Methanolysis and aminolysis of N-acetylmuramic acid lactones: Evidence for the retention of the d- gluco configuration

Abstract

Methanolysis of benzyl α-glycosides of N-acetylmuramic acid lactones with HO-6 free ( 2) and substituted ( 4, 7, 10, and 12) is catalysed by small amounts of silica gel to give, exclusively, the corresponding methyl esters with HO-4 unsubstituted ( 3, 5, 8, 11, 13); opening of the lactone ring proceeds with retention of the d- gluco configuration and can be followed by 1H-n.m.r. spectroscopy. Condensation of 2 with 2-methyl-(3,4,6-tri- O-acetyl-1,2-dideoxy-α- d-glucopyrano)-[2,1- d]-2-oxazoline ( 15) gave the β-(1→6)-linked disaccharide lactone 16 which, on methanolysis, yielded the disaccharide methyl ester 17, also obtained by condensation of 3 and 15. In the presence of imidazole, the lactones 2 and 4 underwent aminolysis with amino acid and peptide esters as nucleophiles to give the N-acetylmuramoylamide derivatives 19–24. The structures of methanolysis and aminolysis products were established by 1H-n.m.r. spectroscopy and independent syntheses.