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 IC₅₀ value was 1.4 µg mL^-1 , showing high inhibitory activity. Subfractions B7-B14 displayed powerful α-glucosidase-inhibitory activities with IC₅₀ 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. © 2018 Society of Chemical Industry.

Benzophenones from Mango Leaves Exhibit α-Glucosidase and NO Inhibitory Activities

Mango (Mangifera indica L.) is a succulent tropical fruit. Bioactive phytochemical investigation has been carried out to the leaves of mango. Three new benzophenone glycosides, along with 14 known compounds, were purified and identified. The novel benzophenones were elucidated to be 2,4,4',6-tetrahydroxy-3'-methoxybenzophenone-3-C-β-d-glucopyranoside (1), 4,4',6-trihydroxybenzophenone-2-O-α-l-arabinofuranoside (7), and 4',6-dihydroxy-4-methoxybenzophenone-2-O-(2″),3-C-(1″)-1″-desoxy-α-l-fructofuranoside (11). The α-glucosidase inhibitory, NO production inhibitory, and antioxidant activities were assessed for the purified benzophenones and triterpenoids. Some benzophenones showed moderate α-glucosidase and NO inhibitory activities. The IC₅₀ value of the α-glucosidase inhibitory of isolated compounds 1, 13, and 14 were 284.93 ± 20.29, 239.60 ± 25.00, and 297.37 ± 8.12 μM, respectively. Most compounds showed moderate effects to reduce the NO content in 50 and 100 μM. The above results of bioactivity powerfully demonstrated the phytochemicals from mango, especially benzophenones, probably partially rational for its antidiabetes and anti-inflammatory.

Structural diversity and bioactivities of natural benzophenones

Natural benzophenones are a class of compounds with more than 300 members, mainly in the Clusiaceae family. We review key benzophenones, and provide an in-depth discussion of their great structural diversity and biological activity.

Chemical constituents from the roots of Ranunculus ternatus and their inhibitory effects on Mycobacterium tuberculosis

Two new benzophenones, methyl (R)-3-[2-(3,4-dihydroxybenzoyl)-4,5-dihydroxyphenyl]-2-hydroxypropanoate (1) and n-butyl (R)-3-[2-(3,4-dihydroxybenzoyl)-4,5-dihydroxyphenyl]-2-hydroxypropanoate (2), were isolated from the roots of Ranunculus ternatus along with the two known compounds vanillic acid (3) and gallic acid (4). Their structures were elucidated by physical and spectroscopic analysis. In addition, compound 1 exhibited obvious activity against tuberculosis, while the activity of a 1:1 mixture of compound 1 plus 4 is better than that of 1 alone.