Two Norditerpenoid Ester Alkaloids from Aconitum bulleyanum

• Abstract
• Materials and Methods
• Rerefences

Abstract

Two new norditerpenoid alkaloids, 8-acetyl-14-p-methoxybenzoate of talatisamine (1) and 14-p-methoxybenzoate of talatisamine (2), were isolated from Aconitum bulleyanum Diels. The structures were elucidated on the basis of spectroscopic and chemical studies.

Aconitum bulleyanum, being collected in the southwest China, is well used in the local places as folk medicine for influenza, itchy rash and snake bites. Five diterpene alkaloids were reported previously [1]. Compounds 1 and 2 were obtained by fractionation of A. bulleyanum as described below. EI-MS of 1 showed M⁺ at m/z 597 was corresponding to the molecular formula C₃₄H₄₇NO₈. Its IR spectrum showed an ester (ν_max 1716), benzoyl (ν_max 1606), an acetyl (ν_max 1255) and no hydroxy group. The NMR spectrum suggested the presence of an N-ethyl group (δ_C = 13.46, 49.34), as well as three methoxy groups (δ_C = 59.46, 56.20, 55.36). The signals and biogenetic considerations indicated that 1 is a norditerpenoid alkaloid [2], [3], [4]. The downfield signals and an aromatic methoxy group showed the presence of a p-methoxybenzoate group attached to the alkaloid. The signal (δ_C 169.78; δ_C 21.72, δ_H 1.34) of an acetate group and the three quaternary carbons (C-8 δ 85.97; C-11 δ 48.73; C-4 δ 38.36) also indicated that 1 was an aconitine-type alkaloid. Being affected by aromatic ring to upfield, an acetate group was attached to C-8 and a p-methoxybenzoate group was attached to C-14 [5]. The HMBC (Table [1]) also exhibited that the H-14 (δ 5.00) and the CH₃ signal (δ_H 1.34) of the acetate group were correlating with the carboxyl carbon (δ_C 166.15) of the methoxybenzoate group and C-8 (δ 85.97) respectively. This was proved by C-14 p-anisylation of talatisamine and C-8 acetylation of 2. Hence, 1 is the 8-O-acetyl-14-p-methoxybenzoate of talatisamine.

The EI-MS of 2 showed a molecular ion at m/z 555 and the molecular formula C₃₂H₄₅NO₇. Its IR spectrum showed a hydroxy (ν_max 3446), an ester (ν_max 1712) and an aromatic (ν_max 1606 ) function. The NMR spectrum also showed the presence of an N-ethyl group (δ_C 13.70; 49.51), as well as three methoxy groups [δ_C 59.58; 56.19; 56.08]. The downfield signals and an aromatic methoxy group (δ_C 55.50) showed a methoxybenzoate moiety attached to 2. The DEPT experiments showed the presence of three quaternary carbons (C-8 δ 73.93; C-11 δ 48.88; C-4 δ 38.63) indicating that 2 is an aconitine-type alkaloid. It was shown that a methoxy group was at C-18 (δ 79.65) and the others were at C-1, C-16. Compound 2, a derivative of talatisamine 3, was confirmed by hydrolysis of 2 to give 3 [2]. Comparing with the ¹³C NMR data of compound 2 and 1 (Table [1]) revealed 2’s C₈-OH being not acetylation. In 2 the δ_C-8 were shifted from 85.97 ppm to 73.93 ppm. The methoxybenzoate moiety was attached to C-14. Therefore 2 is the 14-p-methoxybenzoate of talatisamine.

Materials and Methods

All melting points were measured on a Reichert micromelting apparatus and were uncorrected. NMR spectra were recorded in CDCl₃-d on a Bruker AMX-400. HMQC and HMBC were measured on an INOVA-400. IR spectra were scanned on a Perkin-Elmer 683. MS were taken on a Finigan MAT 212 (220 °C, ionization 70 eV). Optical rotation was measured on Perkin-Elmer polarimeter-341. Column chromatography was on 200∼300 mesh Al₂O₃ and 200∼300 mesh silica gel (Shanghai Fifth Reagent Factory). TLC was on silica gel GF₂₅₄ (Haiyang Chemical Industry Factory, Qingdao). Visualization was made through Dragendorff’s reagent. The developing system is n-hexane-dimethylamine, 8 : 2. The optical rotations were measured at 20 °C. the Talatisamine was obtained from Aconitum gymnandrum Maxim [6].

Plant material: The roots of Aconitium bulleyanum Diels were collected in the mountains of DaLi district in Yunan Province in July 1995 and authenticated by Dr. Xiao-Qiang Ma of Shanghai Institute of Materia Medica. A voucher (No.95 - 75) was deposited in the Herbarium of this institute.

Extraction and isolation: Powered root (5 kg) were extracted with 95 % ethanol (5 L × 3) at room temperature and the ethanol extract was extracted with 1 % aqueous HCl (1 L × 4). The aqueous acidic solution was basified to pH 9 with concentrated NH₄OH and partitioned with CHCl₃. (1 L × 5). The CHCl₃ solution was concentrated to a crude alkaloid fraction (4 g), which was subjected column chromatography (CC) on Al₂O₃ (200 g) eluting with petroleum ether/EtOAc gradient (8 : 2 1000 ml, 9 : 1 4000 ml, 3 : 1 1000 ml, 1 : 11000 ml) with every fraction of 100 ml. The compounds 1 (31 mg, in Fr.9∼15 of 9 : 1; R_f: 0.32) and 2 (8 mg, in Fr. 28∼29 of 1 : 1; R_f: 0.53) were obtained.

