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)-1α
H
,5α
H
, 6α
H
-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)-lα
H
, 5α
H
, 6β
H
, 7α
H
-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;
1
H,
13
C NMR, Distortionless Enhancement by Polarization Transfer (DEPT), and 2D NMR (
1
H-
1
H 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.