Synthesis of modified partial structures of the bacterial cell wall. 1. Lipopeptides containing nonproteinogenic amino acids

Two stereoisomeric lipopeptides 1 and 2 which can be regarded as modified peptidoglycans have been synthesized by using three different reaction sequences. The ene reaction of the α-allylated dipeptide 12 with butyl glyoxylate was used as a key step. The required enantiomerically pure substrates 9, 10, and 23 were obtained by enzymatic hydrolysis of the corresponding racemic α-allylated esters. The absolute configuration of both stereoisomers 1 and 2 was assigned by oxidative cleavage of the double bond in 18 and 19 followed by comparison of the esterified degradation products 28 and 29 with samples of authentic configuration, derived from (R)- and (S)-malic acid