Structural and spectral assignment of three forskolin-like diterpenoids isolated from Plectranthus ornatus

Three labdane diterpenoids were isolated from an acetone extract of Plectranthus ornatus. Their structures, closely related to that of forskolin, were determined by NMR studies. Unambiguous and complete assignments of the H-1 and C-13 NMR chemical shifts for these substances are presented. The assignments are based on 2D shift-correlated [H-1,H-1-COSY,H-1,C-13-gHSQC-(1)J (C,H), H-1, C-13-gHMBC-(n)J (C,H) (n = 2 and 3)] and NOE experiments. Copyright (c) 2005 John Wiley & Sons, Ltd.