New aspects of the formation of 2-substituted thiazolidine-4-carboxylic acids and their thiohydantoin derivatives

Abstract

Aromatic aldehydes reacted readily with (R)-cysteine in boiling acidified methanol to give diastereomeric mixtures of the corresponding 2-(aryl substituted) thiazolidine-4-carboxylic acids. 4-Nitrobenzaldehyde under similar conditions afforded one isomer of 2-(4-nitrophenyl)-thiazolidine-4-carboxylic acid, which epimerized in the NMR solvents into a diastereomeric mixture. 2-Nitrobenzaldehyde reacted with (R)-cysteine to afford 3,5-bis-(2-nitrophenyl)-tetrahydro-1H-thiazolo[3,4-c]oxazol-1-one as the sole product, which collapsed in the NMR solvent into a diastereomeric mixture of the thiazolidine-4-carboxylic acids. The thiazolidine derivatives reacted smoothly with phenyl isothiocyanate to give single isomers of the corresponding thiohydantoins.