Detection by Gas Phase Analytical Methods of Derivatives of Barbiturate Epoxides

MASS SPECTROMETRIC FRAGMENTATION OF TRIMETHYLSILYL AND RELATED ALKYLSILYL DERIVATIVES

This review describes the mass spectral fragmentation of trimethylsilyl (TMS) and related alkylsilyl derivatives used for preparing samples for analysis, mainly by combined gas chromatography and mass spectrometry (GC/MS). The review is divided into three sections. The first section is concerned with the TMS derivatives themselves and describes fragmentation of derivatized alcohols, thiols, amines, ketones, carboxylic acids and bifunctional compounds such as hydroxy- and amino-acids, halo acids and hydroxy ethers. More complex compounds such as glycerides, sphingolipids, carbohydrates, organic phosphates, phosphonates, steroids, vitamin D, cannabinoids, and prostaglandins are discussed next. The second section describes intermolecular reactions of siliconium ions such as the TMS cation and the third section discusses other alkylsilyl derivatives. Among these latter compounds are di- and trialkyl-silyl derivatives, various substituted-alkyldimethylsilyl derivatives such as the tert-butyldimethylsilyl ethers, cyclic silyl derivatives, alkoxysilyl derivatives, and 3-pyridylmethyldimethylsilyl esters used for double bond location in fatty acid spectra. © 2019 Wiley Periodicals, Inc. Mass Spec Rev 0000:1-107, 2019.

On the metabolism of epoxyeicosatrienoic acids by ram seminal vesicles: isolation of 5(6)epoxy-prostaglandin F1 alpha

cis-5(6)Epoxy- and cis-14(15)epoxyeicosatrienoic acid are formed from arachidonic acid by monooxygenases. 5(6)Epoxyeicosatrienoic acid is metabolized by fatty acid cyclooxygenase of ram seminal vesicles and the major products were recently identified as 5(6)epoxy-PGE1 and two stereoisomers of 5-hydroxy-PGI1. The two isomers were likely formed from an unstable intermediate, 5(6)epoxy-PGF1 alpha. The isolation of 5(6)epoxy-PGF1 alpha is described here and 14(15)epoxyeicosatrienoic acid is shown to inhibit fatty acid cyclooxygenase of ram seminal vesicles, albeit less potently than eicosatetraynoic acid (IC50 0.18 and 0.05 mM, respectively).

Biosynthesis of 5,6-dihydroxyprostaglandin E1, and F1α from 5,6-dihydroxyeicosatrienoic acid by ram seminal vesicles

cis-5(6)Epoxy-cis-8,11,14-eicosatrienoic acid was recently found to be metabolized by ram seminal vesicles to 5-hydroxyprostaglandin I 1 alpha and 5-hydroxyprostaglandin I 1 beta, 5(6)epoxyprostaglandin E1 and 5,6-dihydroxyprostaglandin E1. The epoxide can be hydrolyzed by epoxide hydrolases to 5,6-dihydroxy-8,11,14-eicosatrienoic acid. The latter was incubated with microsomes of ram seminal vesicles for 2 min at 37 degrees C and the polar metabolites were purified by reversed phase HPLC and analyzed by capillary column gas chromatography-mass spectrometry. The major metabolite was identified as 5,6-dihydroxyprostaglandin F 1 alpha. In the presence of glutathione (1 mM), 5,6-dihydroxyprostaglandin E1 was also formed. The 3H-labelled vicinal diol and the 3H-labelled epoxide were metabolized to polar products to a similar extent, but the formation of prostaglandin E compounds in the presence of glutathione was lower from the diol than from the epoxide or from arachidonic acid. The likely prostaglandin endoperoxide intermediates in the metabolism of the diol (5,6-dihydroxyprostaglandin G1 and 5,6-dihydroxyprostaglandin H1) thus appear to be less prone to be isomerized to prostaglandin E compounds than prostaglandins G2 and H2 and their 5(6)epoxy counterparts. 5(6)Epoxyprostaglandin E1 and 5,6-dihydroxyprostaglandin E1 can be chemically transformed into 5,6-dihydroxyprostaglandin B1. The latter can be analyzed by HPLC or by mass fragmentography, and a simple chemical synthesis of 5,6-dihydroxyprostaglandin B1 from prostaglandin E2 is described.

Metabolism of 5(6)-expoxyeicosatrienoic acid by ram seminal vesicles. Formation of novel prostaglandin E1 metabolites

5(6)-Epoxy-8,11,14-eicosatrienoic acid was incubated with microsomes or ram seminal vesicles in the presence of glutathione (1 mM) for 2 min at 37 degrees C. Following extractive isolation on octadecasilane silica, the products were purified on straight-phase HPLC and separated into three major polar metabolites, which all showed maximal ultraviolet absorbance at 278 nm after treatment with alkali. The least-polar of the three metabolites was identified by capillary column gas chromatography-mass spectrometry as 5(6)- epoxyprostaglandin E1 and the structure was confirmed by comparison with authentic material. The most-polar metabolite was identified as 5,6- dihydroxyprostaglandin E1, while the metabolite of medium polarity was identified as its delta 5-lactone. When glutathione was omitted, 5-hydroxyprostaglandin I 1 alpha and 5-hydroxyprostaglandin I 1 beta were previously identified as the two major metabolites. These results indicate that the postulated epoxyprostaglandin endoperoxide intermediates, 5(6)- epoxyprostaglandin G1 and 5(6)- epoxyprostaglandin H1, might be substrates for the endoperoxide E isomerase enzyme, since this enzyme requires glutathione as a cofactor.

Analysis of barbiturates by gas chromatography

This review surveys the evolution of gas chromatographic procedures for the quantification of barbiturates as either the free acids or their derivatives obtained by direct and on-column reactions. Among the aspects discussed, some emphasis is placed on recognized and other sources of interference encountered during analyses.

Biotransformation of allylbenzene analogues in vivo and in vitro through the epoxide-diol pathway

1. The epoxidation of allylbenzene, safrole, estragole, eugenol and eugenol methyl ether was investigated in rats pretreated with these compounds and also in vitro using hepatic microsomal preparations and adult rat liver cell cultures. 2. Dihydrodiols were detected in the urine and liver of rats pretreated with allylbenzene compounds. Similarly, incubation of allylbenzene epoxides with hepatic microsomal preparations and adult rat liver cell cultures gave rise to the formation of dihydrodiols.