Saliniketals A and B, bicyclic polyketides from the marine actinomycete Salinispora arenicola

An extensive study of the secondary metabolites produced by several strains of the marine actinomycete Salinispora arenicola has led to the isolation of two unusual bicyclic polyketides, saliniketals A and B (1, 2). The structures, which contain a new 1,4-dimethyl-2,8-dioxabicyclo[3.2.1]octan-3-yl ring, were assigned mainly by 2D NMR spectroscopic methods. Unexpectedly, chemical derivatization of saliniketal A with Mosher's acid chloride resulted in a functional group interconversion of an unsaturated primary amide to the corresponding nitrile in a quantitative yield under unusually mild conditions. Saliniketals A and B were found to inhibit ornithine decarboxylase induction, an important target for the chemoprevention of cancer, with IC50 values of 1.95 +/- 0.37 and 7.83 +/- 1.2 mu g/mL, respectively.