Records of Natural Products

Citrus hystrix has been widely used as beverages, traditional condiments and folk medicines. In this study, 5,6-dihydroxypyranoflavone (1), a new flavonoid with an oxidized prenyl group, and three known phenols (2-4), were separated from the leaves of this plant. Their structures were elucidated using comprehensive spectroscopic data including 1D NMR, 2D NMR and mass spectral analysis. Additionally, 5,6-dihydroxypyranoflavone (1) exhibited moderate antioxidant effect against DPPH and ABTS free radicals with IC50 values of 18.28 ± 0.36 and 12.46 ± 0.82 μM, respectively. The results suggested that the dietary plant Citrus hystrix could be considered as a potential source of natural antioxidants.

Phytochemical analysis of Populus euphratica resins has resulted in the isolation and identification of two undescribed terpenoids, including a new triterpene (1), a new sesquiterpene (2), and nine additional terpenoid (3-11) compounds. The structures of these novel compounds were determined using HR-ESI-MS and NMR (1D and 2D) spectroscopic analyses, combined with ECD calculations. The inhibitory activity of these terpenoids against α-glucosidase was also evaluated, and the results revealed that none of the compounds exhibited significant α-glucosidase inhibitory activity at a concentration of 50 μM. Only compound 1 displayed weak inhibitory activity (1.84 ± 8.96%) compared to the positive control.

Chemical study on the fungal strain Aspergillus sp. TE-65L, which was previously isolated from cultivated tobacco (Nicotiana tabacum L.), led to the production of four steroids including a new ergosterol-type steroid, namely aspergosterol A (1). Their chemical structures were established by detailed spectroscopic analysis of 1D/2D NMR and HRESIMS data. Compound 1 was found to possess anti-phytopathogenic activities against Alternaria alternate, Botrytis cinerea, and Fusarium oxysporum, with MIC values of 4, 8, and 16 μg/mL.

A new chromanone derivative, calophylloidic acid B (2), was isolated from Calophyllum inophyllum resin in Lombok, Indonesia. The structure of the new compound was elucidated as a structural isomer of calophylloidic acid A (1), which we had previously isolated from Indonesian C. inophyllum resin. It exhibited potent antibacterial activity against Staphylococcus aureus and Escherichia coli.