U.S. patent application number 09/775644 was filed with the patent office on 2001-09-27 for methods for the solid phase synthesis of combinatorial libraries of benzimidazol, benzoxazoles, benzothiazoles, and derivatives thereof.
Invention is credited to Laborde, Edgardo, Matsumoto, Yukiharu.
Application Number | 20010024833 09/775644 |
Document ID | / |
Family ID | 26772754 |
Filed Date | 2001-09-27 |
United States Patent
Application |
20010024833 |
Kind Code |
A1 |
Laborde, Edgardo ; et
al. |
September 27, 2001 |
Methods for the solid phase synthesis of combinatorial libraries of
benzimidazol, benzoxazoles, benzothiazoles, and derivatives
thereof
Abstract
The present invention provides an efficient and versatile method
for the synthesis and screening of combinatorial libraries of
benzimidazoles, benzoxazoles, benzothiazoles, and derivatives
thereof. In order to expedite the synthesis of large arrays of
compounds possessing these core structures, a general methodology
for solid phase synthesis of these derivatives is provided. Arrays
of benzimidazoles, benzoxazoles, benzothiazoles, and derivatives
thereof useful as peptidomimetics and for the identification of
agents having antifungal, antiviral, antimicrobial, anticoagulant,
and antiulcer activity, or use in the treatment of inflammation,
hypertension, cancer, and other conditions can be prepared by this
method.
Inventors: |
Laborde, Edgardo; (Foster
City, CA) ; Matsumoto, Yukiharu; (Foster City,
CA) |
Correspondence
Address: |
MORRISON & FOERSTER LLP
2000 PENNSYLVANIA AVE, NW
SUITE 5500
WASHINGTON
DC
20006-1888
US
|
Family ID: |
26772754 |
Appl. No.: |
09/775644 |
Filed: |
February 5, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09775644 |
Feb 5, 2001 |
|
|
|
09313568 |
May 14, 1999 |
|
|
|
60085465 |
May 14, 1998 |
|
|
|
Current U.S.
Class: |
436/518 ;
548/152; 548/217; 548/304.4 |
Current CPC
Class: |
C07D 263/58 20130101;
C07D 263/57 20130101; C40B 40/00 20130101; C07D 235/30 20130101;
C07D 277/66 20130101; C07D 235/18 20130101; C07B 2200/11
20130101 |
Class at
Publication: |
436/518 ;
548/304.4; 548/152; 548/217 |
International
Class: |
C07D 263/54; C07D
235/04 |
Claims
1. A process for the SPOS preparation of 2-substituted
benzimidazoles, benzoxazoles, or benzothiazoles comprising reacting
a resin-bound 1,2-arylenediamine, 2-aminophenol, 2-aminothiophenol,
or substituted derivative thereof with cyanogen bromide, or
reacting a resin-bound 1,2-arylenediamine, 2-aminophenol,
2-aminothiophenol, or substituted derivative thereof with an
aldehyde in the presence of an oxidant, or reacting a support-bound
aldehyde with a 1,2-arylenediamine, 2-aminophenol,
2-aminothiophenol, or substituted derivative thereof in the
presence of an oxidant to form a support-bound substituted
benzimidazole, benzoxazole, or benzothiazole, respectively.
2. The method of claim 1 wherein the reaction is carried out at
room temperature or slightly above room temperature.
3. The method of claim 1 wherein the reaction is carried out at
about 40.degree.-60.degree. C.
4. The method of claim 1 wherein the reaction is carried out in a
solvent selected from the group consisting of methanol (MeOH),
ethanol (EtOH), acetonitrile (MeCN), dimethylformsamide (DMF),
dimethylacetamide (DMA), or combinations thereof.
5. The method of claim 1 wherein the reaction is carried out for a
period of 2 to 48 h.
6. The method of claim 1 wherein the oxidant is selected from a
group consisting of p-chloranil (CA),
7,7,8,8-tetracyanoquinodimethane (TCNQ), benzylidene-malononitrile
(BMCN), tetracyanoethylene (TCNE), 2,3-dicyano-1,4-benzoquinone
(DCBQ), or 2,3-dichloro-5,6-dicyano-1,4-benz- oquinone (DDQ).
7. The method of claim 1 wherein the reaction is carried out at
room temperature, with DMA as the solvent, and TCNE as the
oxidant.
8. The method of claim 1 further comprising cleaving the solid
support with a suitable acid, preferably trifluoroacetic acid (TFA)
in dichloromethane (DCM), to form substituted benzimidazoles,
benzoxazoles, or benzothiazoles.
9. The method of claim 1 wherein the support-bound aldehyde is
resin-bound 4-carboxybenzaldehyde.
10. The method of claim 1 wherein the support-bound
1,2-arylenediamine is resin-bound N,N'-Fmoc-3,4-diaminobenzoic
acid.
11. The method of claim 1 wherein the benzimidazole is selected
from the group consisting of 2-(4-Carboxyphenyl)benzimidazole;
2-(4-Carboxyphenyl)-4-methyl-benzimidazole;
2-(4-Carboxyphenyl)-4-hydroxy- benzimidazole;
2-(4-Carboxyphenyl)-4-nitrobenzimidazole;
2-(4-Carboxyphenyl)-5-ethylbenzimidazole;
2-(4-Carboxyphenyl)-5-benzimida- zolylcarboxylic acid;
2-Phenyl-4-benzimidazolylcarboxylic acid; and 2-(4-Carboxyphenyl)
benzoxazole; 2-(4-Carboxyphenyl) benzothiazole.
12. The method of claim 1 wherein the ratio of 1,2-arylenediamine,
2-aminophenol, or 2-aminothiophenol component to cyanogen bromide
component will typically range from about 1:1.1 to about 1:100,
preferably from about 1:1.1 to about 1:25.
13. The method of claim 1 wherein the ratio of 1,2-arylenediamine,
2-aminophenol, or 2-aminothiophenol component to aldehyde component
and to oxidant component will typically range from about 1:1.1:1.1
to about 1:100:100, preferably from about 1:1.1:1.1 to about
1:25:25, and most preferably from about 1:1.1:1.1 to about
1:10:10.
14. In a process for the preparation of benzimidazole, benzoxazole,
or benzothiazole libraries wherein the improvement comprises a step
selected from the group consisting of reacting a support-bound
1,2-arylenediamine, 2-aminophenol, 2-aminothiophenol, or
substituted derivative thereof with cyanogen bromide under mild
conditions, reacting a support-bound 1,2-arylenediamine,
2-aminophenol, 2-aminothiophenol, or substituted derivative thereof
with an aldehyde in the presence of an oxidant, reacting a
resin-bound aldehyde with a 1,2-arylenediamine, 2-aminophenol,
2-aminothiophenol, or substituted derivative thereof in the
presence of an oxidant, to form a support bound substituted
benzimidazole, benzoxazole, or benzothiazole, respectively.
15. The process for the preparation of benzimidazole, benzoxazole,
or benzothiazole libraries of claim 14 wherein the improvement
further comprises one or more subsequent reactions manipulated to
increase the molecular diversity of the final products selected
from the group consisting of acylation with carboxylic acids or
their acyl derivatives, sulfonylation with sulfonyl chlorides,
reaction with isocyanates or thiocyanates, condensations with
.alpha.,.beta.-unsaturated caboxylic acid chlorides or esters, and
alklations with aldehydes in the presence of a reducing agent.
16. The process for the preparation of benzimidazole, benzoxazole,
or benzothiazole libraries of claim 14 or 15 wherein the
improvement further comprises cleaving the solid support with
triflouric acid (TFA) in dichloromethane (DCM) to form the final
product.
