isolating the respective intermediates.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method of producing a
.beta.-halogeno-.alpha.-aminocarboxylic acid or a salt thereof,
which is useful as a raw material for the production of medicinals,
among others. The invention also relates to a method of producing
an optically active N-protected S-phenyl-L-cysteine or a salt
thereof, which is useful as an intermediate of medicinals, in
particular anti-AIDS drugs, and to a method of producing an
intermediate thereof.
BACKGROUND ART
[0002] The following methods, among others, are known for producing
.beta.-halogeno-.alpha.-aminocarboxylic acids:
[0003] (1) The method which comprises derivatizing a
.beta.-hydroxy-.alpha.-aminocarboxylic acid into the corresponding
.beta.-hydroxy-.alpha.-aminocarboxylic acid ester, then
halogenating the hydroxyl group thereof with a phosphorus halide to
give the corresponding .beta.-halogeno-.alpha.-aminocarboxylic acid
ester, and hydrolyzing the ester group using a hydrohalogenic acid
to give the objective .beta.-halogeno-.alpha.-aminocarboxylic acid.
Specifically, serine is derivatized into serine methyl ester
hydrochloride, the ester salt is then treated with phosphorus
pentachloride to give .alpha.-amino-.beta.-chloropropionic acid
methyl ester hydrochloride, which is further hydrolyzed with
hydrochloric acid. The resulting
.alpha.-amino-.beta.-chloropropionic acid hydrochloride is isolated
by concentrating the reaction mixture to dryness, followed by
crystallization of the residue from a mixture of 1-propanol and
hydrochloric acid [e.g. CHIRALITY, 8:197-200 (1996)]; and
[0004] (2) The method which comprises treating .beta.-phenylserine
monohydrate with thionyl chloride and then with concentrated
hydrochloric acid to give .beta.-chloro-.beta.-phenylalanine
[Gazzetta Chimica Italiana, 119 (1989) p. 215].
[0005] However, in the above method (1), the halogenation of the
hydroxyl group in .beta.position usually involves three reaction
steps, namely protection of the carboxyl group, halogenation of the
hydroxyl group in .beta.position and deprotection of the carboxyl
group. In this case, many difficulties are encountered, for example
the multiplicity of steps required, procedural complexity and low
yields.
[0006] In the above method (2), such difficulties arise as the use
of thionyl chloride in large amounts for the same to serve also as
a solvent and the resulting complicatedness of procedure. As a
result of investigations made by the present inventors, it was
further found that the method is hardly applicable to the
chlorination of serine, threonine or the like.
[0007] Thus, no efficient technology has been established for
producing .beta.-halogeno-.alpha.-aminocarboxylic acids on a
commercial scale.
[0008] On the other hand, such methods of producing optically
active S-phenylcysteine derivatives as mentioned below are known in
the art:
[0009] <Derivatization from serine>
[0010] 1) The method comprising reacting serine with thiophenol in
the presence of tryptophan synthase (EP 754759);
[0011] 2) The method which involves lactonization of a serine
derivative with an azodicarboxylic acid ester [J. Am. Chem. Soc.,
1985, vol. 107, p. 7105; Synth. Commun., 1995, vol. 25 (16), p.
2475];
[0012] 3) The method comprising converting the hydroxyl group of an
N-protected serine ester derivative to a sulfonyloxy group and
substituting a thiophenyl group therefor [Tetrahedron Lett., 1987,
vol. 28, p. 6069; ibid., 1993, vol. 34, p. 6607; EP 604185 A1];
[0013] <Derivatization from starting compounds other than
serine>
[0014] 4) The method comprising reacting cysteine with a
phenyldiazonium salt in the presence of a copper salt [J. Org.
Chem., 1958, vol. 23, p. 1251];
[0015] 5) The method comprising derivatizing from an
aziridinecarboxylic acid derivative in the presence of boron
trifluoride-ethyl ether complex [Bull. Chem. Soc. Jpn, 1983, vol.
56, p. 520];
[0016] 6) The method comprising reacting cysteine with iodobenzene
in the presence of a copper salt [Aust. J. Chem., 1985, vol. 38, p.
899]; and
[0017] 7) The method comprising reacting dehydroalanine with a
chiral nickel complex [Tetrahedron, 1988, vol. 44, p. 5507].
[0018] Since optically active serine, in particular L-serine, is a
readily available compound, a practical method would be provided if
the starting material L-serine could be converted efficiently to an
optically active S-phenylcysteine derivative. However, the method
1), in which a particular enzyme is utilized, and the method 2), in
which a lactone derivative is used as an intermediate, have
problems from the viewpoint of operability, productivity, safety in
reagents handling, and economy, among others. The method 3), in
which the hydroxyl group of an N-protected serine ester derivative
is converted to a sulfonyloxy group and the resulting product is
then subjected to substitution reaction using the sodium salt of a
thiol in N,N-dimethylformamide, is also disadvantageous in that
because it involves the use of a reagent relatively difficult to
handle, for example sodium hydride or potassium hydride, as a base,
it does not always give the desired N-protected S-phenylcysteine
ester in high yield and, in particular, the optical purity is
decreased, as revealed by a study made by the present
inventors.
[0019] On the other hand, the methods 4) through 7), which comprise
derivatization from other starting compounds than serine, cannot be
said to be industrially advantageous, either, since, for example,
the waste treatment is troublesome, materials requiring caution in
handling or expensive materials are used and the yield and
productivity are low.
[0020] In view of the above state of the art, the primary object of
the present invention is to provide a method of producing
.beta.-halogeno-.alpha.-aminocarboxylic acids in an industrially
advantageous manner and a method of producing optically active
S-phenylcysteine derivatives from optically active serine, which is
readily available commercially, in an industrially advantageous
manner.
SUMMARY OF THE INVENTION
[0021] As a result of their intensive investigations made in an
attempt to develop an industrially advantageous method of producing
.beta.-halogeno-.alpha.-aminocarboxylic acids, the present
inventors have surprisingly found an industrially advantageous
production method according to which
.beta.-halogeno-.alpha.-aminocarboxylic acids can be synthesized in
an efficient manner by treating a .beta.-hydroxy-.alpha.-a-
minocarboxylic acid or a salt thereof with an acid with a
halogenating agent.
[0022] On the other hand, in efficiently producing optically active
S-phenylcysteine derivatives from optically active serine, namely
L- or D-serine, the point is how to prevent the optical purity from
decreasing in thiophenylating the activated compound derived from
optically active serine by converting its hydroxyl group to a
leaving group. The present inventors thought that there would be
the possibility of attaining the above object in an industrially
advantageous manner while preventing racemization if an adequately
activated carboxylic acid derivative could be synthesized from
optically active serine by activating the hydroxyl group thereof in
the form of a leaving group and if the thiophenylation could be
realized efficiently. Based on this way of thinking, theymade
intensive investigations and, as a result, found that optically
active .beta.-chloroalanine can be synthesized in an efficient
manner when the above method of producing
.beta.-halogeno-.alpha.-aminocarboxylic acids is utilized. There
are no prior art findings teaching or suggesting that optically
active .beta.-chloroalanine can be produced by directly
chlorinating optically active serine or a salt thereof. The
relevant method of production is thus novel.
[0023] In addition, it was found that the optically active
.beta.-chloroalanine obtained in the above manner can be converted
to an optically active N-protected-.beta.-chloroalanine by
treatment with an amino-protecting agent and that said compound can
be converted to an optically active N-protected-S-phenylcysteine by
reacting with thiophenol under a basic condition. Based on these
and other findings, the present invention has now been completed.
Particularly when the above three-step process is used, optically
active N-protected-S-phenylcysteine derivatives can be produced in
an industrially advantageous manner without any substantial
reduction in the optical purity of the starting material, namely
optically active L- or D-serine.
[0024] Thus, the present invention relates to a method of producing
a .beta.-halogeno-.alpha.-aminocarboxylic acid or a salt
thereof
[0025] which comprises halogenating the hydroxyl group of a
.beta.-hydroxy-.alpha.-aminocarboxylic acid (in which the basicity
of the amino group in .alpha.-position is not masked by the
presence of a substituent on said amino group) or a salt thereof
with an acid by treating the same with a halogenating agent.
[0026] The present invention also relates to a method of producing
an optically active N-protected-.beta.-chloroalanine of the general
formula (2) or a salt thereof according to the above method of
production: 2
[0027] wherein R.sup.1 represents an amino-protecting group and
R.sup.0 represents a hydrogen atom or, taken together with R.sup.1,
an amino-protecting group,
[0028] namely by preparing an optically active .beta.-chloroalanine
of the formula (1) or a salt thereof: 3
[0029] from an optically active serine or a salt thereof with an
acid, and then treating the same with an amino-protecting
agent.
