Garcinia cowa Roxb. ex Choisy (Clusiaceae) is a Thai local edible plant, which has been used for the treatment of diabetes. The aim of this study is to discover and identify bioactive compounds related to antidiabetic properties from the leaf extract of G. cowa. α-Glucosidase inhibitory bioassay-guided isolation of the ethyl acetate extract of the leaves of G.cowa resulted in the isolation and identification of 11 compounds. Of these, a decahydro-1Hxanthene derivative, garciniacowone K (1), was identified as a novel compound. Their structures were characterized by spectroscopic data and by comparison of their NMR spectroscopic data with those previously reported.All compounds were evaluated for their α-glucosidase inhibitory and glucose consumption activities. Compound 2 showed the highest efficacy in inhibiting α-glucosidase enzyme and promoting glucose consumption activity by 3T3-L1 cells, with IC 50 values of 0.5 μM and 13.1 μM, respectively, without causing toxicity to cells.

Five new compoundstwo phloroglucinol benzophenones, garciniacowones F (1) and G (2), and three xanthones, garciniacowones H (3), I (4), and J (5)together with seven known xanthones (6–12) were isolated from the fresh leaves of Garcinia cowa. Their structures were elucidated by detailed analysis of NMR and MS data. Compounds 1 and 2 are phloroglucinol benzophenones containing a polyprenylated bicyclo[3.3.1]­nonane ring system, while compounds 3–5 are rare xanthones having farnesyl (3 and 5) and geranylgeranyl (5) units at C-8. Compounds 1, 3, 4, 7, 8, and 10 exhibited inhibitory effects on NO production in LPS-induced RAW264.7 macrophage cells with IC50 values ranging from 5.4 to 18.6 μM. Compounds 4 and 8 had α-glucosidase inhibitory activities with IC50 values of 15.4 and 11.4 μM, respectively, which were more potent than that of the acarbose control.

Five new aristolactam alkaloids (1−5), dasymaschalolactams A−E, and the first isolation of dasymaschalolactone (17) as a natural product, together with 19 known compounds (6−16 and 18−25) were isolated from the twig extract of Dasymaschalon dasymaschalum. Their structures were elucidated by spectroscopic methods as well as comparisons made from the literature. Compounds 20 and 21 showed α-glucosidase inhibitory activities with IC 50 values of 4.5 and 24.7 μM, respectively.

The phytochemical investigation of the twig and root extracts of Erythrina subumbrans (Hassk.) Merr. (Fabaceae) resulted in the isolation and identification of a new pterocarpan, erythrinocarpan (1), along with 27 known compounds (2-28). All isolated compounds were evaluated for their antidiabetic, antimicrobial, and antiinflammatory properties. Compounds 3, 8, 9, and 22 had α-glucosidase inhibitory activity with IC 50 values of 13.4 AE 0.05, 24.5 AE 0.13, 29.0 AE 0.05, and 12.8 AE 0.14 μM, respectively, while compound 2 inhibited α-amylase activity with an IC 50 value of 67.6 AE 1.12 μM. Compounds 22 and 24 inhibited glycation activity with the IC 50 values of 36.9 AE 0.62 and 40.5 AE 0.37 μM, respectively. From cell-based assays, compound 27 showed the highest ability to induce glucose consumption (IC 50 29.1 AE 0.86 μM) and glucose uptake (2.8-fold), and to inhibit nitric oxide (NO) production (IC 50 52.5 AE 0.56 μM) without cell toxicity. Furthermore, compound 9 showed antimicrobial activities against Gram-positive bacteria and fungi with MIC values ranging from 2-4 μg/mL.

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