Enantiomeric Neolignans and a Sesquiterpene from Solanum erianthum and Their Absolute Configuration Assignment.

One pair of new C-8-C-3'/C-7-O-C-4' linked neolignan enantiomers (1a/1b) and one new guaiane sesquiterpene (2) first featuring the 1(2),9(10)-conjugated double bond were isolated from the stems of Solanum erianthum (Solanceae). Their structures were characterized on the basis of extensive spectroscopic analyses, especially from their 2D nuclear magnetic resonance (NMR) spectra. The absolute configurations of 1a/2b were rigorously elucidated by electronic circular dichroism (ECD) experiments combined with the reversed helicity rule for the 2,3-dihydrobenzo[b]furan chromophore, and compound 2 is the first report on the sterochemical assignment of a guaiane sesquiterpene by using the allylic axial chirality rule for the conjugated diene chromophore in combination with the calculated ECD spectrum.