1H and 13C NMR assignments of new methoxylated furanoflavonoids from Lonchocarpus araripensis

Two new polymethoxylated flavonoids, 2',5',6'-trimethoxy-[2 '',3 '': 3',4']furano dihydrochalcone and 2,4',4,5-tetramethoxy[2,3 : 6,7]-furanodihydroaurone, were isolated from the root barks of Lonchocarpus araripensis, along with the known compounds 3,4,5,6-tetramethoxy-[2,3 :7,8]-furanoflavan,3,6-dimethoxy-1 '',1 ''-dimethylcromene-[2 '',3 '': 7,8]-flavone, 3',4'-methylenodioxy-5,6-dimethoxy-[2 '',3 '' :7,8]-furanoflavone, 3,5,6-trimethoxy-[2 '',3 '' : 7,8]-furanoflavanone, 3,5,6-trimethoxy-[2 '',3 '': 7,8]-furanoflavone, and 6 alpha-hydroxy-medicarpin. The complete H-1 and C-13 NMR assignments of the new furan flavonoids were performed using 1D and 2D pulse sequences, including COSY, HSQC, and HMBC experiments, and comparison with spectral data for analog compounds from the literature, particularly for the new furanodihydroaurone because of several inconsistencies on the carbonyl chemical shifts from the literature. Copyright (C) 2008 John Wiley & Sons, Ltd.