Salinipyrones and pacificanones, mixed-precursor polyketides from the marine actinomycete Salinispora pacifica

Chemical examination of a phylogenetically unique strain of the obligate marine actinomycete Salinispora pacifica led to the discovery of four new polyketides, salinipyrones A and B (1, 2) and pacificanones A and B (3, 4). These compounds appear to be derived from a mixed-precursor polyketide biosynthesis involving acetate, propionate, and butyrate building blocks. Spectral analysis, employing NMR, IR, UV, and CD methods and chemical derivatization, was used to assign the structures and absolute configurations of these new metabolites. Salinipyrones A and B displayed exactly opposite CD spectra, indicating their pseudoenantiomeric relationship. This relationship was shown to be a consequence of the geometric isomerization of one double bond. The phenomenon of polyketide module skipping is proposed to explain the unusual biosynthesis of the salinipyrones and the pacificanones.