C19-Diterpenoid alkaloid arabinosides from an aqueous extract of the lateral root of Aconitum carmichaelii and their analgesic activities.

Acta Pharmaceutica Sinica B 2018;8(3):409–419 Chinese Pharmaceutical Association Institute of Materia Medica, Chinese Academy of Medical Sciences Acta Pharmaceutica Sinica B www.elsevier.com/locate/apsb www.sciencedirect.com ORIGINAL ARTICLE C19-Diterpenoid alkaloid arabinosides from an aqueous extract of the lateral root of Aconitum carmichaelii and their analgesic activities Qinglan Guo†, Huan Xia†, Xianhua Meng, Gaona Shi, Chengbo Xu, Chenggen Zhu, Tiantai Zhang⁎, Jiangong Shi⁎ State Key Laboratory of Bioactive Substance and Function of Natural Medicines, Institute of Materia Medica, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100050, China Received 31 January 2018; received in revised form 1 March 2018; accepted 18 March 2018 KEY WORDS Ranunculaceae; Aconitum carmichaelii; C19-diterpenoid alkaloid; Arabinoside; Aconicarmichosides E−L; Analgesic effect; Structure–activity relationship Abstract Eight new C19-diterpenoid alkaloid arabinosides, named aconicarmichosides E–L (1–8), were isolated from an aqueous extract of the lateral roots of Aconitum carmichaelii (Fu Zi). Their structures were determined by spectroscopic and chemical methods including 2D NMR experiments and acid hydrolysis. Compounds 1–8, together with the previously reported four neoline 14-O-arabinosides from the same plant, represent the only examples of glycosidic diterpenoid alkaloids so far. At a dose of 1.0 mg/kg (i.p.), as compared with the black control, compounds 1, 2, and 4–6 exhibited analgesic effects with 465.6% inhibitions against acetic acid-induced writhing of mice. Structure–activity relationship was also discussed. & 2018 Chinese Pharmaceutical Association and Institute of Materia Medica, Chinese Academy of Medical Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). ⁎ Corresponding authors. E-mail addresses: (Tiantai Zhang), (Jiangong Shi). † These authors made equal contribution to this work. Peer review under responsibility of Institute of Materia Medica, Chinese Academy of Medical Sciences and Chinese Pharmaceutical Association. https://doi.org/10.1016/j.apsb.2018.03.009 2211-3835 & 2018 Chinese Pharmaceutical Association and Institute of Materia Medica, Chinese Academy of Medical Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 410 1. Qinglan Guo et al. Introduction The lateral and principle roots of the poisonous plant Aconitum carmichaelii Debx. (Ranunculaceae), named “Fu Zi” and “Wu Tou” in Chinese, respectively, are important traditional Chinese medicines used for the treatment of rheumatalgia, neuralgia, arrhythmia, acardianeuria, and inflammations1–4. Considerable chemical and pharmacological studies have previously been reported, along with isolation of more than a hundred compounds from various extracts of different parts of A. carmichaelii2–12. Among the reported chemical constituents, diterpenoid alkaloids were recognized as active components, especially the lipophilic diesterified aconitanetype C19-diterpenoid alkaloids were identified as the main toxic constituents. In addition, the previous reports showed that toxicity of these medicines was dramatically reduced by processing and decocting because contents of the toxic diesterified aconitane-type alkaloids were remarkably decreased by the treatments13–16. However, in the chemical studies, organic solvents, such as benzene, chloroform, methanol, and ethanol, were applied for extracting the raw and processed plant materials2–11. The extraction procedures also differ from a classic protocol of utilization by decocting the medicines with water. Therefore, as part of our program to systematically study the chemical diversity of traditional Chinese medicines and their biological effects17–42, an aqueous decoction of the raw lateral roots of A. carmichaelii was investigated. In previous papers, we reported four new hetisan-type, three new napeline-type, a new arcutine-type, and a novel type C20-diterpenoid alkaloids, twenty-six new aconitane-type C19-diterpenoid alkaloids including four unique glycosidic neoline derivatives with isomeric arabinosyls, two new 2-(quinonylcarboxamino)benzoates, and seven new aromatic acid derivatives, as well as solvent-/base-/acid-dependent transformation and equilibration between alcohol iminium and aza acetal forms of the napeline-type C20-diterpenoid alkaloids43–49. This paper describes isolation and structural characterization of eight aconitane-type C19-diterpenoid alkaloid L-arabinosides (1–8, Fig. 1) as well as their analgesic activities from the same decoction. 2. Results and discussion Compound 1 was isolated as a colorless gum with ½α20 D þ25.5 (c 0.20, MeOH). The IR spectrum of 1 showed a strong absorption band (3365 cm−1) due to hydroxyl groups. The (þ)-HR-ESI-MS and NMR spectroscopic data (Experimental Section 4.3.1, and Tables 1 and 2) indicated that 1 had the molecular formula C29H47NO10. The 1H NMR spectrum of 1 in CD3OD showed resonances characteristic for an aconitane-type C19-diterpenoid alkaloid, including an N-CH2CH3 unit at δH 3.30 and 3.25 (1H each, m, H2-20) and 1.43 (3H, t, J ¼ 7.5 Hz, H3-21) and three methoxy groups at δH 3.40 (s, OMe-16), 3.35 (s, OMe-6), and 3.32 (s, OMe-18); four oxymethines at δH 4.33 (brd, J ¼ 7.0 Hz, H-6), 4.19 (brs, H-1), 4.14 (dd, J ¼ 5.0 and 4.5 Hz, H-14), and 3.35 (m, H-16); one nitrogen-bearing methine at δH 3.27 (brs, H-17); an oxymethylene at δH 3.57 and 3.50 (1H each, d, J ¼ 8.0 Hz, H2-18); and a nitrogen-bearing methylene at δH 3.39 and 3.06 (1H each, d, J ¼ 12.5 Hz, H2-19); as well as partially overlapped resonances due to four aliphatic methylenes (H2-2, H2-3, H2-12, and H2-15) and five aliphatic methines (H-5, H-7, H-9, H-10, and H-13) between δH 1.50 and 2.42. Additionally the spectrum showed signals diagnostic for a pentose moiety, consisting of four oxygen-bearing methines at δH 5.11 (d, J ¼ 5.5 Hz, H-1′), 4.16 (dd, J ¼ 8.0 and 5.5 Hz, H-2′), 4.02 (dd, J ¼ 8.0 and 7.0 Hz, H-3′), and 3.76 (m, H-4′), and an oxygen-bearing methylene at δH 3.75 (m, H-5′a) and 3.65 (dd, J ¼ 12.5 and 6.5 Hz, H-5′b). The 13 C NMR and DEPT spectra showed 29 carbon signals corresponding to the above units and three quaternary carbons including an oxygen-bearing carbon at δC 74.6 (C-8). Comparison of the spectroscopic data with those of aconicarmichosides A–D48 indicated that 1 was an isomer of neoline β-L-arabinofuranoside. Specifically compared with the NMR spectroscopic data of aconicarmichoside D48, the resonances of H-1, H-2a, H-5, and H-16 and C-1, C-1′, and C-17 in 1 were remarkably deshielded by ΔδH þ0.19, þ0.38, þ0.05, and þ0.05 and ΔδC þ5.2, –5.9, and þ2.0, respectively, whereas H-2b, H-3b, H-9, and H-13 and C-2 and C-14 were shielded by ΔδH –0.09, –0.26, –0.15, and –0.14 and Δδ (...truncated)