Structure–activity relationships of trans-cinnamic acid derivatives on α-glucosidase inhibition

trans-Cinnamic acid and its derivatives were investigated for the α-glucosidase inhibitory activity. 4-Methoxy-trans-cinnamic acid and 4-methoxy-trans-cinnamic acid ethyl ester showed the highest potent inhibitory activity among those of trans-cinnamic acid derivatives. The presence of substituents at 4-position in trans-cinnamic acid altered the α-glucosidase inhibitory activity. Increasing of bulkiness and the chain length of 4-alkoxy substituents as well as the increasing of the electron withdrawing group have been shown to decrease the inhibitory activity. 4-Methoxy-trans-cinnamic acid was a noncompetitive inhibitor for α-glucosidase, whereas, 4-methoxy-trans-cinnamic acid ethyl ester was a competitive inhibitor. These results indicated that trans-cinnamic acid derivatives could be classified as a new group of α-glucosidase inhibitors.