Structures of furanovibsanins A–G from Viburnum awabuki

The structures of nine new 7-membered vibsane-type diterpenes named furanovibsanin A (1), 3-O-methylfuranovibsanin A (2), furanovibsanin F (3), furanovibsanin B (4), 7-epi-furanovibsanin B (5), furanovibsanin C (6), furanovibsanin D (7), furanovibsanin E (8), and furanovibsanin G (9), isolated from the leaves of Viburnum awabuki, were elucidated by intensive analyses of 2D NMR data and comparison of NMR data of the previously known vibsanins C and E. Their structures feature in a furan or a cyclic enol acetal ring forming on the C-4 and C-5 positions in vibsanin C (12).