Bioactive butenolides from Streptomyces antibioticus TU¨ 99: absolute configurations and synthesis of analogs

The four furanones (butenolides) 1–4, which had been isolated from the fermentation broth of Streptomyces antibioticus TU¨ 99 and in preliminary tests had been shown to be biologically active, were synthesized by reaction of the readily available furanones 9 or 16 with 2-methylpropanal or 2-methylbutanal. In addition, a series of analogs was prepared in a similar way from 16 using different aldehydes. The hitherto unknown absolute configurations of the natural products 1–4 as well as those of all the analogs prepared were determined with Mosher's NMR method and/or X-ray crystallography. Some of the compounds synthesized proved to be active in the quorum sensing system of Chromobacterium violaceum. [Copyright &y& Elsevier]