8-O-Acetyl-14-p-methoxybenzoate of talatisamine (1): Amorphous, [α]_D ²⁰: + 14.3° (CHCl₃, 0.15). IR (KBr): ν _max = 2935, 1716, 1606, 1511, 1278, 1255, 1093, 771 cm^-1. ¹H- and ¹³C-NMR spectra (CDCl₃) are given in Table [1]. EIMS: m/z = 597 (2), 566 (30), 506 (35), 476 (40), 386 (10), 354 (8), 282 (6), 181 (6).

14-p-Methoxybenzoate of talatisamine (2) Amorphous: [α]_D ²⁰: + 12.5° (CHCl₃, 0.15). IR (KBr): ν _max = 3446, 2929, 1712, 1606, 1511, 1168, 1101, 1031, 848, 771 cm^-1. ¹H- and ¹³C-NMR spectra (CDCl₃) are given in Table [1]. EIMS: m/z = 555 (4), 524 [M - OMe]⁺ (100), 420 (6), 404 (30), 386 (6), 354 (4), 282 (4), 181 (10).

Semisynthesis of 2 and 1: 1.5 ml of p-anisyl chloride were titrated at 0 °C to 950 mg of talatisamine dissolved in 3 ml anhydrous pyridine, then a yellow-light powder 2 (510 mg) was obtained by column chromatography on alkali Al₂O₃ (50 g) (petroleum ether/EtOAc, 9 : 1). The above 160 mg of 2 and 100 ml of p-methylbenzenesulfonic acid were added to 1 ml acetic anhydride and kept overnight at room temperature. A yellow-light powder 1 (160 mg) was obtained by preparative TLC over silica gel (R_f: 0.28, CHCl₃/MeOH, 20 : 1).

Hydrolysis of 2: 5 mg of 2 were dissolved in 5 ml methanolic KOH at room temperature overnight. After removing solvent, the residue was extracted with CH₂Cl₂ (20 ml × 5). The extract was dried by Na₂SO₄ and evaporated to give a yellow residue (4 mg), which was purified by preparative TLC over silica gel (R_f: 0.17, CHCl₃/MeOH, 20 : 1) to afford talatisamine identified with an authentic sample [2], [6].

Rerefences

• 1 Ma X Q, Jiang S H, Zhu D Y. Diterpenoid alkaloids of Aconitum bulleyanum Diels.  Zhongguo Zhongyao Zazhi. 1998;  11 679
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• 2 Meriçli H, Meriçli F, Becker H, Ilarslan R, Ulubelen A. 3-hydroxytalatisamine from Aconitum nasutum .  Phytochemistry. 1996;  42 909
  CrossrefPubMedSearch in Google Scholar
• 3 Ding L S, Chen Y Z, Wu F E. New diterpenoid alkaloids from Aconitum vilmorinianum Kom.  Acta Chim Sin. 1992;  50 405
  PubMedSearch in Google Scholar
• 4 Meriçli H, Meriçli F, Seyhan G V, Özçelik H, Kilinçer N, Ferizli A G, Ulubelen A. Cyphoplectine, a norditerpene alkaloid for Delphinium cyphoplectrum .  Heterocycles. 1999;  51 1843
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• 5 Jiang S H, Hong S H, Zhou B N, Zhu Y L, Zhu R H, Zhen P J, Wang M. Studies on the Chinese drug, Aconitum spp. XIV. Studies on the chemical structure of delavaconitine.  Acta Chim Sinica. 1987;  45 1101
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• 6 Jiang S H, Guo S H, Zhou B N, Wang S X, Yi F S, Ji L J. Alkaloids from Aconitum gymnandrum Maxim (I).  Acta Pharmaceutica Sinica. 1986;  21 279
  PubMedSearch in Google Scholar

Prof. Pei-ming Yang

Shanghai Institute of Pharmaceutical Industry

1320 Beijing road (w.)

Shanghai 200040

P.R.China

Email: yangpm@online.sh.cn

Fax: +86-21-62470851

Rerefences

• 1 Ma X Q, Jiang S H, Zhu D Y. Diterpenoid alkaloids of Aconitum bulleyanum Diels.  Zhongguo Zhongyao Zazhi. 1998;  11 679
  PubMedSearch in Google Scholar
• 2 Meriçli H, Meriçli F, Becker H, Ilarslan R, Ulubelen A. 3-hydroxytalatisamine from Aconitum nasutum .  Phytochemistry. 1996;  42 909
  CrossrefPubMedSearch in Google Scholar
• 3 Ding L S, Chen Y Z, Wu F E. New diterpenoid alkaloids from Aconitum vilmorinianum Kom.  Acta Chim Sin. 1992;  50 405
  PubMedSearch in Google Scholar
• 4 Meriçli H, Meriçli F, Seyhan G V, Özçelik H, Kilinçer N, Ferizli A G, Ulubelen A. Cyphoplectine, a norditerpene alkaloid for Delphinium cyphoplectrum .  Heterocycles. 1999;  51 1843
  PubMedSearch in Google Scholar
• 5 Jiang S H, Hong S H, Zhou B N, Zhu Y L, Zhu R H, Zhen P J, Wang M. Studies on the Chinese drug, Aconitum spp. XIV. Studies on the chemical structure of delavaconitine.  Acta Chim Sinica. 1987;  45 1101
  PubMedSearch in Google Scholar
• 6 Jiang S H, Guo S H, Zhou B N, Wang S X, Yi F S, Ji L J. Alkaloids from Aconitum gymnandrum Maxim (I).  Acta Pharmaceutica Sinica. 1986;  21 279
  PubMedSearch in Google Scholar

Prof. Pei-ming Yang

Shanghai Institute of Pharmaceutical Industry

1320 Beijing road (w.)

Shanghai 200040

P.R.China

Email: yangpm@online.sh.cn

Fax: +86-21-62470851