First synthesis of the antifungal oidiolactone C from trans-communic acid: cytotoxic and antimicrobial activity in podolactone-related compounds.

The synthesis of the fungicide oidiolactone C starting from diterpenic trans-communic acid was carried out with an overall yield of 11.7%. The key step in the process consists of a new bislactonization reaction catalyzed by Pd(II), which gives rise to the podolactone-type tetracyclic skeleton from a norlabdadienedioic acid. We also carried out a study of the structure-biological activity of different natural podolactones and their synthetic precursors. Thus, the highest cytotoxic activity was found in dienic dilactones with ether-type substitutions on C-17, whereas the closure of the gamma-lactone ring is not critical for presenting a maximal antimicrobial activity.