Chemistry of Leucomycins. XII. Application of the Modified Polonovski Reaction to Leucomycin-A3 N-Oxide

An aglycone moiety of leucomycin-A3 (1), leuconolide-A3-5, 18-hemiacetal (3), was isolated by the application of a modified Polonovski-reaction to leucomycin-A3 N-oxide (2). Two neutral macrolides, 2'-O-acetyl-3'-N-desdimethylamino-3'-oxo-leucomycin-A3 (5) and 2'-O-acetyl-3'-N-desmethyl-N-acetyl leucomycin-A3 (8) in which the mycaminose moiety of 1 was modified, were also isolated from the same reaction. In a similar manner, an aglycone, 9-dehydro-18-dihydro-leuconolide-A3 (12) was obtained from 9-dehydro-18-dihydro-leucomycin-A3 (10). While the latter as an isomer of 1, differing with respect to the position of carbonyl group on the lactone ring, has significant antimicrobial activity neither its aglycone 12 nor the aglycone of leucomycin-A3 show antimicrobial activity.