U.S. patent application number 16/578764 was filed with the patent office on 2020-04-16 for difluoroalkylcyclopropyl amino acids and esters, and syntheses thereof.
The applicant listed for this patent is AbbVie Inc.. Invention is credited to Michael J. Abrahamson, David R. Hill, Kirill A. Lukin, Jianzhang Mei.
Application Number | 20200115329 16/578764 |
Document ID | / |
Family ID | 60189564 |
Filed Date | 2020-04-16 |
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United States Patent
Application |
20200115329 |
Kind Code |
A1 |
Lukin; Kirill A. ; et
al. |
April 16, 2020 |
DIFLUOROALKYLCYCLOPROPYL AMINO ACIDS AND ESTERS, AND SYNTHESES
THEREOF
Abstract
The invention provides methods of synthesizing compounds in an
asymmetric or enantioenriched fashion, wherein the compounds are
useful intermediates in the synthesis of viral protease
inhibitors.
Inventors: |
Lukin; Kirill A.; (Vernon
Hills, IL) ; Mei; Jianzhang; (Lake Forest, IL)
; Hill; David R.; (Gurnee, IL) ; Abrahamson;
Michael J.; (Chicago, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
AbbVie Inc. |
North Chicago |
IL |
US |
|
|
Family ID: |
60189564 |
Appl. No.: |
16/578764 |
Filed: |
September 23, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15789133 |
Oct 20, 2017 |
10421712 |
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16578764 |
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14802392 |
Jul 17, 2015 |
9809534 |
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15789133 |
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62026854 |
Jul 21, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C07C 67/347 20130101;
C07C 69/08 20130101; C07C 2601/14 20170501; C12P 41/005 20130101;
C07C 271/24 20130101; C07C 211/27 20130101; C07C 211/35 20130101;
C07C 67/31 20130101; C07C 269/06 20130101; C07B 2200/07 20130101;
C07C 67/343 20130101; C07C 69/708 20130101; C07C 69/74 20130101;
C12P 7/62 20130101; C07C 67/333 20130101; C07C 2601/02 20170501;
C07C 269/08 20130101; C07C 269/00 20130101; C07C 69/65 20130101;
C07C 269/06 20130101; C07C 271/24 20130101; C07C 269/08 20130101;
C07C 271/24 20130101; C07C 269/00 20130101; C07C 271/24 20130101;
C07C 67/31 20130101; C07C 69/708 20130101; C07C 67/343 20130101;
C07C 69/65 20130101 |
International
Class: |
C07C 271/24 20060101
C07C271/24; C12P 7/62 20060101 C12P007/62; C07C 67/347 20060101
C07C067/347; C07C 67/333 20060101 C07C067/333; C07C 69/74 20060101
C07C069/74; C07C 269/06 20060101 C07C269/06; C12P 41/00 20060101
C12P041/00; C07C 269/08 20060101 C07C269/08; C07C 269/00 20060101
C07C269/00; C07C 211/35 20060101 C07C211/35; C07C 211/27 20060101
C07C211/27; C07C 69/65 20060101 C07C069/65 |
Claims
1-16. (canceled)
17. A method, comprising combining a compound of formula A with a
compound of formula B at a first temperature for a first period of
time in the presence of a first metal, a first solvent, and
optionally a first base, thereby forming a first product mixture
comprising a compound of formula C, wherein formula A is
##STR00104## formula B is ##STR00105## formula C is ##STR00106## R
is alkyl; and and R' is alkyl.
18. The method of claim 17, wherein the first metal comprises
TiCl.sub.4, TiOR.sub.4, CeCl.sub.3, Ce.sub.2(SO.sub.4).sub.3,
CaCl.sub.2, MgCl.sub.2, Ti(Oi-Pr).sub.3Cl or Ti(OEt).sub.3Cl.
19. The method of claim 17, wherein the first base is present; and
the first base comprises (i-Pr).sub.2EtN, triethylamine,
EtNH.sub.2, Et.sub.2NH, or (iPr).sub.2NH.
20. The method of claim 19, wherein the first base is
triethylamine.
21. The method of claim 17, wherein the first metal is CeCl.sub.3
or MgCl.sub.2; and the first base is absent.
22. The method of claim 17, wherein the first metal is CeCl.sub.3
or MgCl.sub.2; and the first metal is present in a catalytic
quantity.
23. The method of claim 17, wherein the first metal is TiCl.sub.4,
TiOR.sub.4, Ti(Oi-Pr).sub.3Cl, or Ti(OEt).sub.3Cl; and the first
metal is present in a stoichiometric quantity.
24. The method of claim 17, wherein the first solvent comprises
MeOH, EtOH, n-PrOH, i-PrOH, tetrahydrofuran (THF), methyl
tert-butyl ether, ethyl acetate, dioxane, DMF, acetonitrile, or
DMSO.
25. The method of claim 24, wherein the first metal is TiCl.sub.4,
TiOR.sub.4, Ti(Oi-Pr).sub.3Cl, or Ti(OEt).sub.3Cl.
26. The method of claim 24, wherein the first metal is CeCl.sub.3
or MgCl.sub.2.
27. The method of claim 17, wherein the first temperature is from
about -10.degree. C. to about 15.degree. C.
28. The method of claim 17, wherein the first period of time is
from about 6 h to about 18 h.
29. The method of claim 17, further comprising heating the first
product mixture at a second temperature.
30. The method of claim 29, wherein the first product mixture is
maintained at the second temperature for a second period of
time.
31. The method of claim 17, further comprising heating the first
product mixture at a third temperature.
32. The method of claim 31, wherein the first product mixture is
maintained at the third temperature for a third period of time.
33. The method of claim 17, further comprising isolating the
compound of formula C from the first product mixture, thereby
forming substantially pure compound of formula C.
34. The method of claim 17, wherein R is ethyl, n-propyl, or
isopropyl.
35. The method of claim 17, wherein the compound of formula C is
##STR00107##
36. The method of claim 17, wherein the compound of formula C is
##STR00108##
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of priority to U.S.
Provisional Patent Application Ser. No. 62/026,854, filed Jul. 21,
2014, the contents of which are hereby incorporated by
reference.
BACKGROUND
[0002] Complex biologically active molecules are challenging,
expensive, and time-consuming to synthesize. Synthesizing chiral,
non-racemic compounds with good enantio- and diastereoselectivity
is even more challenging. An example of such a molecule is Compound
1:
##STR00001##
This compound is a potent inhibitor of the hepatitis C virus (HCV)
NS3/4A protease; it shows broad genotype activity and substantially
improved in vitro profile compared to earlier generation HCV NS3/4A
protease inhibitors. While synthetic routes to this compound exist,
the existing methods typically require, for example, high catalyst
loading, dilute reaction conditions, and the use of expensive
starting materials. Of particular interest is the
difluoromethylcyclopropyl amino acid substituent. Previous
synthetic methods relied upon corrosive fluorination chemistry to
synthesize this feature; however, such fluorination reactions are
difficult to adapt for large-scale production of Compound 1.
[0003] There exists a need for new synthetic methods to construct
enantioenriched difluoroalkylcyclopropyl amino acids and
esters.
SUMMARY OF THE INVENTION
[0004] In certain embodiments, the invention relates to a compound,
or a salt thereof, having a structure selected from:
##STR00002##
wherein, independently for each occurrence,
[0005] R is alkyl; and
[0006] R' is alkyl.
[0007] In certain embodiments, the invention relates to a
hydrolysis method comprising:
[0008] contacting, in an eighth solvent, a compound of formula I
with a fifth base, thereby forming a compound of formula J;
[0009] wherein
[0010] formula I is
##STR00003##
[0011] formula J is
##STR00004##
or a salt thereof; and
[0012] R is alkyl.
[0013] In certain embodiments, the invention relates to an
enantioenrichment method comprising:
[0014] subjecting a compound of formula F to simulated moving bed
chromatography, thereby obtaining the enantioenriched compound of
formula I;
[0015] wherein
[0016] formula F is
##STR00005##
[0017] formula I is
##STR00006##
and
[0018] R is alkyl.
[0019] In certain embodiments, the invention relates to a method
according to reaction scheme A:
##STR00007##
[0020] wherein R is alkyl.
[0021] In certain embodiments, the invention relates to a
sequential selective hydrolysis method comprising:
[0022] selectively hydrolyzing with a first enzyme the
2S-enantiomer of a compound of formula D, thereby forming a
fourteenth product mixture;
[0023] separating from the fourteenth product mixture an
enantioenriched amount of the 2R-enantiomer of a compound of
formula D, thereby forming a fifteenth product mixture comprising
an enantioenriched compound of formula G;
[0024] regioselectively hydrolyzing with a second enzyme the
compound of formula G, thereby forming a sixteenth product mixture
comprising a compound of formula H,
[0025] wherein
[0026] formula D is
##STR00008##
[0027] formula G is
##STR00009##
[0028] formula H is
##STR00010##
or a salt thereof; and
[0029] R is alkyl.
[0030] In certain embodiments, the invention relates to a method
according to reaction scheme B:
##STR00011##
[0031] wherein R is alkyl.
[0032] In certain embodiments, the invention relates to a
cyclopropanation method comprising:
[0033] heating a compound of formula C and trimethylsulfoxonium
iodide in the presence of a second base and a second solvent at a
fourth temperature for a fourth period of time, thereby forming a
third product mixture comprising a compound of formula D,
[0034] wherein
[0035] formula C is
##STR00012##
[0036] formula D is
##STR00013##
and
[0037] R is alkyl.