17. A library of benzimidazoles, benzoxazoles, or benzothiazoles or
derivatives thereof comprising a plurality of different compounds
prepared in accordance with the methods of any one of claims 14, 15
and 16.
18. A library of benzimidazoles, benzoxazoles, or benzothiazoles or
derivatives thereof comprising a plurality of different compounds,
each compound covalently linked to a solid support, wherein each of
said compounds comprises at least one substituted benzimidazole
group, benzoxazole group, or benzothiazole group, or a group
derived from a substituted benzimidazole, benzoxazole, or
benzothiazole group which group is prepared by reacting a
support-bound 1,2-arylenediamine, 2-aminophenol, 2-aminothiophenol,
or substituted derivative thereof with cyanogen bromide under mild
conditions, reacting a support-bound 1,2-arylenediamine,
2-aminophenol, 2-aminothiophenol, or substituted derivative thereof
with an aldehyde in the presence of an oxidant, reacting a
resin-bound aldehyde with a 1,2-arylenediamine, 2-aminophenol,
2-aminothiophenol, or substituted derivative thereof in the
presence of an oxidant, to form a support bound substituted
benzimidazole, benzoxazole, or benzothiazole, respectively.
19. A library of benzimidazoles, benzoxazoles, or benzothiazoles or
derivatives thereof comprising a plurality of different compounds,
each compound covalently linked to a solid support, wherein each of
said compounds comprises at least one substituted benzimidazole
group, benzoxazole group, or benzothiazole group, or a group
derived from a substituted benzimidazole, benzoxazole, or
benzothiazole group which group is prepared by reacting a
support-bound 1,2-arylenediamine, 2-aminophenol, 2-aminothiophenol,
or substituted derivative thereof with cyanogen bromide under mild
conditions, reacting a support-bound 1,2-arylenediamine,
2-aminophenol, 2-aminothiophenol, or substituted derivative thereof
with an aldehyde in the presence of an oxidant, reacting a
resin-bound aldehyde with a 1,2-arylenediamine, 2-aminophenol,
2-aminothiophenol, or substituted derivative thereof in the
presence of an oxidant, to form a support bound substituted
benzimidazole, benzoxazole, or benzothiazole, respectively, and
cleaving the support bound substituted benzimidazole, benzoxazole,
or benzothiazole, respectively, with a suitable acid, preferably
trifluoroacetic acid (TFA) in dichloromethane (DCM), to form the
library of benzimidazoles, benzoxazoles, or benzothiazoles or
substituted derivatives thereof.
Description
[0001] This application claims priority to U.S. Provisional Ser.
Application No. 60/085,465 filed May 15, 1998, the contents of
which are incorporated herein by reference.
TECHNICAL FIELD
[0002] The present invention provides a method for the
combinatorial synthesis and screening of libraries of
benzimidazoles, benzoxazoles, benzothiazoles, and derivatives
thereof. In order to expedite the synthesis of compound libraries
possessing these core structures, the present invention also
provides a general method for the solid phase synthesis of
benzimidazoles, benzoxazoles, benzothiazoles, and derivatives
thereof. The method involves a cyclization reaction between a
1,2-arylenediamine, 2-aminophenol, or 2-aminothiophenol and an
aldehyde or cyanogen bromide, respectively. Either the
1,2-arylenediamine, 2-aminophenol, or 2-aminothiophenol component,
or the aldehyde component, may be covalently attached to the solid
support.
BACKGROUND ART
[0003] The synthesis and screening of small molecule combinatorial
libraries is an important tool in drug discovery. A convenient
format for the generation of these libraries is the preparation of
compounds on a solid support. Solid-phase organic synthesis (SPOS)
is especially useful for many synthetic transformations, since
reagents can be used in large excess to drive reactions to
completion, and any unreacted amount of reagents and soluble
byproducts can be easily removed by filtration (see Thompson and
Ellman 1996, Chem. Rev. 96:555.; Herkens et al. 1996, Tetrahedron
52:4527; Fruchtel and Jung 1996, Angew. Chem. Int. Ed. Engl.
35:17-42; Balkenhold et al. 1996, Angew. Chem. Int. Ed. Engl.
35:2288-2337).
[0004] Substituted heterocyclic compounds offer a high degree of
molecular diversity and have proven to be broadly useful as
therapeutic agents. The benzimidazole, benzoxazole, and
benzothiazole ring systems, in particular, are present in many
known herbicides, fungicides, and drugs used in human as well as
veterinary medicine. The generic structure and numbering system of
these compounds are shown below. 1
[0005] Benzimidazoles, benzoxazoles, and benzothiazoles have been
shown to exhibit antiviral (Salluja et al. 1996, J. Med. Chem.
39:881-891), antiulcer (Cereda et al. 1987, Eur. J. Med. Chem.
22:527-537; Kugishima et al. 1994, Heterocyclic Chem.
31:1557-1559.), antihistaminic (Jerchee et al. 1952, Liebigs
Annalen der Chemie 575:173; Janssens at al. 1981, Chem. Abstr.
94:30579), analgesic (Hunger at al. 1957, Experientia 13:400),
antihelmintic (Gyurik et al. 1981, U.S. Pat. No. 4,258,198; 1981,
Chem Abstr. 95:7284), antibacterial (Kusumi et al. 1988, J. Am.
Chem. Soc. 110:2954; Suto et al. 1995, Tetrahedron Lett. 36:7213;
Chaney et al. 1974, J. Am. Chem. Soc. 96:1932; David et al. 1982,
J. Antibiotic. 35:1409; Westly et al. 1983, J. Antibiotic.
36:1275), antiparasitic (Haugwitz et al. 1979, J. Med. Chem.
22:1113; Haugwitz et al. 1982, J. Med. Chem. 25:969), and
antiinflammatory properties (Dunwell et al. 1975, J. Med. Chem.
18:53; Dunwell et al. 1975, J. Med. Chem. 18:1158; Evans et al.
1977, J. Med. Chem. 20:169; Dunwell et al. 1977, J. Med. Chem.
20:797), or other biologically relevant actions such as inhibition
of elastase (Edwards et al. 1992, J. Am. Chem. Soc. 114:1854;
Edwards et al. 1995, J. Med. Chem. 38:87; Edward et al. 1995, J.
Med. Chem. 38:3972), and H.sub.2-antagonist properties (Katsura et
al. 1992, Chem. Pharm. Bull. 40:371; Katsura et al. 1992, Chem.
Pharm. Bull. 40:1424).
[0006] In spite of their importance as pharmacophoric scaffolds,
there has been a lack of mild and efficient techniques for
synthesizing benzimidazoles, benzoxazoles, and benzothiazoles on a
solid support and, particularly, for producing libraries of
derivatives for biological screening. Thus, the development of
strategies for the solid phase synthesis of these heterocyclic
systems and derivatives thereof is not only highly desirable, but
also economically advantageous (see Nefzi et al. 1997, Chem. Rev.
97:449-472).
