An efficient and convenient synthesis of deuterium-labelled seminolipid isotopomers and their ESI-MS characterization

Dipartimento di Chimica, Biochimica e Biotecnologie per la Medicina, Università di Milano, Via Saldini 50, 20133-Milano, Italy.
Chemistry and Physics of Lipids (Impact Factor: 2.42). 05/2008; 152(2):78-85. DOI: 10.1016/j.chemphyslip.2008.02.002
Source: PubMed


Seminolipids 1a and 1b and galactosylalkylacylglycerols 2a and 2b, labelled with deuterium on the alkyl or acyl chain, respectively, were obtained isotopically and chemically pure through a straightforward synthesis from protected glycidyl galactoside 3 in an overall 22% yield. The identity and purity of compounds was ascertained by NMR spectroscopy and ESI mass spectrometry analysis. These labelled compounds are important as internal standards for quantification of these lipids by mass spectrometry, and they could also be used in metabolic studies in in vitro and even in vivo systems. Extension of the procedure could provide a route for the preparation of isotopomers of other compounds of the same general class.

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    ABSTRACT: The first synthesis of the sulfonate analogue of seminolipid, the main sulfoglycolipid in mammalian sperm, is reported. Installation of the sulfonate unit was accomplished by a quite unexplored strategy based on Horner-Wadsworth-Emmons olefination on a 3 '-keto-galactoside, followed by stereoselective double bond reduction.
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    ABSTRACT: Seminolipid, also known as sulfogalactosylglycerolipid (SGG), plays important roles in male reproduction. Therefore, an accurate and sensitive method for SGG quantification in testes and sperm is needed. Here we compare SGG quantitation by the traditional colorimetric Azure A assay with LC-ESI-MS/MS using multiple reaction monitoring (MRM). Inclusion of deuterated SGG as the internal standard endowed accuracy to the MRM method. The results showed reasonable agreement between the two procedures for purified samples, but for crude lipid extracts, the colorimetric assay significantly overestimated the SGG content. Using ESI-MS/MS MRM, C16:0-alkyl/C16:0-acyl SGG of Cgt(+/⁻) mice was quantified to be 406.06 ± 23.63 μg/g testis and 0.13 ± 0.02 μg/million sperm, corresponding to 78% and 87% of the wild-type values, respectively. CGT (ceramide galactosyltransferase) is a critical enzyme in the SGG biosynthesis pathway. Cgt⁻/⁻ males depleted of SGG are infertile due to spermatogenesis arrest. However, Cgt(+/⁻) males sire offspring. The higher than 50% expression level of SGG in Cgt(+/⁻) animals, compared with the wild-type expression, might be partly due to compensatory translation of the active CGT enzyme. The results also indicated that 78% of SGG levels in Cgt(+/⁻) mice were sufficient for normal spermatogenesis.
    Preview · Article · Dec 2010 · The Journal of Lipid Research
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