Wikipedia
Sporolides A and B are novel polycyclic macrolides from the obligate marine bacterium Salinispora tropica (which is found in ocean sediment) that are composed of a chlorinated cyclopenta[a]indene ring and a cyclohexenone moiety. They are only the second class of compounds isolated from Salinispora, and their unique carbon skeleton provides a clear indication of the tremendous potential of marine actinomycetes as a source of novel secondary metabolites. The structures and absolute stereochemistries of both metabolites were elucidated using a combination of NMR spectroscopy and X-ray crystallography, and are considered unique for two reasons:
- both compounds appear to be polyketides and therefore derived from acetate units,
- the number of oxidized carbons is amazing, with 23 of 24 carbons either oxygenated or sp2 - hybridized.
The complex aromatic structure of the sporolides is hypothesized to be derived from an unstable nine-membered ring enediyne precursor, which undergoes Bergman cyclization to generate a p-benzyne intermediate. A nucleophilic attack by chloride accounts for the 1:1 mixtures and for the single chlorine in enediyne-derived natural products. This mechanism has been recently demonstrated in laboratory experiments, and can account for the biosynthesis of sporolides.