Enzymatic resolution of aryl and thio-substituted acids

Details Enzymatic resolution of aryl and thio-substituted acids Enzymatic resolution of aryl and thio-substituted acids

2001-09-05

2003-09-16

Lilling, Herbert J. (Department: 1651)

Chemistry: molecular biology and microbiology

Micro-organism, tissue cell culture or enzyme using process...

Preparing sulfur-containing organic compound

C435S136000, C435S197000

Reexamination Certificate

active

06620600

ABSTRACT:

BACKGROUND OF THE INVENTION
Over the last several years compounds have been reported in the patent and technical literature as possessing angiotensin converting enzyme (ACE) inhibitory activity or neutral endopeptidase (EC 3.4.24.11; NEP) inhibitory activity. Additional compounds have been identified that possess both inhibitory activities. These dual inhibitor compounds are of interest as cardiovascular agents particularly in the treatment of hypertension, congestive heart failure, and renal disease. These compounds are also referred to as vasopeptidase, dual metalloprotease, NEP/ACE, or ACE/NEP inhibitors.
Omapatrilat is such a vasopeptidase inhibitor which is currently undergoing clinical evaluation. Omapatrilat has the chemical name [4S-[4&agr;(R*), 7&agr;,10a&bgr;]]-octahydro-4-[(2-mercapto-1-oxo-3-phenylpropyl)amino]-5-oxo-7H-pyrido[2,1-b][1,3]thiazepine-7-carboxylic acid and the structural formula:
Omapatrilat, its preparation, and its use in treating cardiovascular disease are disclosed by Robl in U.S. Pat. No. 5,508,272.
Gemopatrilat having the chemical name [S-(R*, R*)]-hexahydro-6-[(2-mercapto-1-oxo-3-phenylpropyl)amino]-2,2-dimethyl-7-oxo-1 H-azepine-1-acetic acid is another vasopeptidase inhibitor which is currently undergoing clinical evaluation. This compound has the structural formula:
This compound, its preparation, and its use in treating cardiovascular diseases are disclosed by Karanewsky et al. in U.S. Pat. No. 5,552,397. Processes for preparing vasopeptidase inhibitors including omapatrilat and gemopatrilat are disclosed by Kronenthal et al in WO 99/35145 and processes for preparing omapatrilat and omapatrilat intermediates are disclosed by Godfrey et al in U.S. Pat. Nos. 6,166,227 and 6,248,882, by Moniot et al. in U.S. Pat. No. 6,162,913, by Hanson et al. in U.S. Pat. No. 6,140,088, and by Patel et al. in WO 00/14265. Other processes for preparing omapatrilat intermediates are disclosed by Taoka et al. in U.S. Pat. No. 6,174,707, by Tanaka et al. in U.S. Pat. No. 6,174,711, and by Boesten et al. in U.S. Pat. Nos. 6,133,002 and 6,222,052.
Methods for producing thio aryl and thio-substituted acid moieties such as those incorporated into such vasopeptidase inhibitors are costly. For example, unnatural amino acids such as D-phenylalanine can be converted to &agr;-halides with retention of configuration (using diazotization conditions) and stereospecifically inverted to an appropriate thio-containing intermediate. However, the cost of enantiomerically pure D-phenylalanine is high. Methods are needed that produce the desired enantiomer from inexpensive starting materials.
Methods of using lipases in aqueous buffers to stereoselectively produce a desired acid from 2-acetylthio-3-phenylpropionic acid ester have been described in JP2000-23693A. However, usable e.e. values are not obtained with a particularly desirable enzyme, the lipase obtained from
Mucor Meihei
and marketed by Novo Nordisk Biotech, Inc. (soon to be Novozymes, Inc.) as Lipozyme IM. An improved method is needed to obtain higher e.e. values and to allow the reuse of the enzyme.
Furthermore, the art contains no detail on how to purify the crude product from stereoselection using the lipozyme IM enzyme to a product that would be suitable for pharmaceutical use (>98.5% ee). A method is needed for this.
Also, there is no demonstration of how to reuse the recovered unreacted ester. If the recovered ester is not reused, then the cost will be prohibitive. Methods for the reuse of the unreacted ester are also desired.
SUMMARY OF THE INVENTION
The invention provides a method of resolving a racemic mixture of a compound of formula I to obtain a desired enantiomer:
wherein Ar is C
6
or C
10
aromatic group that can be substituted with H, C
1
to C
6