[0038] In certain embodiments, the compound of formula C is in
admixture with
##STR00014##
[0039] In certain embodiments, the invention relates to a
condensation method comprising:
[0040] combining a compound of formula A with a compound of formula
B at a first temperature for a first period of time in the presence
of a first metal, a first solvent, and optionally a first base,
thereby forming a first product mixture comprising a compound of
formula C,
[0041] wherein
[0042] formula A is
##STR00015##
[0043] formula B is
##STR00016##
[0044] formula C is
##STR00017##
[0045] R is alkyl; and
[0046] and R' is alkyl.
[0047] In certain embodiments, the first product mixture further
comprises
##STR00018##
DETAILED DESCRIPTION OF THE INVENTION
I. Overview
[0048] In certain embodiments, the invention relates to a method of
synthesizing compound 54, a difluoroamino acid, that is based on a
Knoevenagel condensation, cyclopropanation, and resolution
sequence. In certain embodiments, the resolution is accomplished by
simulated moving bed chromatography. In certain embodiments, the
resolution is an enzymatic resolution. In certain embodiments, the
inventive synthesis of compound 54 eliminates the need for
corrosive fluorination chemistry.
##STR00019##
[0049] In certain embodiments, the invention relates to the
synthesis of cyclopropyl diester 76. In certain embodiments, 76 is
synthesized via a two-step Knoevenagel
condensation/cyclopropanation sequence.
[0050] In certain embodiments, the invention relates to a method of
synthesizing 79. In certain embodiments, 79 is synthesized by
selective enzymatic hydrolysis. In certain embodiments, 79 is
resolved from a racemic mixture (78) by simulated moving bed (SMB)
chromatography or the like.
II. Definitions
[0051] Listed below are definitions of various terms used to
describe this invention. These definitions apply to the terms as
they are used throughout this specification and claims, unless
otherwise limited in specific instances, either individually or as
part of a larger group. The number of carbon atoms in a hydrocarbyl
substituent can be indicated by the prefix "C.sub.x-C.sub.y," where
x is the minimum and y is the maximum number of carbon atoms in the
substituent.
[0052] The term "alkyl" as used herein, refers to a saturated,
straight- or branched-chain hydrocarbon radical typically
containing from 1 to 20 carbon atoms. For example, "C.sub.1-C.sub.6
alkyl" or "C.sub.1-C.sub.8 alkyl" contains from one to six, or from
one to eight, carbon atoms, respectively.
[0053] Examples of alkyl radicals include, but are not limited to,
methyl, ethyl, propyl, isopropyl, n-butyl, tert-butyl, neopentyl,
n-hexyl, heptyl, octyl radicals and the like.
[0054] The term "cycloalkyl" denotes a monovalent group derived
from a monocyclic or polycyclic saturated carbocyclic ring
compound. Examples of cycloalkyl include, but are not limited to,
cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl,
bicyclo[2.2.1]heptyl, and bicyclo[2.2.2]octyl and the like.
[0055] The term "amino-protecting group," as used herein, refers to
a labile chemical moiety that can protect an amino group against
undesired reactions during synthetic procedures. After said
synthetic procedure(s) the amino-protecting group as described
herein may be selectively removed. Suitable amino-protecting groups
are described generally in T. H. Greene and P. G. M. Wuts,
Protective Groups in Organic Synthesis, 3rd edition, John Wiley
& Sons, New York (1999). Examples of amino-protecting groups
include, but are not limited to, t-butoxycarbonyl,
9-fluorenylmethoxycarbonyl, benzyloxycarbonyl, and the like.
[0056] The term "protected amino," as used herein, refers to an
amino group protected with an amino-protecting group as defined
above.
[0057] As used herein, the term "salt" includes "pharmaceutically
acceptable salts," which are, within the scope of sound medical
judgment, suitable for use in contact with the tissues of humans
and other vertebrates, preferably mammals, without undue toxicity,
irritation, allergic response and the like, and are commensurate
with a reasonable benefit/risk ratio. Pharmaceutically acceptable
salts are well known in the art. For example, S. M. Berge, et al.
describe pharmaceutically acceptable salts in detail in J.
Pharmaceutical Sciences, 66: 1-19 (1977). Such salts can be
prepared in situ during isolation and purification of reaction
products as described herein, or separately, such as by reacting a
free base function with a suitable acid, such as an organic acid.
Examples of pharmaceutically acceptable salts include, but are not
limited to, hydrochloride, hydrobromide, phosphate, sulfate,
perchlorate, acetate, maleate, tartrate, citrate, succinate, or
malonate. Other pharmaceutically acceptable salts include, but are
not limited to, adipate, alginate, ascorbate, aspartate,
benzenesulfonate, benzoate, bisulfate, borate, butyrate,
camphorate, camphorsulfonate, cyclopentanepropionate, digluconate,
dodecylsulfate, ethanesulfonate, formate, fumarate, glucoheptonate,
glycerophosphate, gluconate, hemisulfate, heptanoate, hexanoate,
hydroiodide, 2-hydroxy-ethanesulfonate, lactobionate, lactate,
laurate, lauryl sulfate, malate, methanesulfonate,
2-naphthalenesulfonate, nicotinate, nitrate, oleate, oxalate,
palmitate, pamoate, pectinate, persulfate, 3-phenylpropionate,
phosphate, picrate, pivalate, propionate, stearate, sulfate,
thiocyanate, p-toluenesulfonate, undecanoate, valerate salts, and
the like. Representative alkali or alkaline earth metal salts
include sodium, lithium, potassium, calcium, or magnesium salts,
and the like. Further pharmaceutically acceptable salts include,
when appropriate, ammonium, quaternary ammonium, and amine cations
associated with counterions such as halide, hydroxide, carboxylate,
sulfate, phosphate, nitrate, alkyl having from 1 to 6 carbon atoms,
sulfonate and aryl sulfonate. Particularly preferred salts for
organic compounds having carboxylic acid functionality include
metal salts and quaternary amine salts.
[0058] As used herein, the term "enantioenriched" means a mixture
of enantiomers in which one of the two enantiomers is present in a
larger amount. This term also encompasses an enantiomerically pure
compounds (i.e., a compound having an enantiomeric excess (ee)
greater than about 90%, greater than about 95%, preferably greater
than about 98%, most preferably greater than 99%).
[0059] Various aspects of the invention are described in further
detail herein.
III. Exemplary Compounds
[0060] In certain embodiments, the invention relates to a compound,
or a salt thereof, having a structure selected from:
##STR00020##
wherein, independently for each occurrence,
[0061] R is alkyl; and
[0062] R' is alkyl.
[0063] In certain embodiments, the invention relates to any one of
the compounds described herein, wherein R is lower alkyl.
[0064] In certain embodiments, the invention relates to any one of
the compounds described herein, wherein R is ethyl.
[0065] In certain embodiments, the invention relates to any one of
the compounds described herein, wherein R is propyl.
[0066] In certain embodiments, the invention relates to any one of
the compounds described herein, wherein R is isopropyl.
[0067] In certain embodiments, the invention relates to
##STR00021##
or a salt thereof.
[0068] In certain embodiments, the invention relates to
##STR00022##
In certain embodiments, the invention relates to
##STR00023##
in crystalline form.
[0069] In certain embodiments, the invention relates to
##STR00024##
In certain embodiments, the invention relates to
##STR00025##
in crystalline form.
[0070] In certain embodiments, the invention relates to
##STR00026##
In certain embodiments, the invention relates to
##STR00027##
in crystalline form.
[0071] In certain embodiments, the invention relates to
##STR00028##
In certain embodiments, the invention relates to
##STR00029##
in crystalline form.
[0072] In certain embodiments, the invention relates to
##STR00030##
In certain embodiments, the invention relates to
##STR00031##
in crystalline form.
[0073] In certain embodiments, the invention relates to
##STR00032##
In certain embodiments, the invention relates to
##STR00033##
in crystalline form.
[0074] In certain embodiments, the invention relates to
##STR00034##
[0075] In certain embodiments, the invention relates to
##STR00035##
[0076] In certain embodiments, the invention relates to
##STR00036##
In certain embodiments, the invention relates to
##STR00037##
in crystalline form.
[0077] In certain embodiments, the invention relates to
##STR00038##
In certain embodiments, the invention relates to
##STR00039##
in crystalline form.
[0078] In certain embodiments, the invention relates to
##STR00040##
In certain embodiments, the invention relates to
##STR00041##
in crystalline form.
[0079] In certain embodiments, the invention relates to
##STR00042##
In certain embodiments, the invention relates to
##STR00043##
in crystalline form.
[0080] In certain embodiments, the invention relates to
##STR00044##
[0081] In certain embodiments, the invention relates to
##STR00045##
[0082] In certain embodiments, the invention relates to
##STR00046##
[0083] In certain embodiments, the invention relates to
##STR00047##
[0084] In certain embodiments, the invention relates to
##STR00048##
wherein R' is ethyl.
[0085] In certain embodiments, the invention relates to
##STR00049##
wherein R' is propyl.
[0086] In certain embodiments, the invention relates to
##STR00050##
wherein R' is isopropyl.
[0087] In certain embodiments, the invention relates to
##STR00051##
[0088] In certain embodiments, the invention relates to
##STR00052##
IV. Exemplary Methods and Uses
[0089] The compounds and processes of the present invention will be
better understood in connection with the following illustrative
methods by which the compounds of the invention may be prepared. It
will be understood that any reaction described herein, in any of
its variations, can be combined in sequence with one or more of the
other reactions described herein, in any of their variations,
substantially in analogy with the sequence shown in Scheme 1.
[0090] In certain embodiments, the invention relates to a
hydrolysis method comprising:
[0091] contacting, in an eighth solvent, a compound of formula I
with a fifth base, thereby forming a compound of formula J;
[0092] wherein
[0093] formula I is
##STR00053##
[0094] formula J is
##STR00054##
or a salt thereof; and
[0095] R is alkyl.
