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Ramoplanin is a glycolipodepsipeptide antibiotic active against Gram-positive bacteria including vancomycin-resistant enterococci. Ramoplanin inhibits bacterial cell wall biosynthesis by a mechanism different from that of glycopeptides and hence does not show cross-resistance with these antibiotics. The systemic use of ramoplanin has been so far prevented because of its low local tolerability when injected intravenously. To overcome this problem, the fatty acid side chain of ramoplanin was selectively removed and replaced with a variety of different carboxylic acids. Many of the new ramoplanin derivatives showed antimicrobial activity similar to that of the natural precursor coupled with a significantly improved local tolerability. Among them the derivative in which the 2-methylphenylacetic acid has replaced the di-unsaturated fatty acid side chain (48) was selected as the most interesting compound and submitted to further in vitro and in vivo characterization studies.

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...