D,L-3,4-dehydroproline is resolved in high optical yield by conversion to its N-protected derivative, treatment with R(+)alpha-methyl-p-nitrobenzylamine to form the diastereomeric salts, fractional crystallization, decomposition of the L-R salt and regeneration of the secondary amine group. The product L-3,4-dehydroproline obtained in extremely high optical purity is useful as an inhibitor of collagen synthesis.
3-Pyrroline-2-carboxylic acid derivatives of the formula I ##STR1## are prepared by eliminating the sulfonic acid residue, with the aid of a base, from a compound of the formula II ##STR2##
This invention relates to a process for the optical resolution of DL-.alpha.-methyl-.beta.-acylthiopropionic acids of the formula [I], ##STR1## wherein R is a lower alkyl group having 1-4 carbon atoms, phenyl or substituted phenyl bearing methyl or chloro radical; a method for the racemization of an optically active .alpha.-methyl-.beta.-acylthiopropionic acid of the formula [Ia], ##STR2## wherein R is as defined above; and a process for the synthesis of captopril of the formula [II], ##STR3## using the D-acid [Ia] as an intermediate. The optically active .alpha.-methyl-.beta.-acylthiopropionic acids are useful as intermediates for the production of medicines, for example, captopril or its congeners.
