Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2001-10-25
2003-09-23
McKane, Joseph K. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C548S243000
Reexamination Certificate
active
06624311
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for the enantioselective enzymatic aminolysis of racemic 2-[3-(4-cyanophenyl)-4,5-dihydro-5-isoxazolyl]acetate ((R/S)-I) by methyl N
&agr;
-Boc-L-&agr;,&bgr;-diaminoproprionate.p-toluene-sulfonic acid to produce (R)-methyl-3-[[[3-(4-cyanophenyl)-4,5-dihydro-5-isoxazolyl]-acetyl]amino]-N-(butoxycarbonyl)-L-alanine. More specifically, this invention pertains to a process for the enantioselective enzymatic aminolysis of racemic isobutyl 2-[3-(4-cyanophenyl)-4,5-dihydro-5-isoxazolyl]-acetate by methyl N
&agr;
-Boc-L-&agr;,&bgr;-diamino-proprionate.p-toluenesulfonic acid to produce (R)-methyl-3-[[[3-(4-cyanophenyl)-4,5-dihydro-5-isoxazolyl]-acetyl]amino N-(butoxycarbonyl)-L-alanine.
BACKGROUND OF THE INVENTION
The pharmaceutical industry seeks production methods for chiral compounds in high yield and chiral purity. The product of the present invention is useful as a precursor for a pharmaceutical agent of high value in this industry. Specifically, (R)-methyl-3-[[[3-(4-cyanophenyl)-4,5-dihydro-5-isoxazolyl]acetyl]amino]-N-(butoxycarbonyl)-L-alanine ((R,S)-1) is useful as an intermediate in the preparation of roxifiban, a non-peptide platelet glycoprotein IIb/IIIa antagonist which has antithrombotic activity.
The large-scale preparation of roxifiban has previously been described (Zhang et al.,
J. Org. Chem.
62:2466-2470 (1997); Zhang et al.,
Tetrahedron Lett.
37:4455-4458 (1996)). A key part of this published synthesis is the production of (R,S)-1 in two steps, where racemic isobutyl ester (R/S)-2 is first converted to chiral acid (R)-3 and chiral isobutyl ester (S)-2 via enzymatic resolution in an aqueous reaction mixture (Scheme 1). After isolation from the product mixture of the first step, (R)-3 is reacted in a second step with thionyl chloride and diamine (S)-4, followed by addition of diisopropylethylamine (DIEA) to produce (R,S)-1. In a separate step, recovered (S)-2 is racemized to (R/S)-2 for recycle. This enzymatic resolution-based epimerization sequence provided (R)-3 in 70% yield (after one recycle) from racemate (R/S)-2, and (R)-3 was subsequently converted to (R,S)-1 in 82% yield.
The enzyme-catalyzed enantioselective aminolysis of racemic esters to produce chiral amides is well-known (Gotor,
Bioorg. Med. Chem.
7:2189-2197 (1999)). Aminolysis of rac-2-methyloctanoate by (R)-1-phenylethylamine in the presence of
Candida antartica
lipase (Novozym 435) produced (R)-2-methyloctanoic (R)-1-phenylethylamide in 30-40% diastereomeric excess (de) at approximately 100% conversion (Vorde et al.,
Tetrahedron: Asymmetry
7:1507-1513 (1996)). Resolution of chiral amines by reaction with an iso-alkyl ester in the presence of an enantioselective lipase such as
1
Candida antartica
lipase produced a chiral amide in high enantiomeric excess (WO 99/31264). A systematic study of the enzymatic aminolysis of racemic 2-methyl butyrate by benzylamine found that the lipases from
Rhizopus niveus, Candida antartica
B and porcine pancreas were highly enantioselective (84%-87% ee), while
Candida rugosa
and
Pseudomonas cepacia
lipases were neither highly active nor enantioselective (15% ee and 12% ee, respectively) (de Castro et al.,
Tetrahedron
54:2877-2892 (1998)).
Candida antartica
lipase catalyzed the enantioselective aminolysis of racemic 3-hydroxyesters (Garcia et al.,
Tetrahedron: Asymmetry
4:2199-2210 (1993)) or racemic 2-alkylesters or 2-haloesters (Quiros et al.,
Tetrahedron: Asymmetry
4:1105-1112 (1993)) by aliphatic amines, and the degree of enantioselectivity was dependent on the substrate and nucleophile. For the enzymatic aminolysis of dimethyl 3-hydroxyglutarate by aliphatic and aromatic amines,
Candida antartica
lipase yielded enantiopure monoamidation products with very high yield, while no amidation products were observed in the presence of lipases from
Candida cylindracea
and
Pseudomonas cepacia
under identical reaction conditions (Puertas et al.,
J. Org Chem.
61:6024-6027 (1996)).
