α-glucosidase inhibitors from dendrobium delacourii, dendrobium gibsonii and aerides multiflora

In this study, three plants from the Orchidaceae family, i.e., Dendrobium delacourii, Dendrobium gibsonii, and Aerides multiflora, were investigated for their chemical constituents and α-glucosidase inhibitory activities. A total of thirty compounds were isolated and structurally characterized. Eleven known compounds were identified from Dendrobium delacourii, including hircinol, ephemeranthoquinone, densiflorol B, moscatin, 4,9-dimethoxy-2,5-phenanthrenediol, gigantol, batatasin III, lusianthridin, 4,4',7,7'-tetrahydroxy-2,2'-dimethoxy-9,9',10,10'-tetrahydro-1,1'-biphenanthrene, phoyunnanin E, and phoyunnanin C. Two new compounds, i.e., dihydrodengibsinin and dendrogibsol, were isolated from Dendrobium gibsonii, along with seven known compounds including ephemeranthol A, dengibsinin, nobilone, aloifol I, lusianthridin, denchrysan A, and 4-methoxy-9H-fluorene-2,5,9-triol. Four new compounds, i.e., aerimultins A-C and dihydrosinapyl dihydroferulate, and six known compounds, which include methoxycoelonin, gigantol, imbricatin, agrostonin, dihydroconiferyl dihydro-p-coumarate and 5-methoxy-9,10-dihydrophenanthrene-2,3,7-triol, were obtained from Aerides multiflora. All the isolated compounds were evaluated for α-glucosidase inhibitory activity. When compared with the drug acarbose (IC50 value 514.4 ± 9.2 µM), eight dimeric compounds showed potent activity: 4,4',7,7'-tetrahydroxy-2,2'-dimethoxy-9,9',10,10'-tetrahydro-1,1'-biphenanthrene, phoyunnanin E, phoyunnanin C, dendrogibsol, aerimultins A-C and agrostonin) (IC50 values 5.2 – 77.0 µM). Seven monomeric compounds exhibited moderate activity: moscatin, gigantol, lusianthridin, 6-methoxycoelonin, imbricatin, dihydroconiferyl dihydro-p-coumarate, and 5-methoxy-9,10-dihydrophenanthrene-2,3,7-triol (IC50 values 115.2 - 390.1 µM). The other compounds displayed no activity, including hircinol, ephemeranthoquinone, densiflorol B, 4,9-dimethoxy-2,5-phenanthrenediol, batatasin III, dihydrodengibsinin, ephemeranthol A, dengibsinin, nobilone, aloifol I, dechrysan A, 4-methoxy-9H-fluorene 2,5,9-triol, and dihydrosinapyl dihydroferulate (less than 50 % inhibition at 100 µg/ml). The kinetic studies on the most potent compounds, i.e., phoyunnanin C, phoyunnanin E, dendrogibsol, and aerimultin C revealed that all were non-competitive inhibitors with a higher affinity to the α-glucosidase enzyme than the drug acarbose.