Chemical Constituents of Physalis alkekengi var. franchetii

Abstract

The fruit calyxes of Physalis alkekengi L. var. franchetii (Mast.) Makino (Solanaceae) have been used as a traditional medicine in South East Asia for treating urinary problems, asthma, cough, and inflammation [1]. There have been phytochemical reports on various types of compounds from P. alkekengi var. franchetii, including physalins [2–5], flavonoids [2], megastigmane glycosids [6], and alkaloids [7]. The extracts and some isolates of this plant were reported to have diverse biological activities such as antitumor [3], antibacterial [4], antioxidant [4], cytotoxic [5], and hypoglycemic activities [7]. As a part of our ongoing research to find bioactive compounds from traditional herbal medicines, a phytochemical investigation on the fruit calyxes of P. alkekengi var. franchetii has been performed and resulted in the isolation of five known compounds. Compounds 1–5 were identified as 3 ,7-dimethylquercetin (rhamnazin; 1) [8], 3 ,4 ,7-trimethylquercetin (2) [9], physalin B (3) [10], isophysalin B (4) [11], and 3 -methoxy-2,3-dihydro-4,7-didehydrophysalin B (5) [12] by analyses of their MS and 1D and 2D NMR data as well as by comparison of their spectroscopic data with the literature values. The known flavonoids 1 and 2 were isolated for the first time as constituents of P. alkekengi as well as P. alkekengi var. franchetii. Moreover, 1 has never been isolated previously from the genus Physalis. The known physalins 3–5 have been previously reported from the fruit calyxes of P. alkekengi var. franchetii. The dried fruit calyxes of P. alkekengi var. franchetii (8 kg) were extracted with 95% MeOH overnight at room temperature. The MeOH extract (793 g) was then suspended in water and partitioned with hexane, EtOAc, and n-BuOH, sequentially. The hexane fraction (85 g) was subjected to silica gel column chromatography (CC) eluted with gradient mixtures of hexane–EtOAc (1:0 0:1), affording 14 fractions (H01–H14). Fraction H08 (1.1 g) was subjected to silica gel CC eluted with hexane–acetone (4:1 0:1), yielding 1 (40.69 mg) and 10 subfractions (H08-01–H08-10). Fraction H08-07 (14.39 mg) was chromatographed on a Sephadex LH-20 column using 100% MeOH to afford 2 (1.05 mg). The EtOAc fraction (17 g) was separated by silica gel CC eluted with gradient mixtures of MeOH in CH2Cl2 (0 1%), affording 18 subfractions (E01–E18). Fraction E10 (1.6 g) was subjected to silica gel CC eluted with gradient mixtures of MeOH in CHCl3 (0 1%), yielding 3 (90.09 mg) and 11 subfractions (E10-01–E10-11). The combined subfractions E10-03 (180.3 mg) and E10-04 (234.2 mg) were subjected to reversed-phase CC eluted with gradient mixtures of CH3CN–H2O (1:1 2:1) and then purified by preparative HPLC using an isocratic mixture of CH3CN–H2O (2:1, 2 mL/min) as a solvent system to afford 4 (tR 68.8 min, 7.14 mg) and 5 (tR 55.2 min 1.10 mg).