The antioxidant activity of a series of flavonoids against peroxyl radicals generated from thermal homolysis of 2, 2'-azobis-amidinopropane was determined by the Total Oxyradical Scavenging Capacity (TOSC) assay. Seven flavonoids with hydroxy and/or methoxy substitution were analyzed and compared to the water-soluble vitamin E analogue Trolox. The most active compound was the flavonol quercetin, followed by its 3-glycoside derivative rutin; these were 7 and 5 times, respectively, better scavengers of peroxyl radical than Trolox. Among the flavones with both hydroxy and methoxy substitution, the most active against peroxyl radicals was the 5,6,4'-trihydroxy-7,8,3'-trimethoxyflavone (thymonin), with a TOSC value 1.5 times greater than that of Trolox. The activity of the remaining flavones was in the following relative order: 5, 4'-dihydroxy-6,7,8,3'-tetramethoxyflavone > 5-hydroxy-3,6,7,3', 4'-pentamethoxyflavone (artemetin) > 5,4'-dihydroxy-3,6, 7-trimethoxyflavone > 5,6,7,8,2',3',4',5'-octamethoxyflavone (agehoustin A). The data suggest a potential role for dietary intake of flavonoid-containing foods in lowering the risk of certain pathophysiologies that have been associated with free-radical-mediated events.

An investigation of BF3-mediated rearrangements of parthenolide [1] provided micheliolide [5] as a major product. Minor reaction products included 10 (14)-dehydro-5 alpha-hydroxy-trans-guaianolide [2], 9,10-dehydro-5 alpha-hydroxy-trans-guaianolide [3], the xanthanolide 2-desoxy-6-epi-parthemollin [4], 1,2-dehydro-4 alpha-hydroxyguaianolide [6], 11,13-dehydrocompressanolide [7], and bicyclo[6.2.0]dec-10(14)-en-12,6-olide [8]. Their mechanisms of formation were interpreted as rearrangements involving carbocation intermediates.

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In an attempt to study the structural dependence of antimycobacterial activity of the guaianolide dehydrocostus lactone and its derivatives, m-chloroperoxybenzoic acid oxidations of dehydrocostus lactone (1a) were performed. Three new monoepoxides, one previously synthesized diepoxide, and two new diepoxides were obtained. Two of the monoepoxides are C-10 epimers (3a, 3b), while the 4(15)-monoepoxide (2) has the 4alpha-O-configuration. The known diepoxide (4a) contains a C-10 alpha-epoxide and a beta-epoxide at C-4. The diepoxides 4b and 4c, each with a C-4 alpha-epoxy group, differ in the configuration of the epoxide ring at C-10. Allylic oxidation of dehydrocostus lactone (1a) with selenium dioxide/tert-butyl hydroperoxide afforded the known 3-epizaluzanin C (1b). The relative configurations of compounds 1b-4c were established by 1D and 2D NMR techniques (1H, 13C, COSY, NOESY, HMQC, and HMBC) as well as comparison with literature data. The molecular structures of lactones 1b, 4a, and 4c were determined by single-crystal X-ray diffraction. In radiorespirometric bioassays against Mycobacterium tuberculosis and Mycobacterium avium, dehydrocostus lactone (1a) exhibited minimum inhibitory concentrations of 2 and 16 microgram/mL, respectively. In contrast, its monoepoxides (2, 3a, and 3b) and diepoxides (4a-c), as well as its hydrogenated derivatives and other analogues (1b, 1c, 5, and 6), showed significantly lower activities against M. tuberculosis.