[0096] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the fifth base comprises KOH,
NaOH, or LiOH, preferably NaOH or LiOH.
[0097] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the eighth solvent comprises
EtOH, n-PrOH, i-PrOH, ethyl acetate, dioxane, DMF, acetonitrile,
water or DMSO, preferably water or acetonitrile, or a mixture of
water and EtOH, n-PrOH, or i-PrOH.
[0098] In certain embodiments, the invention relates to an
enantioenrichment method comprising:
[0099] to subjecting a compound of formula F to simulated moving
bed chromatography, thereby obtaining the enantioenriched compound
of formula I;
[0100] wherein
[0101] formula F is
##STR00055##
[0102] formula I is
##STR00056##
and
[0103] R is alkyl.
[0104] In certain embodiments, the invention relates to a method
according to reaction scheme A:
##STR00057##
[0105] wherein R is alkyl.
[0106] In certain embodiments, the invention relates to a method
according to reaction scheme A':
##STR00058##
[0107] wherein R is alkyl.
[0108] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the fourth base comprises
i-Pr.sub.3N, (i-Pr).sub.2EtN, or triethylamine, preferably
triethylamine.
[0109] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the fourth base comprises
i-Pr.sub.3N, (i-Pr).sub.2EtN, triethylamine, EtNH.sub.2,
Et.sub.2NH, or (iPr).sub.2NH, preferably a tertiary amine, such as
triethylamine.
[0110] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the seventh solvent comprises
heptane, toluene, methyl tert-butyl ether, or dioxane, preferably
heptane.
[0111] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the N.sub.3-- source is a
diarylphosphorylazide (such as diphenylphosphorylazide) or
tosylazide, preferably diphenylphosphorylazide.
[0112] In certain embodiments, the invention relates to any one of
the methods described herein, further comprising crystallizing the
reaction product of reaction scheme A or reaction scheme A' to
obtain the compound in a crystalline form.
[0113] In certain embodiments, the invention relates to a
sequential selective hydrolysis method comprising:
[0114] selectively hydrolyzing with a first enzyme the
2S-enantiomer of a compound of formula D, thereby forming a
fourteenth product mixture;
[0115] separating from the fourteenth product mixture an
enantioenriched amount of the 2R-enantiomer of a compound of
formula D, thereby forming a fifteenth product mixture comprising
an enantioenriched compound of formula G;
[0116] regioselectively hydrolyzing with a second enzyme the
compound of formula G, thereby forming a sixteenth product mixture
comprising a compound of formula H,
[0117] wherein
[0118] formula D is
##STR00059##
[0119] formula G is
##STR00060##
[0120] formula H is
##STR00061##
or a salt thereof; and
[0121] R is alkyl.
[0122] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the selective hydrolysis the
2S-enantiomer of a compound of formula D takes place in a first
buffer.
[0123] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the first buffer comprises
sodium phosphate.
[0124] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the first buffer comprises
sodium phosphate at a concentration from about 0.25 M to about 0.75
M. In certain embodiments, the invention relates to any one of the
methods described herein, wherein the first buffer comprises sodium
phosphate at a concentration of about 0.3 M, about 0.4 M, about 0.5
M, about 0.6 M, or about 0.7 M.
[0125] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the first buffer comprises
sodium phosphate at about pH 7.
[0126] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the first enzyme is RML
enzyme.
[0127] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the second enzyme is yvaK
esterase.
[0128] In certain embodiments, the invention relates to any one of
the methods described herein, further comprising isolating the
compound of formula H from the sixteenth product mixture, thereby
obtaining substantially pure compound of formula H.
[0129] In certain embodiments, the invention relates to a method
according to reaction scheme B:
##STR00062##
[0130] wherein R is alkyl.
[0131] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the third base comprises
BnMe3NOH (Triton B), CsOH, ammonium hydroxide, tetraalkylammonium
hydroxide (such as tetrabutylammonium hydroxide), KOH, NaOH, or
LiOH, preferably KOH or tetrabutylammonium hydroxide.
[0132] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the third solvent comprises
t-BuOH, n-BuOH, n-PrOH, i-PrOH, EtOH, MeOH, or water, preferably
i-PrOH, n-PrOH, EtOH, or water.
[0133] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the fifth temperature is from
about 15.degree. C. to about 40.degree. C., for example, about
15.degree. C., about 20.degree. C., about 23.degree. C., about
25.degree. C., about 30.degree. C., about 35.degree. C., or about
40.degree. C., preferably about 23.degree. C.
[0134] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the fifth period of time is
from about 1 h to about 18 h, for example, about 2 h, about 3 h,
about 4 h, about 5 h, about 6 h, about 7 h, about 8 h, about 9 h,
about 10 h, about 11 h, about 12 h, about 13 h, about 14 h, about
15 h, about 16 h, about 17 h, or about 18 h.
[0135] In certain embodiments, the invention relates to any one of
the methods described herein, further comprising the step of
crystallizing the reaction product of reaction scheme B to obtain
the compound in a crystalline form.
[0136] In certain embodiments, the invention relates to any one of
the methods described herein, further comprising the step of
contacting the reaction product of reaction scheme B with a base to
obtain a salt of the compound. In certain embodiments, the
invention relates to any one of the methods described herein,
further comprising the step of contacting the reaction product of
reaction scheme B with a base to obtain a salt of the compound in a
crystalline form.
[0137] In certain embodiments, the invention relates to any one of
the methods described herein,
[0138] wherein the reaction product of reaction scheme B is
##STR00063##
[0139] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the reaction product of
reaction scheme B is
##STR00064##
[0140] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the reaction product of
reaction scheme B is
##STR00065##
[0141] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the reaction product of
reaction scheme B is
##STR00066##
[0142] In certain embodiments, the invention relates to a
cyclopropanation method comprising:
[0143] heating a compound of formula C and trimethylsulfoxonium
iodide in the presence of a second base and a second solvent at a
fourth temperature for a fourth period of time, thereby forming a
third product mixture comprising a compound of formula D,
[0144] wherein
[0145] formula C is
##STR00067##
[0146] formula D is
##STR00068##
and
[0147] R is alkyl.
[0148] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the compound of formula C is
present in a mixture with
##STR00069##
and R' is alkyl.
[0149] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the second base comprises
NaH, LiH, NaHMDS, LiHMDS, KOt-Bu, or NaOt-Bu, preferably
KOt-Bu.
[0150] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the second base comprises
NaH, LiH, NaHMDS, LiHMDS, KOt-Bu, NaOt-Bu, (iPr).sub.2NH,
triethylamine, preferably KOt-Bu.
[0151] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the second solvent comprises
dimethylformamide (DMF), THF, methyl tert-butyl ether, ethyl
acetate, dioxane, acetonitrile, or DMSO, preferably DMF.
[0152] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the fourth temperature is
from about 35.degree. C. to about 75.degree. C., for example, about
35.degree. C., about 40.degree. C., about 45.degree. C., about
50.degree. C., about 55.degree. C., about 60.degree. C., about
65.degree. C., about 70.degree. C., or about 75.degree. C.,
preferably about 55.degree. C.
[0153] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the fourth period of time is
from about 1 h to about 8 h, for example, about 1 h, about 2 h,
about 3 h, about 4 h, about 5 h, about 6 h, about 7 h, or about 8
h, preferably about 5 h.
[0154] In certain embodiments, the invention relates to any one of
the methods described herein, further comprising isolating the
compound of formula D from the third product mixture, thereby
forming substantially pure compound of formula D.
[0155] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the compound is
##STR00070##
[0156] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the compound is
##STR00071##
[0157] In certain embodiments, the invention relates to a
condensation method comprising:
[0158] combining a compound of formula A with a compound of formula
B at a first temperature for a first period of time in the presence
of a first metal, a first solvent, and optionally a first base,
thereby forming a first product mixture comprising a compound of
formula C,
[0159] wherein
[0160] formula A is
##STR00072##
[0161] formula B is
##STR00073##
[0162] formula C is
##STR00074##
[0163] R is alkyl; and
[0164] and R' is alkyl.
[0165] In certain embodiments, the invention relates to any one of
the methods described herein,
[0166] wherein the first product mixture further comprises
##STR00075##
[0167] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the first metal comprises a
titanium Lewis acid, such as a titanium alkoxide halide.
[0168] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the first metal comprises
TiCl.sub.4, TiOR.sub.4, CeCl.sub.3, Ce.sub.2(SO.sub.4).sub.3,
CaCl.sub.2, MgCl.sub.2, Ti(Oi-Pr).sub.3Cl or Ti(OEt).sub.3Cl.
[0169] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the first base is present;
and the first base comprises (i-Pr).sub.2EtN, or triethylamine,
preferably triethylamine.
[0170] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the first base is present;
and the first base comprises (i-Pr)2EtN, triethylamine, EtNH2,
Et.sub.2NH, or (iPr).sub.2NH, preferably a tertiary amine, such as
triethylamine.
[0171] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the first metal is CeCl.sub.3
or MgCl.sub.2; and the first base is absent.
[0172] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the first metal is CeCl.sub.3
or MgCl.sub.2; and the first metal is present in a catalytic
quantity.
[0173] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the first metal is
TiC;.sub.4, TiOR.sub.4, Ti(Oi-Pr).sub.3Cl, or Ti(OEt).sub.3Cl; and
the first metal is present in a stoichiometric quantity.
[0174] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the first solvent comprises
MeOH, EtOH, n-PrOH, i-PrOH, tetrahydrofuran (THF), methyl
tert-butyl ether, ethyl acetate, dioxane, DMF, acetonitrile, or
DMSO, preferably THF.
