Analysis of Sterols

Goad, L. John; Akihisa, Toshihiro

doi:10.1007/978-94-009-1447-6

Cited by 283 publications

(227 citation statements)

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“…13 C NMR spectra of individual compounds were recorded in CDCl 3 by using a Jeol EX 270 spectrometer equipped with a DELTA station. 13 C peak assignments of the individual terpenoids were made by comparison with published data (18,(28)(29)(30)(31). To measure specific enhancements in 13 C, a carbon atom needed to be identified that should show no enrichment from 13 C-enriched acetate according to either the MVA pathway or the MEP route by way of the glyoxylate shunt.…”

Section: Methodsmentioning

confidence: 99%

Isoprenoid biosynthesis in the diatoms Rhizosolenia setigera (Brightwell) and Haslea ostrearia (Simonsen)

Massé

Belt

Rowland

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

106

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Isoprenoid biosynthesis in the widespread diatomaceous algae, Rhizosolenia setigera (Brightwell) and Haslea ostrearia (Simonsen), results not only in the production of diterpenoids, triterpenoids, and sterols but, unusually for diatoms, also in the production of sesterterpenoids. By using 13 C and 2 H isotopic labeling techniques followed by NMR and mass spectrometry, specific inhibition of mevalonate (MVA) and methylerythritol (MEP) pathways, and comparison with the natural 13 C͞ 12 C isotope ratios of the lipids, the different biosynthetic pathways of the sesterterpenes and other isoprenoids have now been determined. Surprisingly, whereas the sesterterpenes (⌬ 7(20) -haslenes) in R. setigera were made by the MVA pathway, as were the related triterpenoid rhizenes and desmosterol, in H. ostrearia the structurally similar ⌬ 6(17) -haslenes and the major sterol, 24-ethylcholest-5-en-3␤-ol, were instead biosynthesized by the MEP route. Phytol was biosynthesized in both diatoms by the MEP route. Subfractionation of R. setigera cells revealed that although phytol was located in the chloroplasts, the haslenes, rhizenes, and sterols were present in the cytoplasm. The observations described here for R. setigera and H. ostrearia show that terpenoid biosynthesis in diatoms is species-dependent and cannot simply be grouped according to structural type. Triterpenes appear to be made by the MVA route as in higher plants, whereas sesterterpenes and sterols can be made by either the MVA or MEP routes. In neither organism were the isoprenoids biosynthesized by leucine metabolism. Sesterterpene and triterpene biosynthesis in diatoms has not been investigated previously.A lthough all isoprenoids are biosynthesized from isopentenyl diphosphate (IDP), IDP itself can be produced by several different routes. In addition to the mevalonate (MVA) route, a MVA-independent pathway has been described, yielding IDP from pyruvate and glyceraldehyde 3-phosphate, with 1-deoxy-D-xylulose 5-phosphate and 2-C-methyl-D-erythritol 4-phosphate (MEP) identified as intermediates (1). In addition, IDP in some parasitic protozoa appears to be biosynthesized both by the MVA route and by direct incorporation of leucine (2). Many authors have studied the distribution of the MVA and MEP pathways within a large number of organisms by incorporation of 13 C-or 2 H-labeled precursors (for reviews see refs. 1, 3, and 4), by use of highly specific inhibitors of the MVA and MEP pathways (5, 6), or by measuring the distribution of the genes of both pathways (7,8). Jux and coworkers (9) demonstrated that natural 13 C͞ 12 C isotope ratios of individual lipids could also be used to distinguish between the pathways. Based on these four approaches, it has been established that archaea, certain bacteria, yeasts, fungi, and some protozoa and animals use only the MVA pathway, whereas many bacteria, green algae, and some protists rely on the MEP pathway (10). Some algae, some streptomycetes, mosses, and liverworts, two marine diatoms, and higher plants appear to use both ro...

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Section: Methodsmentioning

confidence: 99%

Isoprenoid biosynthesis in the diatoms Rhizosolenia setigera (Brightwell) and Haslea ostrearia (Simonsen)

Massé

Belt

Rowland

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

106

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“…3, Route 4). The fragment ion peak at m/z 343 ( [M-129] ϩ ) of non-labeled campesterol-TMS is attributed to loss of C-1, -2, and -3 and a TMS-ether group of the A-ring (35), as shown in Fig. 3.…”

Section: Incorporation Of [2-mentioning

confidence: 99%

Contribution of the Mevalonate and Methylerythritol Phosphate Pathways to the Biosynthesis of Gibberellins inArabidopsis

