New Guaianolides and Xanthine Oxidase Inhibitory Flavonols from Ajania fruticulosa

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Abstract
Two new guaianolides (1 and 2) were isolated from the aerial parts of Ajania fruticulosa along with a triterpene (α-amyrin), two plant sterols (β-sitosterol and daucosterol), four flavonols [santin (3), axillarin (4), centaureidin, and 5,7,4‘-trihydroxy-3,3‘-dimethoxyflavone], and five sesquiterpenes [ketoplenolide B, 9β-hydroxyeudesma-4,11(13)-dien-12-oic acid, 9β-acetoxyeudesma-4,11(13)-dien-12-oic acid, 1α,4α,10α-trihydroxy-9α-angeloyloxyguaia-2,11(13)-dien-12,6α-olide, and 3β,4α-dihydroxyguaia-11(13),10(14)-dien-12,6α-olide]. The structures of the new guaianolides were established as 1α-hydroperoxy-4β,8α,10α,13-tetrahydroxyguaia-2-en-12,6α-olide (1) and 1α-hydroperoxy-4α,10α-dihydroxy-9α-angeloyloxyguaia-2,11(13)-dien-12,6α-olide (2), respectively. Xanthine oxidase assays of all isolates revealed that santin (3) and axillarin (4) inhibited the enzyme with IC50 values of 36.5 and 36.0 μM (that of allopurinol used as a positive control in the study was 24.2 μM), respectively.