[0175] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the first metal is
TiCl.sub.4, TiOR.sub.4, Ti(Oi-Pr).sub.3Cl, or Ti(OEt).sub.3Cl; and
the first solvent comprises MeOH, EtOH, n-PrOH, i-PrOH,
tetrahydrofuran (THF), methyl tert-butyl ether, ethyl acetate,
dioxane, DMF, acetonitrile, or DMSO, preferably THF.
[0176] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the first metal is CeCl.sub.3
or MgCl.sub.2; and the first solvent comprises MeOH, EtOH, n-PrOH,
i-PrOH, tetrahydrofuran (THF), methyl tert-butyl ether, ethyl
acetate, dioxane, DMF, acetonitrile, or DMSO, preferably MeOH,
EtOH, n-PrOH, or i-PrOH.
[0177] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the first temperature is from
about -10.degree. C. to about 15.degree. C., for example about
-10.degree. C., about -5.degree. C., about 0.degree. C., about
5.degree. C., about 10.degree. C., or about 15.degree. C.,
preferably about 0.degree. C.
[0178] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the first period of time is
from about 6 h to about 18 h, for example, about 6 h, about 7 h,
about 8 h, about 9 h, about 10 h, about 11 h, about 12 h, about 13
h, about 14 h, about 15 h, about 16 h, about 17 h, or about 18 h,
preferably about 12 h.
[0179] In certain embodiments, the invention relates to any one of
the methods described herein, further comprising heating the first
product mixture at a second temperature.
[0180] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the second temperature is
from about 16.degree. C. to about 30.degree. C., for example, about
20.degree. C., about 23.degree. C., about 25.degree. C., or about
30.degree. C., preferably about 23.degree. C.
[0181] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the first product mixture is
maintained at the second temperature for a second period of
time.
[0182] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the second period of time is
from about 1 h to about 3 h, for example, about 1 h, about 1.5 h,
about 2 h, about 2.5 h, or about 3 h, preferably about 1.5 h.
[0183] In certain embodiments, the invention relates to any one of
the methods described herein, further comprising heating the first
product mixture at a third temperature.
[0184] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the third temperature is from
about 35.degree. C. to about 75.degree. C., for example, about
35.degree. C., about 40.degree. C., about 45.degree. C., about
50.degree. C., about 55.degree. C., about 60.degree. C., about
65.degree. C., about 70.degree. C., or about 75.degree. C.,
preferably about 55.degree. C.
[0185] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the first product mixture is
maintained at the third temperature for a third period of time.
[0186] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the third period of time is
from about 1 h to about 3 h, for example, about 1 h, about 1.5 h,
about 2 h, about 2.5 h, or about 3 h, preferably about 1.5 h.
[0187] In certain embodiments, the invention relates to any one of
the methods described herein, further comprising isolating the
compound of formula C from the first product mixture, thereby
forming substantially pure compound of formula C.
[0188] In certain embodiments, the invention relates to any one of
the methods described herein, wherein R is ethyl.
[0189] In certain embodiments, the invention relates to any one of
the methods described herein, wherein R is propyl.
[0190] In certain embodiments, the invention relates to any one of
the methods described herein, wherein R is isopropyl.
[0191] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the compound of formula C
is
##STR00076##
[0192] In certain embodiments, the invention relates to any one of
the methods described herein, wherein the compound of formula C
is
##STR00077##
[0193] In certain embodiments, the invention relates to any one of
the methods described herein, further comprising the steps outlined
in any other method described herein.
[0194] In certain embodiments, the invention relates to the use of
any one of the compounds described herein in the manufacture of a
medicament.
[0195] Definitions of variables in the structures in the schemes
herein are commensurate with those of corresponding positions in
the formulae delineated herein.
[0196] The compounds described herein contain one or more
asymmetric centers and thus give rise to enantiomers,
diastereomers, and other stereoisomeric forms that may be defined,
in terms of absolute stereochemistry, as (R)- or (S)-, or as (D)-
or (L)- for amino acids. Optical isomers may be prepared from their
respective optically active precursors by the procedures described
above, or by resolving the racemic mixtures. The resolution can be
carried out in the presence of a resolving agent, by chromatography
or by repeated crystallization or by some combination of these
techniques which are known to those skilled in the art. Further
details regarding resolutions can be found in Jacques, et al.,
Enantiomers. Racemates, and Resolutions (John Wiley & Sons,
1981).
[0197] The synthesized compounds can be separated from a reaction
mixture and further purified by a method such as column
chromatography, high pressure liquid chromatography, or
recrystallization. As can be appreciated by the skilled artisan,
further methods of synthesizing the compounds of the formulae
herein will be evident to those of ordinary skill in the art.
Additionally, the various synthetic steps may be performed in an
alternate sequence or order to give the desired compounds. In
addition, the solvents, temperatures, reaction durations, etc.
delineated herein are for purposes of illustration only and one of
ordinary skill in the art will recognize that variation of the
reaction conditions can produce the desired bridged macrocyclic
products of the present invention. Synthetic chemistry
transformations and protecting group methodologies (protection and
deprotection) useful in synthesizing the compounds described herein
are known in the art and include, for example, those such as
described in R. Larock, Comprehensive Organic Transformations, VCH
Publishers (1989); T. W. Greene and P. G. M. Wuts, Protective
Groups in Organic Synthesis, 2d. Ed., John Wiley and Sons (1991):
L. Fieser and M. Fieser, Fieser and Fieser's Reagents for Organic
Synthesis, John Wiley and Sons (1994); and L. Paquette, ed.,
Encyclopedia of Reagents for Organic Synthesis, John Wiley and Sons
(1995), and subsequent editions thereof.
[0198] The recitation of a listing of chemical groups in any
definition of a variable herein includes definitions of that
variable as any single group or combination of listed groups. The
recitation of an embodiment for a variable herein includes that
embodiment as any single embodiment or in combination with any
other embodiments or portions thereof.
EXEMPLIFICATION
[0199] The present invention is further illustrated by the
following Example which should not be construed as limiting in any
way. The Examples and discoveries described herein are
representative. As such, the studies and results described in the
Examples section herein may be used as a guideline.
Example 1--Synthesis of 54 via Cyclopropanation
Overview
[0200] The cyclopropanation route for the synthesis of compound 54
is outlined in Scheme 1. The synthesis starts with the Knoevenagel
condensation of diethylmalonate 74 with hemi-acetal 73 followed by
cyclopropanation to give diester 76. The Knoevenagel condensation
of malonate esters with the aldehyde hemiacetal 73 can be conducted
with Lewis acids such as TiCl.sub.4, Ti(OEt).sub.4,
TiCl(OEt).sub.3, CeCl.sub.3, Ce.sub.2(SO.sub.4).sub.3, MgCl.sub.2,
CaCl.sub.2 and the like. Two methods were developed for the
conversion of the racemic diester 76 into the enantiomerically pure
acid 54. The first method involves simulated moving bed
chromatographic resolution of the racemic ester 78 to give the
resolved (R,R) ester 79. The second method utilizes enzymatic
resolution of 76 to prepare the resolved (R,R) acid 96. Both
methods converge at the last step in the saponification of the
resolved ester 79 to the acid 54.
Knoevenagel Condensation with Catalytic CeCl.sub.3/NaI
##STR00078##
[0201] To a flask was charged CeCl.sub.13 (1.54 g, 6.25 mmol, 0.05
equiv), NaI (0.94 g, 6.25 mmol, 0.05 equiv) and ethanol (80 mL) and
the mixture was stirred with heating to 65.degree. C. At reaction
temperature of 65.degree. C. a pre-mixed solution of diethyl
malonate (20 g, 125 mmol) and 21.0 g difluoroacetaldehyde ethyl
hemiacetal (90% w/w, 150 mmol, 1.2 equiv) was charged. The
resulting mixture was stirred at 60-65.degree. C. Upon completion
the reaction was cooled to ambient temperature and inorganic solids
were filtered off. The filtrate was concentrated under vacuum to
near completion, diluted with dimethylformamide (DMF) (74 g), and
concentrated under vacuum to remove the residual ethanol. The DMF
solution is used directly in the next step as both 75a and 75b are
converted to product in the cyclopropanation step.
Knoevenagel Condensation with Catalytic MgCl.sub.2
##STR00079##
[0202] To a flask was charged MgCl.sub.2 (1.189 g,12.49) and EtOH
(140 mL, 200 proof) and to this solution at ambient temperature,
difluoroacetaldehyde ethyl hemiacetal (38.5 g, 90% w/w, 275 mmol,
1.1 equiv) was charged, followed by addition of diethyl malonate
(40.0 g, 250 mmol).
[0203] The resulting mixture was stirred at 60-65.degree. C. Upon
completion the reaction mixture was cooled to ambient temperature
and concentrated under vacuum to remove most of the ethanol. The
mixture was filtered to remove inorganic salts, DMF (74 g) was
added to the filtrate, and concentrated under vacuum to remove the
residual ethanol. The DMF solution is used directly in the next
step.
[0204] Alternatively the reaction mixture can be worked up by
concentration under vacuum to remove most of the ethanol, addition
of methyl tert-butyl ether (MTBE) (300 mL) and washing with 150 mL
1 M HCl and then 150 mL brine. The MTBE solution is dried with
MgSO.sub.4, filtered, concentrated under vacuum, diluted with DMF,
and concentrated under vacuum to remove the residual MTBE. The DMF
solution is used directly in the next step.
[0205] Other Lewis acids catalysts which have been tested include
CaCl.sub.2 and Ce.sub.2(SO.sub.4).sub.3.
