Ephedra sinica, an important plant in Chinese traditional medicine, contains a complex mixture of proanthocyanidin oligomers as major constituents; however, only the minor components have been chemically characterized. In this study, oligomers with relatively large molecular weights, which form the main body of the proanthocyanidin fractions, were separated by adsorption and size-exclusion chromatography. Acid-catalyzed degradation in the presence of mercaptoethanol or phloroglucinol led to the isolation of 18 fragments, the structures of which were elucidated from their experimental and TDDFT-calculated ECD spectra. The results indicated that (−)-epigallocatechin was the main extension unit, while catechin, the A-type epigallocatechin–gallocatechin dimer, and the A-type epigallocatechin homodimer, were identified as the terminal units. Among the degradation products, thioethers of gallocatechin with 3,4-cis configurations, a B-type prodelphinidin dimer, a prodelphinidin trimer with both A- and B-type linkages, and a prodelphinidin dimer with an α-substituted A-type linkage were new compounds. In addition, a phloroglucinol adduct of an A-type prodelphinidin dimer, a doubly-linked phloroglucinol adduct of epigallocatechin, and a unique product with a flavan-3-ol skeleton generated by the rearrangement of the aromatic rings were also isolated.

Background and Objectives: Despite the growing number of herbal preparations being marketed as supplements to treat diabetes mellitus, no sufficient data are currently available to guarantee the effectiveness of such preparations. The study, therefore, aimed (1) to provide additional data by investigating the efficacy of four medicinal plants in reducing the breakdown of carbohydrates to glucose via α-glucosidase inhibition, and (2) to determine the active principles responsible for such activity. Methodology: Spectrophotometric method using 96-well plates was employed to determine inhibition of yeast α-glucosidase by the different plant extracts. IC50, a measurement of inhibitory activity, was extrapolated from the concentration-% inhibition graphs generated. Phytochemical screening was done using the standard methods available in literature for the determination of reducing substances, tannins or polyphenols, flavonoids, glycosides, steroids and triterpenoids and alkaloids. Results: Out of the 16 crude extracts prepared, the ethanolic extracts of Logerstroemio specioso and Syzygium samarangense showed concentration-dependent % inhibition, with IC50 of 116 ± 4 ± 6.71 ug/mL and 11 ± 76 ± 7.88 ug/mL, respectively. Phytochemical screening of L. specioso ethanolic extract indicated presence of tannins, triterpenes or sterols, flavonoids and anthraquinones. Tannins, sterols or triterpenes and flavonoids were identified in the crude ethanolic extract of S. somorongense. Upon subjecting this to modified Kupchan fractionation, the ethyl acetate and aqueous fractions showed the highest activity against the enzyme with IC50 of 124.4 ± ± 3.23 ug/mL and 10±19 ± 2.78 ug/mL, respectively. Flavonoids were the only phytochemicals detected exclusively in these fractions of S. samarangense. Conclusion and Recommendations: Among the four medicinal plants with reported anti-diabetic property, L. specioso and S. somorongense were able to inhibit α-glucosidase. Triterpenes or sterols are considered the active constituents in L. specioso, while flavonoids are those considered active in S. samarangense. Further characterization through isolation and elucidation of the α-glucosidase inhibitor/s present in the crude ethanolic extract is needed to identify the exact chemical composition of the enzyme inhibitor.