Structural Modifications of the Active Site in Teicoplanin and Related Glycopeptides. 1. Reductive Hydrolysis of the 1,2- and 2,3-Peptide Bonds

Abstract

Reaction of teicoplanin glycopeptides with sodium borohydride in aqueous ethanol solutions produced open pentapeptide derivatives in which the amide bond between amino acids 2 and 3 was hydrolyzed and the carboxyl group of amino acid 2 was reduced to a primary alcohol. Other glycopeptides of the dalbaheptide family, such as vancomycin, ristocetin, and A-40,926, underwent selective reductive hydrolysis (RH) of the heptapeptide backbone at the same position as in teicoplanins, while antibiotic A-42,867 and vancomycin hexapeptide were resistant. Also, teicoplanin and vancomycin were resistant to RH-treatment when the N-terminus was protected as carbamate. In contrast, open hexapeptides in which the 1,2-peptide bond was hydrolyzed and the carboxyl group of amino acid 1 was reduced to hydroxymethyl were obtained from carbamate derivatives of sugar-free compounds deglucoteicoplanin (TD) and vancomycin−aglycon (VA) under RH-conditions. Limited to BOC or CBZ-TD, the 3,4-amide bond was also affected. A possible RH-mechanism is proposed for natural glycopeptides and their derivatives. Teicoplanin-derived RH penta- and hexapeptides maintained residual antibacterial activity. As other analogous RH-glycopeptides, they are key intermediates for the synthesis of new members of this family of antibiotics. A synthetic approach to ring-closed derivatives of TD hexapeptide alcohol (TDHPA) and their activities are also reported.