SYNTHESIS OF BICYCLIC PYRIDINE TRIPEPTIDES

Dinicotinic acid reacted with L-phenylalanine affording N-dinicotinoyl-bis-L-phenylalanine (VII). The same product was also obtained by mild alkaline hydrolysis of the corresponding ester VI. Coupling of VII with L-ornithine or L-ornithine methyl ester gave rise to the formation of the desired chiral bicyclic tripeptides IIIa and IIIb as enniatin analogues.