[0030] The present invention further provides a method of producing
an optically active N-protected-S-phenylcysteine of the general
formula (3) or a salt thereof: 4
[0031] wherein R.sup.1 represents an amino-protecting group and
R.sup.0 represents a hydrogen atom or, taken together with R.sup.1,
an amino-protecting group,
[0032] which comprises preparing an optically active
N-protected-.beta.-chloroalanine or a salt thereof according to the
production method mentioned above and then reacting the same with
thiophenol under a basic condition.
[0033] In the following, the invention is described in detail.
DETAILED DISCLOSURE OF THE INVENTION
[0034] The .beta.-hydroxy-.alpha.-aminocarboxylic acid to be used
in the practice of the invention is not particularly restricted
but, basically, is one whose amino group retains its basicity
without being masked by the presence of a substituent thereon, for
example an acyl type amino-protecting group. The basic skeleton of
the above .beta.-hydroxy-.alpha.-aminocarboxylic acid is
.alpha.-amino-.beta.-hydro- xypropionic acid (also called serine),
and one, two or three of the three hydrogen atoms on the carbon
chain other than those of the amino, hydroxyl and carboxyl groups
of the basic skeleton may be substituted with another group or
other groups unless the halogenation reaction is adversely
affected. Further, one or two of the hydrogen atoms of the above
amino group may be substituted with a substituent or substituents
(e.g. alkyl, aralkyl, aryl, etc.) unless the halogenation reaction
is adversely affected and unless the basicity of the amino group is
jeopardized.
[0035] As typical examples of the
.beta.-hydroxy-.alpha.-aminocarboxylic acid, there may be
mentioned, among others, serine, threonine, allothreonine,
.beta.-phenylserine and the like. The salt of the
.beta.-hydroxy-.alpha.-aminocarboxylic acid with an acid is not
particularly restricted, either, but includes, among others, such
salts as serine hydrochloride, threonine hydrochloride,
allothreonine hydrochloride and .beta.-phenylserine hydrochloride.
The above salt may be prepared and isolated in advance, or may be
prepared in the reaction vessel or formed during reaction. When
these .beta.-hydroxy-.alpha.-amino- carboxylic acids are used, the
products are .beta.-halogeno-.alpha.-aminop- ropionic acids (i.e.
.beta.-haloalanines), .beta.-halogeno-.alpha.-aminobu- tyric acids,
.beta.-halogeno-.beta.-phenyl-.alpha.-aminopropionic acids (i.e.
.beta.-halophenylalanines), etc. It is a matter of course that the
above .beta.-hydroxy-.alpha.-aminocarboxylic acids may be used in
an optically active form.
[0036] The halogenating agent to be used in the practice of the
invention includes, among others, thionyl halides and phosphorus
halides, specifically thionyl chloride, thionyl bromide, phosphorus
pentachloride, phosphorus trichloride, phosphorus oxychloride,
phosphorus tribromide, etc. From the viewpoint of reaction yield
and ease of handling, however, thionyl halides are preferred, in
particular thionyl chloride is most preferred. The above
halogenating agent is used in an amount of, for example 1 to 10
moles, preferably 1 to 4 moles, more preferably 1 to 2 moles, per
mole of the substrate .beta.-hydroxy-.alpha.-aminocarboxylic acid
or a salt thereof with an acid. Basically, the above amount is the
number of moles of the basic skeletal unit of the
S-hydroxy-.alpha.-amino- carboxylic acid and, in cases where a
plurality of such basic skeletal units as mentioned above are
contained in each molecule or where the another or other
substituents consume the halogenating agent or a group consuming
said agent is contained, for instance, it is considered necessary
to increase the amount of the halogenation agent by the
corresponding equivalent amount.
[0037] The treatment with the halogenating agent in the production
method of the present invention is preferably carried out in a
solvent. Preferred as the solvent in that case are, for example,
1,2-dimethoxyethane, 1,4-dioxane, tetrahydrofuran, diethylene
glycol dimethyl ether, triethylene glycol dimethyl ether,
tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl
ether, tert-butyl methyl ether, dibutyl ether, diethyl ether and
like ether solvents; acetonitrile, methylene chloride, ethyl
acetate and other aprotic solvents. These maybe used singly or two
or more of them may be used combinedly. Among them, ether solvents
are preferred and, in particular, ether solvents miscible with
water, such as 1,2-dimethoxyethane, 1,4-dioxane, tetrahydrofuran,
diethylene glycol dimethyl ether, triethylene glycol dimethyl
ether, tetraethylene glycol dimethyl ether and polyethylene glycol
dimethyl ether, are more preferred. It is of course possible to use
another solvent or other solvents within limits within which no
adverse effect is produced.
[0038] The treatment with the above halogenating agent can be
carried out in the presence of an amine or a salt thereof. The
amine or the salt thereof is not particularly restricted but
includes, for example, triethylamine, trimethylamine,
diisopropylethylamine, tetramethylethylenediamine, pyridine,
dimethylaminopyridine, imidazole, triethylamine hydrochloride,
trimethylamine hydrochloride, diisopropylethylamine hydrochloride
and the like. Among them, tertiary amines such as trimethylamine
and triethylamine or salts thereof are preferred. More preferred is
triethylamine or its hydrochloride.
[0039] The above amine or its salt is added preferably in an amount
of 0.1 to 30 mole percent, more preferably 1 to 10 mole percent,
based on the substrate .beta.-hydroxy-.alpha.-aminocarboxylic acid
or a salt thereof.
[0040] In a mode of practice of the present invention which is more
preferred in attempting to attain a higher reaction yield, the
treatment with the above halogenating agent, preferably thionyl
chloride, is carried out in the presence of a hydrogen halide,
preferably hydrogen chloride (gas). The hydrogen halide is used in
an amount of, for example, not less than about 1 molar equivalent,
preferably an amount exceeding 2.0 molar equivalents, more
preferably an amount of not less than about 3 molar equivalents,
based on the .beta.-hydroxy-.alpha.-aminocarboxylic acid.
Generally, by using the hydrogen halide in an amount of about 3 to
10 molar equivalents, it is possible to carry out the above
treatment very smoothly. Like the case mentioned above, it is
fundamentally understood that the amount mentioned above
corresponds to the number of molar equivalents per basic skeletal
unit of the .beta.-hydroxy-.alpha.-a- minocarboxylic acid (the
hydrohalogenic acid salt of a
.beta.-hydroxy-.alpha.-aminocarboxylic acid corresponds to the
presence of 1.0 molar equivalent of the corresponding hydrogen
halide relative to the .beta.-hydroxy-.alpha.-aminocarboxylic
acid). The concentration of the hydrogen halide in the reaction
mixture is, for example, not less than about 1 mole, preferably not
less than about 2 moles, more preferably not less than about 3
moles, per liter of solvent. The above treatment can be carried out
smoothly at a hydrogen halide concentration not higher than the
saturated concentration in the reaction system. The above treatment
may be carried out in the presence of an amine or a salt
thereof.
[0041] Referring specifically to a simple reaction procedure taken
as an example, a suspension composed of a
.beta.-hydroxy-.alpha.-aminocarboxyli- c acid (e.g. L-serine) and
1,4-dioxane, for instance, is almost or completely saturated with
hydrogen chloride gas, thionyl chloride is then added and, after
completion of the addition, the mixture is moderaly or vigorously
stirred preferably at room temperature to 100.degree. C., more
preferably at 40.degree. to 80.degree. C., preferably for 0.5 to 30
hours, more preferably for 1 to 20 hours, to give the corresponding
.beta.-chloro-(-aminocarboxylic acid [e.g.
L-.alpha.-amino-.beta.-chlorop- ropionic acid (also called
.beta.-chloro-L-alanine)].
[0042] The .beta.-halogeno-.alpha.-aminocarboxylic acid obtained by
the above halogenation may be isolated prior to the use in the next
step or may be used without isolation.
[0043] The above .beta.-halogeno-.alpha.-aminocarboxylic acid may
be isolated, for example, by such a technique as column
chromatography commonly used in isolating amino acids. Said acid
can be isolated in a simple and efficient manner by the method
mentioned below, however.
[0044] For isolating the above
.beta.-halogeno-.alpha.-aminocarboxylic acid in the form of a
hydrohalogenic acid salt, for example hydrochloride, after
completion of the reaction, during which the precipitation of the
desired product proceeds (namely reaction/crystallization proceeds)
with the progress of the treatment with the above halogenating
agent, the reaction mixture is subjected, either as such or after
concentration, to conventional treatment for solid-liquid
separation, such as filtration or centrifugation, whereby the
desired product can be recovered in a very simple manner and in
high yields. In the step of isolation, it is of course possible to
reduce the content of or remove those relatively low boiling
components remaining in the reaction mixture after the halogenation
reaction, such as sulfur dioxide, the excess hydrogen halide (e.g.
hydrogen chloride) and the unreacted halogenating agent (e.g.
thionyl halide), in advance, according to need. By concentrating
the reaction mixture, it is also possible to recover the reaction
solvent.
