Pyxipyrrolones : novel cytotoxic myxobacterial metabolites : structure elucidation and biosynthesis proposal

In our search for new secondary metabolites from myxobacteria, a strain from the genus Pyxidicoccus was investigated. This led to the identification of a new natural product class showing structural novelty and interesting biological activity. Isolation and structure elucidation of two analogs led to the identification of pyxipyrrolone A and B, harboring the novel 3-methylene-2,3,4,5,6,7,8,9-octahydro-1H-benzo[e]isoindol-1-one scaffold. Mosher’s ester analysis combined with NMR studies allowed the determination of all stereocenters but one. Genome sequencing of the producer strain led to the identification of a putative biosynthetic gene cluster for the pyxipyrrolones. The compounds showed activity against several cancer cell lines (μM range) with pyxipyrrolone B having 2- to 11-fold higher activity than A, although they differ only by one methylene group.