Enzymatic hydrolysis of methyl 3,3-difluoro-2-amino esters. Synthesis of d- and l-3,3-difluoro-2-amino acids and their derivatives

Abstract

The hydrolysis of methyl d,l-3,3-difluorophenyl alanate ( 1a) and methyl d,l-3,3-difluoro-2-aminobutanoate ( 1b) and their N-acetyl derivatives 2a and 2b by subtilisin has been studied. All derivatives examined were enzymatically resolved to separable mixtures of the corresponding 3,3-difluoro- l-amino acids ( 3a and 3b) or N-acetylamino acids ( 5a and 5b) and the unchanged 3,3-difluoro d-amino esters ( 4a and 4b) or N-acetylamino esters ( 6a and 6b). Acidic hydrolysis of methyl 3,3-difluoro- d-phenyl alanate ( 4a) or its N-acetyl derivative 6a led to 3,3-difluoro- d-phenyl alanime ( 8a). In the same manner, l- and d-2-amino-3,3-difluorobutanoic acids 7b and 8b were prepared starting from 5b and 6b. Optical purity and enantiomeric excess were determined by GC analysis of the N-acetyl esters and by NMR analysis determined in the presence of Eu(tfc) 3. By these methods, unchanged methyl 3,3-difluoro- d-amino ester derivatives showed an ee of ≥ 90% while l-amino acids were estimated to have ≥ 95% ee.