[0045] For isolating the above
.beta.-halogeno-.alpha.-aminocarboxylic acid in the free form, the
acid coexisting in the reaction mixture after the halogenation
reaction is converted to a salt, preferably a salt soluble in an
organic solvent and water (e.g. lithium halide such as lithium
chloride) using a base, -preferably a basic lithium compound such
as lithium hydroxide or lithium carbonate, for instance, and the
above .beta.-halogeno-.alpha.-aminocarboxylic acid is caused to
crystallize out from an organic solvent, water or a medium composed
of an organic solvent and water while causing dissolution of the
above resulting salt in such medium. The subsequent separation
using a conventional solid-liquid separation procedure, such as
filtration or centrifugation, gives the desired product in a simple
and convenient manner. Since, generally, the conversion of acids to
salts is preferably carried out in the presence of water, it is
desirable to attempt to reduce the solubility of the
.beta.-halogeno-.alpha.-aminocarboxylic acid, which is a
water-soluble compound, or, in other words, increase the
precipitate amount, by using a water-miscible organic solvent as
said organic solvent.
[0046] The above water-miscible organic solvent specifically
includes, but is not limited to, 1,2-dimethoxyethane, 1,4-dioxane,
tetrahydrofuran, diethylene glycol dimethyl ether, triethylene
glycol dimethyl ether, tetraethylene glycol dimethyl ether,
polyethylene glycol dimethyl ether, acetonitrile, methanol,
ethanol, n-propanol, isopropanol, tert-butanol and acetone, among
others. Among these, acetone, in particular, is preferred from the
viewpoint of increased precipitation of water-soluble
.beta.-halogeno-.alpha.-aminocarboxylic acids, production of
crystals having good characteristics, ease of handling and
inexpensiveness, among others.
[0047] Since the above .beta.-halogeno-.alpha.-aminocarboxylic acid
has a high solubility in water, it is desirable, for attaining
increased precipitation, to reduce the amount of water, use the
above water-miscible organic solvent in a volume ratio of not less
than 1 relative to water and maintain the final cooling temperature
at a low level, preferably not higher than 10.degree. C., more
preferably not higher than 0.degree. C. The solubility of the above
.beta.-halogeno-.alpha.-aminocarboxylic acid tends to increase in
the presence of lithium chloride or the like, hence it is effective
to use acetone combinedly so that the precipitation may be
maximized.
[0048] In the step of adding a basic lithium compound for
converting the coexisting acid to the salt form for causing
precipitation of the above .beta.-halogeno-.alpha.-aminocarboxylic
acid, the reaction mixture is preferably adjusted to weak acidity
to neutrality, specifically to the vicinity of the isoelectric
point of the .beta.-halogeno-.alpha.-aminocar- boxylic acid. When
the R -halogeno-.alpha.-aminocarboxylic acid is an
.alpha.-amino-.beta.-halopropionic acid or
.alpha.-amino-.beta.-halobutyr- ic acid, the pH is preferably
adjusted to about 4 to 7.
[0049] Specifically, in a simple procedure, taken as an example,
for isolating the above .beta.-halogeno-.alpha.-aminocarboxylic
acid in its free form, those relatively low boiling components
remaining in the reaction mixture after the halogenation reaction,
such as sulfur dioxide, excess hydrogen halide (e.g. hydrogen
chloride) and unreacted halogenating agent (e.g. thionyl halide),
are preferably reduced in amount or removed in advance, the pH is
then adjusted at a low temperature using a basic lithium compound
such as lithium hydroxide or lithium carbonate, preferably lithium
hydroxide, a small amount (preferably minimum amount) of water, and
the resulting precipitate, i.e.
.beta.-halogeno-.alpha.-aminocarboxylic acid, is collected using a
medium mainly comprising a water miscible organic solvent used as
the halogenation reaction solvent, preferably a water-miscible
ether solvent. Alternatively, after reducing or removing in advance
those relatively low boiling components remaining in the reaction
mixture after the halogenation reaction, such as sulfur dioxide,
the excess hydrogen halide (e.g. hydrogen chloride) and the
unreacted halogenating agent (e.g. thionyl halide), the reaction
solvent is replaced with a small amount (preferably minimum amount)
of water at a low temperature and, if necessary after treatment
with an adsorbent such as activated carbon and/or separation of the
insoluble matter by filtration for the purpose of removing
impurities and/or decoloration, the pH is adjusted using a basic
lithium compound such as lithium hydroxide or lithium carbonate,
preferably lithium hydroxide and a small amount (preferably minimum
amount) of water, the precipitation of the
.beta.-halogeno-.alpha.-aminoc- arboxylic acid is fully caused by
combinedly using the above water-miscible organic solvent,
preferably acetone; said acid can then be recovered.
[0050] In cases where the above
.beta.-halogeno-.alpha.-aminocarboxylic acid is submitted to the
next step without isolation, those relatively low boiling
components remaining in the reaction mixture after the halogenation
reaction, such as sulfur dioxide, the excess hydrogen halide (e.g.
hydrogen chloride) and the unreacted halogenating agent (e.g.
thionyl halide), are reduced or removed beforehand, and the
reaction solvent is replaced with water at a low temperature, for
instance, and, if necessary the pH is adjusted with a base such as
sodium hydroxide or lithium hydroxide and, further, if necessary
treatment with an adsorbent such as activated carbon and/or
separation of the insoluble matter by filtration is conducted for
the purpose of removing impurities and/or decoloration, whereafter
the above .beta.-halogeno-.alpha.-aminocarboxyli- c acid can be
used in the form of an aqueous solution.
[0051] A preferred method of purifying and isolating the above
.beta.-halogeno-.alpha.-aminocarboxylic acid is now described. This
is a method of purifying and isolating the
.beta.-halogeno-.alpha.-aminocarbox- ylic acid in its free form. In
the method (1) mentioned below, the
.beta.-halogeno-.alpha.-aminocarboxylic acid can be used and, in
the method (2) mentioned below, the
.beta.-halogeno-.alpha.-aminocarboxylic acid or a salt thereof can
be used, and the salt of the
.beta.-halogeno-.alpha.-aminocarboxylic acid is preferably a
hydrohalogenic acid salt such as hydrochloride. It is of course
possible to use an optically active form of the above
.beta.-halogeno-.alpha.-amin- ocarboxylic acid.
[0052] (1) Using water as a good solvent and a water-miscible
organic solvent as a poor solvent, the
.beta.-halogeno-.alpha.-aminocarboxylic acid is caused to
crystallize out. Preferably, the
.beta.-halogeno-.alpha.-aminocarboxylic acid is caused to
crystallize out from an aqueous solution thereof in the presence of
a water-miscible organic solvent. If necessary, treatment with an
adsorbent such as activated carbon and/or filtration of the
insoluble matter may be combined for the purpose of removing
impurities and/or decoloration.
[0053] (2) Treatment of the aqueous solution containing the
.beta.-halogeno-.alpha.-aminocarboxylic acid and hydrogen halide
with a basic lithium compound, such as lithium hydroxide or lithium
carbonate, for converting the (hydrohalogenic) acid to the salt is
combined with precipitation of the
.beta.-halogeno-.alpha.-aminocarboxylic acid in its free form using
water as a good solvent and a water-miscible organic solvent as a
poor solvent. Basically, the above-mentioned technique for
isolating the .beta.-halogeno-.alpha.-aminocarboxylic acid in its
free form from the halogenation reaction mixture can be utilized.
Preferably, the .beta.-halogeno-.alpha.-aminocarboxylic acid or a
salt thereof (preferably a hydrohalogenic acid salt such as
hydrochloride) is first caused to coexist with, preferably
dissolved in, an aqueous solution of a hydrohalogenic acid, such as
hydrochloric acid, or water. The pH is adjusted generally to 3 or
below, preferably to 2 or below, and the amount of water required
for fluidization, preferably dissolution is preferably minimized.
Then, if necessary, treatment with an adsorbent such as activated
carbon and/or insoluble matter separation by filtration is carried
out for the purpose of removing impurities and/or decoloration.