[0007] Benzimidazoles, benzoxazoles, and benzothiazoles are usually
prepared in solution by heating a 1,2-arylenediamine,
2-aminophenol, or 2-aminothiophenol with carboxylic acids or their
derivatives (chlorides, anhydrides, esters, amides, imino esters)
at elevated temperatures and/or in the presence of strong acids
(see Preston, P. N. Benzimidazoles and Congeneric Tricyclic
Compounds. In Heterocyclic Compounds; Preston, P. N., Ed.; John
Wiley & Sons, NY, 1981, Vol. 40, pp 6-60). These conditions,
however, are not always suitable for solid phase organic synthesis,
particularly when thermally sensitive polymeric supports and/or
acid-labile linkers are employed. In spite of this fact, the
current methods for the solid phase synthesis of benzimidazoles and
benzoxazoles are for the most part based on the above general
approach and, therefore, subjected to its limitations. For example,
Phillips and Wei (Tetrahedron Lett. 37 (1996) pp.4887-4890)
disclose a process for the solid phase synthesis of benzimidazoles
that includes heating an immobilized 1,2-arylenediamine with an
imino ester. Although the use of an imino ester allows one to carry
out the reaction under essentially neutral conditions, a large
excess of the reagent (ca. 30 eq.) and prolonged heating (ca.
55.degree.-90.degree. C. for 24-40 h) are still needed to induce
heterocycle ring formation. Imino esters, on the other hand, are
not readily available reagents and must be individually prepared,
isolated, and purified by conventional methods before they can be
used in the synthesis of combinatorial libraries.
[0008] Wang and Hauske (Tetrahedron Lett. 38 (1997) pp.6529-6532)
disclose a method for the solid phase synthesis of benzoxazoles
that involves a two-step reaction, in which a carboxylic acid is
first amidated with a 2-aminophenol, and the resulting amidophenol
is then cyclized intramolecularly. This method relies on the
selective amidation of the resin-bound carboxylic acid with a
2-aminophenol without concomitant esterification, and in the
intramolecular nature of the process.
[0009] Benzimidazoles have also been obtained in solution by
treatment of a 1,2-arylenediamine with aldehydes and an oxidizing
agent (see Chikashita et al. 1987, Bull. Chem. Soc. Jpn.
60:737-746; Yadagiri and Lown 1990, Synth. Commun. 20:955-963;
Ptzold et al. 1992, Synth. Commun. 22:281-288; Vanden Eynde et al.
1995, Tetrahedron 51:5813-5818), or by treatment of a 1,2
arylenediamine with cyanogen bromide (see Rastogi and Sharma 1983,
Synthesis 861-882). Although not as widely publicized as the
thermal cyclization of 1,2-arylenediamines with carboxylic acids or
their derivatives, these alternative methods are known to afford
benzimidazoles under very mild conditions.
[0010] A few of these methods have been applied to the solid phase
synthesis of benzimidazoles from either immobilized aldehydes (see
Sun et al. 1998, Bioorg. Med. Chem. Lett. 8:361-364) or immobilized
1,2-arylenediamines (see Mayer et al. 1998, Tetrahedron Lett.
39:6655-6658), but not both. In the first case, the oxidizing agent
used is nitrobenzene and the reaction is still performed at high
temperature (ca. 130.degree. C.); in the second case, the oxidizing
agent is DDQ and the reaction is carried out at or near room
temperature.
DESCRIPTION OF THE INVENTION
[0011] The description of the invention is provided according to
the following outline.
OUTLINE
[0012] 1. Terminology
[0013] 2. Disclosure of the Invention
[0014] 2.1. Overview
[0015] 2.2. The 1,2-Arylenediamine, 2-Aminophenol, and
2-Aminothiophenol Component
[0016] 2.3. The Aldehyde Component
[0017] 3. The Reaction Conditions
[0018] 3.1. Immobilization of the Arylenediamine, Aminophenol,
Aminothiophenol, or Aldehyde Component
[0019] 3.2. Reaction of Solid-Supported 1,2-Arylenediamines,
2-Aminophenols, or 2-Aminothiophenols with Cyanogen Bromide
[0020] 3.3. Reaction of Solid-Supported 1,2-Arylenediamines,
2-Aminophenols, or 2-Aminothiophenol with Aldehydes
[0021] 3.4. Reaction of Solid-Supported Aldehydes with
1,2-Arylenediamines, 2-Aminophenols, or 2-Aminothiophenols
[0022] 4. Preparation of Derivatives of Benzimidazoles,
Benzoxazoles, and Benzothiazoles
[0023] 5. Cleavage and Analysis of Products
[0024] 6. Preparation of Arrays of Benzimidazoles, Benzoxazoles,
and Benzothiazoles
[0025] 1. Terminology
[0026] Unless otherwise stated, the following terms, abbreviations,
and pictorial representations used in the description,
specifications, and claims of the invention have the meanings given
below:
[0027] "Alkyl" refers to a straight chain, branched, or cyclic
chemical group containing only carbon and hydrogen, such as methyl,
--(CH.sub.2).sub.n--, tert-butyl, and cyclopentyl. Alkyl groups can
be either unsubstituted or substituted with one or more
substituents, e.g., halogen, hydroxy, alkoxy, amino, mercapto,
acyloxy, carboxy, aryl, heteroaryl, or other functionality which
may be suitably blocked, if necessary for purposes of the
invention, with a protecting group. Typically, alkyl groups will
comprise 1 to 12 carbon atoms, preferably 1 to 10, and more
preferably 1 to 8 carbon atoms.
[0028] "Alkoxy" refers to the group alkyl--O--.
[0029] "Aryl" or "Ar" refers to an aromatic carbocyclic group
having a single ring (e.g., phenyl) or multiple condensed rings
(e.g., naphthyl), which can be either unsubstituted or substituted
with alkyl, halogen, hydroxy, alkoxy, mercapto, amino, nitro,
cyano, carboxy, and carboalkoxy. Preferred aryl groups include
phenyl, 1-naphthyl, 2-naphthyl, biphenyl, and the like.
[0030] "Aryloxy" refers to the group aryl--O--.
[0031] "Heteroaryl" or "HetAr" refers to a monovalent unsaturated
aromatic carbocyclic group having a single ring (e.g., furanyl,
pyridyl, thiophenyl) or multiple condensed rings (e.g.,
benzimidazolyl, indolizinyl) and containing at least one
heteroatom, such as N, O, or S, within the ring, which can
optionally be unsubstituted or substituted with alkyl, halogen,
hydroxy, alkoxy, mercapto, amino, nitro, cyano, carboxy, and other
substituents.
[0032] "Arylalkyl" refers to the groups --R'--Ar and --R'--HetAr,
where R' is an alkyl group, Ar is an aryl group, and HetAr is a
heteroaryl group. Examples of arylalkyl groups include benzyl (Bn)
and furfuryl.
[0033] "Amino" or "amine" refers to the group --NR'R", where R' and
R" are independently selected from the group consisting of
hydrogen, alkyl, aryl, arylalkyl, and heteroaryl. In a primary
amino group, both R' and R" are hydrogen, whereas in a secondary
amino group, either, but not both, R' and R" is hydrogen.
[0034] "Carboxy" or "carboxyl" refers to the group --COOH.
[0035] "Carboalkoxy" refers to the group --COOR', where R' is an
alkyl group.
[0036] "Carboaryloxy" refers to the groups --COOAr and --COOHetAr,
where Ar is an aryl group and HetAr is a heteroaryl group.
[0037] "Carboalkyl" refers to the group --CO--R', where R' is an
alkyl group.
[0038] "Carboaryl" refers to the groups --CO--Ar and --CO--HetAr,
where Ar is an aryl group and HetAr is a heteroaryl group.
[0039] "Chemical library" or "combinatorial library" or "compound
library" or "array" is an intentionally created collection of
different compounds, usually prepared in parallel, and screened for
biological activity in a variety of different formats (e.g., in
solution or tethered to resin beads, silica chips, or other solid
supports).
[0040] "Building block" refers to any molecule that can be
covalently attached to other molecules to generate structurally
different compounds.
