Regio- and diastereoselective synthesis and X-ray structure determination of (+)-2-deoxyoryzalexin S from (+)-podocarpic acid. Structural nonidentity with its nominal natural isolated enantiomer.

(+)-2-Deoxyoryzalexin S (1), the nominal enantiomer of a diterpenoid isolated in Chile from Calceolaria species, was regio- and diastereoselectively synthesized from (+)-podocarpic acid. (+)-2-Deoxyoryzalexin S (1) was characterized also as its acetyl derivative, (+)-2, whose structure was confirmed by X-ray crystallographic analysis. Surprisingly, comparison of the data recorded for (+)-1 and (+)-2 and those reported in the literature for the Calceolaria isolated diterpenoid 1 and its derivative (-)-2 showed some differences, suggesting that the latter do not possess the proposed structures.