alkyl, trifluoromethyl or halo, R
5
is halo or —S—R
1
, wherein R
1
is H or acetyl, and R
2
is H or C
1
to C
6
alkyl, the method comprising: reacting a compound of formula I wherein the compound is an ester whereby R
2
is C
1
to C
6
alkyl with a lipase derived from
Mucor meihei
to stereoselectively hydrolyze the ester bond to produce an acid; and isolating the acid, wherein the reaction is conducted in a solvent comprising 80% to 98% v/v % organic phase and a residue of water phase (which can be buffered).
Another aspect of the invention provides a method of stereoselectively producing a desired enantiomer of a compound of formula I:
wherein Ar is C
6
or C
10
aromatic group that can be substituted with H, C
1
to C
6
alkyl, trifluoromethyl or halo, R
1
is H or acetyl, and R
2
is H or C
1
to C
6
alkyl, the method comprising: reacting Ar—CH
2
—X, where X is a leaving group, with R
4
—C(O)—CH
2
—C(O)O—R
2
*, wherein R
2
* and R
4
are independently C
1
to C
6
alkyl; reacting a resulting compound of formula II:
with a halogenating agent which comprises an N-halo substituted amide, N-halosubstituted imide, N-halo substituted thioamide, or N-halo substituted thioimide as the halogenating moiety to produce, with or without an additional hydrolysis of the ester, a compound of formula III:
wherein Y is the leaving group; reacting the compound of formula III with Z—S—R
1
*, wherein R
1
* is acetyl, and Z is K, Na, or other cation to produce a compound of formula I*: and
conducting one of the following stereoselective reactions: (a) (1) reacting the compound of formula III with a hydrolase that is stereoselective for the ester; (2) isolating the desired resulting acid; (3) racemizing residual compound of formula III; and (4) conducting at least one additional iteration of steps (a)(1) and (a)(2) with the racemized residual compound of formula III, wherein the reacting with Z—S—R
1
* is conducted with stereoselective inversion of the chiral carbon; or (b) (1) reacting the compound of formula I* with a hydrolase that is stereoselective for the ester; (2) isolating the desired resulting acid; (3) racemizing residual compound of formula I*; and (4) conducting at least one additional iteration of steps b(1) and b(2) with the residual racemized compound of formula I*.
The method may further comprise: crystallizing the compound of formula I* to obtain the compound of formula I* in increased enantiomeric purity. In a preferred embodiment the isomeric purity of the compound of formula I* is at least 98% ee.
The method may further include reacting with a catalytic amount of tetraalkylammonium halide in the racemization steps of a(3) and b(3).
In one preferred embodiment of the method, the halogenating agent is N,N-dibromo-5,5-dimethylhydantoin. In another preferred embodiment the halogenating agent is N,N-dichloro-5,5-dimethylhydantoin.
In a further aspect, the invention provides a method of preparing a compound of formula II:
wherein R
2
and R
4
are independently C
1
to C
6
alkyl, the method comprising: reacting at least five equivalents of R
4
—C(O)—CH
2
—C(O)O—R
2
with ArCH
2
Cl wherein Ar is C
6
or C
10
aromatic group that can be substituted with C
1
to C
6
alkyl or halo, wherein the reaction is conducted in a solution consisting essentially of the reactants and no more than 1.2 molar equivalents of a base source of sodium or potassium C
2
to C
6
alkoxide, which can be provided in the corresponding alcohol. In a preferred embodiment the alkoxide concentration in the base source is at least 3 M.
DETAILED DESCRIPTION OF THE INVENTION
This invention relates to the methods of stereoselectively producing desired enantiomers of important intermediates for producing pharmaceuticals.
The invention relates to a method for the enzymatic resolution of aryl and thiosubstituted acids. Additionally, a process for the preparation of the enzyme substrate aryl and thiosubstituted acid derivatives are disclosed.
The methods of the invention are described with reference to formulas I, I*, II and III, as outlined above in the Summary. Ar is C
6
or C
10
aromatic group that can be substituted with H, C
1
to C
6
alkyl (preferably C
1
to C
3
), trifluoromethyl or halo, R
5
is halo or

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