[0041] "Combinatorial chemistry" or "combinatorial synthesis"
refers to an ordered strategy for the parallel synthesis of diverse
molecular entities which leads to the generation of chemical
libraries. The strategy consists of the systematic and repetitive
covalent connection of structurally different building blocks to
each other to yield large arrays of compounds.
[0042] "Linker" refers to a molecule or group of molecules
covalently attached to the solid support on one end and to the
first building block on the other end. Linkers have different
molecular structures and, therefore, different lengths, shapes,
sizes, degree of hydrophobicity and hydrophilicity, steric bulk,
and chemical reactivity. The selection of a linker in solid phase
synthesis is dependent on both the synthetic scheme and the
biological screening format.
[0043] "Solid support" refers to a material or group of materials
having a rigid or semi-rigid surface, appropriate size, shape, and
porosity, and high chemical resistance. Examples of solid supports
are glass, silica, cellulose, polystyrene cross-linked with
divinylbenzene, polystyrene-polyethyleneglycol copolymer, and other
support materials commonly used in peptide, polymer, and
small-molecule solid phase synthesis.
[0044] "Resin" refers to a solid support material which has been
grafted with a linker for attachment of the first building block.
Examples of preferred resins are Wang resin (a polystyrene-based
resin with a 4-alkoxybenzyl alcohol linker), Rink amide resin (a
polystyrene-based resin with a
4-(2',4'-dimethoxyphenylaminomethyl)phenoxymethyl linker), and
Sasrin resin (a polystyrene-based resin with a
2-methoxy-4-alkoxybenzyl alcohol linker). Other preferred resins
are described in the Combinatorial Chemistry & Solid Phase
Organic Chemistry Handbook published by NovaBiochem, La Jolla,
Calif.; the Solid Phase Sciences catalog published by Solid Phase
Sciences, San Rafael, Calif., or the Rapp Polymere catalog
published by Rapp Polymere GmbH, Tubingen, Germany.
[0045] Resins are usually depicted as follows: 2
[0046] Immobilization of a building block onto a resin is usually
depicted as follows: 3
[0047] wherein the type of functional group used for attachment
will depend on the nature of both the compound to be synthesized
and the resin employed.
[0048] "Protecting group" or "PG" refers to a chemical group that
exhibits the following characteristics: (a) reacts selectively with
the desired functionality to give a derivative that is stable to
the ensuing reactions to which it will be subjected; (b) can be
selectively removed from the derivative to afford the desired
functionality in good yield, and (c) the conditions for its removal
do not compromise the integrity of other functional groups.
Examples of protecting groups can be found in Greene et al. 1991,
Protective Groups in Organic Synthesis, 2nd. Ed., John Wiley &
Sons, Inc., New York.
[0049] Abbreviations: The following abbreviations are intended to
have the following meaning:
1 API = Atmospheric Pressure Ionization DCC =
Dicyclohexylcarbodiimide DCM = Dichloromethane DIC =
Diisopropylcarbodiimide DIEA = Diisopropylethylamine DMA =
Dimethylacetamide DMAP = 4-Dimethylaminopyridine DMF =
Dimethylformamide DMSO = Dimethylsulfoxide ES = Electrospray EtOH =
Ethanol Fmoc = Fluorenylmethoxycarbonyl HBTU =
O-Benzotriazol-1-yl-N,N,N',N'-tet- ramethyluronium
hexafluorophosphate HOBt = 1-Hydroxybenzotriazole HPLC =
High-Performance Liquid Chromatography MeCN = Acetonitrile MeOH =
Methanol MS = Mass Spectrum MSNT =
1-(Mesitylene-2-sulfonyl)-3-nitro-1,2,- 4-triazole NMI =
1-Methylimidazole NMR = Nuclear Magnetic Resonance PG = Protecting
group SPOS = Solid Phase Organic Synthesis TBTU =
O-Benzotriazol-1-yl)-N,N,N',N'-tetrameth- yluronium
tetrafluoroborate TCNE = Tetracyanoethylene TEA = Triethylamine TFA
= Trifluoroacetic acid THF = Tetrahydrofuran
[0050] 2. Disclosure of the Invention
[0051] 2.1. Overview
[0052] The present invention discloses an efficient and versatile
approach for the combinatorial synthesis and screening of libraries
of benzimidazoles, benzoxazoles, benzothiazoles, and derivatives
thereof. In order to expediently synthesize a combinatorial library
of benzimidazoles, benzoxazoles, benzothiazoles, and derivatives
thereof, a generalized methodology for the solid phase synthesis of
these compounds is also provided. This methodology overcomes the
limitations of previous approaches for the solid phase synthesis of
benzimidazoles and benzoxazoles, and provides the first example of
a solid phase synthesis of benzothiazoles.
[0053] In one aspect of the invention, the method of synthesizing
benzimidazoles, benzoxazoles, benzothiazoles, and derivatives
thereof, comprises the steps of first immobilizing a
1,2-arylenediamine, 2-aminophenol, 2-aminothiophenol, or a
synthetic precursor thereof, onto a solid support; removing any
protecting groups or performing other operations upon said
synthetic precursor to unmask the amino, hydroxy, and mercapto
functionalities, and treating the resulting 1,2-arylenediamine,
2-aminophenol, or 2-aminothiophenol with cyanogen bromide to form
the corresponding heterocycles, which is depicted below: 4
[0054] In another aspect of the invention, the method of
synthesizing benzimidazoles, benzoxazoles, benzothiazoles, and
derivatives thereof, comprises the steps of first immobilizing a
1,2-arylenediamine, 2-aminophenol, 2-aminothiophenol, or a
synthetic precursor thereof, onto a solid support; removing any
protecting groups or performing other operations upon said
synthetic precursor to unmask the amino, hydroxy, and mercapto
functional groups, and treating the resulting 1,2-arylenediamine,
2-aminophenol, or 2-aminothiophenol, either sequentially or
simultaneously, with an aldehyde and an oxidizing agent to form the
corresponding heterocycles, which is depicted as follows: 5
[0055] In "Reaction 2", the resin-bound 1,2-arylene diamine can be
attached to the solid support through a linker off the aromatic
ring as shown in the scheme (first reaction), or through a
substituent off one of the nitrogens as shown below: 6
[0056] In yet another aspect, the method of synthesizing
benzimidazoles, benzoxazoles, benzothiazoles, and derivatives
thereof, comprises the steps of first immobilizing an aldehyde, or
a synthetic precursor thereof, onto a solid support; removing any
protecting groups or performing other operations upon said
synthetic precursor to unmask the aldehyde functional group, and
treating the resulting aldehyde, either sequentially or
simultaneously, with an 1,2-arylenediamine, 2-aminophenol, or
2-aminothiophenol and an oxidizing agent to form the corresponding
heterocycles, which is depicted as follows: 7
[0057] 2.2. The 1,2-Arylenediamine, 2-Aminophenol, and
2-Aminothiophenol Component
[0058] According to the above embodiments, the 1,2-arylenediamine,
2-aminophenol, and 2-aminothiophenol component preferably comprises
compounds of formula I, II, and III, respectively: 8
[0059] wherein R.sub.1 is selected from the group consisting of
hydrogen, alkyl, halogen, hydroxy, alkoxy, aryloxy, amino, carboxy,
carboalkoxy, cyano, and nitro, and R.sub.2 is selected from the
group consisting of alkyl, aryl, heteroaryl, arylalkyl, or
substituted arylalkyl.
[0060] Depending on the combinatorial or synthetic scheme, the
1,2-arylenediamine, 2-aminophenol, and 2-aminothiophenol component
may contain additional substituents on the phenyl ring. If
necessary, these substituents can be protected with an appropriate
protecting group.
