A New Triterpene Saponin from the Tubers of Stachys sieboldii

Abstract

Stachys sieboldii MIQ. (Labiatae) is native to Northern China and widely distributed in North America, Asia, and Europe. S. sieboldii has been used in Chinese folk medicine for the treatment of ischemic stroke, senile dementia, and various gastrointestinal problems. Previous phytochemical and pharmacological studies on this plant reported the isolation of terpenes, flavonoids, and phenolic compounds, and it having antimicrobial, antioxidant, and antitumor activities. In our continuing efforts to study the secondary metabolites of natural plant sources, the MeOH extract of S. sieboldii was investigated, and a new triterpene saponin, Sieboldii saponin A (1), was isolated, together with five known compounds (2-6). The structures of the isolates (1-6) were elucidated by means of spectroscopic methods and chemical evidences. Sieboldii saponin A (1) was isolated as a colorless gum. The molecular formula was determined to be C42H66O15 from the molecular ion peak [M + H] at m/z 811.4480 (calcd. for C42H67O15: 811.4480) in the positive-ion HRFABMS. The IR spectrum at 3421 cm indicated that 1 possessed hydroxyl group. The H-NMR spectrum of 1 (Table 1) displayed the signals of an olefinic proton at δH 5.30 (1H, br t, J = 3.5 Hz, H-12), a couple of exomethylene protons at δH 4.72 and 4.67 (each 1H, br s, H-30), two oxygenated methine protons at δH 3.92 (1H, m, H-2) and 3.82 (1H, m, H-3), a couple of oxymethylene protons at δH 3.55 and 3.28 (each 1H, d, J = 11.2 Hz, H-23), one methine proton at δH 2.30 (1H, d, J = 11.9 Hz, H-18), four tertiary methyl protons at δH 1.21 (3H, s, H-27), 1.07 (3H, s, H-25), 0.86 (3H, s, H-26), and 0.82 (3H, s, H-24), one secondary methyl proton at δH 1.05 (3H, d, J = 6.3 Hz, H-29), and two sugar anomeric protons at δH 5.45 (1H, d, J = 7.7 Hz, H-1′) and 4.77 (1H, d, J = 7.7 Hz, H-1′′). The C-NMR spectrum showed a total of 42 carbon signals, of which 30 carbons were to be assigned to the aglycone and the remaining 12 carbons to the sugar moieties. The C-NMR and DEPT spectra included one carboxylic carbon at δC 175.9, five methyl carbons at δC 22.7, 16.5, 16.2, 16.0, and 15.3, four olefinic carbons at δC 152.9, 138.9, 125.8, and 104.1, two oxygenated methine carbons at δC 77.3 and 65.8, one oxygenated methylene carbon at δC 69.9, four methine carbons at δC 54.9, 47.3, 42.9, and 37.1, eight methylene carbons at δC 41.0, 38.4, 32.4, 31.8, 28.6, 23.5, 23.1, and 17.5, five quaternary carbons at δC 48.1, 42.0, 41.2, 39.7, and 37.3, and 12 remaining signals at δC 102.6, 77.4, 76.6, 74.5, 71.0, and 62.2, and at δC 92.6, 77.3, 77.2, 76.8, 69.4, and 61.0 assignable to two glucose moieties. From these data, compound 1 was presumed to be of urs-12-en-28-oic acid skeleton with terminal double bond. The HMBC correlations of H29/C-20 and H-30/C-19 and C-21 confirmed a secondary