Caught between triterpene- and steroid-metabolism: 4α-carboxylic pregnane-derivative from the marine alga-derived fungus Phaeosphaeria spartinae.

Investigation of the fungus Phaeosphaeria spartinae, an endophyte of the marine red alga Ceramium sp., led to the isolation of spartopregnenolone (1), a metabolite whose structure includes features of triterpenes and steroids, i.e. a Δ(8,9) double bond as occurring in lanosterol type triterpenoids, a carboxyl group at C-4 which is characteristic for intermediates on the way from triterpenes to steroids and an acetyl side chain as typical for pregnane type steroids. The unusual structure of compound 1 was established from extensive spectroscopic investigations and is best described as a 4α-carboxy-8,9-pregnene derivative.