Kasahara¹,

Hanada²,

Kuzuyama³

et al. 2002

Journal of Biological Chemistry

242

179

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Gibberellins (GAs) are diterpene plant hormones essential for many developmental processes. Although the GA biosynthesis pathway has been well studied, our knowledge on its early stage is still limited. There are two possible routes for the biosynthesis of isoprenoids leading to GAs, the mevalonate (MVA) pathway in the cytosol and the methylerythritol phosphate (MEP) pathway in plastids. To distinguish these possibilities, metabolites from each isoprenoid pathway were selectively labeled with 13 C in Arabidopsis seedlings. Efficient 13 C-labeling was achieved by blocking the endogenous pathway chemically or genetically during the feed of a 13 C-labeled precursor specific to the MVA or MEP pathways. Gas chromatography-mass spectrometry analyses demonstrated that both MVA and MEP pathways can contribute to the biosyntheses of GAs and campesterol, a cytosolic sterol, in Arabidopsis seedlings. While GAs are predominantly synthesized through the MEP pathway, the MVA pathway plays a major role in the biosynthesis of campesterol. Consistent with some crossover between the two pathways, phenotypic defects caused by the block of the MVA and MEP pathways were partially rescued by exogenous application of the MEP and MVA precursors, respectively. We also provide evidence to suggest that the MVA pathway still contributes to GA biosynthesis when this pathway is limiting.

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“…In general, electron ionization (EI) mass spectra of trimethylsilyl ethers or esters exhibit a significant [M Ϫ 15] ϩ ion formed by loss of a methyl group bonded to silicon, which is very useful in determining the molecular mass. It is very important to note that EI mass spectra of trimethylsilyl derivatives may be employed not only for molecular weight determinations, but also for structural deductions [4].Trimethylsilyl group migrations during EI fragmentation process are common [5,6] and take place by means of ion-neutral complexes [7]. These rearrangements are generally considered useful for deducing structures of unknown spectra [8]; however, in some cases, misleading conclusions may be drawn.…”

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Hydrogen and trimethylsilyl transfers during EI mass spectral fragmentation of hydroxycarboxylic and oxocarboxylic acid trimethylsilyl derivatives

Rontani

Aubert²

2008

J. Am. Soc. Mass Spectrom.

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This paper, describing electron ionization mass spectral fragmentation of some hydroxycarboxylic and oxocarboxylic acid trimethylsilyl derivatives, focuses on the formation of fragment ions resulting from the interactions between the two functionalities of these compounds. These interactions result in the formation of fragment ions at [CH 2 ilylation is by far the major derivatization procedure for GC/MS analyses [1][2][3]. Silyl derivatives are formed when active proton displacement (in ϪOH, ϪSH, or ϪNH groups) by an alkylsilyl group occurs. The most common silylation procedure is trimethylsilylation. Trimethylsilyl derivatives combine thermal stability and high volatility. In general, electron ionization (EI) mass spectra of trimethylsilyl ethers or esters exhibit a significant [M Ϫ 15] ϩ ion formed by loss of a methyl group bonded to silicon, which is very useful in determining the molecular mass. It is very important to note that EI mass spectra of trimethylsilyl derivatives may be employed not only for molecular weight determinations, but also for structural deductions [4].Trimethylsilyl group migrations during EI fragmentation process are common [5,6] and take place by means of ion-neutral complexes [7]. These rearrangements are generally considered useful for deducing structures of unknown spectra [8]; however, in some cases, misleading conclusions may be drawn. Though trimethylsilyl group migrations usually occur through five-to eight-member-ring transition states [9], intense long-range migration of the trimethylsilyl group was previously observed in the case of trimethylsilyl derivatives of some steroid compounds [8, 10 -13]. The capability of the trimethylsilyl group to migrate over a wide range of distances was also demonstrated in the case of semirigid or rigid molecules [5]. Recently, a significant transfer of trimethylsilyl group towards the carbonyl group was also observed during EI fragmentation of the trimethylsilyl derivatives of long-chain -hydroxycarboxylic and -dicarboxylic acids [14], showing that such migrations may also occur in the case of nonrigid structures.Hydrogen transfers between distant functionalities during EI fragmentation processes are also well known [6,15,16], for this reaction hydrogen activation is needed and is caused by groups such as keto, amino, ether, trimethylsilyloxy, as well as by chain branching and unsaturation.In the present work, which is a part of a more general study of the synergistic effects during EI mass fragmentation of polyfunctional compounds [14,[17][18][19], we describe EI mass spectral fragmentation of several hydroxycarboxylic and oxocarboxylic acid trimethylsilyl derivatives, which involves trimethylsilyl and hydrogen transfers.The characterization of such compounds appears to be of great environmental importance [20,21]. Indeed, it was previously demonstrated that autoxidative processes could induce a bias during alkenone-based paAddress reprint requests to Dr.

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Analysis of Sterols

Cited by 283 publications

References 0 publications

Isoprenoid biosynthesis in the diatoms Rhizosolenia setigera (Brightwell) and Haslea ostrearia (Simonsen)

Isoprenoid biosynthesis in the diatoms Rhizosolenia setigera (Brightwell) and Haslea ostrearia (Simonsen)

Contribution of the Mevalonate and Methylerythritol Phosphate Pathways to the Biosynthesis of Gibberellins inArabidopsis

Hydrogen and trimethylsilyl transfers during EI mass spectral fragmentation of hydroxycarboxylic and oxocarboxylic acid trimethylsilyl derivatives

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