[0061] In a more preferred embodiment, the 1,2-arylenediamine,
2-aminophenol, and 2-aminothiophenol component is selected from the
group consisting of, but not limited to, 1,2-phenylenediamine;
N-methyl-1,2-phenylenediamine; 2,3-diaminonitrobenzene;
3,4-diaminobenzoic acid; 3-amino-4-(N-benzylamino)benzoic acid;
2,3-diaminophenol; 3,4-diaminophenol; 2-aminophenol;
3-amino-4-hydroxybenzoic acid; 4-amino-3-hydroxy-benzoic acid;
2-aminothiophenol; 3-amino-4-mercaptobenzoic acid;
4-amino-3-mercapto-benzoic acid. The 1,2-arylenediamine,
2-aminophenol, and 2-aminothiophenol component, if not commercially
available, can be prepared by standard chemical procedures.
[0062] 2.3. The Aldehyde Component
[0063] According to the above embodiments, the aldehyde component
preferably comprises a compound of formula IV, V, or VI: 9
[0064] wherein R.sub.3 is an alkyl or arylalkyl group, Ar is an
aryl group, and HetAr is a heteroaryl group, either unsubstituted
or preferably substituted with one or more substituents selected
from the group consisting of alkyl, halogen, hydroxy, alkoxy,
mercapto, amino, nitro, cyano, carboxy, and carboalkoxy. If
necessary, these substituents can be protected with an appropriate
protecting group.
[0065] In a more preferred embodiment, the aldehyde component is
selected from the group consisting of, but not limited to,
benzaldehyde; 2-formylbenzenesulfonic acid;
5-formyl-2-furansulfonic acid; 4-fluorobenzaldehyde;
2-hydroxybenzaldehyde; 3-hydroxybenzaldehyde;
4-hydroxybenzaldehyde; 3,4-dihydroxybenzaldehyde;
3,5-dihydroxybenzaldehy- de; 2-nitrobenzaldehyde;
4-nitrobenzaldehyde; 4-dimethyl-aminobenzaldehyde- ;
4-hydroxy-3-nitrobenzaldehyde; 5-nitro-2-furaldehyde;
5-nitro-2-thiophenecarboxaldehyde; 2-carboxybenzaldehyde;
3-carboxybenzaldehyde; 4-carboxy-benzaldehyde; 4-formylcinnamic
acid. The aldehyde component, if not commercially available, can be
prepared by standard chemical procedures.
[0066] 3. The Reaction Conditions
[0067] 3.1. Immobilization of the Arylenediamine, Aminophenol,
Aminothiophenol, or Aldehyde Component
[0068] According to the present invention, a 1,2-arylenediamine,
2-aminophenol, or 2-aminothiophenol component is reacted with
either cyanogen bromide or an aldehyde component and an oxidant
component, to yield a benzimidazole, benzoxazole, benzothiazole, or
a derivative thereof. The 1,2-arylenediamine, 2-aminophenol, or
2-aminothiophenol component, or the aldehyde component, can be
utilized in a soluble format or can be attached to a solid
support.
[0069] According to the latter embodiment, the 1,2-arylenediamine,
2-aminophenol, or 2-aminothiophenol component, or the aldehyde
component, will include a functionality which can covalently bind
the molecule to the solid support. This functionality will be
present in the molecule in addition to the 1,2-diamino,
2-amino-1-hydroxy, or 2-amino-1-mercapto groups, or to the aldehyde
group, or protected derivatives or synthetic precursors
thereof.
[0070] The choice of functionality used for attaching the
1,2-arylenediamine, 2-aminophenol, or 2-aminothiophenol component,
or the aldehyde component, to the solid support will depend on the
nature of the compound to be synthesized and the type of resin
employed. Preferred functionalities include, but are not limited
to, halogen, hydroxy, amino, and carboxy. Conditions for coupling
monomers and polymers to solid supports through these functional
groups are known in the art; illustrative examples are given in
reaction scheme 4. 10
[0071] 3.2. Reaction of Solid-Supported 1,2-Arylenediamines,
2-Aminophenols, or 2-Aminothiophenols with Cyanogen Bromide
[0072] In a preferred embodiment, an immobilized
1,2-arylenediamine, 2-aminophenol, or 2-aminothiophenol component
is treated with a solution of cyanogen bromide, usually at ambient
temperature, and for a period of 2 to 24 h. However, depending on
the nature of the components, those skilled in the art will
recognize that it may be necessary to perform the reaction at
temperatures other than ambient and for periods of time longer than
24 h.
[0073] The reaction is typically performed in an organic solvent,
such as acetonitrile, dichloromethane, tetrahydrofuran, methanol,
aqueous methanol, dimethylformamide, or dimethylacetamide. Most
preferably, acetonitrile and dichloromethane are used. The ratio of
1,2-arylenediamine, 2-aminophenol, or 2-aminothiophenol component
to cyanogen bromide component will typically range from about 1:1.1
to about 1:100, preferably from about 1:1.1 to about 1:25.
[0074] Hydrogen bromide is formed as a secondary product of the
reaction. In some instances, it may be necessary to neutralize the
hydrogen bromide formed by addition of an exogenous base. In a
preferred embodiment, the exogenous base will be soluble in the
reaction solvent. Particularly preferred exogenous bases include
tri(lower alkyl)amines, such as diisopropylethylamine (DIEA) or
triethylamine (TEA).
[0075] 3.3. Reaction of Solid-Supported 1,2-Arylenediamines,
2-Aminophenols, or 2-Aminothiophenols with Aldehydes
[0076] In a preferred embodiment, an immobilized
1,2-arylenediamine, 2-aminophenol, or 2-aminothiophenol component
is treated, either sequentially or simultaneously, with an aldehyde
component and an oxidant component, usually at ambient temperature,
and for a period of 2 to 24 h. However, depending on the nature of
the components, those skilled in the art will recognize that it may
be necessary to perform the reaction at temperatures other than
ambient and for periods of time longer than 24 h.
[0077] The oxidant employed in the reaction is selected from a
group consisting of p-chloranil (CA);
7,7,8,8-tetracyanoquinodimethane (TCNQ); benzylidenemalononitrile
(BMCN); tetracyanoethylene (TCNE); 2,3-dicyano-1,4-benzoquinone
(DCBQ), or 2,3-dichloro-5,6-dicyano-1,4-benz- oquinone (DDQ). Most
preferably, TCNE is used.
[0078] The ratio of 1,2-arylenediamine, 2-aminophenol, or
2-aminothiophenol component to aldehyde component and to oxidant
component will typically range from about 1:1.1:1.1 to about
1:100:100, preferably from about 1:1.1:1.1 to about 1:25:25, and
most preferably from about 1:1.1:1.1 to about 1:10:10.
[0079] The reaction is typically performed in an organic solvent,
such as tetrahydrofuran, dichloromethane, methanol, , acetonitrile,
dimethylformamide, dimethylacetamide, or combinations thereof. Most
preferably, dichloromethane and dimethylacetamide are used.
[0080] In some instances, the reaction is performed in the presence
of a dehydrating agent which is some embodiments may serve to
catalyze the condensation reaction. Preferred dehydrating agents
include molecular sieves, magnesium sulfate, trimethyl
orthoformate, and the like.