While adjusting the pH with a basic lithium compound such as
lithium hydroxide or lithium carbonate, the hydrohalogenic acid is
converted to a salt (a lithium halide such as lithium chloride)
soluble in the organic solvent and water, and the
.beta.-halogeno-.alpha.-aminoca- rboxylic acid is caused to
precipitate using the water-miscible organic solvent as a poor
solvent while the above salt is caused to remain dissolved without
precipitation. Thereafter, the acid is recovered by a conventional
solid-liquid separation procedure, such as filtration or
centrifugation. Alternatively, the
.beta.-halogeno-.alpha.-aminocarboxyli- c acid or a salt thereof
(preferably a hydrohalogenic acid salt thereof, such as
hydrochloride) is dissolved in a medium comprising water or an
aqueous solution of a hydrohalogenic acid, such as hydrochloric
acid, and an organic solvent miscible with water. The pH after
dissolution is adjusted generally to 3 or below, preferably to 2 or
below. Then, if necessary, treatment with an adsorbent such as
activated carbon and/or insoluble matter separation by filtration
is carried out for the purpose of removing impurities and/or
decoloration. The .beta.-halogeno-.alpha.-a- minocarboxylic acid is
caused to precipitate by adjusting the pH (converting the
hydrohalogenic acid, if present, to the form of a salt) using a
basic lithium compound such as lithium hydroxide or lithium
carbonate while the above salt formed (lithium halide such as
lithium chloride) is caused to remain dissolved without
precipitation. Thereafter, the desired acid is recovered by a
conventional solid-liquid separation procedure such as filtration
or centrifugation.
[0054] The water-miscible organic solvent to be used in the above
methods (1) and (2) specifically includes, but is not limited to,
1,2-dimethoxyethane, 1,4-dioxane, tetrahydrofuran, diethylene
glycol dimethyl ether, triethylene glycol dimethyl ether,
tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl
ether, acetonitrile, methanol, ethanol, n-propanol, isopropanol,
tert-butanol and acetone, among others. Among these, acetone, in
particular, is preferred from the viewpoint of increased
precipitation of the .beta.-halogeno-.alpha.-amino- carboxylic
acid, which is a water-soluble compound, obtaining crystals with
good characteristics, ease of handling and inexpensiveness, among
others.
[0055] Since the .beta.-halogeno-.alpha.-aminocarboxylic acid has a
high solubility in water, it is desirable, for attaining increased
precipitation, to reduce the amount of water, use the above
water-miscible organic solvent in a volume ratio of not less than 1
relative to water and maintain the final cooling temperature at a
low level, preferably not higher than 10.degree. C., more
preferably not higher than 0.degree. C. The solubility of the above
.beta.-halogeno-.alpha.-aminocarboxylic acid tends to increase in
the presence of lithium chloride or the like, hence it is effective
to use acetone combinedly so that the precipitation may be
maximized.
[0056] In the step of crystallization or precipitation of the above
.beta.-halogeno-.alpha.-aminocarboxylic acid, the pH is adjusted to
weak acidity to neutrality, specifically to the vicinity of the
isoelectric point of the .beta.-halogeno-.alpha.-aminocarboxylic
acid. When the .beta.-halogeno-.alpha.-aminocarboxylic acid is an
.alpha.-amino-.beta.-halopropionic acid or
.alpha.-amino-.beta.-halobutyr- ic acid, the pH is preferably
adjusted to about 4 to 7.
[0057] Most preferred as the above hydrohalogenic acid is hydrogen
chloride (hydrochloric acid) and, as the above basic lithium
compound, lithium hydroxide or lithium carbonate, in particular
lithium hydroxide, is preferred.
[0058] Since the above .beta.-halogeno-.alpha.-aminocarboxylic acid
is not always stable, care is preferably taken in contacting the
same with a base so as to effect contacting thereof with water or
an aqueous medium approximately under acidic or neutral conditions,
for instance. Generally, the acid is handled preferably under
acidic to neutral conditions, for example at a pH of not higher
than 7, and at low temperatures.
[0059] According to the method of the present invention,
.beta.-halogeno-.alpha.-aminocarboxylic acids can efficiently be
synthesized from .beta.-hydroxy-.alpha.-aminocarboxylic acids in
one reaction step, and high quality
.beta.-halogeno-.alpha.-aminocarboxylic acids or salts thereof can
be isolated in high yields. Further, when the above reaction is
carried out using the .beta.-hydroxy-.alpha.-aminocarbo- xylic acid
in an optically active form, the corresponding optically active
.beta.-halogeno-.alpha.-aminocarboxylic acid having the same
configuration as that of the substrate can be obtained while the
optical purity of the starting material is substantially maintained
without accompanying substantial racemization.
[0060] For converting the optically active .beta.-chloroalanine
obtained from an optically active serine or a salt thereof
according to the above production method to an optically active
N-protected-S-phenylcysteine, two methods are conceivable, one
comprising treatment with an amino-protecting agent, followed by
thiophenylation and the other comprising treatment with an
amino-protecting agent following thiophenylation. However, studies
made by the present inventors revealed that the method comprising
treatment with an amino-protecting agent followed by
thiophenylation is preferred from the viewpoint of yield and
operability. The method comprising treatment with an
amino-protecting agent following thiophenylation cannot give
satisfactory yields since the optically active .beta.-chloroalanine
is unstable particularly under thiophenylation conditions.
[0061] The method of the present invention for producing the
optically active N-protected-.beta.-chloroalanines of the general
formula (2) given above or salts thereof comprises producing an
optically active .beta.-chloroalanine or a salt thereof by treating
an optically active serine or a salt of an optically active serine
with an acid with a chlorinating agent and then treating that
product with an amino-protecting agent. In this production method,
the reaction for obtaining the optically active
.beta.-chloroalanine or a salt thereof can be carried out in the
same manner as mentioned above.
[0062] In the above general formula (2), R.sup.1 represents an
amino-protecting group. As the amino-protecting group, there may be
mentioned those described in Theodora W. Green: Protective Groups
in Organic Synthesis, 2nd edition, John Wiley & Sons, published
1990, such as benzyloxycarbonyl, ethoxycarbonyl, methoxycarbonyl,
tert-butoxycarbonyl, acetyl, tosyl, benzoyl, phthaloyl and the
like. The range of choice also includes such protective groups as
(3S)-tetrahydrofuranyloxycarbonyl, 3-hydroxy-2-methylbenzoyl whose
hydroxyl group may optionally be protected, and the like. However,
benzyloxycarbonyl is preferred among others.
[0063] In the above general formula (2), R.sup.0 generally
represents a hydrogen atom but may also represent such an
amino-protecting group as phthaloyl together with R.sup.1.
[0064] The above amino-protecting agent corresponds to the above
amino-protecting group and includes conventional amino-protecting
agents without any particular restriction. Thus, mention maybe made
of, for example, benzyl chloroformate, ethyl chloroformate, methyl
chloroformate, di-tert-butyl dicarbonate, benzoyl chloride, acetyl
chloride, p-toluenesulfonyl chloride, phthalic anhydride, and
N-carboethoxyphthalimide. The range of choice further includes
(3S)-tetrahydrofuranyl chloroformate, 3-hydroxy-2-methylbenzoyl
chloride whose hydroxyl group may optionally be protected, and the
like. Among them, benzyl chloroformate is preferred.
[0065] While the treatment with the above amino-protecting agent
may be carried out using an optically active .beta.-chloroalanine
isolated, it is preferred that the amino group protection be
effected by treating, with the above amino-protecting agent, an
aqueous medium containing an optically active .beta.-chloroalanine
as obtained in the manner mentioned above. In either case, abase is
used and the base to be used is, for example, sodium hydroxide or
potassium carbonate. The above treatment with an amino-protecting
agent may be carried out in any medium comprising water and/or an
organic solvent.
[0066] The solvent to be used in that case is not particularly
restricted but may be, for example, 1,2-dimethoxyethane,
1,4-dioxane, tetrahydrofuran, diethylene glycol dimethyl ether,
triethylene glycol dimethyl ether, tetraethylene glycol dimethyl
ether, polyethylene glycol dimethyl ether, tert-butyl methyl ether,
dibutyl ether, diethyl ether or a like other ether solvent;
acetonitrile, methylene chloride, ethyl acetate, acetone, toluene
or a like other aprotic solvent.
[0067] Taking carbobenzyloxylation as an example, the method for
the above amino group protection is now specifically described. To
an aqueous medium containing an optically active
.beta.-chloroalanine, for instance, there is added benzyl
chloroformate in an amount of 1 to 2 molar equivalents, preferably
about 1.0 molar equivalent, relative to the substrate, at a
temperature at which the solvent will not freeze, up to 30.degree.
C., more preferably at a temperature not higher than 5.degree. C.,
while maintaining the pH at 8 to 13, preferably 9 to 12, more
preferably 9 to 10, by adding a base, such as sodium hydroxide or
potassium carbonate, and the resulting mixture is stirred at a
temperature at which the solvent will not freeze, up to 30.degree.
C., more preferably at a temperature not higher than 5.degree. C.,
preferably for 1 to 30 hours. If necessary, the reaction mixture
may be washed with an organic solvent immiscible with water or with
an aqueous medium, for example toluene, for the purpose of removing
the unreacted portion of benzyl chloroformate and the byproduct
benzyl alcohol.
[0068] The optically active N-protected-.beta.-chloroalanine
produced in the above manner can be isolated, for example by a
conventional extraction procedure followed by column
chromatography.
