9-epi-leucomycin A5. Synthesis and antimicrobial activity.

9-epi-Leucomycin A5 has been obtained from leucomycin A5 (I) by the following reaction sequence. Leucomycin A5 (I) was treated with Collins reagent (CrO3-pyridine) in the presence of water (13%) to provide 9-dehydroleucomycin A5 (II) in 95% yield. The formyl group was internally protected by the reaction of II with acetic anhydride-K2CO3 to afford 18,2'-di-O-acetyl-9-dehydroleucomycin A5-3,18-hemiacetal (III). Sodium borohydride reaction of II provided a 1 : 1 mixture of natural I and its 9-epimer, 9-epi-leucomycin A5 (IV), which were separated by silica gel chromatography. It was observed that the antimicrobial activities of both enantiomers were virtually identical with some tests strains but that of IV is reduced in comparison with I in some bacteria such as Staphylococcus epidermidis sp-al-1 and Streptococcus pyogenes N. Y. 5.