Abstract
Centaurothamnus maximus (family Asteraceae), is a leafy shrub indigenous to the southwestern Arabian Peninsula. With a paucity of phytochemical data on this species, we set out to chemically characterize the plant. From the aerial parts, two newly identified guaianolides were isolated: 3β-hydroxy-4α(acetoxy)-4β(hydroxymethyl)-8α-(4-hydroxy methacrylate)-1αH,5αH, 6αH-gual-10(14),11(13)-dien-6,12-olide (1) and 15-descarboxy picrolide A (2). Seven previously reported compounds were also isolated: 3β, 4α, 8α-trihydroxy-4-(hydroxymethyl)-lαH, 5αH, 6βH, 7αH-guai-10(14),11(13)-dien-6,12-olide (3), chlorohyssopifolin B (4), cynaropikrin (5), hydroxyjanerin (6), chlorojanerin (7), isorhamnetin (8), and quercetagetin-3,6-dimethyl ether-4’-O-β-d-pyranoglucoside (9). Chemical structures were elucidated using spectroscopic techniques, including High Resolution Fast Atom Bombardment Mass Spectrometry (HR-FAB-MS), 1D NMR; 1H, 13C NMR, Distortionless Enhancement by Polarization Transfer (DEPT), and 2D NMR (1H-1H COSY, HMQC, HMBC) analyses. In addition, a biosynthetic pathway for compounds 1–9 is proposed. The chemotaxonomic significance of the reported sesquiterpenoids and flavonoids considering reports from other Centaurea species is examined.
Highlights
Centaurothamnus maximus Wagentz and Dittri (Asteraceae) is a branched shrub that grows to a height of ca. 1.5 m [1]
We describe the isolation and identification of two new guaianolide sesquiterpene lactones, 3β-hydroxy-4α(acetoxy)-4β(hydroxymethyl)8α-(4-hydroxy methacrylate)-1αH,5αH,6αH-gual-10(14),11(13)-dien-6,12-olide (1) and 15descarboxy picrolide A (2), as well as seven known compounds, 3β,4α,8 α-trihydroxy4-(hydroxymethyl)-lαH,5αH,6βH,7αH-guai-10(14),11(13)-dien-6,12-olide (3), chlorohyssopifolin B (4) [16], cynaropicrin (5) [17], hydroxyjanerin (6) [18], chlorojanerin (7) [19], isorhamnetin (8) [20], and quercetagetin-3,6-dimethyl ether-4’-O-β-D-pyranoglucoside Molecules 2021, 26, x FOR PEER REV(IE9W) [21] (Figure 1)
Twenty-one carbons were detected through the 13C NMR spectrum (Table 1), which was incompatible with its molecular formula
Summary
Centaurothamnus maximus Wagentz and Dittri (Asteraceae) is a branched shrub that grows to a height of ca. 1.5 m [1]. Centaurothamnus maximus Wagentz and Dittri (Asteraceae) is a branched shrub that grows to a height of ca. Thistle-like magenta flowers 3–4 cm long at the end of the branches have a faint sweet scent [2]. Centaurothamnus is a monotypic genus from Centaurea and endemic to the mountains of the southwestern Arabian Peninsula. The genus is highly restricted in Saudi Arabia to cliffs and steep hillsides and is represented by ca. C. maximus is a paleoendemic species that presently grows in Yemen without any known traditional uses. This may be in part due to the plant’s limited distribution to high mountains cliffs and slopes in Yemen [3]
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