[0069] The method of the present invention for producing optically
active N-protected-S-phenylcysteines of the above general formula
(3) or salts thereof comprises treating an optically active serine
or a salt of an optically active serine with an acid with a
chlorinating agent, then treating the thus-obtained optically
active .beta.-chloroalanine with an amino-protecting agent, and
further reacting the resulting optically active
N-protected-.beta.-chloroalanine or a salt thereof with thiophenol
under a basic condition. In the above general formula (3), R.sup.0
and R.sup.1 are the same as the R.sup.0 and R.sup.1 specifically
mentioned above. In this production method, the reactions for the
production of the optically active N-protected-.beta.-chloroalanine
or a salt thereof can be carried out in the same manner as
mentioned above.
[0070] The thiophenylation of the above optically active
N-protected-.beta.-chloroalanine can be carried out using an
optically active N-protected-.beta.-chloroalanine isolated in the
manner mentioned above. It is also possible to adjust the pH of the
reaction mixture after amino-protecting agent treatment, add
thiophenol directly thereto and effecting the reaction in that
reaction mixture.
[0071] The above step of reacting the optically active
N-protected-.beta.-chloroalanine with thiophenol can be conducted
in water and/or an organic solvent under a basic condition. The
organic solvent is not particularly restricted but includes, for
example, ether solvents such as 1,2-dimethoxyethane, 1,4-dioxane,
tetrahydrofuran, diethylene glycol dimethyl ether, triethylene
glycol dimethyl ether, tetraethylene glycol dimethyl ether,
polyethylene glycol dimethyl ether, tert-butyl methyl ether,
dibutyl ether and diethyl ether; and other aprotic solvents such as
acetonitrile, methylene chloride, ethyl acetate, acetone and
toluene, among others.
[0072] The above thiophenol is used generally in an amount of 1 to
5 molar equivalents, preferably 1 to 3 molar equivalents, more
preferably about 1.5 molar equivalents, relative to the optically
active N-protected-.beta.-chloroalanine.
[0073] For effecting the above thiophenylation under a basic
condition, an inorganic base or the like is preferably added as a
base. The inorganic base is not particularly restricted but may be,
for example, sodium hydrogen carbonate, potassium hydrogen
carbonate, sodium carbonate, potassium carbonate or sodium
hydroxide. An alkaline pH buffering agent may also be used.
[0074] The amount of the above base to be used may vary depending
on the species thereof. In the case of sodium hydroxide or sodium
carbonate, for instance, it is used in an amount of 1 to 5 molar
equivalents, preferably 1 to 3 molar equivalents, relative to the
optically active N-protected-.beta.-chloroalanine. The pH of the
reaction mixture is preferably about 9 to 11. Under strongly
alkaline conditions, the yield tends to decrease due to side
reactions. After completion of the reaction, the product can be
isolated, for example by acidifying the reaction mixture with
hydrochloric acid, sulfuric acid or the like, extracting the
mixture with an organic solvent such as ethyl acetate,
concentrating the extract and subjecting the concentrate to column
chromatography, for instance.
[0075] The above thiophenylation can be effected, for example by
adding a base such as sodium hydroxide and sodium carbonate to a
solution composed of an optically active
N-protected-.beta.-chloroalanine and an amount of water to give a
starting material concentration of 5 to 30% (w/v), preferably at
0.degree.to 30.degree. C., to thereby preferably adjust the pH to 9
to 11, and further adding thiophenol in an amount of 1 to 5 molar
equivalents, preferably 1 to 3 molar equivalents, relative to the
optically active N-protected-.beta.-chloroalanine, followed by
stirring preferably at 30.degree. to 90.degree. C., more preferably
40.degree. to 70.degree. C. The order of addition of the reagents
is not always restricted to the one mentioned above. For example,
the thiophenylation can also be effected by adding a base to an
aqueous solution containing thiophenol and an optically active
N-protected-.beta.-chloroalanine or by adding thiophenol and a base
simultaneously to an aqueous solution of an optically active
N-protected-.beta.-chloroalanine.
[0076] In the production method of the present invention, by
conducting, without isolating the intermediates, the three steps,
namely the step of treating an optically active serine or a salt of
an optically active serine with an acid with a chlorinating agent,
the step of treating the resulting optically active
.beta.-chloroalanine with an amino-protecting agent and the step of
reacting the resulting optically active
N-protected-.beta.-chloroalanine with thiophenol under a basic
condition, it is possible to obtained the corresponding optically
active N-protected-S-phenylcysteine derivative in a simple and
efficient manner. It is also possible to conduct, without isolating
the intermediate, the two steps, namely the step of treating an
optically active .beta.-chloroalanine with an amino-protecting
agent and the step of reacting the resulting optically active
N-protected-.beta.-chloroalanine with thiophenol under a basic
condition.
[0077] The optically active N-protected-S-phenylcysteine obtained
from the corresponding optically active serine or a salt thereof by
the production method of the present invention has an optical
purity as high as 98% e.e. at the step prior to purification by
crystallization, for instance. Thus, according to the present
invention, an optically active N-protected-S-phenylcysteine having
the same configuration as that of the substrate can be produced
from the optically active serine or a salt thereof while
substantially maintaining the optical purity thereof without
accompanying substantial racemization.
[0078] The optically active N-protected-S-phenylcysteine, in
particular N-carbobenzyloxy-S-phenyl-L-cysteine, is a compound very
useful as an intermediate of HIV protease inhibitors (WO 9532185),
for instance.
BEST MODES FOR CARRYING OUT THE INVENTION
[0079] The following examples illustrate the present invention in
further detail. They are, however, by no means limitative 10 of the
scope of the present invention.
EXAMPLE 1
[0080] Production of .beta.-chloro-L-alanine hydrochloride L-Serine
(5.0 g, 0.0476 mol) was added to 50 ml of 1,4-dioxane, and hydrogen
chloride gas was introduced into the resulting solution with
stirring at room temperature. On that occasion, the hydrogen
chloride in the solution amounted to 14.5 g (0.3977 mol). To the
solution was added slowly 12.5 g (0.1051 mol) of thionyl chloride,
and the reactor inside temperature was then adjusted to 50.degree.
C. After about 6 hours of stirring, this solution was concentrated
to about half the original volume. The concentrate was cooled to
0.degree. to 10.degree. C., and 50 ml of water was added gradually
so as to maintain this temperature. HPLC analysis of this solution
revealed the formation of 6.9 g (0.0431 mol) of
.beta.-chloro-L-alanine hydrochloride (yield: 91 mole %).
EXAMPLE 2
[0081] Production of S-chloro-L-alanine hydrochloride L-Serine (5.0
g, 0.0476 mol) was added to 50 ml of 1, 4-dioxane, and hydrogen
chloride gas was introduced into the resulting solution with
stirring at room temperature. On that occasion, the hydrogen
chloride in the solution amounted to 11.2 g (0.3072 mol). To the
solution was added slowly 6.2 g (0.0521 mol) of thionyl chloride,
and the reactor inside temperature was then adjusted to 45.degree.
C. After about 20 hours of stirring, this solution was concentrated
to about half the original volume. The concentrate (slurry) was
filtered, the cake was washed with 10 ml of 1,4-dioxane and the wet
crystals were dried under reduced pressure (40.degree. C., not
higher than 10 mm Hg) to give dry crystals. HPLC analysis of the
crystals obtained revealed that the yield of
.beta.-chloro-L-alanine hydrochloride as pure substance was 7.2 g
(0.0450 mol).
[0082] The IR, .sup.1H-NMR and .sup.13C-NMR data of the
.beta.-chloro-L-alanine hydrochloride obtained were in complete
agreement with those of the .beta.-chloro-L-alanine hydrochloride
purchased from Aldrich Chemical Co.
EXAMPLE 3
[0083] Production of -chloro-L-alanine
[0084] Milk white crystals (purity 95.2% by weight, containing 3.6
g (0.0225 mol) of .beta.-chloro-L-alanine hydrochloride) obtained
in the same manner as in Example 2 were added to 14 ml of water to
give a slurry. This slurry was completely dissolved by slowly
adding about 2 g of concentrated hydrochloric acid. To the solution
was added 0.1 g of 50% activated carbon, and the mixture was
stirred at room temperature for about 10 minutes. The activated
carbon was filtered off under reduced pressure and washed with 1 ml
of water. The filtrate and washings obtained were cooled to
0.degree. to 10.degree. C., and the pH was adjusted to 5.5 by
gradually adding a saturated aqueous solution of lithium hydroxide
while maintaining that temperature, to give a slurry. Acetone (42
ml) was gradually added to this slurry to thereby cause sufficient
precipitation of crystals, the resulting mixture was cooled to
-10.degree. to 0.degree. C. and maintained at that temperature for
about 1 hour. The precipitate crystals were filtered off, the cake
was washed with 14 ml of acetone, and the wet crystals obtained
were dried under reduced pressure (40.degree. C., not higher than
10 mm Hg) to give 2.65 g of .beta.-chloro-L-alanine as white
crystals. HPLC analysis of these crystals revealed a purity of
99.9% by weight and a yield of pure .beta.-chloro-L-alanine of 2.65
g (0.0214 mol).
