Norditerpenoid alkaloids from Delphinium kohatense Munz

ORIGINAL ARTICLE Rec. Nat. Prod. 9:1 (2015) 76-80 Norditerpenoid alkaloids from Delphinium kohatense Munz Farzana Shaheen*1, Manzoor Ahmad2, Tania Shamim Rizvi1 and Liaqat Ali*1,3 1 HEJ Research Institute of Chemistry, International Center for Chemical and Biological Sciences, University of Karachi, Karachi-75270, Pakistan 2 Department Chemistry, University of Malakand, Chakdara, Dir (L), Pakistan 3 Department of Biological Sciences and Chemistry, University of Nizwa, Birkat Al-Mauz, Nizwa-616, Oman (Received October 7, 2013; Revised March 10, 2014; Accepted July 8, 2014) Abstract: A new aconitine-type norditerpenoid alkaloid, kohatenine (1) [10β-hydroxy-1α,8β,16β-trimethoxy6α,14α-diacetyl-N-ethyl aconitane], along with four known alkaloids, condelphine (2), talatisamine (3), peregrine (4), and 14-O-acetyltalatisamine (5), was isolated from the aerial parts of Delphinium kohatense Munz. The structure of the new compound was deduced on the basis of combined MS (EI and FAB) and NMR (1D and 2D) spectroscopic techniques. The known compounds were confirmed by comparison of the physical and spectroscopic data with those reported in literature. Keywords: Norditerpenoid alkaloids; Kohatenine; Delphinium kohatense; Ranunculaceae. © 2015 ACG Publications. All rights reserved. 1. Introduction Delphinium (Larkspur), an important genus of the family Ranunculaceae, is well known for its potential uses in medicine [1]. The genus is recognized as a rich source of biologically active and structurally complex diterpenoid and norditerpenoid alkaloids with febrifuge, sedative, cardiotonic and analgesic activities [2-5]. D. kohatense Munz is a 15-30 cm high perennial herb found at an elevation of 1800-2300 m in the dry places of India and northern areas of Pakistan and Jammu & Kashmir [6]. To the best of our knowledge no phytochemical work has been reported on this plant. Previously, we have reported many diterpenoid and norditerpenoid alkaloids from Aconitum and Delphinium species [7-10]. In the present paper, we describe the isolation, characterization and structure elucidation of new aconitine-type norditerpenoid alkaloid, kohatenine (1), along with four known compounds; condelphine (2) [11], talatisamine (3) [11], peregrine (4) [12], and 14-O-acetyltalatisamine (5) [13] (Figure 1). The structure of compound 1 was elucidated on the basis of spectroscopic techniques. 2. Material and Methods 2.1. General Optical rotations were measured on a JASCO DIP 360 polarimeter. IR Spectra were recorded on a Bruker, VECTOR 22 spectrophotometer. EI-MS and HREI-MS were recorded on mass spectrometers JEOL JMS HX 110. The 1H and 13C NMR Spectra were recorded on Bruker NMR spectrometers * Corresponding authors: ; Phone: +92-3002848287 Fax: +92-2134819018, ; Phone: +968-25446608 Fax: +968-25446612 The article was published by Academy of Chemistry of Globe Publications www.acgpubs.org/RNP © Published 09/23/2014 EISSN: 1307-6167 Shaheen et al., Rec. Nat. Prod. (2015) 9:1 76-80 77 operating at 400 MHz (100 MHz for 13C). The chemical shift values are reported in ppm (δ) and the coupling constants (J) are given in Hz. For TLC, precoated plates (silica gel 60F-254, E. Merck) were used. The TLC plates were viewed under UV at 254 and 366 nm and by spraying with Dragendorff‘s reagent. Solvent system, n-hexane: acetone: diethylamine (90:9.5:0.5), was used in chromatographic separations. 