Isolation and structural elucidation of two new labdane diterpenoids from the aerial part of Roylea cinerea

Abstract Two new labdane diterpenoids, cinereanoid A ( 1 ) and cinereanoid B ( 2 ), along with five known compounds, calyone ( 3 ), pilloin ( 4 ), 1-methylindole-3-carboxaldehyde ( 5 ), β-sitosterol ( 6 ) and stigmasterol ( 7 ) were isolated from the aerial parts of Roylea cinerea (Lamiaceae). The new structures were determined by using IR, MS, 1D, 2D NMR spectroscopy. The structure of both new compounds was further confirmed by single crystal X-ray crystallographic analysis. In this study we have also reported single crystal X-ray structure of compound 3 which unambiguously confirmed the relative stereochemistry of tertiary hydroxyl and methyl groups, as it was not established by earlier report. Compounds 4 and 5 were isolated for the first time from this plant. In view of very few reports about this species, this report has increased the phytochemical knowledge about R. cinerea .