[0085] The .beta.-chloro-L-alanine obtained had an optical purity
of not less than 99.9% e.e. as determined by HPLC analysis under
the conditions shown below.
[0086] <Analytical conditions>
[0087] Column: Tosoh TSK-Gel Enantio L1 (4.6 mm.times.250 mm)
[0088] Mobile phase: 0.5 M CuSO.sub.4 aq./acetonitrile=80/20
[0089] Column temperature: 40.degree. C.
[0090] Detection wavelength: 254 nm
[0091] Flow rate: 1.0 ml/min
[0092] Retention time: .beta.-chloro-L-alanine 9.3 min
.beta.-chloro-D-alanine 7.8 min
EXAMPLE 4
[0093] Production of .beta.-chloro-L-alanine
[0094] L-Serine (30.0 g, 0.2855 mol) was added to 600 ml of
1,4-dioxane, and hydrogen chloride gas was introduced into the
resulting solution with stirring at room temperature. On that
occasion, the hydrogen chloride in the solution amounted to 133.1 g
(3.6508 mol). To the solution was added slowly 40.8 g (0.3426 mol)
of thionyl chloride, and the reactor inside temperature was then
adjusted to 40.degree. C. After about 20 hours of stirring, the
liquid (slurry) was concentrated to about half the original volume.
The concentrate (slurry) was cooled to 0.degree. to 10.degree. C.,
and 200 ml of water was added gradually so as to maintain that
temperature, to thereby cause dissolution of the precipitate. The
resulting solution was further concentrated until the weight became
about 200 g, 3.0 g of 50% activated carbon was then added, and the
mixture was stirred at room temperature for about 10 minutes. The
activated carbon was filtered off under reduced pressure and washed
with 10 ml of water. The filtrate and washings obtained were
combined and further concentrated to a weight of about 120 g. This
concentrate was cooled to 0.degree. to 10.degree. C., and the pH
was adjusted to 5.5 by gradually adding a saturated aqueous
solution of lithium hydroxide while maintaining that temperature,
to give a slurry. To this slurry was gradually added 600 ml of
acetone for effecting sufficient precipitation of crystals, and the
slurry was then cooled to -10.degree. to 0.degree. C. and
maintained at this temperature for about 1 hour. The precipitate
crystals were filtered off under reduced pressure and the cake was
washed with 100 ml of acetone. The wet crystals thus obtained were
dried under reduced pressure (40.degree. C., not higher than 10 mm
Hg) to give 32.6 g of .beta.-chloro-L-alanine as dry crystals. HPLC
analysis of the crystals revealed a purity of 99.8% by weight and a
yield of pure .beta.-chloro-L-alanine of 32.5 g (0.2625 mol)
EXAMPLE 5
[0095] Production of .beta.-chloro-D-alanine hydrochloride
[0096] D-Serine (5.0 g, 0.0476 mol) was added to 50 ml of
1,4-dioxane, and hydrogen chloride gas was introduced into the
resulting solution with stirring at room temperature. On that
occasion, the hydrogen chloride in the solution amounted to 11.5 g
(0.3154 mol). To the solution was added slowly 6.2 g (0.0521 mol)
of thionyl chloride, and the reactor inside temperature was then
adjusted to 45.degree. C. After about 20 hours of stirring, this
solution was concentrated to about half the original volume. The
concentrate (slurry) was filtered, the cake was washed with 10 ml
of 1,4-dioxane and the wet crystals were dried under reduced
pressure (40.degree. C., not higher than 10 mm Hg) to give dry
crystals. HPLC analysis of the crystals obtained revealed that the
yield of .beta.-chloro-D-alanine hydrochloride as pure substance
was 7.0 g (0.0438 mol) . The thus-obtained .beta.-chloro-D-alanine
hydrochloride had an optical purity of not less than 99.9% e.e. as
determined by the same method as mentioned in Example 3.
EXAMPLE 6
[0097] Production of .beta.-chloro-L-alanine hydrochloride
[0098] L-Serine (5.0 g, 0.0476 mol) was added to 50 ml of each of
the reaction solvents specified in Table 1, and hydrogen chloride
gas was introduced into the resulting solution with stirring at
room temperature until saturation with hydrogen chloride. To the
solution was added slowly 12.5 g (0.1051 mol) of thionyl chloride,
and the reaction was effected under the conditions shown in Table
1. The reaction mixture (slurry) was concentrated to about half the
original volume. The concentrate was cooled to 0.degree. to
10.degree. C. and 50 ml of water was added slowly so as to maintain
this temperature. This solution was analyzed by HPLC and the yield
as .beta.-chloro-L-alanine hydrochloride was determined. The
results thus obtained are shown in Table 1.
1TABLE 1 Reaction Reaction Solvent temperature Reaction time Yield
1,2-Dimethoxyethane 50.degree. C. 10 hrs 97% Tetrahydrofuran
40.degree. C. 30 hrs 92% Triethylene glycol 50.degree. C. 10 hrs
93% dimethylether
EXAMPLE 7
[0099] Production of (.alpha.S,
.beta.R)-.alpha.-amino-.beta.-hydroxybutyr- ic acid
hydrochloride
[0100] L-Threonine (10.14 g, 0.0851 mol) was added to 100 ml of 1,
4-dioxane, and hydrogen chloride gas was introduced into the
resulting solution with stirring at room temperature. On that
occasion, the hydrogen chloride in the solution amounted to 15.5 g
(0.4251 mol). To the solution was added slowly 12.2 g (0.1022 mol)
of thionyl chloride, and the reactor inside temperature was then
adjusted to 50.degree. C. After about 10 hours of stirring, this
solution was concentrated to about half the original volume. The
concentrate (slurry) was filtered, the cake was washed with 20 ml
of 1,4-dioxane and the wet crystals were dried under reduced
pressure (40.degree. C., not higher than 10 mm Hg) to give dry
crystals. HPLC analysis of the crystals obtained revealed that the
yield of (.alpha.S, .beta.R)-.alpha.-amino-.beta.-hydroxybutyric
acid hydrochloride as pure substance was 12.2 g (0.0701 mol).
[.alpha.].sub.D.sup.20 +16.1.degree. (c=1.0, water) (lit.,
[.alpha.].sub.D.sup.20+17.8.degree. (c=1.0, water) [CHIRALITY 9,
656-660 (1997)].
EXAMPLE 8
[0101] Production of (.alpha.S,
.beta.R)-.alpha.-amino-.beta.-hydroxybutyr- ic acid
[0102] Milk white crystals [purity 94.9% by weight, containing 5.0
g (0.0287 mol) of (.alpha.S,
.beta.R)-.alpha.-amino-.beta.-hydroxybutyric acid hydrochloride]
obtained in the same manner as in Example 7 were added to 19 ml of
water to give a slurry. This slurry was completely dissolved by
slowly adding about 2.8 g of concentrated hydrochloric acid. To the
solution was added 0.1 g of 50% activated carbon, and the mixture
was stirred at room temperature for about 10 minutes. The activated
carbon was filtered off under reduced pressure and washed with 1 ml
of water. The filtrate and washings obtained were combined and
cooled to 0.degree. to 10.degree. C., and the pH was adjusted to
5.5 by gradually adding a saturated aqueous solution of lithium
hydroxide while maintaining that temperature, to give a slurry.
Acetone (58 ml) was gradually added to this slurry to thereby cause
sufficient precipitation of crystals, the resulting mixture was
cooled to -10.degree. to 0.degree. C. and maintained at that
temperature for about 1 hour. The precipitate crystals were
filtered off, the cake was washed with 19 ml of acetone, and the
wet crystals obtained were dried under reduced pressure (40.degree.
C., not higher than 10 mm Hg) to give 3.75 g of (.alpha.S,
.beta.R)-.alpha.-amino-.beta.-chlorobutyric acid as white crystals.
HPLC analysis of these crystals revealed a purity of 99.8% by
weight and a yield of pure (.alpha.S,
.beta.R)-.alpha.-amino-.beta.-chlorobutyric acid of 3.74 g (0.02272
mol). mp 176.degree. C. (decomp.) (lit., mp 176.degree. C.
(decomp.) [Yakugaku Kenkyu, 33, 428-437 (1961)].
[0103] The IR, .sup.1H-NMR and .sup.13C-NMR data of the (.alpha.S,
.beta.R)-.alpha.-amino-.beta.-chlorobutyric acid thus obtained as
crystals were in complete agreement with those of the crystalline
(.alpha.S, .beta.R)-.alpha.-amino-.beta.-chlorobutyric acid
separately synthesized by the method mentioned below.
