Structural and Stereochemical Studies of Naturally Occurring Longipinene Derivatives

Article abstract of DOI:10.1021/jo00221a003

The introduction of a double bond into the six-membered ring of the rastevione (1) skeleton gave a compound (8) whose spectral data are in excellent agreement with those of a substance previously thought to be 12.Further selective elimination of the oxygen atom from C-8 gave 14, previously formulated as 16.This allows us to reassign the structures of several longipinenetriolones and longipinenediolones found as constituents of Stevia and Polypteris.The selective derivatization of 14 followed by controlled cleavage of the seven-membered ring permitted us to assign the H-7 and H-9 NMR signals, which in turn allows us to ascertain the positions at which ester residues are placed by nature.Some NMR signals are reassigned in view of the results of a 13C/1H heteronuclear chemical shift correlation experiment.