New isocoumarins and flavonoids from Citrus grandis Osbeck fruits and their antidiabetic activities

Citrus grandis Osbeck. (Rutaceae) is an evergreen shrub only distributed in Jeju island, Korea. Traditionally, C. grandis Osbeck, which is called as “Dangyuja”, “Dangyuji”, or “Daeyuji”, has been used as a folk remedy for fever. The fruits of C. grandis were used at various ceremonies in Jeju island, Korea [1]. In recent studies, it was reported that C. grandis had two times higher organic acid content than C. junos and four times more vitamin C content than lemons [2], [3]. However, there are few studies on the other chemical constituents and biological activities of C. grandis fruits. Therefore, the present study focused on the isolation and identification of active compounds from the fruits of this plant, as well as evalutaion of protective effects of the isolated compounds on pancreatic islet damaged by alloxan in a zebrafish (Danio rerio) larvae model. C. grandis fruits were extracted with aqueous methanol, and the concentrared extract was partitioned into EtOAc, n-BuOH, and H₂O fractions. The repeated normal and reverse-phase column chromatographies on EtOAc and n-BuOH fractions led to the isolation of three new isocoumarins, citragrandin A−C (1−3), three known coumarins (4−6), and four known flavonoids (7−10). The compounds were identified based in classical spectroscopic methods such as NMR and HRMS. Some of the isolated compounds showed radical scavenging activities in DPPH and ABTS radical experiments and some exhibitied protective effects on pancreatic islet damaged by alloxan in zebrafish (Danio rerio) larvae.

Fig. 1 Isolated compounds from the fruits of Citrus grandis Osbeck. Glc: O-β-D-glucopyranosyl, 6-RG: O-α-L-rhamnopyranosyl-(1→6)-O-β-D-glucopyranosyl.

• References

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