REFERENCE EXAMPLE 1
[0104] Alternative synthesis of (.alpha.S,
.beta.R)-.alpha.-amino-.beta.-c- hlorobutyric acid
[0105] Using thionyl chloride and methanol, threonine was
derivatized into threonine methyl ester hydrochloride, which was
then treated with thionyl chloride to give
.alpha.-amino-.beta.-chlorobutyric acid methyl ester hydrochloride.
This was then converted to .alpha.-amino-.beta.-chloroprop- ionic
acid hydrochloride by hydrolyzing with hydrochloric acid. The
.alpha.-amino-.beta.-chloropropionic acid hydrochloride was
crystallized and isolated by the same technique as mentioned in
Example 8.
EXAMPLE 9
[0106] Production of .beta.-chloro-L-alanine hydrochloride
[0107] L-Serine hydrochloride (6.7 g, 0.0473 mol) was added to 50
ml of 1,4-dioxane. To the solution was added slowly 6.8 g (0.0572
mol) of thionyl chloride at room temperature, and the reactor
inside temperature was then adjusted to 60.degree. C. After about 3
hours of stirring, this solution was concentrated to about half the
original volume. The concentrate was cooled to 0.degree. to
10.degree. C., and 50ml of water was added gradually so as to
maintain this temperature. HPLC analysis of this solution revealed
the formation of 4.6 g (0.0287 mol) of .beta.-chloro-L-alanine
hydrochloride (yield 61 mole %)
COMPARATIVE EXAMPLE 1
[0108] L-Serine (20.0 g, 0.1903 mol) was added to 49.8 g (0.4187
mol) of thionyl chloride, and the mixture was warmed to 60.degree.
C. and stirred for 6 hours. This solution was hydrolyzed and then
analyzed by HPLC. No .beta.-chloro-L-alanine peak was observed but
peaks due to unreacted L-serine and various impurities were
observed.
COMPARATIVE EXAMPLE 2
[0109] L-Serine (15.0 g, 0.1427 mol) was added to 150 ml of
toluene, and hydrogen chloride gas was blown into the resulting
solution at room temperature until saturation. To this solution was
added 37.4 g (0.3140 mol) of thionyl chloride, and the mixture was
then warmed to 80.degree. C. and stirred for 20 hours, This
solution was hydrolyzed and then analyzed by HPLC. Peaks of various
impurities were observed and the peak of .beta.-chloro -L-alanine
corresponded only to a trace amount. (The above reaction mixture
contained a tar-like substance and had a deep black color.)
COMPARATIVE EXAMPLE 3
[0110] L-Serine (15.0 g, 0.1427 mol) was added to 150 ml of
methylene chloride, and hydrogen chloride gas was blown into the
resulting solution at room temperature until saturation. To this
solution was added 37.4 g (0.3140 mol) of thionyl chloride, and the
mixture was then warmed to 40.degree. C. and stirred for 16 hours,
This solution was hydrolyzed and then analyzed by HPLC. Peaks of
various impurities were observed and the peak of
.beta.-chloro-L-alanine corresponded only to a trace amount. (The
above reaction mixture contained a tar-like substance and had a
deep black color.)
EXAMPLE 10
[0111] Production of N-carbobenzyloxy-.beta.-chloro-L-alanine
[0112] L-Serine hydrochloride (0.4 g, 2.84 mmol) and 0.029 g (0.28
mmol) of triethylamine were suspended in 4 ml of diethylene glycol
dimethyl ether. Thereto was added dropwise 0.67 g (5.68 mmol) of
thionyl chloride at room temperature in a nitrogen gas atmosphere.
After 2 hours of stirring at 60.degree. C., 8 ml of water was added
while maintaining the reaction mixture inside at 15.degree. C. or
below, and the whole mixture was stirred at room temperature for 30
minutes. Further, 1.6 g of potassium carbonate was added to make
the pH about 10 and, thereafter, 0.956 g (5.68 mmol) of benzyl
chloroformate was added dropwise. After overnight standing at room
temperature, the reaction mixture was washed with ethyl acetate,
the aqueous layer obtained was cooled with ice and acidified with
50% sulfuric acid and then extracted with ethyl acetate. The
solvent was distilled off and the residue was purified by column
chromatography to give 0.3 g (1.16 mmol, 41%) of
N-carbobenzyloxy-.beta.-- chloro-L-alanine.
[0113] The N-carbobenzyloxy-.beta.-chloro-L-cysteine obtained gave
the following .sup.1H-NMR and IR data.
[0114] .sup.1H-NMR (400 MHz, CDCl.sub.3) .delta. (ppm): 3.85-4.06
(m, 2H), 4.80-4.82 (m, 1H), 5.14 (s, 2H), 5.70 (d, J=7.8 Hz, 1H),
7.36 (s, 5H)
[0115] IR (neat): 3034, 1720, 1516, 1456, 1203, 1066, 855, 754, 698
(cm.sup.-1)
EXAMPLE 11
[0116] Production of N-carbobenzvloxy-.beta.-chloro-L-alanine
[0117] L-Serine hydrochloride (0.4 g, 2.84 mmol) and 0.029 g (0.28
mmol) of triethylamine were suspended in 4 ml of
1,2-dimethoxyethane. Thereto was added dropwise 0.67 g (5.68 mmol)
of thionyl chloride at room temperature in a nitrogen gas
atmosphere. After 2 hours of stirring at 60.degree. C., 8 ml of
water was added while maintaining the reaction mixture inside at
15.degree. C. or below, and the whole mixture was stirred at room
temperature for 30 minutes. Further, 1.6 g of potassium carbonate
was added to make the pH about 10 and, thereafter, 0.956 g (5.68
mmol) of benzyl chloroformate was added dropwise. After overnight
standing at room temperature, the reaction mixture was cooled with
ice and acidified with 50% sulfuric acid. The solution obtained was
analyzed by HPLC, which revealed the formation of
N-carbobenzyloxy-.beta.-chloro-L- -alanine in a yield of 42% (1.18
mmol). The analytical conditions were as shown below. Analytical
conditions (N-carbobenzyloxy-.beta.-chloro-L-alan-
ine/N-carbobenzyloxy-L-serine)
[0118] Column: YMC-Pack ODS-A A-303 (250 mm.times.4.6 mm)
[0119] Mobile phase: Phosphate buffer (pH=3.0)
:acetonitrile=60:40
[0120] Flow rate: 1.0 ml/min
[0121] Sample injection size: 20 .mu.l
[0122] Sample solvent: acetonitrile
[0123] Retention time:
[0124] 6.2 min (N-carbobenzyloxy-.beta.-chloro-L-alanine)
[0125] 3.9 min (N-carbobenzyloxy-L-serine)
EXAMPLE 12
[0126] Production of N-carbobenzyloxy-.beta.-chloro-L-alanine
[0127] L-Serine hydrochloride (0.1 g, 0.71mmol) and7.2mg (0.07
mmol) of triethylamine were suspended in a solvent composed of 1 ml
of acetonitrile and 0.1 ml of diethylene glycol dimethyl ether.
Thereto was added dropwise 0.167 g (1.42 mmol) of thionyl chloride
at room temperature in a nitrogen gas atmosphere. After 2 hours of
stirring at 60.degree. C., 2 ml of water was added while
maintaining the reaction mixture inside at 15.degree. C. or below,
and the whole mixture was stirred at room temperature ofor 30
minutes. Further, 0.4 g of potassium carbonate was added to make
the pH about 10 and, thereafter, 0.239 g (1.52 mmol) of benzyl
chloroformate was added dropwise. After overnight standing at room
temperature, the reaction mixture was cooled with ice and acidified
with 50% sulfuric acid. The solution obtained was analyzed by HPLC
by the same procedure as mentioned in Example 11, which revealed
the formation of N-carbobenzyloxy-.beta.-chloro-L-alanine in a
yield of 34% (0.24 mmol).
EXAMPLE 13
[0128] Production of N-carbobenzyloxy-S-phenyl-L-cysteine
[0129] N-Carbobenzyloxy-.beta.-chloro-L-alanine (0.108 g, 0.42
mmol) was dissolved in 0.5 ml of water and, then, 0.097 g (0.92
mmol) of sodium carbonate was added. Thereafter, 0.054 g (0.50
mmol) of thiophenol was added dropwise at room temperature in a
nitrogen gas atmosphere. After 2 hours of stirring at 60.degree.
C., the reaction mixture was cooled with ice and acidified with 1 N
hydrochloric acid, and then extracted with ethyl acetate. The
solvent was distilled off and the residue was purified by column
chromatography to give 0.112 g (0.34 mmol, 81%) of
N-carbobenzyloxy-S-phenyl-L-cysteine. The compound obtained had an
optical purity of not less than 98% e.e. The optical purity was
determined by HPLC. The analytical conditions are shown below.
