New antibiotic napyradiomycins A2 and B4 and stereochemistry of napyradiomycins.

Abstract
Napyradiomycins A2 and B4, new members of the napyradiomycins, have been isolated from the culture broth of Chainia rubra MG802-AF1. The structure of napyradiomycin A2 was elucidated as 16-hydroxy-17-methylenenapyradiomycin A1 by NMR studies. The absolute structure of napyradiomycin B4 was determined as 13-hydroxy-13-methylnapyradiomycin B1 by X-ray crystallography and therefore the configuration of C(4a) in other napyradiomycins is assumed as the R configuration. The geometrical isomerism of napyradiomycin C1 was estimated as 12E and 16E by nuclear Overhauser effect experiments.

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