[0081] 3.4. Reaction of Solid-Supported Aldehydes with
1,2-Arylenediamines, 2-Aminophenols, or 2-Aminothiophenols
[0082] In a preferred embodiment, an immobilized aldehyde is
treated, either sequentially or simultaneously, with a
1,2-arylenediamine, 2-aminophenol, or 2-aminothiophenol component
and an oxidant component, usually at ambient temperature, and for a
period of 2 to 24 h. However, depending on the nature of the
components, those skilled in the art will recognize that it may be
necessary to perform the reaction at temperatures other than
ambient and for periods of time longer than 24 h.
[0083] The oxidant employed in the reaction is selected from a
group consisting of p-chloranil (CA);
7,7,8,8-tetracyanoquinodimethane (TCNQ); benzylidenemalononitrile
(BMCN); tetracyanoethylene (TCNE); 2,3-dicyano-1,4-benzoquinone
(DCBQ), or 2,3-dichloro-5,6-dicyano-1,4-benz- oquinone (DDQ). Most
preferably, TCNE is used.
[0084] The ratio of aldehyde component to 1,2-arylenediamine,
2-aminophenol, or 2-aminothiophenol component and to oxidant
component will typically range from about 1:1.1:1.1 to about
1:100:100, preferably from about 1:1.1:1.1 to about 1:25:25, and
most preferably from about 1:1.1:1.1 to about 1:10:10.
[0085] The reaction is typically performed in an organic solvent,
such as tetrahydrofuran, dichloromethane, methanol, ethanol,
acetonitrile, dimethylformamide, dimethylacetamide, or combinations
thereof. Most preferably, dichloromethane and dimethylacetamide are
used.
[0086] In some instances, the reaction is performed in the presence
of a dehydrating agent which is some embodiments may serve to
catalyze the condensation reaction. Preferred dehydrating agents
include molecular sieves, magnesium sulfate, trimethyl
orthofornate, and the like.
[0087] 4. Preparation of Derivatives of Benzimidazoles,
Benzoxazoles, and Benzothiazoles
[0088] The benzimidazoles, benzoxazoles, or benzothiazoles prepared
according to the method described in the present invention can be
further manipulated using any one or more of a variety of
transformations to increase the molecular diversity of the final
products.
[0089] For example, the 2-amino group of the benzimidazoles,
benzoxazoles, or benzothiazoles formed in the reaction of
1,2-arylenediamines, 2-aminophenols, or 2-aminothiophenols with
cyanogen bromide, respectively, can be acylated with carboxylic
acids or their acyl derivatives (e.g., chlorides or anhydrides) to
form amides; sulfonylated with sulfonyl chlorides to form
sulfonamides; reacted with isocyanates or isothiocyanates to form
ureas or thioureas; condensed with .alpha.,.beta.-unsaturated
carboxylic acid chlorides or esters to yield fused 2-oxo-pyrimidyl
derivatives, or alkylated with aldehydes in the presence of a
reducing agent (e.g., NaBH.sub.4, NaCN(BH.sub.3), Na(OAc).sub.3BH),
to give secondary amines. These examples are illustrated in FIG. 1.
Other preferred transformations of 2-aminobenzimidazoles, which may
be applied to their congeneric heterocyclic compounds, are
described in Rastogi and Sharma 1983, Synthesis 861-882.
[0090] The above examples are illustrative; other transformations,
such as oxidation of the sulfur atom of benzothiazoles, alkylation
of the heterocyclic nitrogens of benzimidazoles, and the like, will
be apparent to those skilled in the art.
[0091] For purposes of simplicity, FIG. 1 shows benzimidazoles,
benzoxazoles, and benzothiazoles obtained from resin-bound
1,2-arylenediamines, 2-aminophenols, or 2-aminothiophenols and
cyanogen bromide; however, the corresponding benzimidazoles,
benzoxazoles, or benzothiazoles obtained from resin-bound
1,2-arylenediamines, 2-aminophenols, or 2-aminothiophenols and
aldehydes, or from resin-bound aldehydes and 1,2-arylenediamines,
2-aminophenols, or 2-aminothiophenols can also be further
derivatized.
[0092] 5. Cleavage and Analysis of Products
[0093] For some applications, it may desirable to have a
"support-free" or "soluble" library of molecules. Soluble molecules
can be useful for a variety of purposes, including structural
analysis and screening for activity in a particular assay. The
generation of support-free molecular libraries and the
solubilization of compounds synthesized on a solid support can be
accomplished by techniques known in the art.
[0094] Typically, the linkers employed to immobilize a molecule to
a solid support can be cleaved under a variety of conditions,
including treatment with acid, base, nucleophiles (i.e., groups
capable of donating electrons), oxidants, reducing agents, and
light. Examples of resins with cleavable linkers are described in
the Combinatorial Chemistry & Solid Phase Organic Chemistry
Handbook published by NovaBiochem, La Jolla, Calif.
[0095] In a preferred embodiment, acid-sensitive linkers such as
those present in Wang resin, Sasrin resin, and Rink amide resin can
be employed in the solid phase synthesis of benzimidazoles,
benzoxazoles, benzothiazoles, and derivatives thereof, described in
the present invention. Thus, if desired, the immobilized products
can be cleaved from the solid support by treatment with an acid,
and the support-free benzimidazoles, benzoxazoles, benzothiazoles,
and derivatives thereof, released into solution.
[0096] The nature and amount of acid used in the cleavage step will
depend on the specific resin employed in the solid phase synthesis,
and on the chemical stability of the products. Preferably, the acid
will be selected from the group consisting of acetic acid (AcOH),
trifluoroacetic acid (TFA), hydrochloric acid (HCl), and
hydrofluoric acid (HF). Most preferably, trifluoroacetic acid is
used.
[0097] The acid is usually employed in solution, with water and
dichloromethane being the preferred solvents. The amount of acid in
the solution will typically range from about 1% (v/v) to about 95%
(v/v), preferably from about 1% (v/v) to about 50% (v/v), and most
preferably from about 1% (v/v) to about 25% (v/v).
[0098] The support-free benzimidazoles, benzoxazoles, and
benzothiazoles, or derivatives thereof, can be analyzed by standard
analytical methods, such as thin-layer chromatography (TLC),
high-performance liquid chromatography (HPLC), nuclear magnetic
resonance spectroscopy (NMR), infrared spectroscopy (IR), and mass
spectrometry (MS). Combinatorial libraries are preferably analyzed
by a combination of HPLC and MS, herein referred to as "LC/MS,"
which provides information on the identity as well as the purity of
the cleaved products.
[0099] 6. Preparation of Arrays of Benzimidazoles, Benzoxazoles,
and Benzothiazoles
[0100] The method for the solid phase synthesis of benzimidazoles,
benzoxazoles, benzothiazoles, and derivatives thereof, disclosed in
the present invention can be used to prepare and screen large
numbers of compounds, in the hundreds, the thousands, and even in
the ten thousands in a reasonable period of time. Synthesis may be
coordinated with screening in various different ways to assay
compounds from unusually large libraries in a timely manner.
[0101] Accordingly, the method of synthesis described above is
preferably used to prepare more than 2, preferably more than 10,
preferably more than 40, and more preferably more than 90 different
compounds simultaneously. Moreover, the method described herein can
be utilized in a stepwise fashion as well as in a one step
condensation reaction, thereby decreasing significantly the number
of reactions required for the preparation of a combinatorial
library. For example, a 288-component library can be readily
prepared in one step by condensing a solid supported
1,2-arylenediamine, a 2-aminophenol, and a 2-aminothiophenol each
with a set of 96 different aldehydes under the conditions described
in this invention. Alternatively, a 288-component combinatorial
library can be prepared in two steps by condensing a solid
supported 1,2-arylenediamine, a 2-aminophenol, and a
2-aminothiophenol each with cyanogen bromide under the conditions
described in this invention, and then reacting the
2-aminobenzimidazole, 2-aminobenzoxazole, or 2-aminobenzothiazole
with 96 different carboxylic acids or their acyl derivatives. The
2-aminobenzimidazole, 2-amino-benzoxazole, or 2-aminobenzothiazole
prepared in the first step can also be reacted with different
sulfonyl chlorides, isocyanates, thioisocyanates, or aldehydes and
a reducing agent, to increase the total number of library
components.