[0130] Optical purity determination conditions
(N-carbobenzyloxy-S-phenyl--
L-cysteine/N-carbobenzyloxy-S-phenyl-D-cysteine)
[0131] Column: DAICEL CHIRALPAK AS (250 mm.times.4.6 mm)
[0132] Mobile phase: (hexane/tert-butyl methyl
ether/trifluoroacetic acid=800/200/2):ethanol=85:15
[0133] Flow rate: 1.2 ml/min
[0134] Sample injection size : 10 .mu.l
[0135] Temperature: 35.degree. C.
[0136] Sample solvent: (hexane/tert-butyl methyl
ether/trifluoroacetic acid=800/200/2):ethanol=80:20
[0137] Retention time
[0138] 4.5 min (N-carbobenzyloxy-S-phenyl-L-cysteine)
[0139] 5.6 min (N-carbobenzyloxy-S-phenyl-D-cysteine)
[0140] The results of .sup.1H-NMR and IR analysis of the
N-carbobenzyloxy-S-phenyl-L-cysteine obtained were as follows:
[0141] .sup.1H-NMR (400 MHz, CDCl.sub.3) .delta. (ppm): 3.41 (dd,
J=5.1, 14.2 Hz, 2H), 4.61-4.63 (m, 1H), 5.07 (s, 2H), 5.56 (d,
J=7.3 Hz, 1H), 7.17-7.55 (m, 10H)
[0142] IR (neat): 3036, 1686, 1532, 1281, 1059, 737 (cm.sup.-1)
EXAMPLE 14
[0143] Production of N-carbobenzyloxy-S-phenyl-L-cysteine
[0144] N-Carbobenzyloxy-.beta.-chloro-L-alanine (0.091 g, 0.35
mmol) was dissolved in 0.45 ml of water and, then, 0.065 g (0.77
mmol) of sodium hydrogen carbonate was added. Thereafter, 0.046 g
(0.42 mmol) of thiophenol was added dropwise at room temperature in
a nitrogen gas atmosphere. After 2 hours of stirring at 60.degree.
C., the reaction mixture was cooled with ice and acidified with 1 N
hydrochloric acid, and then extracted with ethyl acetate. The
solvent was distilled off and the residue was purified by column
chromatography to give 0.097 g (0.29 mmol, 84%) of
N-carbobenzyloxy-S-phenyl-L-cysteine. The product obtained had an
optical purity of not less than 98% e.e. as determined by HPLC
analysis following the same procedure as in Example 13.
EXAMPLE 15
[0145] Production of N-carbobenzyloxy-S-phenyl-L-cysteine
[0146] N-Carbobenzyloxy-.beta.-chloro-L-alanine (0.137 g, 0.53
mmol) was dissolved in 0.68 ml of water and, then, 0.58 ml of 2 N
aqueous sodium hydroxide was added. Thereafter, 0.069 g (0.63 mmol)
of thiophenol was added dropwise at room temperature in a nitrogen
gas atmosphere. After 2 hours of stirring at 60.degree. C., the
reaction mixture was cooled with ice and acidified with 1 N
hydrochloric acid, and then extracted with ethyl acetate. The
solvent was distilled off and the residue was purified by column
chromatography to give 0.107 g (0.32 mmol, 61%) of
N-carbobenzyloxy-S-phenyl-L-cysteine. The product obtained had an
optical purity of not less than 98% e.e. as determined by HPLC
analysis in the same manner as in Example 13.
EXAMPLE 16
[0147] Production of N-carbobenzyloxy-S-phenyl-L-cysteine
[0148] L-Serine hydrochloride (10.0 g, 70.6 mmol) and 0.073 g (7.1
mmol) of triethylamine were dissolved in 100 ml of diethylene
glycol dimethyl ether, and 16.8 g (141.2 mmol) of thionyl chloride
was added dropwise at room temperature in a nitrogen gas
atmosphere. After 2 hours of stirring at 60.degree. C., 200 ml of
water was added while maintaining the reaction system at 15.degree.
C. or below, and the resulting mixture was stirred at room
temperature for 30 minutes. Further, 50 g of potassium carbonate
was added to make the pH about 10 and, then, 17.9 g (141.2 mmol) of
benzyl chloroformate was added dropwise. After overnight standing
at room temperature, 10 g of potassium carbonate was again added to
make the pH about 10 and, then, 10.7 g (97.1 mmol) of thiophenol
was added dropwise at room temperature in a nitrogen gas
atmosphere. After 2 hours of stirring at 60.degree. C., the
reaction mixture was cooled with ice and acidified with 50%
sulfuric acid, and extracted with ethyl acetate. The solvent was
distilled off and the residue was purified by column chromatography
to give 8.7 g (26.2 mmol, 37%) of
N-carbobenzyloxy-S-phenyl-L-cysteine. The product obtained had an
optical purity of not less than 98% e.e. as determined by HPLC
analysis in the same manner as in Example 13.
EXAMPLE 17
[0149] Production of N-carbobenzyloxy-S-phenyl-L-cysteine
[0150] .beta.-Chloro-L-alanine hydrochloride (15.7 g, 98.1mmol) was
added to 160 ml of water and dissolution was effected. The reactor
inside was cooled to 0.degree. to 5.degree. C. and the pH was
adjusted to 10 by dropwise addition of about 36 g of a 30% (by
weight) aqueous solution of sodium hydroxide with vigorous
stirring. While maintaining the inside temperature at 0.degree. to
5.degree. C., 20.5 g (120.0 mmol) of benzyl chloroformate was added
dropwise over 1 hour with vigorous stirring and then stirring was
continued for 4 hours, during which the pH of the reaction mixture
was maintained at 9.5 to 10.5 by dropwise addition of about 16 g of
a 30% (by weight) aqueous solution of sodium hydroxide. The
reaction mixture obtained was assayed for
N-carbobenzyloxy-.beta.-chloro-- L-alanine by HPLC and the yield
thereof was found to be 25.1 g (97.5 mmol).
[0151] To the reaction mixture obtained was added dropwise 22.0 g
(200.0 mmol) of thiophenol with vigorous stirring. During the
dropping, the pH of the reaction mixture was maintained at 9.7 to
10.3 by dropwise addition of about 26 g of a 30% (by weight)
aqueous solution of sodium hydroxide. In a nitrogen atmosphere, the
inside temperature was raised to 50.degree. C. and the reaction was
allowed to proceed for 3.5 hours, during which the pH of the
reaction mixture was maintained at 9.7 to 10.3 by dropwise addition
of about 1 g of a 30% (by weight) aqueous solution of sodium
hydroxide. To the reaction mixture obtained was gradually added
dropwise about 20 g of concentrated hydrochloric acid over 3 hours
with vigorous stirring to thereby adjust the slurry pH to 3. The
resulting precipitate crystals of
N-carbobenzyloxy-S-phenyl-L-cysteine were filtered off under
reduced pressure and sufficiently deprived of the liquid reaction
medium by washing with two 100-ml portions of water, to give wet
crystals of N-carbobenzyloxy-S-phenyl-L-cysteine [29.8 g (89.9
mmol) as pure N-carbobenzyloxy-S-phenyl-L-cysteine]. The optical
purity of the N-carbobenzyloxy-S-phenyl-L-cysteine obtained was
99.9% e.e.
COMPARATIVE EXAMPLE 4
[0152] Production of S-phenyl-L-cysteine
[0153] A 20% (by weight) aqueous solution of sodium carbonate (2.23
g, 0.0042 mol) was added to 0.97 g (0.0088 mol) of thiophenol, and
the mixture was stirred at room temperature for 0.5 hour. To this
solution was added a solution composed of 1.08 g (0.0088 mol) of
.beta.-chloro-L-alanine and water, and the reaction was allowed to
proceed for 5 hours, during which the pH of the reaction mixture
was maintained at 8 to 10 while adding 5.14 g (0.0097 mol) of a 20%
(by weight) aqueous solution of sodium carbonate. To the reaction
mixture obtained were added 30 ml of toluene, 20 ml of water and
about 3 g of concentrated hydrochloric acid in a nitrogen
atmosphere to thereby adjust the pH to 0.5. The aqueous layer after
separation from the organic layer was washed with two 30-ml
portions of toluene to remove the remaining portion of thiophenol,
to give 34.3 g of an aqueous solution of S-phenyl-L-cysteine.
[0154] HPLC analysis of the aqueous solution obtained revealed that
the yield as pure S-phenyl-L-cysteine was 0.45 g (0.0023 mol, 26.0%
yield) . A marked extent of decomposition of
.beta.-chloro-L-alanine was observed.
INDUSTRIAL APPLICABILITY
[0155] The present invention, constituted as above, makes it
possible to produce .beta.-halogeno-.alpha.-aminocarboxylic acids,
which are useful as starting materials for the production of
medicinals, as well as optically active
N-protected-S-phenylcysteines, which are useful as intermediates of
medicinals, and intermediates thereof, in a simple, efficient and
industrially advantageous manner and on a commercial scale.
* * * * *