2.2. Plant Material The plant, Delphinium kohatense, was collected from Swat, KPK, Pakistan, in May 2004, and was identified by Prof. Dr. Habib Ahmad, Chairman, Department of Botany, Hazara University Dhodial. A voucher specimen (KD-03) was deposited in the herbarium of the Department. OCH3 OH H OCH3 OCH3 OCOCH3 OH H H H N N OH OH H H H3CO H3CO Condelphine (2) Talatisamine (3) OCH3 OCH3 H OCH3 OCH3 OH OCOCH3 H H H N N OCH3 OH H H OCOCH3 Peregrine (4) H3CO 14-O-Acetyltalatisamine (5) Figure 1. Structures of compounds 2-5 2.3. Extraction and Isolation Dried and powdered aerial parts (4 kg) of the plant were extracted exhaustively with 80% ethanol at room temperature. The filtrate was evaporated in vacuum to yield 200 g of the residue. The residue was partitioned in different solvents on the basis of increasing polarity to get n-hexane (8.5 g), chloroform (13.4 g), ethyl acetate (12.8 g), and n-butanol (48.6 g). The crude chloroform fraction (13.4g) was subjected to column chromatography and eluted with n-hexane with gradient of chloroform upto 100% and methanol upto 20%. Five fractions were obtained. On repeated flash column chromatography using solvent system n-hexane-acetonediethylamine (90:9.5:0.5), four diterpenoid alkaloids; condelphine (2) (4.2 mg), isotalatizidine (3) (3.9 mg), peregrine (4) (5.1 mg), and 14-O-acetyltalatisamine (5) (4.8 mg)] were obtained. Kohatenine (1) [10β-hydroxy-1α, 6β, 16β-trimethoxy-6β, 14α-diacetyl-N-ethyl aconitane] (4.5 mg) was obtained from sub-fraction (F-3) by repeated flash column chromatography using solvent system n-hexane-acetonediethylamine (85:14.5:0.5). Norditerpenoid alkaloids from Delphinium kohatense munz 78 2.4. 10β-hydroxy-1α,8β-trimethoxy-6α,14α-diacetyl-N-ethylaconitane (Kohatenine) White amorphous powder (4.5 mg): [α]D30 +14 (c 0.34, C2H5OH); IR (CHCl3): νmax 3500, 3406, 2927, 1732, 1246, 1092 cm-1; 1H-NMR (400 MHz, CDCl3): see Table 1; 13C NMR (CDCl 3, 100 MHz): see Table 1; EI-MS (70 eV): m/z (rel. int.) 521 [M]+ (5), 490 [M+-OMe] (11), 478 [M+-Ac] (9), 475 [M+-OMe-Me] (17), 462 [M+-OAc] (22), 416[M+-OMe-OAc-Me] (9), 404 (6), 368 (6), 85 (66), 83 (100), 58 (17); (-)FAB-MS: m/z 520.3 [M+ - 1]; HR-EI-MS m/z 521.2927 (calculated for C28H43NO8 521.2932, [M]+) 3. Results and Discussion Compound 1 was isolated from the crude 80% ethanolic extract of D. kohatense Munz as an amorphous powder. The EI-MS showed the molecular ion at m/z 521. The negative FAB-MS showed the quasimolecular ion [M-1]+ at m/z 520.3 consistent with the formula, C28H42NO8, for the deprotonated ion. The molecular formula, C28H43NO8, of compound 1 was further confirmed through HR-EI-MS showing the molecular ion at m/z 521.2927 (calculated for C28H43NO8 521.2932). The other prominent fragments in the mass spectrum were observed at m/z 490 [M+-OMe], 478 [M+-Ac], 475 [M+-OMe-Me], 462 [M+-OAc], 416 [M+-OMe-OAc-Me], 404, 368, 85, 83, 58, characteristics of alkaloids with an aconitine type skeleton (Figure 2) [14]. The IR spectrum of compound 1 showed absorption bands at 3500, and 3406 cm-1 (OH group), 1732, and 1246 cm-1 (COO), 1092 cm-1 (C-O), and 2927 cm-1 (C═C). M+ - OCOCH3 M+ M+ - COCH3 C26H40NO6 m/z 462 C28H43NO8 m/z 521 C26H40NO7 m/z 478 M+ - OCH3 - OCOCH3 - CH3 M+ - OCH3 M+ - OCH3 - CH3 C23H31NO5 m/z 416 C27H40NO7 m/z 490 C26H37NO7 m/z 475 Figure 2. Major mass fragmentations in compound 1 The 1H NMR spectrum of compound 1 exhibited signals for N-ethyl group, three methoxy groups, two acetyl groups and nine methine protons. The overall spectral data of compo (...truncated)