Characteristics of proanthocyanidins in leaves of Chamaecyparis obtusa var. formosana as strong α‐glucosidase inhibitors

BACKGROUND In recent decades, there has been a growing demand for natural products with a view to using them as α ‐glucosidase inhibitors for reducing postprandial hyperglycemia. In this study, the hot water extract (HWE) from Chamaecyparis obtusa var. formosana (Hayata) Rehder (Cupressaceae) leaves and its soluble fractions were screened for α ‐glucosidase inhibition properties. The n ‐butanol‐soluble fraction of HWE was further fractionated into 14 subfractions (B1–B14) using a Sephadex LH‐20 column. The α ‐glucosidase‐inhibitory activities and proanthocyanidin contents of all subfractions were determined. The structural characteristics of proanthocyanidins in proanthocyanidin‐rich fractions were also elucidated. RESULTS HWE produced a dose‐dependent inhibition of α ‐glucosidase at low dose. Its IC 50 value was 1.4 µg mL −1 , showing high inhibitory activity. Subfractions B7–B14 displayed powerful α ‐glucosidase‐inhibitory activities with IC 50 values ranging between 1 and 0.015 µg mL −1 and contained abundant proanthocyanidins exceeding 300 mg g −1 . The proanthocyanidins with higher mean degree of polymerization (mDP), higher proportions of procyanidin dimer (A1 or A2) and ( epi )afzelechin of extension units and a lower proportion of epicatechin of terminal units displayed high α ‐glucosidase‐inhibitory activities. CONCLUSION Proanthocyanidins in HWE were viewed as potential natural α ‐glucosidase inhibitors for decreasing postprandial hyperglycemia. The results indicated that specific structural characteristics of proanthocyanidins would be required for α ‐glucosidase‐inhibitory activity.