Knoevenagel Condensation With TiCl(OEt).sub.3
##STR00080##
[0207] Titanium (IV) ethoxide (3.6 kg, 15.7 mol) and 2-MeTHF (18.5
kg) were charged to a flask. Acetyl chloride (1.2 kg, 15.7 mol) was
added, rinsing with 2-MeTHF (2.0 kg). The mixture heated to reflux
for 2 h and then cooled to 20.degree. C. and held overnight. The
mixture was cooled to -3.degree. C. and diethyl malonate (1.2 kg,
7.5 mol) was added, rinsing with 2-MeTHF (1.7 kg). The
difluoroacetaldehyde ethyl hemiacetal (1.0 kg, 7.5 mol) was added,
rinsing with 2-MeTHF (1.7 kg). Then triethylamine (1.6 kg, 15.7
mol) was added and the mixture stirred at 0.degree. C. for 4 h. The
mixture was gradually heated to 50-57 .degree. C. and mixed for 2 h
and then cooled to 20.degree. C. and held overnight. The mixture
was cooled to 3.degree. C. and quenched with 1 M HCl (10.9 kg),
mixed at 15.degree. C., and the layers separated. The organic layer
was wash with 1 M HCl (6.2 kg) and then 20% brine (6.8 kg). The
product solution was dried with MgSO.sub.4, filtered, rinsing with
2-MeTHF. The filtrate was concentrated under vacuum to near
completion, DMF (4.7 L) was added, and the concentration continued
to remove the 2-MeTHF. The DMF solution is used directly in the
next reaction.
Cyclopropanation
##STR00081##
[0209] To a flask was charged potassium tert-butoxide (1.0 kg, 9.0
mol, 1.2 equiv), trimethylsulfoxonium iodide (2.0 kg, 9.0 mol, 1.2
equiv), and DMF (7.0 L). The mixture was stirred for 2 h, and then
a solution of 75a and 75b (7.5 mol theoretical) mixture in DMF was
added. The reaction was heated to 55.degree. C. for 3.5 h and then
cooled to 5.degree. C. and mixed overnight. The reaction was
quenched with a cold mixture of MTBE (14.4 L) and water (14.4 L),
then mixed and warmed and the layers separated. The aqueous layer
was re-extracted with MTBE (14.4 L) and the combined organic layers
were washed with 20% brine (2.times.6.8 kg), and then with water
(2.times.6 kg). The product solution was concentrated and solvent
switched to EtOH and assayed for 80% yield of 76.
Chemical Hydrolysis
##STR00082##
[0211] Tetrabutylammonium hydroxide (40 wt % aqueous, 4.3 kg) was
added to the EtOH solution of compound 76 (7.5 mol theoretical from
74) and mixed at 20.degree. C. Upon reaction completion, MTBE (14.4
L) was added and the mixture was cooled and 0.5 M HCl (14.4 L) was
added. The mixture was warmed to 20.degree. C.; the aqueous layer
was separated and re-extracted with MTBE (6 L). The combined
organic layers were washed with 20% brine solution (6.8 kg), and
then water (6 L). The product was crystallized as the
dicyclohexylamine salt from MTBE/heptanes. After filtration and
drying a total of 1124 g of compound 77 was isolated (38% yield
from 74).
Curtius Rearrangement
##STR00083##
[0213] To a flask was charged compound 77 dicyclohexylammonium
(DCHA) salt (1.1 kg) and MTBE (11 L) and the mixture was washed
twice with 7% phosphoric acid (11 L, 5.2 L), once with 20% brine
(3.1 kg), and once with water (2.8 L). The organic layer was
diluted with heptane (5.5 L) and concentrated under vacuum to a
volume of .about.4 L. Then tert-butanol (1.1 kg) and heptane (4 L)
were added followed by triethylamine (437 g). The mixture was
heated to reflux (76.degree. C.) and then diphenylphosphorylazide
(757 g) was added over 1.5 h. After heating for 10 h, the mixture
was cooled to 20.degree. C. and concentrated under vacuum to a
volume of .about.4 L. The mixture was diluted with MTBE (5.8 L) and
successively washed with 5% aqueous citric acid (5.8 L), 8% aqueous
NaHCO.sub.3 (3.2 kg), 20% brine (3.4 kg), and water (3 L). The
product solution in MTBE was solvent switched to acetonitrile
(CH.sub.3CN or MeCN or ACN) and the final solution assayed for 542
g of 78 for a 68% yield.
Simulated Moving Bed Resolution
##STR00084##
[0215] Racemic Boc amino acid ethyl ester 78 was subjected to
simulated moving bed chromatography (SMB) to yield the (1R,2R)
enantiomer 79.
Saponification
##STR00085##
[0217] A solution of the Boc amino ethyl ester 79 (2 g, 7.16 mmol)
in acetonitrile (10 mL) was treated with a solution of LiOH (193
mg, 7.88 mmol 1.1 equiv) in water (10 mL). The mixture was stirred
at ambient temperature overnight. Upon reaction completion, 15%
aqueous citric acid was added to achieve a pH of 4-4.5. The mixture
was concentrated under vacuum to remove the acetonitrile and the
resulting mixture was diluted with 5 mL water. The resulting slurry
was mixed overnight at ambient temperature, filtered and washed
with 4 mL water. The wet cake was dried in a vacuum oven to give an
isolated yield of 80%.
Enzymatic Resolution
##STR00086##
[0219] The racemic diester 76 (1 g) was dissolved in 300 mL of 0.5
M sodium phosphate buffer, pH 7.0. To the reaction was added 15.3
mL of 3.times. dialyzed RML enzyme. The reaction was incubated at
30.degree. C. and 125 revolutions per minute (rpm) for 96 hrs. Upon
reaction completion, the desired unreacted (R) diester 98 was
recovered from the aqueous reaction phase by extraction into MTBE
(2.times.60 mL). The (S) acid 97 remained in the aqueous layer. The
combined MTBE extracts were dried using magnesium sulfate,
concentrated in vacuo and the recovered diester 98 was then
dissolved in 0.5 M 150 mL sodium phosphate, pH 7.0 for use in the
second resolution step.
[0220] YvaK clarified cell lysate (10 mL) was added to the solution
of diester 98 in the sodium phosphate buffer. The reaction was
incubated at 30.degree. C. and 125 rpm for 96 hrs. Upon reaction
completion, the pH was adjusted to 3 by addition of 5 N HCl. The
acid product 96 was recovered from reaction aqueous phase by
repeated extraction with MTBE (3.times.60 mL). The combined MTBE
extracts were dried using magnesium sulfate and evaporated in vacuo
to remove MTBE. The final recovered product (1S,2R) acid 96 in MTBE
was filtered through Celite.
[0221] The acid 96 can be converted into the DCHA salt as described
for compound 77. The acid 96, or its DCHA salt, can be converted
into acid 54 by following the procedures described for the Curtius
rearrangement (converting 77 to 78) and saponification (converting
79 to 54).
[0222] RML Dialysis Procedure: Mucor miehei lipase (RML, 6 mL) was
placed in .about.10 inches of 6-8 kDa molecular weight cut-off
(MWCO) dialysis membrane and dialyzed for 4 hours in 2 liters of
0.1M sodium phosphate buffer, pH 7.0 at 4.degree. C. and approx.
125 rpm. After 4 hours, the buffer was exchanged for 2 L of fresh
0.1M sodium phosphate buffer, pH 7.0 for an additional 24 hours.
After 24 hours, the buffer was exchanged a third time for 2 L of
fresh 0.1 M sodium phosphate buffer, pH 7.0 for an additional 24
hours. The final dialysis product results in .about.18 mL of
3.times. dialyzed RML.
[0223] YvaK Clarified Cell Lysate-Enzyme Preparation Procedure:
Bacillus subtilis esterase `yvaK` (Gene ID-BSU33620) was inserted
into pET21b vector at MCS between NdeI and BamHI restriction sites
and transformed into BL21(DE3) competent cells. The yvaK esterase
was subsequently expressed by growing the culture at 30.degree. C.,
225 rpm until an OD600 of 0.5-0.8. Protein expression was induced
with isopropyl .beta.-D-1-thiogalactopyranoside (IPTG) to 0.1 mM
and incubated for another for 18 hours. The resulting cell culture
was pelleted by centrifugation at 3750 rpm, 30 min, 4.degree. C.
and stored at -80.degree. C. until use. Cell pellets were
resuspended in 0.5 M sodium phosphate buffer, pH 7.0 at a ratio of
1:10 resuspension buffer volume to expression culture volume.
Resuspended culture was sonicated on ice three times for 30 s and
centrifuged at 3750 rpm, 30 min, 4.degree. C. The resulting
supernatant was used as the clarified cell lysate solution.
Example 2
Stage 1. Titanium-Mediated Knoevenagel
##STR00087##
[0225] A 2-L three-necked round bottom flask, equipped with a
mechanical stirrer, pressure equalizing addition funnel and reflux
condenser, was charged with chlorotitanium triisopropoxide (74.4 g,
68.2 mL, 285 mmol) and 570 mL THF [Note: Chlorotitanium
triisopropoxide is a solid at room temperature. We found that
warming the bottle in a 55.degree. C. bath for 30 min provided an
oil that could be easily transferred via syringe]. The solution was
cooled to 0.degree. C. and held at this temperature for 20 min. The
solution was then charged with diisopropyl malonate (26.9 g, 27.1
mL, 143 mmol) and difluoroacetaldehyde ethyl hemiacetal (20 g, 143
mmol, 90% purity) [Note: The purity was confirmed by .sup.1H-NMR
using 1,3-Bis(trifluoromethyl)-5-bromobenzene as an internal
standard]. The addition funnel was charged with triethylamine (28.9
g, 40 mL, 285 mmol) and added dropwise over 20 min [Note:
triethylamine hydrochloride begins precipitating upon addition].
