Electrospray tandem mass spectrometric analysis of zeaxanthin and its oxidation products.

Carotenoids have been implicated in protection of the eye from light-mediated photo-toxicity caused by free radicals. Under conditions of normal oxidative stress the carotenoids serve as protective antioxidants; however, when the oxidative stress exceeds the antioxidant capacity, carotenoids can be oxidized into numerous cleavage products. The determination and identification of oxidized carotenoids in biological samples remains a major challenge due to the small sample size and low stability of these compounds. We investigated the reaction of various zeaxanthin cleavage products with O-ethyl hydroxylamine to evaluate their levels in a biological sample. For this, a sensitive and specific electrospray tandem mass spectrometry (ESI-MS/MS) was developed, avoiding the classical lower sensitive and specific HPLC-UV and fluorescence absorption methods. Protonated molecules [M + H](+) of carotenoids upon collision-induced dissociation produced a number of structurally characteristic product ions. A series of complicated clusters of product ions differing in 14 (CH(2))and 26 (C(2)H(2))Da was characteristic of the polyene chain of intact carotenoids. All carotenoid ethyl oximes of zeaxanthin cleavage products were characterized by the losses of 60 and 61 Da in their MS/MS spectra. Through the application of the LC/MS/MS method, we identified two oxime derivatives of 3-hydroxy-beta-ionone and 3-hydroxy-14'-apocarotenal with protonated molecules at m/z 252 and m/z 370 respectively, in a human eye sample.

Novel diarylheptanoids of Alpinia blepharocalyx.

The seeds of Alpinia blepharocalyx K. Schum. (Zingiberaceae) is used in Chinese traditional medicine for the treatment of stomach disorders. From the ether fraction of a 95% ethanolic extract, which showed hepatoprotective and antiproliferative activities, we isolated 16 novel diarylheptanoids bearing a chalcone or a flavanone moiety [calyxins A-H; epicalyxins B-D, G, and H; 6-hydroxycalyxin F; and blepharocalyxins A and B] together with seven known compounds, while the residual fraction of the ethanolic extract gave 32 novel diarylheptanoids namely, calyxins A, E-G, and I-M; epicalyxins B, F, I-K, and M; deoxycalyxin A; blepharocalyxins C-E; neocalyxins A and B; (3S,5S)- and (3S,5R)-3-hydroxy-1-(4-hydroxyphenyl)-5-methoxy-7-phenyl-6E-heptene, (3S,5S)- and (3S,5R)-3-hydroxy-1-(4-hydroxyphenyl)-5-ethoxy-7-phenyl-6E-heptene, (3S)-3-methoxy-1,7-bis(4-hydroxyphenyl)-6E-hepten-5-one, 1,7-bis(4-hydroxyphenyl)-hepta-4E,6E-dien-3-one, (3S,7R)-5,6-dehydro-1,7-bis(4-hydroxy-phenyl)-4"-de-O-methyl-centrolobine, (3S,5S,6S,7R)-5,6-dihydroxy-1,7-bis(4-hydroxyphenyl)-4"-de-O-me-thylcentrolobine, (3S,5R,6S,7R)- and (3S,5S,6R,7R)-5,6-dihydroxy-1,7-bis(4-hydroxyphenyl)-4"-de-O-methyl-centrolobine, 1,2- dihydro-bis(de-O-methyl)curcumin, and (3S,7S)-5,6-dehydro-4"-de-O-methylcentrolobine, and one known diarylheptanoid [(3S,5S)-3,5-dihydroxy-1,7-bis(4-hydroxyphenyl)heptane] together with 12 other known phenolic compounds. Moreover, in vitro NO inhibitory and antiproliferative activities of the isolated compounds were also tested and the active constituents identified.

Rapid screening and identification of cytochalasins by electrospray tandem mass spectrometry.

The cytochalasin class of fungal metabolites was analyzed by electrospray ionization tandem mass spectrometry (ESI-MS/MS) with the aim of developing a methodology for their rapid identification in microbial extracts. ESI-MS analyses of reference cytochalasins were performed and several product ions were produced in MS/MS experiments on parent ions that are structurally characteristic. A precursor ion search was performed to detect cytochalasins in an ethyl acetate extract of fungal strain RK97-F21. Three cytochalasins were detected and one of the components was identified as epoxycytochalasin H by comparing the tandem mass spectra of the product ions with those of reference compounds. This finding was further validated by LC/MS and LC/MS/MS experiments.