Diastereoselective Pictet–Spengler condensation of tryptophan with α-amino aldehydes as chiral carbonyl components

The Pictet–Spengler reaction of Trp with α-amino aldehydes derived from l and d-amino acids was studied in terms of double stereodifferentiation. The results observed for d-amino aldehydes represent ‘matched’ situation (one diastereoisomer was formed) whereas with l-amino aldehydes ‘mismatched’ (two diastereoisomers were formed). The conformation of newly formed six-membered ring was analyzed. It was found that stable conformers were different for cis and trans isomers.