[0102] Those skilled in the art will recognize the above format as
one that can be performed on any array, e.g. 96-well filtration
plate, preferably with but also without the aid of automated liquid
dispensing equipment.
[0103] The method of synthesis of benzimidazoles, benzoxazoles,
benzothiazoles, and derivatives thereof, described in the present
invention is particularly suitable for the generation of
combinatorial libraries because of the following attributes: (a)
the synthesis of benzimidazoles, benzoxazoles, benzothiazoles, and
derivatives thereof, takes place at room temperature and under
neutral conditions; (b) reaction times are usually 1 day or less;
(c) most reagents are commercially available; (d) chemical yield
and purity of the products are very high, thereby requiring small
amounts of solid supported starting material; (e) the oxidative
cyclization reaction between 1,2-arylenediamines, 2-aminophenols,
or 2-aminothiophenols and aldehydes is highly chemoselective and
tolerates a wide range of substituents on either component, which
enhances the structural diversity of the compounds that can be
prepared by this method; (f) in the oxidative cyclization process,
either the 1,2-arylenediamine, 2-aminophenol, or 2-aminothiophenol
component, or the aldehyde component, can be immobilized onto the
solid support, which also contributes to increase the structural
diversity of the compounds that can be prepared by this approach;
(g) the method provides a general and uniform protocol for the
synthesis of all three classes of heterocycles, i.e.,
benzimidazoles, benzoxazoles, and benzothiazoles. Furthermore,
compound libraries possessing these core structures can be prepared
from a common resin-bound aldehyde, thereby maximizing the value
and efficiency of the synthetic process.
BRIEF DESCRIPTION OF THE DRAWINGS
[0104] FIG. 1 illustrates the versatility of our approach towards
benzimidazoles, in particular, the preparation from either
resin-bound diamines or resin-bound aldehydes. This enhances
molecular diversity of the combinatorial libraries that may be
prepared.
[0105] FIG. 2 illustrates the possible reactions associated with a
multi-step process for creating diverse libraries.
EXAMPLES
[0106] The following examples are included for the purpose of
illustrating the invention and are not intended to limit its scope
in any matter.
Example 1
[0107] Preparation of Resin-Bound 4-Carboxybenzaldehyde 11
[0108] 4-Carboxybenzaldehyde (2.61 g, 17.4 mmol), DCC (2.19 g, 17.4
mmol), HOBt (1.17 g, 8.7 mmol), and DMAP (1.06 g, 8.7 mmol) were
dissolved in dry DMA (8.1 mL). The solution was added to Wang resin
(15.0 g, subn. 0.58 mmol/g, 8.7 mmol), and the resulting suspension
was shaken at room temperature for 24 h. The resin was filtered,
washed successively with DMA, DCM, and dried under high vacuum. The
loading of the resin was determined by direct cleavage of an
aliquot with 20% (v/v) TFA in DCM, and subsequent analysis of the
product by HPLC.
Example 2
[0109] Preparation of Resin-Bound N,N'-Fmoc-3,4-Diaminobenzoic Acid
12
[0110] A solution of N,N'-Fmoc-3,4-diaminobenzoic acid (3.76 g, 6.3
mmol), MSNT (1.40 g, 4.7 mmol), and NMI (1.03 g, 12.6 mmol) in 6:1
DMA-DCM (35 mL) was added to Wang resin (5.00 g, subn. 0.63 mmol/g,
3.2 mmol), and the suspension was shaken at room temperature for 24
h. The resin was filtered, washed successively with DMA and DCM,
and dried under high vacuum. The substitution of the resin was
determined by direct cleavage of an aliquot with 20% (v/v) TFA in
DCM, and subsequent analysis of the product by HPLC.
Example 3
[0111] 2-(4-Carboxyphenyl)benzimidazole 13
[0112] Resin-bound 4-carboxybenzaldehyde (subn. 0.65 mmol/g, 400
mg, 0.26 mmol) was suspended in DMA (3 mL) and treated with
1,2-phenylenediamine (2.6 mmol) and TCNE (2.6 mmol). The suspension
was sonicated for 1 h and shaken at 25.degree. C. for an additional
22 h. The resin was filtered, washed with DMA, DCM, and dried under
high vacuum. The benzimidazole was cleaved from the solid support
with 20% (v/v) TFA in DCM (2.times.5 mL, 15 min) and the combined
filtrates were evaporated to give the title compound. .sup.1H NMR
(d.sub.6-DMSO) .delta. 7.35-7.43 (m, 2H), 7.69-7.78 (m, 2H), 8.19
(d, 2H, J=8.3 Hz), 8.26-8.34 (m, 2H), 12.50-14.20 (br s,
CO.sub.2H). MS (API-ES.sup.+) m/z 239 (M+H).
Example 4
[0113] 2-(4-Carboxyphenyl)-4-methylbenzimidazole 14
[0114] This compound was prepared according to the procedure
described in Example 3. .sup.1H NMR (d.sub.6-DMSO) .delta. 2.64 (s,
3H, CH3), 7.15-7.37 (m, 2H), 7.50-7.62 (m, 1H), 8.12-8.25 (m, 2H),
8.30-8.43 (m, 2H), 12.30-14.10 (br s, 1H, CO.sub.2H). MS
(API-ES.sup.+) m/z 253 (M+H).
Example 5
[0115] 2-(4-Carboxyphenyl)-4-hydroxybenzimidazole 15
[0116] This compound was prepared according to the procedure
described in Example 3. .sup.1H NMR (d.sub.6-DMSO) .delta. 6.81 (d,
1H, J=7.7 Hz), 7.10-7.30 (m, 2H), 8.17 (d, 2H, J=8.3 Hz), 8.34 (d,
2H, J=7.8 Hz), 10.2-10.9 (br s, 1H, OH), 12.40-13.80 (br s, 1H,
CO.sub.2H). MS (API-ES.sup.+) m/z 255 (M+H)
Example 6
[0117] 2-(4-Carboxyphenyl)-4-nitrobenzimidazole 16
[0118] This compound was prepared according to the procedure
described in Example 3. .sup.1H NMR (d.sub.6-DMSO) .delta. 7.47 (t,
1 H, J=8.1 Hz), 8.10-8.15 (m, 3H), 8.16 (d, 1 H, J=8.1 Hz), 8.48
(d, 2H, J=8.4 Hz), 12.40-14.00 (br s, 1H, CO.sub.2H). MS
(API-ES.sup.+) m/z 284 (M+H).
Example 7
[0119] 2-(4-Carboxyphenyl)-5-benzimidazolylcarboxylic Acid 17
[0120] This compound was prepared according to the procedure
described in Example 3. .sup.1H NMR (d.sub.6-DMSO) .delta. 7.72 (d,
1H, J=8.4 Hz), 7.89 (dd, 1H, J=8.5, 1.6 Hz), 8.14 (d, 2H, J=8.4
Hz), 8.23 (br. s, 1H), 8.32 (d, 2H, J=8.4 Hz), 12.20-13.80 (br. s,
2H, CO.sub.2H). MS (API-ES.sup.+) m/z 283 (M+H).