In addition to lipases, other enzymes can catalyze the enantioselective aminolysis of racemic esters. In the presence of a D-aminopeptidase from
Ochrobactrum anthropi,
the stereoselective aminolysis of racemic D,L-alanine methyl ester by a variety of alkyl and benzyl amines produced the corresponding D-alanine N-alkylamide in >99% ee (Kato et al.,
Tetrahedron
45:5743-5754 (1989)). Thiolsubtilisin catalyzed the quantitative aminolysis of Z-L-phenylalanine p-chorophenyl ester by glycinamide to produce Z-L-Phe-Gly-NH
2
, but no reaction was observed with Z-D-phenylalanine p-chorophenyl ester (Nakatsuka et al.,
J. Am. Chem. Soc.
109:3808-3010 (1987)). Papain catalyzed the aminolysis of Bz-L-Ala-OMe by L-Val-NH
2
to produce Bz-L-Ala-L-Val-NH
2
, but no reaction was observed with Bz-D-Ala-OMe (Mitin et al.,
Int. J. Peptide Protein Res.
23:528-534 (1984)).
Many additional examples exist which demonstrate that achieving a highly-enantioselective enzymatic aminolysis of a racemic ester depends on not only the choice of enzyme, but also on the chemical structure of the ester and the amine. The optimal choice of enzyme and substrate is therefore not easily predicted, but most often must be determined by a careful screening of a variety of enzymes while varying the chemical structure of potential substrates.
The problem to be solved, therefore, is to provide a facile, reliable method for the production (R)-methyl-3-[[[3-(4-cyanophenyl)-4,5-dihydro-5-isoxazolyl]acetyl]amino]-N-(butoxycarbonyl)-L-alanine ((R,S)-1) in high diasteriomeric excess.
SUMMARY OF THE INVENTION
The instant invention relates to a process for the enantioselective enzymatic aminolysis of racemic 2-[3-(4-cyanophenyl)-4,5-dihydro-5-isoxazolyl]acetate ((RIS)-I) by methyl N
&agr;
-Boc-L-&agr;,&bgr;-diaminoproprionate.p-toluenesulfonic acid (S-4) to produce (R)-methyl-3-[[[3-(4-cyanophenyl)-4,5-dihydro-5-isoxazolyl]acetyl]amino]-N-(butoxycarbonyl)-L-alanine ((R,S)-1). More specifically, this invention pertains to a process for the enantioselective enzymatic aminolysis of racemic isobutyl 2-[3-(4-cyanophenyl)-4,5-dihydro-5-isoxazolyl]-acetate (R/S)-2 by (S)-4 to produce (R,S)-1, which is useful in the preparation of the isoxazoline-based platelet glycoprotein IIb/IIIa antagonist roxifiban.
DETAILED DESCRIPTION OF THE INVENTION
Applicants have solved the stated problem with the disclosed method and reaction conditions that produce (R,S)-1 with a diasteriomeric excess as high as 92%. The instant invention is an alternative method for preparing (R,S)-1, where the direct, enzyme-catalyzed aminolysis of racemic 2-[3-(4-cyanophenyl)-4,5-dihydro-5-isoxazolyl]-acetate ((R/S)-I) by diamine (S)-4 to directly produce (R,S)-1 with high diastereoselectivity has been achieved.
Relative to previously known methods to prepare (R,S)-1, the claimed invention reduces the number of process steps to prepare (R,S)-1, generates less waste, and permits facile product recovery. The process eliminates one of two reaction steps and several costly reagents from the previous method of preparation. For example, when isobutyl 2-[3-(4-cyanophenyl)-4,5-dihydro-5-isoxazolyl]acetate (R/S)-2 is used as the ester in the enzyme-catalyzed aminolyis reactions (Scheme 2), the desired product (R,S)-1 has been prepared with a diasteriomeric excess as high as 92%.
[1] Thus in one embodiment, the present invention provides for a novel process for the enantioselective enzymatic aminolysis of racemic 2-[3-(4-cyanophenyl)-4,5-dihydro-5-isoxazolyl]acetate ((R/S)-I),
wherein R
1
is selected from the group comprising of unsubstituted or substituted C
1
-C
6
alkyl or alkenyl, C
3
-C
6
cycloalkyl, substituted or unsubstituted aryl, substituted or unsubstituted arylalkyl, or substituted or unsubstituted heteroaryl alkyl,
by methyl N
&agr;
-Boc-L-&agr;,&bgr;-diaminop
DiCosimo Robert
Ma Philip
Pesti Jaan A.
Bristol-Myers Squibb Pharma Company
McKane Joseph K.
Saeed Kamal
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