Streptomyces showdoensis

The C-glycosyl nucleoside antibiotic showdomycin (38) was first isolated from Streptomyces showdoensis [72]. Its structure has striking similarity to uridine (39) and pseudouridine (40), but is distinguished by exhibiting a maleimide moiety (Fig. 19). The known high electrophilicity of this group towards S -nucleophiles... 

Unlike the (3-lactones and (3-lactams, the mode of action of the unusual C-glucosyl nucleoside-based natural product showdomycin is unknown. Nevertheless, this compound has been shown to possess potent antibiotic properties, with results obtained in vitro suggesting a role as a suicide inhibitor of uridine metabolism [11]. Isolated from the bacteria Streptomyces showdoensis, showdomycin contains an electrophilic moiety, malaimide, in place of the base (cf. the structures of uridine or pseudouridine). 

Streptomyces showdoensis incorporates 95% 1-[ C] or 2-[ C]acetate into showdomycin (1) in the maleimide ring only [22], and this confirms earlier C findings. The exclusive incorporation of l-[ C]acetate at C-1, and 2-[ C]acetate at C-2, C-3 and C-4 can be explained with reference to the Krebs cycle and the malic enzyme. C Spectra on 0.1 M solutions of labelled showdomycin in 13 mm tubes required 6 hr accumulation time. Furthermore, C-labelled alanine, proline, glycine and serine have been fed to the bacterium Serratia marcescens [23] to trace the origin of the carbon atoms in its tripyrrole metabolite, prodigiosin (2). The methoxy group is probably derived from methionine whereas the C-2 methyl is from alanine. 

Showdomycin (4) was first isolated in 1964 by Nishimura [64JAN(A)148] from culture filtrates of Streptomyces showdoensis and then from other... 

C9H11NO6, Mr 229.19, platelets, mp. 160-161 °C, [a]D° +49.9° (HjO), soluble in water, ethanol, acetone, unstable in neutral or alkaline solution. S. is a nucle-oside antibiotic from Streptomyces showdoensis with antitumor properties. 

Ozaki, M., Tagawa, S. and Kimura, T. Fermentation products of Streptomyces. I. Accumulation of orotic acid and orotidine by a mutant of Streptomyces showdoensis. Hakka To Taisha, 26, 24-30 (1972) (Japan.)... 

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