Chemical components of Aconitum barbatum var. puberulum and their cytotoxic and antibacterial activities

Abstract Nineteen compounds, including seventeen alkaloids O-methylarmepavine (1), (S)6methoxy1(4methoxybenzyl)2methyl 1,2,3,4tetrahydroisoquinolin7ol (2), (+)-(IR,laR)-lahydroxymagnocurarin (3), (6R,6aS,P)-(+)-corydine (4), (+)-N-methyllaurotetanine (5), magnoflorine (6), 3-hydroxy-1,2-dimethoxy-5-methyl-5H-dibenzoindol-4-one (7), imperialine (8), crispine B (9), (S)-1-(3-methoxyphenyl)-N-methylpropan-2-amine (10), methyl 2- (acetamino)benzoate (11), 2-carboxyoxanilic acid methylester (12), 4-[2-(methoxycarbonyl) anilino]-4-oxobutanoic acid methyl ester (13), N-methylcorydaldine (14), N-methyl-6,7- dimethoxyisoquinolone (15), (5S,6R,7S,8R)-5-amino-(2Z,4Z)-1,2,3-trihybuta-2,4-dienyloxypentane- 6,7,8,9-tetraol (16), nicotinic acid (17), and two megastigmane type compounds, S(+)- dehydrovomifoliol (18) and megastigmane (19), were isolated from the Aconitum barbatum var. puberulum Ledeb. Compounds 1–3 and 5–19 were isolated from this plant for the first time, of which compound 11 was isolated from natural source for the first time. Cytotoxicity evaluation revealed that compound 5 displayed mild cytotoxicity against the Hela cell lines (IC50 13.69 ± 0.036 μM). Antibacterial activity evaluation revealed that compounds 1 and 6 showed strong antibacterial activity against the Gram-positive bacterium, S. aureus. Graphical Abstract


Introduction
The genus Aconitum belongs to the Ranunculaceae family, comprising of approximately 400 species, is distributed in the temperate regions of the northern hemisphere region, such as Asia, Europe and North America. Many species of this genus have been widely used in folk medicine as an anesthetic, anti-inflammatory, sedative and to treatment of rheumatism and toothache (Chen et al. 2017;Yu et al. 2017;Samanbay et al. 2018;Jiang et al. 2019;Luo et al. 2020).
Aconitum barbatum var. puberulum Ledeb., widely distributed in the eastern part of Xinjiang, Shanxi, Hebei, as well as in the Siberia region of Mongolia and Russia, is a perennial herb belonging to Ranunculaceae family (Wang and Warnock 1979). It has been used as a folk medicine for a long period of time in China to treatment of stomach-ache, rheumatic arthritis, lymphatic tuberculosis and some other inflammations (State Administration of Traditional Chinese Medicine 1999). Previous phytochemical investigations of this plant revealed that 70 compounds including diterpenoid alkaloids, aporphine alkaloids, benzamide derivatives, flavonoids, steroids and monoterpene glycosides, respectively (De-Quan and Das 1983; Sun and Yuan 2008;Mu et al. 2012;Ablajan et al. 2021). In our previous phytochemical researches on A. barbatum var. puberulum grown in Central Asia, seven new diterpenoid alkaloids, including an unprecedented carbon skeleton of C 20 -diterpenoid alkaloid, together with 11 known diterpenoid alkaloids were obtained. Some of them showed moderate antiarrhythmic and antimicrobial activities (Ablajan et al. 2021). The results showed that the chemical composition of A. barbatum var. puberulum grown in Central Asia was different from other regions. In order to take full advantage of this characteristic plant resource in Central Asia, it is necessary for us to further study on its non-diterpenoid alkaloids to clarify its chemical composition and pharmacological activity. This led to isolation of nineteen known compounds (1-19) (Figure 1), including seventeen alkaloids and two megastigmane glycosides. In this paper, the isolation, structure identification and biological activities of these compounds are described.

Results and discussion
It was reported that the alkaloids of A. barbatum var. puberulum growing in Shanxi province showed cytotoxicity, antioxidant and antimicrobial capacities (Sun et al. 2009;Ablajan et al. 2021). In our study, all of the compounds were also tested for their cytotoxicity activity and antibacterial activity. Among these tested, compound 5 exhibited moderate cytotoxicity against the Hela cell lines with the IC 50 values of 13.69 lM (Dox: 0.23 ± 0.04 lM) (Supplementary material, Table S1). For the antibacterial activity test, compounds 1 and 12 presented moderate inhibitory capacities against the C. albicans; Compound 16 showed moderate inhibitory activity and compounds 1, 7, 10, and 12 showed weak inhibitory capacities against the E. coli; Compounds 1and 6 showed strong inhibitory activity, compounds 2, 4, 12, 13 and 16 presented moderate inhibitory capacities, while compound 5 showed weak inhibitory activity against the S. aureus (Supplementary material, Table S2).

Conclusion
In summary, seventeen alkaloids, together with two megastigmane type compounds were isolated from the Aconitum barbatum var. puberulum Ledeb. Compounds 1-3 and 5-19 were isolated for the first time from this plant. All the compounds were assayed for their cytotoxicity and antibacterial activities. Compound 5 exhibited strong cytotoxicity against the Hela cell lines with the IC 50 values of 13.69 lM. Compounds 1-2, 4-7, 10, 12, 13 and 16 presented different levels of inhibitory capacities against the Gram-positive bacterium (C. albicans and S. aureus) and Gram-negative bacterium (E. coli). Our research shows that this plant is rich in different types of alkaloids with good biological activities, which are worth for further investigation.

Disclosure statement
No potential conflict of interest was reported by the authors.