Chrysomycin B

The yellow antibiotic chrysomycin, isolated in crystalline form in 1955, is found to consist of two closely related components, a major one, chrysomycin A, and a minor one, chrysomycin B. They differ only through the replacement of a vinyl group of chrysomycin A by methyl in chrysomycin B. The absorption spectrum of chrysomycin A is identical with that of the antitumor antibiotic toromycin (gilvocarcin V, 2064A), while that of chrysomycin B is similarly identical with the one of gilvocarcin M (2064B). The structures of these antibiotics (toromycin, the glivocarcins, and 2064A and B) have been elucidated recently. Chrysomycins A and B thus contain the same chromophores as gilvocarcins V and M, respectively; comparison of 1H and 13C NMR spectra confirms this identity. The chrysomycins differ from these other antibiotics in the C-glycosidic side-chain, which is a methylpentose in the gilvocarcins, a 3,5-dimethylpentose in the chrysomycins. Structure and relative configuration of the latter are given. The biological activity and possible biosynthesis of the chrysomycins are discussed.

A simple microtiter assay for the detection of compounds that bind DNA is described. Agents that displace methyl green from DNA are detected spectrophotometrically by a decrease in absorbance at 630 nm. The feasibility of using the assay for detecting DNA-active compounds in fermentation extracts was assessed, and the activities of reference compounds in the methyl green assay and an ethidium bromide displacement method were compared.

The biosynthetic origin of the carbon atoms in the chromophores of chrysomycins A and B was investigated in feeding experiments using 13C labeled acetates and propionate. A biosynthetic scheme is proposed involving the condensation and rearrangement of a decaketide intermediate which contains either propionate (chrysomycin A) or acetate (chrysomycin B) as the chain initiator.