Upon complete addition of triethylamine, the mixture was stirred at
0.degree. C. for 12 h (complete consumption of diisopropyl
malonate). The mixture was then warmed to ambient temperature and
allowed to stir for 1.5 hours. After this time, the mixture was
warmed to 55.degree. C. (bath temp) and stirred for an additional
1.5 h [Note: .sup.1H-NMR analysis showed nearly complete conversion
to the alkylidene malonate and <5% of the intermediate alcohol.
At this point .about.15% of the fully transesterified (bis-ethyl
ester) alkylidene malonate was present. This product can be reduced
to .about.5% by addition of titanium tetraisopropoxide (30.4 g,
31.7 mL, 107 mmol) and allowing the reaction to proceed at
55.degree. C. for an additional 12 h.]. When the reaction was
complete, it was cooled to 0.degree. C. with an ice bath, diluted
with 500 mL methyl tent-butyl ether (MTBE), and quenched by slow
addition of 250 mL 1 N HCl [Note: The mixture became very thick
after the addition of 50 mL of 1 N HCl. Upon addition of another 50
mL, the thick suspension became an easily stirred suspension and
after complete addition of HCl the solids were completely
dissolved]. The biphasic mixture was poured into a 3-L separatory
funnel and the layers were cut. The bottom aqueous phase was
extracted with an additional 500 mL MTBE [Note: The phase
separation was much slower with the second extraction and took
.about.20 min for clean phase separation]. The bottom aqueous layer
was again extracted with 500 mL MTBE, giving a very clean phase
cut. The organics were combined and washed with 100 mL 1 N HCl. The
phases cut and the organics washed with 500 mL sat. aq. NaCl. The
organic phase was dried over MgSO.sub.4, filtered, and concentrated
under reduced pressure. The mass of the crude oil was 36.3 g
(theory=35.7 g). This material was used without further
purification.
Stage 2. Cyclopropanation with Corey's Salt
##STR00088##
[0226] [Note: Reagent charges are based on 100% purity from the
previous reaction]. A 500-mL three-necked round bottom flask,
equipped with a mechanical stirrer and reflux condenser, was
charged with potassium tert-butoxide (19.3 g, 172 mmol),
trimethylsulphoxonium iodide (37.8 g, 172 mmol), and 140 mL
dimethylformamide (DMF) [Note: Trimethylsulphoxonium iodide
(Corey's salt) purchased from Aldrich was a pale yellow solid when
received. Recrystallization of the salt from water (15 g/150 mL
H.sub.2O) followed by grinding of the solid to a powder and drying
at 80.degree. C. overnight provided white crystals]. After 20 min
of stirring a clear solution was produced and was allowed to stir
for an additional 1.5 h. To the solution of the ylide was added a
solution of the alkylidene malonate (35.8 g, 143 mmol) prepared
above in 30 mL DMF [Note: An exotherm was noted upon addition and
an easily stirred precipitate is formed]. The reaction vessel was
placed in a preheated oil bath at 55.degree. C. and stirred at this
temperature for 2 h. After this time, the solution was cooled to
room temperature (an ice bath can be used to aid in the cooling
process) and 150 mL H.sub.2O and 500 mL MTBE pre-cooled to
0.degree. C. The biphasic mixture was stirred at 0.degree. C. for
15 min and the mixture was poured into a 3-L separatory funnel and
the layers were cut. The bottom aqueous phase was extracted three
times with 500 mL MTBE. The organic layers were combined and washed
with H.sub.2O (2.times.250 mL) and brine (2.times.250 mL). The
organic phase was dried over MgSO.sub.4, filtered, and concentrated
in vacuo. The mass of the crude oil was 35 g (theory=37.8 g). This
material was used without further purification.
Stage 3. Mono-Hydrolysis
##STR00089##
[0228] [Note: Reagent charges are based on 100% purity from the
previous reaction]. A 500-mL three-necked round bottom flask,
equipped with a mechanical stirrer and pressure equalizing addition
funnel, was charged with the bis-isopropyl ester (32.1 g, 121 mmol)
and isopropanol (150 mL). The addition funnel was charged with a
solution of KOH (9.6 g, 145 mmol, 85%) in H.sub.2O (30 mL). The KOH
solution was added over 4 h. The mixture was allowed to stir for an
additional 2 h at room temperature [Note: .sup.1H-NMR analysis
indicated .about.94% conversion and a 4:1 mixture of mono-acid to
di-acid]. The reaction mixture was cooled to 0.degree. C. and held
at this temperature for 20 min before the addition of 55 mL 2 N HCl
(.about.pH 2). The majority of the organic layer was removed under
reduced pressure and the remaining aqueous layer was poured into a
separatory funnel with the aid of MTBE. The aqueous layer was
extracted with MTBE (2.times.250 mL). The organics were then washed
with 100 mL sat. aq. NaCl, dried over MgSO.sub.4, filtered, and
concentrated under reduced pressure.
[0229] The crude oil was dissolved in a heptane:MTBE mixture (4:1,
300 mL) and cooled to 0.degree. C. Dibenzylamine (24 g, 23.4 mL,
121 mmol) was added to the cooled solution and the resulting slurry
was stirred at 0.degree. C. for 1 h [Note: A sonicating bath can be
used if a gel is formed on the bottom of the flask. Sonicating the
mixture for 20 min appears to break up the gel and produces an
easily stirred suspension.] The solids were filtered and washed
with 500 mL heptane to provide the crude dibenzylamine salt (48
g).
[0230] In order to remove the diacid by-product, the crude salt
(containing both the mono-acid and di-acid salts, .about.4:1) was
placed in a 2-L round bottom flask with 500 mL MTBE. The mixture
was heated at 60.degree. C. for 30 min and cooled to room
temperature [Note: the mono-acid salt is in solution and the
di-acid salt remains as a solid]. The remaining solid was filtered
from the mixture. [Note: The solid may be analyzed to ensure that
the mono-acid salt has been completely solubilized. The above
process can be repeated as necessary, adjusting the volume of MTBE
used]. The MTBE was then removed under reduced pressure to provide
an off white solid. Recrystallization of the mono-acid salt from
isopropyl alcohol (IPA) (100 mL) and drying under reduced pressure
provided the title compound (27.5 g, 54% overall yield) as a white
solid.
Stage 4. Curtius Rearrangement
##STR00090##
[0232] Salt Break: A 1-L round bottom flask, equipped with a teflon
coated magnetic stirbar, was charged with the above dibenzylamine
salt (20.3 g, 10.75 mmol) and MTBE (200 mL). To this suspension was
added a 15% H.sub.3PO.sub.4 solution (w/w, 200 mL) and the
resulting mixture was stirred at room temperature for 45 min. The
resulting solution was poured into a 1-L separatory funnel and the
layers were cut. The top organic layer was washed with an
additional 50 mL 15% H.sub.3PO.sub.4 and the layers cut. The
organic layer was then washed with sat. aq. NaCl, the layers cut,
and the organics dried over MgSO.sub.4. After filtration of the
MgSO.sub.4, the solvent was removed in vacuo. The free acid was
azeotropically dried with toluene (3.times.50 mL toluene) to remove
water to under 100 ppm. The final toluene solution (.about.20 mL
total volume) contained 96 ppm water (Karl Fischer).
[0233] Curtius Rearrangement: A separate 1-L three-necked flask
equipped with a mechanical stirrer and pressure equalizing addition
funnel, was charged with t-BuOH (200 mL), triethylamine (9.8 g,
13.5 mL, 97 mmol), and the toluene solution of the carboxylic acid
[Note: t-BuOH was stirred over 4-.ANG. molecular sieves at
35.degree. C. for 2 hours to remove water to under 100 ppm]. The
mixture was then heated to 90.degree. C. (bath temperature). The
addition funnel was charged with a solution of DPPA (13.3 g, 10.4
mL, 48.4 mmol) in toluene (50 mL). The DPPA solution was added over
a 5-hour period and the mixture was allowed to stir for an
additional 6 hours after complete addition. The solvent removed
under reduced pressure and the crude oil was dissolved in 500 mL
MTBE and added to a 1-L separatory funnel. The organic phase was
first washed 100 mL 5% citric acid and the layers cut. The organic
phase was then washed with 100 mL sat. aq. NaHCO3 and the layers
cut. The organics were then washed with 100 mL H.sub.2O and the
layers cut. Finally the organics were washed with 100 mL sat. aq.
NaCl and the layers cut. The organic phase was dried over
MgSO.sub.4, filtered, and concentrated to provide a tan solid. The
solid was crystallized from a minimal amount of heptane (.about.40
mL) to provide 10.3 g of a light-brown crystalline solid (.about.4%
of the symmetrical urea by-product was contained in this material).
[Note: The urea by-product can be removed by passing the mixture
through a 25-g plug of silica gel eluting with 25% ethyl acetate
(EtOAc) in hexanes. This provided 9.9 g of the product as a white
crystalline solid.] After passing the mother liquor through a 10-g
plug of silica gel and recrystallizing from heptane, an additional
1.6 g of the Boc-amino ester was obtained. The total mass of the
product was 11.5 g corresponding to an 81% yield.
Example 3
Stage 1. Titanium-Mediated Knoevenagel
##STR00091##
[0235] A 2-L three-necked round bottom flask, equipped with a
mechanical stirrer, pressure equalizing addition funnel and reflux
condenser, was charged with chlorotitanium triethoxide (15.3 g, 70
mmol) and 140 mL THF. The solution was cooled to 0.degree. C. and
held at this temperature for 20 min. The solution was then charged
with diethyl malonate (5.61 g, 5.34 mL, 35 mmol) and
difluoroacetaldehyde ethyl hemiacetal (4.9 g, 35 mmol, 90% purity)
[Note: The purity was confirmed by .sup.1H-NMR using
1,3-Bis(trifluoromethyl)-5-bromobenzene as an internal standard].
