Diterpenoids with α-glucosidase inhibitory activities from the fruits of Vitex trifolia Linn.

Viticis Fructus, known as "Man-jing-zi", are the fruits of the traditional Chinese medicine Vitex trifolia Linn. and its variant Vitex trifolia Linn. var. simplicifolia. These fruits are used as folk medicines to treat various diseases. Although V. trifolia is useful for treating diabetes, the antidiabetic effect of its purified constituents is still under investigation. The phytochemical investigation on the ethanol extract of the fruits of V. trifolia yielded four new labdane diterpenoids vitetrolins A-D (1-4), together with seven (5-11) known analogs. The structures of these compounds were elucidated by spectroscopy techniques and the absolute configuration of 4 was determined by electronic circular dichroism (ECD) calculations. The isolated diterpenoids were evaluated for their α-glucosidase inhibitory activities. Compounds 5, 6, 8, and 9 exhibited moderate inhibitory activities against α-glucosidase with IC50 values ranging from 44.9 ± 6.1 to 70.5 ± 5.5 µM.