Two new sesquiterpenes from Artemisia annua L.
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Two new sesquiterpenes from Artemisia annua L. Yukiko Takenaka1 · Satoko Seki1 · Toyoyuki Nishi2 · Takao Tanahashi1 Received: 5 June 2020 / Accepted: 9 July 2020 © The Japanese Society of Pharmacognosy 2020
Abstract Investigation of the dried whole plants of Artemisia annua led to the isolation of two new sesquiterpenes, artemanins A (1) and B (2), along with twenty-nine known compounds. The structures of the new compounds were elucidated by spectroscopic and chemical means. Keywords Artemisia annua · Asteraceae · Sesquiterpenes · Artemanin · Structure elucidation
Introduction Artemisia annua L., belonging to family Asteraceae, is widely distributed in temperate zones of Europe, North America, India, and Eastern Asia. The leaves of A. annua L., ‘Qinghao’, have been traditionally used as a treatment for malaria, inflammation, and intermittent fever [1, 2]. Previous biological studies on the active components of A. annua discovered artemisinin [qinghaosu (QHS)], an unusual sesquiterpene lactone with an endoperoxide moiety, as the antimalarial constituent [3, 4]. The medicinal value of this sesquiterpene prompted intensive studies on this plant species and led to the isolation of a variety of terpenoids, flavonoids, coumarins, and phenylpropanoids [5]. The contents of artemisinin and related sesquiterpenes in A. annua were reported to be dependent on chemotypes such as European, Chinese, and Vietnamese strains [6]. From Japanese A. annua, only artemisinin, artemisinic acid, arteannuin B, and artemisitene were detected [7]. We cultivated seeds of A. annua originating from a wild population in Kyoto, Japan in the field and re-examined its constituents to isolate two new sesquiterpenes 1 and 2 as well as twenty-nine known compounds. Herein, we report the isolation and structural elucidation of
* Takao Tanahashi tanahash@kobepharma‑u.ac.jp 1
Kobe Pharmaceutical University, 4‑19‑1, Motoyamakita‑machi, Higashinada‑ku, Kobe 658‑8558, Japan
The Nippon Shinyaku Institute for Botanical Research, 39, Sakanotsuji‑cho, Oyake, Yamashina‑ku, Kyoto 607‑8182, Japan
2
two new compounds by extensive analysis using 1D and 2D NMR spectra and chemical means.
Results and discussion The CHCl3 soluble fraction and 1-BuOH soluble fraction of a methanolic extract of the dried whole plants of A. annua were fractionated by a combination of chromatographic procedures to afford two new sesquiterpenes, 1 and 2, together with seven known sesquiterpenes: arteannuin B (3) [8, 9], arteannuic acid [10], arteannuin E [10], α-epoxyarteannuic acid [11], β-caryophyllene oxide [12], (1S,6R,7R,10R)-6-carboxy-10-methyl-α-methylene-1-(1oxobutyl)-cyclohexaneacetic acid (4) [13], and arteannoide E (5) [14] (Fig. 1); five flavonoids: penduletin [15, 16], artemetin [17, 18], chrysosplenetin [19], casticin [15, 19], and astragalin [20]; three coumarins: coumarin [21], scopoletin [15, 22], and scopolin [23]; two normegastigmans: corchoionoside C [24] and citroside A [25]; and stigmasterol [26], annphenone [27], a mixture of icosyl-, docosyl-, an
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