The addition funnel was charged with triethylamine (7.09 g, 9.8 mL,
70 mmol) and added dropwise over 20 min [Note: triethylamine
hydrochloride begins precipitating upon addition]. Upon complete
addition of triethylamine, the mixture is stirred at 0.degree. C.
for 12 h (complete consumption of diethyl malonate). The mixture is
then warmed to ambient temperature and allowed to stir for 1.5
hours. After this time, the mixture is warmed to 55.degree. C.
(bath temp) and stirred for an additional 1.5 h. When the reaction
was complete, it was cooled to 0.degree. C. with an ice bath,
diluted with 200 mL MTBE, and quenched by slow addition of 50 1 N
HCl. The biphasic mixture was poured into a 1-L separatory funnel
and the layers were cut. The bottom aqueous phase was extracted
with an additional 100 mL MTBE. The bottom aqueous layer was again
extracted with 100 mL MTBE, giving a very clean phase cut. The
organics were combined and washed with 25 mL 1 N HCl. The phases
cut and the organics washed with 50 mL sat. aq. NaCl. The organic
phase was dried over MgSO.sub.4, filtered, and concentrated under
reduced pressure. The mass of the crude oil was 7.62 g (theory=7.78
g). This material was used without further purification.
Stage 2. Cyclopropanation with Corey's Salt
##STR00092##
[0236] [Note: Reagent charges are based on 100% purity from the
previous reaction]. A 25-mL round bottom flask, equipped with a
teflon coated magnetic stirbar, was charged with potassium
tert-butoxide (535 mg, 4.76 mmol, 97% purity),
trimethylsulphoxonium iodide (1.05 g, 4.76 mmol), and 5 mL DMF
[Note: Trimethylsulphoxonium iodide (Corey's salt) purchased from
Aldrich was a pale yellow solid when received. Recrystallization of
the salt from water (15 g/150 mL H.sub.2O) followed by grinding of
the solid to a powder and drying at 80.degree. C. overnight
provided white crystals]. After 15 min of stirring a clear solution
was produced and was allowed to stir for an additional 1 h. To the
solution of the ylide was added a solution of the alkylidene
malonate (882 mg, 3.97 mmol) prepared above in 2.5 mL DMF [Note:
the reaction is exothermic]. The reaction vessel was placed in a
preheated oil bath at 55.degree. C. and stirred at this temperature
for 5 h. After this time, the solution was cooled to room
temperature and poured into a mixture of 10 mL H.sub.2O and 25 mL
MTBE precooled to 0.degree. C. The biphasic mixture was stirred at
0.degree. C. for 5 min then allowed to warm to room temperature.
The mixture was poured into a 125-mL separatory funnel and the
layers were cut. The bottom aqueous phase was extracted with an
additional 25 mL MTBE. The organic layers were combined and washed
with sat. aq. NaCl (15 mL). The organic phase was dried over
MgSO.sub.4, filtered, and concentrated in vacuo. The mass of the
crude oil was 845 mg (theory=938 mg). The material was used without
further purification.
Stage 3. Mono-Hydrolysis
##STR00093##
[0238] [Note: Reagent charges are based on 100% purity from the
previous reaction]. A 100-mL round bottom flask, equipped with a
magnetic stirbar, was charged with the diester (5.50 g, 23.3 mmol),
ethanol (25 mL) and water (5 mL). To this mixture was added
potassium hydroxide (1.27 g, 22.70 mmol) and the reaction stirred
at room temperature. After 12 h, the mixture was cooled to
0.degree. C. and acidified with 20 mL 1 N HCl (.about.pH 2). The
solvent was removed in vacuo and the remaining aqueous layer poured
into a 250-mL separatory funnel with the aid of MTBE. The aqueous
layer was extracted with MTBE (200 mL). The organic phase was
washed with 25 mL sat. aq. NaCl, dried over MgSO.sub.4, filtered,
and concentrated under reduced pressure to give 4.5 g of a crude
pale yellow oil.
[0239] The crude oil was dissolved in a heptane:MTBE mixture (4:1,
60 mL) and cooled to 0.degree. C. Dibenzylamine (4.6 g, 4.5 mL,
23.3 mmol) was added to the cooled solution and the resulting
slurry was stirred at 0.degree. C. for 1 h. The solid was filtered
and washed with heptane (100 mL) to provide 7.3 g of the crude
dibenzylamine salt. To the crude solid was added MTBE (150 mL) and
the mixture heated to reflux and held at this temperature for 10
min. At this point most of the solid had dissolved and the flask
was then cooled to room temperature and the remaining solid
(diacid.Bn2NH) was collected by filtration. The MTBE solution of
the mono-acid was evaporated and the remaining solid was
recrystallized from 5:1 EtOH:H2O (25 mL) to provide 4.9 g (52%
overall) of the title compound as a white solid.
Stage 4. Curtius Rearrangement (DPPA)
##STR00094##
[0241] Salt Break: A 250-mL round bottom flask, equipped with a
teflon coated magnetic stirbar, was charged with the above
dibenzylamine salt (5.6 g, 13.81 mmol) and MTBE (70 mL). To this
suspension was added a 15% H.sub.3PO.sub.4 solution (w/w, 70 mL)
and the resulting mixture was stirred at room temperature for 45
min. The resulting solution was poured into a 500-mL separatory
funnel and the layers were cut. The top organic layer was washed
with an additional 20 mL 15% H.sub.3PO.sub.4 and the layers cut.
The organic layer was then washed with sat. aq. NaCl, the layers
cut, and the organics dried over MgSO.sub.4. After filtration of
the MgSO.sub.4, the solvent was removed in vacuo. The free acid was
azeotropically dried with toluene (3.times.25 mL toluene) to remove
water to under 100 ppm.
[0242] Curtius Rearrangement: A separate 500-mL three-necked flask
equipped with a mechanical stirrer and pressure equalizing addition
funnel, was charged with t-BuOH (125 mL), triethylamine (2.79 g,
3.9 mL, 27.6 mmol), and the toluene solution of the carboxylic acid
[Note: t-BuOH was stirred over 4-.ANG. molecular sieves at
35.degree. C. for 2 hours to remove water to under 100 ppm]. The
mixture was then heated to 90.degree. C. (bath temperature). The
addition funnel was charged with a solution of DPPA (3.80 g, 3 mL,
13.8 mmol) in toluene (25 mL). The DPPA solution was added over a
4-hour period and the mixture was allowed to stir for an additional
6 hours after complete addition. The solvent removed under reduced
pressure and the crude oil was dissolved in 200 mL MTBE and added
to a 500-mL separatory funnel. The organic phase was first washed
50 mL 5% citric acid and the layers cut. The organic phase was then
washed with 50 mL sat. aq. NaHCO.sub.3 and the layers cut. The
organics were then washed with 50 mL H.sub.2O and the layers cut.
Finally the organics were washed with 50 mL sat. aq. NaCl and the
layers cut.
[0243] The organic phase was dried over MgSO.sub.4, filtered, and
concentrated to provide a tan solid. The solid was crystallized
from a minimal amount of heptane (.about.15 mL) to provide 3.2 g of
a white crystalline solid (.about.3% of the symmetrical urea
by-product was contained in this material). [Note: The urea
by-product can be removed by passing the mixture through a 15-g
plug of silica gel eluting with 25% EtOAc in hexanes. This provided
3.06 g of the product as a white crystalline solid.]
Alternate Stage 4. Curtius Rearrangement (Mixed Anhydride)
##STR00095##
[0245] 1. Salt Break: A 500-mL round bottom flask, equipped with a
teflon coated magnetic stirbar, was charged with the above dibenzyl
amine salt (10.85 g, 26.8 mmol) and MTBE (100 mL). To this
suspension was added a 15% H.sub.3PO.sub.4 solution (w/w, 100 mL)
and the resulting mixture was stirred at room temperature for 20
min. The resulting solution was poured into a 250-mL separatory
funnel and the layers were cut. The top organic layer was washed
with an additional 50 mL 15% H.sub.3PO.sub.4 and the layers cut.
The organic layer was then washed with sat. aq. NaCl, the layers
cut, and the organics dried over MgSO.sub.4. After filtration of
the MgSO.sub.4, the solvent was removed in vacuo.
[0246] 2. Mixed Anhydride Formation: The resulting oil was charged
to a 250-mL round bottom flask, equipped with a teflon coated
magnetic stirbar. To the residue was added dry acetone (55 mL) and
triethylamine (5.6, 4.1 g, 40.2 mmol) followed by ethyl
chloroformate (3.9 mL, 4.4 g, 40.2 mmol) at 0.degree. C. over 10
min. The resulting mixture was stirred at 0.degree. C. for 1 h.
After this time, sodium azide (4.36 g, 67.0 mmol) in 45 mL H.sub.2O
was added at 0.degree. C. over 15 min. The mixture was stirred at
this temperature for an additional 30 min. Toluene (110 mL) and
water (110 mL) were added and the mixture poured into a 500 mL
separatory funnel. The layers were cut and the top organic layer
was washed with water (50 mL) and sat. aq. NaCl (50 mL). The
organic phase was dried over MgSO.sub.4, filtered, and concentrated
under reduced pressure. The resulting oil was azeotropically dried
with toluene by adding 25 mL of toluene and removing the solvent
via rotary evaporation (3.times.25 mL toluene).