Example 8
[0121] 2-Phenyl-4-benzimidazolylcarboxylic Acid 18
[0122] Resin-bound N,N'-Fmoc-3,4-diaminobenzoic acid (subn.0.23
mmol/g, 350 mg, 0.081 mmol) was treated with 20% (v/v) piperidine
in DMA (3.times.2 mL.times.5 min.) to remove the Fmoc protecting
groups. After the third treatment, the resin was washed with DMA
and DCM, and then treated with a suspension of benzaldehyde (17.4
mg, 0.164 mmol) and TCNE (21.0 mg, 0.164 mmol) in DMA (3 mL). The
mixture was sonicated for 1 h, and shaken at room temperature for
an additional 23 h. The resin was filtered, washed with DMA, DCM,
and dried under high vacuum. The benzimidazole was cleaved from the
solid support with 20% (v/v) TFA in DCM (2.times.5 mL, 15 min) and
the combined filtrates were evaporated to give the title compound.
.sup.1H NMR (CD.sub.3OD) .delta. 7.50-7.80 (m, 3H), 7.64 (d, 2H,
J=8.4 Hz), 7.97 (d, 2H, J=8.4 Hz), 8.05-8.20 (m, 2H), 8.38 (s, I
H). MS (API-ES.sup.-) m/z 237 (M-H).
Example 9
[0123] 2-(4-Carboxyphenyl)benzoxazole 19
[0124] Resin-bound 4-carboxybenzaldehyde (subn. 0.60 mmol/g, 400
mg, 0.24 mmol) was treated with a solution of 2-aminophenol (262
mg, 2.4 mmol) in DMA (3 mL). The suspension was shaken at room
temperature for 24 h. Tetracyanoethylene (307 mg, 2.4 mmol) was
added, and the mixture stirred at room temperature for an
additional 24 h. The resin was filtered, washed with DMA and DCM,
and dried under high vacuum. The benzoxazole was cleaved from the
solid support with 20% (v/v) TFA in DCM (2.times.5 mL, 15 min) and
the combined filtrates were evaporated to give the title compound.
.sup.1H NMR (CD.sub.3OD) .delta. 7.36-7.45 (m, 2H), 7.62-7,67 (m,
1H), 7.72-7.77 (m, 1H), 8.17 (d, 2H, J=8.3 Hz), 8.29 (d, 2H, J=8.3
Hz). MS (API-ES.sup.+) m/z 240 (M+H).
Example 10
[0125] 2-(4-Carboxyphenyl)benzothiazole 20
[0126] A solution of 2-aminothiophenol (300 mg, 2.4 mmol) in DMA (3
mL) was added to resin-bound 4-carboxybenzaldehyde (subn. 0.60
mmol/g, 400 mg, 0.24 mmol), followed by TCNE (307 mg, 2.4 mmol).
The suspension was shaken at 25.degree. C. for 24 h. The resin was
filtered, washed with DMA and DCM, and dried under high vacuum. The
resin-bound benzothiazole was cleaved from the solid support with
20% (v/v) TFA in DCM (2.times.5 mL, 15 min) and the combined
filtrates were evaporated to give the title compound. .sup.1H NMR
(d.sub.6-DMSO) .delta. 7.52 (t, 1H, J=7.6 Hz), 7.60 (t, 1H, J=7.0
Hz), 8.12 (d, 2H, J=8.4 Hz), 8.23 (d, 2H, J=8.4 Hz), 8.00-8.40 (m,
2H). MS (API-ES.sup.+) m/z 256 (M+H).
[0127] Representative structures, yields, and purities of cleaved
products obtained from the condensation of resin-bound
1,2-arylenediamines, 2-aminophenols, or 2-aminothiophenols with
aldehydes or cyanogen bromide, or from the condensation of
resin-bound aldehydes with 1,2-arylenediamines, 2-aminophenols, or
2-aminothiophenols, are given in Table 1.
2TABLE 1 Structure, Yield, and Purity of Benzimidazoles,
Benzoxazoles, and Benzothiazoles Prepared on Solid Phase.sup.a,b
Structure Yield Purity 21 99 81 22 99 78 23 81 60 24 90 91 25 94 79
26 88 74 27 99 65 28 66 91 29 99 74 30 95 93 31 85 91 32 47 84 33
63 74 34 77 81 35 61 80 36 79 78 37 85 88 38 88 85 .sup.aPurity
refers to percent of product in the cleaved material, determined by
HPLC .sup.bYield refers to percent amount of product relative to
the substitution level of the resin, corrected for purity.
[0128] The above description is illustrative and not restrictive.
Many variations of the invention will become apparent to those
skilled in the art upon review of this disclosure. Merely by way of
example a range of suitable process times, reaction temperatures,
and other reaction conditions may be utilized, as well as
additional reaction types for creating a diverse array of
compounds. The scope of the invention should therefore be
determined not merely with reference to the above description, but
instead with reference to the appended claims along with a full
scope of equivalents.
[0129] Synthesis of Combinatorial Libraries
[0130] A number of techniques for the creation of combinatorial
libraries having desired degrees of molecular diversity exist, one
of which involves the use of combinatorial techniques. Suitable
combinatorial techniques include those described in U.S. Pat. Nos.
5,840,500, 5,847,150, 5,852,028, 5,856,107, 5,856,496, 5,859,027
and 5,861,532. These techniques can be performed on solid or in
solution phase.
[0131] The preferred process of the present invention is a solid
phase synthesis (SPS) based approach. The reaction is carried out
on macroscopic particles made of material insoluble in the reaction
medium. The scaffold is generally linked to the surface of the
support to form the scaffold-support reagent. This link is selected
so that it places the compound in the reaction medium. The
chemistry of the link is selected so that it can be selectively
cleaved in a subsequent step, thereby releasing the synthesized
product. Suitable SPS supports can be selected form commercially
available resins. The scaffold-support reagent can be prepared
batch wise prior to placement in the array, if desired. Each
synthetic modification of the scaffold compound is prepared in
sufficient quantity to permit its screening and analysis using
conventional methodology, e.g., HPLC, mass spectral analysis and
the assays described in the references cited in the background
section.
[0132] The array of synthesized compounds is screened using
conventional methodology and scored. The compounds can be
chemically characterized using conventional techniques, e.g. mass
spec and HPLC, before or after the screening process. The assay and
individual synthetic steps can be automated. Adjustments in the
synthetic approach are possible on a real-time basis.
[0133] Typically, synthesis in a 96-well plate (an 8 by 12 array)
permits eight or twelve distinct scaffold resins to be distributed
across the rows or down the columns, respectfully. These resins can
then be reacted sequentially with any desired series of reactants.
The diversity of the molecular array can be controlled to achieve
any desired degree of diversity.
[0134] Typically, synthesis in a 96-well plate (an 8 by 12 array)
permits eight or twelve distinct scaffold resins to be distributed
across the rows or down the columns, respectfully (see Meyers et
al. 1995, Molecular Diversity 1:13-20). These resins can then be
reacted sequentially with any desired series of reactants. The
diversity of the molecular array can be controlled to achieve any
desired degree of diversity.
[0135] The reactions can be monitored and products characterized at
each synthetic step, if desired. Reaction conditions can also be
varied. Appropriate blocking groups can be added and removed to
direct a desired synthesis route. These methods are capable of
constructing, tens of thousands of molecules in a relatively short
time span.
[0136] Incorporation by Reference
[0137] To the extent necessary to understand or complete the
disclosure of the present invention, all publications, patents, and
patent applications mentioned herein are expressly incorporated by
reference therein to the same extent as though each were
individually so incorporated.
* * * * *