A New Saponin from the Seeds of Zizyphus jujuba var. spinosa

Abstract

Sour jujube (Zizyphus jujuba Miller var. spinosa Hu ex H. F. Chou) is a thorny, rhamnaceous deciduous plant distributed widely throughout tropical and subtropical regions. The dried seeds are named sanjoin (Zizyphi Spinosi Semen) in Korean and have a thousand-year history of use in traditional medicine as a sedative for treating mild anxiety, nervousness and sleep-related problems. Previous phytochemical investigations on the seeds of this plant have resulted in the isolation of saponins, flavone C-glycosides, cyclopeptide alkaloids, triterpenoids, and others. These compounds exhibit multiple activities, such as hypnotic, histamine-release inhibitory, anti-inflammatory and sedative, inhibition of foam cell formation, adjuvant, and cardiotonic effects. Our previous studies focused on isolating the flavonoid-C-glycosides and the sedative activities of these flavonoids. In the continuing search for new chemicals and biomarkers from Z. jujuba var. spinosa for quality control studies of related herbal medicines, 8 flavonoids, along with 3 other known components, were isolated. In the present investigation, we report the isolation and structural elucidation of a new saponin, named jujuboside A2 (1), together with three known saponins, zizyphus saponin III (2), jujuboside B (3), jujuboside A (4), and a known sesquiterpene glucoside, dihydrophaseic acid 3-O-β-D-glucopyranoside (5), from the seeds of Z. jujuba var. spinosa. Compound 1 was obtained as a colorless amorphous powder. Its molecular formula was established as C58H94O26 from the [M−H] peak at m/z 1205.5961 (Calcd for C58H93O26: 1205.5955) in the HR-FAB-MS. The IR absorption bands at 3414, 1647, and 1043 cm implied the presence of hydroxyl, double bond, and glycosidic C-O functionalities. Acid hydrolysis of compound 1 with 5% HCl afforded a mixture of ebelin lactone and 17(Z)-ebelin lactone as the aglycon and D-glucose, 6-deoxy-L-talose, D-xylose, and L-arabinose as the sugar components identified on GLC analysis of the thiazolidine derivatives. The Hand C-NMR spectra of 1 suggested the presence of a jujubogenin moiety [δH 0.72, 0.97, 1.09, 1.10, 1.38, 1.67, and 1.70 (all s, CH3-19, CH3-29, CH3-18, CH3-28, CH3-21, CH3-26, and CH3-27), 3.18 (dd, J = 4.0, 11.7 Hz, H-3), 5.20 (br t, J = 9.5 Hz, H-23), and 5.53 (br d, J = 7.9 Hz, H-24)] and five monosaccharide units through easily identifiable signals for anomeric protons and carbons [δH 4.86 (d, J = 5.2 Hz), 4.90 (d, J = 7.7 Hz), 5.00 (d, J = 7.6 Hz), 5.43 (d, J = 7.3 Hz), and 6.11 (br s); δC 104.4, 105.2, 103.6, 106.0, and 101.7)]. The (−)-FAB-MS showed an [M−H] ion at m/z 1205, which was consistent with a pentasaccharide glycoside carrying two glucose, one 6-deoxyL-talose, two pentose (xylose and arabinose) units, and an aglycon with a molecular mass of 472. The presence of other