Gakolanone: a new benzophenone derivative from Garcinia kola Heckel stem-bark

Gakolanone (3',5'-digeranyl-2',4',6',3-tetrahydroxybenzophenone; 1), a novel benzophenone derivative was isolated from the hexane extract of Garcinia kola Heckel stem-bark along with three known 3-8'' linked biflavonoids: 3'',4',4''',5,5'',7,7''-heptahydroxy-3,8''-biflavanone (2); 3'',4',5,5'',5''',7,7''-heptahydroxy-4-methoxy-3,8''-biflavanone (3) and 4',4''',5,5'',7,7''-hexahydroxy-3,8''-biflavanone (4) from the ethanol extract. The compounds were characterized primarily using 1 D and 2 D nuclear magnetic resonance spectroscopy and mass spectrometry and by comparing with literature. The compounds were subjected to in-vitro alpha-amylase enzyme inhibitory assay using DNSA (3,5-dinitrosalicylic acid) reagent with acarbose used as the standard drug. All the compounds were found to show alpha-amylase inhibitory activities with IC50 of 21.4 +/- 1.5, 9.9 +/- 0.2, 15.3 +/- 2.3, 12.9 +/- 2.3 mu g/mL respectively. All the compounds exhibited better alpha-amylase inhibitory activities than the standard drug, acarbose (IC50= 38.1 +/- 8.3 mu g/mL).