cistrans isomerization of 2‐(4‐pyridyl)‐substituted thiazolidine‐4‐carboxylic acids: pH dependence by 1H and 13C NMR

Abstract
The presence of two diastereoisomeric thiazolidines obtained by the reaction of L‐cysteine or L‐cysteine ethyl ester and pyridoxal or pyridoxal‐5‐phosphate is demonstrated by 1H and 13CNMR spectroscopy. Fast interconversion of isomers occurs in neutral or alkaline solution.