3. Curtius Rearrangement: A separate three-necked 500-mL round
bottom flask, equipped with a teflon coated magnetic stirbar,
reflux condenser, and pressure equalizing addition funnel was
charged with toluene (90 mL) and tent-butanol (90 mL) and was set
to reflux (bath temp=85.degree. C.). The solution of the acyl azide
in 54 mL toluene was charged to the addition funnel and added to
the refluxing solution of toluene:tert-butanol over 30 min. The
solution was held at reflux for 10 h before cooling to room
temperature. The solvent was removed under reduced pressure and the
resulting oil was dissolved in 10:1 heptane:MTBE (25 mL) at room
temperature. This solution was seeded with 500 mg of authentic
material and allowed to sit at room temperature for 30 min. At this
point, the mixture containing the precipitated product was cooled
to 0.degree. C. and allowed to stand for an additional 30 min. The
product was collected by vacuum filtration and the solid washed
with 50 mL ice-cold heptane. The solids were dried under vacuum to
provide 5.6 g (75% yield) of the desired compound as a white
solid.
Alternate Stage 4. Curtius Rearrangement (DPPA, 2 Mmol Scale)
[0247] A 25-mL round bottom flask, equipped with a teflon coated
magnetic stirbar and reflux condenser, was charged with the
mono-acid (435 mg, 2.09 mmol), tert-butanol (5 mL), and 4-.ANG.
molecular sieves (2.00 g, 1 g/mmol, powdered). The mixture was
stirred for 15 min followed by addition of triethylamine (317 mg,
0.437 mL, 3.13 mmol) and diphenyl phosphorazidate (575 mg, 0.45 mL,
2.09 mmol). The reaction mixture was placed in an oil bath,
preheated to 90.degree. C. (bath temp). The mixture was stirred at
this temperature for 10 h. At this point, the molecular sieves were
filtered from the reaction (washing with 10 mL toluene). The
volatiles were removed under reduced pressure and the remaining
residue dissolved in diethyl ether (25 mL). The organic layer was
washed with 5% aqueous citric acid (15 mL), sat. aq. sodium
bicarbonate (15 mL), and sat. aq. sodium chloride (15 mL). The
organics were dried over MgSO.sub.4, filtered, and concentrated
under reduced pressure to provide a pale yellow oil [Note: the
material does not require purification at this point and can be
subjected directly to ester hydrolysis]. Purification of the crude
oil on silica gel (25 g) eluting with 25% EtOAc in hexanes provided
409 mg (70% yield) of the desired compound as a clear oil, which
solidified upon standing.
Example 4
##STR00096##
[0249] A 1-L three-necked flask equipped with a mechanical stirrer
and addition funnel was charged with ethanol (200 mL) and ethyl
difluoroacetate (25 g, 21.2 mL, 201 mmol). The flask was placed in
a pre-cooled -20.degree. C. bath. The solution was held at this
temperature for 30 min. Sodium borohydride (7.5 g, 198 mmol) was
added in three 2.5 g portions over 1.5 h (additions were at 30 min
intervals). Upon complete addition, the mixture was stirred for an
additional 1 h (.sup.1H-NMR analysis indicated complete conversion)
[Note: 1-mL aliquots were sampled from the reaction and quenched
with 1 mL 1 N HCl at -78.degree. C. The solutions were then diluted
with diethyl ether (5 mL). The organic phase was removed with a
pipet and evaporated to .about.1 mL. 0.25 mL of the ethanol
solution was added to the NMR tube diluted with 1 mL CDCl.sub.3].
At this point, the addition funnel was charged with 1 N HCl (200
mL) and dropwise addition was started. The addition was complete
within 30 min and the mixture was allowed to warm to 0.degree. C.
The mixture was diluted with diethyl ether (500 mL) and poured into
a 2-L separatory funnel. The phases were cut and the organic phase
washed with brine (250 mL). The organics were dried over
MgSO.sub.4, filtered, and concentrated under reduced pressure
(0.degree. C. bath temp, 150 mm Hg) to a volume of .about.200
mL.
[0250] The ethanol solution was transferred to a 1-L round bottom
flask equipped with a teflon coated magnetic stirbar and addition
funnel. The addition funnel was charged with a solution of
NaHSO.sub.3 (20.97 g, 201 mmol) in 100 mL H.sub.2O. The sodium
bisulfite solution was added over 30 min and the mixture was
allowed to stir for 24 h at which point the solvent and water were
removed under reduced pressure producing a white solid. To the
solid was added 100 mL ethanol and the mixture was gently heated to
50.degree. C. (with swirling) to remove the product from the walls
of the flask. The solids were filtered and washed with 200 mL
hexanes to give a white powder.
[0251] After drying under vacuum 23.4 g of the bisulfite adduct
were obtained corresponding to a 63% yield.
Example 5
[0252] Triethoxytitanium(IV) chloride: A 250-mL round bottom flask,
equipped with a teflon coated magnetic stirbar and a reflux
condenser was charged with heptane (100 mL), tetraethoxytitanium
(21.76 g, 20 mL, 95 mmol, 99.9% purity), and acetyl chloride (7.5
g, 6.8 mL, 95 mmol). The mixture was heated at reflux (bath temp
100.degree. C.) for 90 min producing a yellow solution. The
solution was cooled to room temperature and the reflux condenser
was replaced with a short-path distillation apparatus. The bath
temperature was increased to 130.degree. C. and the heptane was
allowed to distill from the pot. After removal of the solvent, the
distillation apparatus was carefully placed under vacuum
(.about.0.1 mm Hg) and the bath temperature increased to
180.degree. C. The product distilled at 140.degree. C. to give a
viscous yellow oil (15.3 g, 73% yield).
Example 6--Asymmetric Synthesis of 1 Using Ellman's Auxiliary
[0253] Since its introduction in the late nineties, enantiopure
tert-butanesulfinamide has shown widespread utility as a versatile
chiral auxiliary. Condensation of tert-butanesulfinamide with
aldehydes and ketones proceeds under mild conditions and provides
activated imines that can participate in a number of highly
diastereoselective reactions. Subsequent removal of the
tert-butanesulfinyl group proceeds under mild conditions to reveal
amine products.
[0254] Enantiopure Tert-Butanesulfinamide (Ellman's Chiral
Auxiliary) may be Used to Construct a Cyclopropyl Amino Acid
(Scheme 2).
##STR00097##
[0255] The synthesis of the glycine unit derived from Ellman's
chiral auxiliary began with condensation of enantioenriched
tert-butanesulfinamide and ethyl glyoxylate in the presence of a
water scavenger, such as MgSO.sub.4, to provide imine 2. Subsequent
reduction of the imine with sodium borohydride, e.g., at 0.degree.
C., provided glycine 3 (for example, as shown in Scheme 3).
##STR00098##
[0256] The amine was protected with a group that is readily cleaved
under conditions that cleave the sulfinyl group; carbamates (e.g.,
tert-butyloxycarbonyl (Boc)) and ether (e.g., methoxymethyl (MOM))
based protecting groups were synthesized. Protection as the Boc
derivative was performed by reacting the sulfonamide 3 with a Boc
source (e.g., Boc2O or BocCl) in the presence of
4-dimethylaminopyridine (DMAP) in a solvent such as acetonitrile
(Table 1, entry 3).
TABLE-US-00001 TABLE 1 Evaluation of Protecting Groups ##STR00099##
Entry Conditions Solvent Yield 1 Boc.sub.2O, n-BuLi THF 25% 2
Boc.sub.2O, NaH THF 15% 3 Boc.sub.2O, DMAP MeCN 95% 4 MOM-Cl,
n-BuLi THF 0% 5 MOM-Cl, NaH THF 0% 6 MOM-Cl, DMAP MeCN 33%
[0257] A Horner-Wadsworth-Emmons olefination combined the
glycine-derived phosphonate 7 and difluoromethyl hemiacetal 5 into
enoate 8 (such as depicted in Scheme 4). However, the undesired
olefin isomer predominated, as confirmed by 2-D nuclear magnetic
resonance (NMR) analysis.
##STR00100##
[0258] So, a similar phosphonate that would incorporate the chiral
auxiliary from Ellman's amine was designed and prepared.
Phosphonate 9 was prepared by condensation of Ellman's amine and
ethyl glyoxylate. Lithium hexamethyldisilazane (LiHMDS) was used at
low temperature in tetrahydrofuran (THF), which provides 9 in 54%
yield (Table 2, entry 3).
TABLE-US-00002 TABLE 2 Synthesis of Chiral Phosphonate 9
##STR00101## ##STR00102## Entry Conditions Solvent Temperature
Yield 1 Me.sub.3SiCl, Et.sub.3N CH.sub.2Cl.sub.2 0.degree. C. to rt
20% 2 K.sub.2CO.sub.3 CH.sub.2Cl.sub.2 0.degree. C. to rt 33% 3
LiHMDS THF -78.degree. C. 54%
[0259] Finally, olefin 10 was prepared. Without optimization, 10
was produced in 29% yield (olefin geometry was not determined)
using KOt-Bu as the base (Scheme 5).
##STR00103##
INCORPORATION BY REFERENCE
[0260] The contents of all references (including literature
references, issued patents, published patent applications, and
co-pending patent applications) cited throughout this application
are hereby expressly incorporated herein in their entireties by
reference. Unless otherwise defined, all technical and scientific
terms used herein are accorded the meaning commonly known to one
with ordinary skill in the art.
EQUIVALENTS
[0261] Those skilled in the art will recognize, or be able to
ascertain using no more than routine experimentation, many
equivalents to the specific embodiments of the invention described
herein. Such equivalents are intended to be encompassed by the
following claims. The contents of all references, patents, and
published patent applications, and patent applications cited
throughout this application are incorporated herein by
reference.
* * * * *