α-Glucosidase inhibition of natural curcuminoids and curcumin analogs

Natural curcumin (1), demethoxycurcumin (2) and bisdemethoxycurcumin (3) isolated from Curcuma longa (turmeric), and synthetic curcumin analogs (A1–7,B1–7,C1–6 and D1–7) were evaluated in vitro for the α-glucosidase inhibitory activity via UV and circular dichroism (CD) spectroscopy. The results indicated that natural curcuminoid compound 3 showed a remarkable inhibitory effect with IC50 of 23.0 μM, and the synthetic compounds A2, B2, C2 and D2 showed potent inhibitory effects with IC50 of 2.8, 2.6, 1.6 and 8.2 μM, respectively. Kinetic study exhibited that the mechanism of α-glucosidase inhibition of both 3 and C2 was non-competitive. The structure activity relationship revealed that the ortho dihydroxyl groups could form a more tight interaction with α-glucosidase to exert more potential inhibitory activities.

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