Fargosides A-E, Triterpenoid Saponins from Holboellia fargesii.

Abstract

The medicinal plant Holboellia fargesii REAUB. (Lardizabalaceae) is a tree which grows in the southwest region of the People's Republic of China. Its stems, roots, and fruits have been used as folk medicine for the treatment of cough, lumbago, nephritis and abdominal hernia in Yunnan Province. 1,2) However, there has been no previous chemical study of this plant. Preliminary evaluation indicated that H. fargesii contains saponins. The potential medicinal importance and our continuing interest in the chemistry of saponins prompted us to initiate a chemical investigation of this plant. In this paper, we report the isolation and structure elucidation of five new triterpenoid saponins (1-5) from the roots of this species. Results and DiscussionAn ethanolic extract of roots of H. fargesii was suspended in water and then partitioned successively with EtOAc and nBuOH. The n-BuOH soluble fraction, on chromatographic purification over Diaion HP-20 resin, followed by repeated medium-pressure liquid chromatography (MPLC) and HPLC purification, gave five new triterpenoid saponins, termed fargosides A-E (1-5).Fargoside A (1) gave quasi-molecular ions at m/z 775 [MϩNa] ϩ and 791 [MϩK] ϩ by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) MS. The molecular formula of C 40 H 64 O 13 was confirmed by high resolution (HR)-FAB-MS. The IR spectrum of 1 showed an absorption bond for a carbonyl group at 1685 cm Ϫ1. The 13 C-NMR spectrum showed 40 carbon signals, of which 29 were assigned to the aglycon moiety and 11 were assigned to the sugar moiety (Tables 1-3 5, 16.5, 17.4, 25.7, 26.1 and 27.9, and sp 2 hybrid carbons at d 122.7 (d) and 144.4 (s), together with information from the 1 H-NMR spectrum (six methyl proton singlets and a broad triplet olefinic proton at d 5.54), indicated that the aglycon had an olean-12-ene skeleton.3) Detailed analysis of various two-dimensional (2D) NMR spectra such as double-quantum filtered 1 H-1 H shift correlation spectroscopy (DQF-COSY), heteronuclear multiple quantum coherence (HMQC), heteronuclear multiple bond correlation (HMBC) and phase-sensitive nuclear Overhauser enhancement spectroscopy (NOESY) spectra indicated that the structural features in the A, B, C and D rings of the aglycon were similar to those of oleanolic acid. 4) However, direct bond and long-range correlation data suggested that one of the geminal methyl groups at C-20 had been replaced by a hydroxyl group, forming 29-noroleanolic acid. In the NOESY spectrum (Fig. 1), H-18 was correlated with the methyl group at C-20, indicating that the hydroxyl group was in an a-configuration. These results suggested that the aglycon of 1 was 3b,20a-dihydroxy-29-norolean-12-en-28-oic acid. A related compound, 3b,20x-dihydroxy-30(or 29)-

New 30-Noroleanane Triterpenoid Saponins from Holboellia coriacea Diels

“…The positive HR-ESIMS of 1 showed an [M + Na] + at m/z 787.4248, which, taken together with the 13 C-NMR data analysis, indicated the molecular formula C 41 H 64 O 13 . The 13 C-NMR spectrum displayed 41 signals, of which 12 carbons were assignable to sugar moieties and 29 carbons to the aglycone moiety (Table 1). On the basis of 13 C-NMR and DEPT spectra, the carbons for the aglycone were identified as five methyls, four olefinic carbons, an oxy-methine carbon, a carbonyl carbon, 10 methylenes, three methines, and five quaternary carbons.…”

“…The positive HR-ESIMS of 1 showed an [M + Na] + at m/z 787.4248, which, taken together with the 13 C-NMR data analysis, indicated the molecular formula C41H64O13. The 13 C-NMR spectrum displayed 41 signals, of which 12 carbons were assignable to sugar moieties and 29 carbons to the aglycone moiety (Table 1).…”

“…The 13 C-NMR spectrum displayed 41 signals, of which 12 carbons were assignable to sugar moieties and 29 carbons to the aglycone moiety (Table 1). On the basis of 13 C-NMR and DEPT spectra, the carbons for the aglycone were identified as five methyls, four olefinic carbons, an oxy-methine carbon, a carbonyl carbon, 10 methylenes, three methines, and five quaternary carbons. The HSQC spectrum of 1 displayed corresponding five angular methyl groups (δH 0.94 (s, 3H); 1.02 (s, 3H); 1.12 (s, 3H); 1.20 (s, 3H); 1.22 (s, 3H)), a broad singlet olefinic proton at δH 5.45, and two exo-methylene protons at δH 4.65 (s) and 4.71 (s).…”

“…These NMR data suggested that the structure of 1 should be a noroleanane triterpenoid saponin [4]. After comparison of the 1 H and 13 C-NMR data with those of closely related analogues, the aglycone was characterized as 3β-hydroxy-30-norolean-12,20(29)-dien-28-oic acid (akebonoic acid) [7], a common triterpene aglycon occurring in the genera of Lardizabalaceae. The β-orientation of the hydroxyl group at C-3 was confirmed by an NOE correlation of H-3 with Hα-5 ( Figure S7) and the proton spin-coupling constant of H-3 (δH 3.44 (dd, J = 9.9, 5.6 Hz)).…”

“…Based upon all of the above evidence, the structure of 1 was elucidated as akebonoic acid 28-O-β-D-glucopyranosyl-(1 11 Ñ6 1 )-β-D-glucopyranosyl ester. 13 C-NMR data ( Table 2) with those of 1, compound 2 was found to have the same aglycone (akebonoic acid) and sugar moiety as those in 1, but an additional trans-caffeoyl moiety which was proposed according to the presence of an aromatic ABX system (δ H 7.54, br s; 7.09, dd, J = 8.2, 1.9 Hz; 7.17, d, J = 8.2 Hz), together with two coupled doublets (J = 15.8 Hz) at δ H 6.61 and 7.91 and the signal of an ester carbon C=O at δ C 167.1 [12]. The trans-caffeoyl moiety was deduced to be bound at C-6 11 of the sugar moiety via an ester linkage from the deshielded signal of the protons H-6 11 ( Table 2) and from long-range correlations of H-6 11 (4.88 (dd, J = 11.8, 5.5 Hz)/5.03 (dd, J = 11.8, 1.6 Hz)) with C=O (δ C 167.1) observed in the HMBC spectrum ( Figure S13).…”