Applications of boronate derivatives in the study of ceramides by gas-liquid chromatography-mass spectrometry

Methaneboronate derivatives of ceramides possess excellent gas-liquid chromatographic properties and give informative mass spectra. Molecular ions, present at high abundance where an unsaturated acyl substituent is present, are accompanied in the electron impact mass spectra by fragment ions which denote the acyl group and long-chain base. In the gas-liquid chromatographic-mass spectrometric analyses of natural ceramides, as methaneboronate derivatives, the properties of open-tubular columns are exploited to give good separations in moderate analysis times. An application is made to the analysis of ceramides derived from sphingomyelin of human arterial tissue.

Trimethylsilyl group migration during electron impact and chemical ionization mass spectrometry of the trimethylsilyl ethers of 20-hydroxy-5alpha-pregnan-3-ones and 20-hydroxy-4-pregnen-3-ones

The electron impact and chemical ionization (isobutane) mass spectra of the TMS derivatives of 20-hydroxy-5alpha-pregnan-3-ones and 20-hydroxy-4-pregnen-3-ones include ions [M--44]+-attributable to loss of a CH3CHO fragment from C-17 with migration of the TMS group to the charge-retaining fragment. Mass spectra of isotopically labelled ([3-18O], [20-18O] and [2H9-TMS]) analogues are consistent with this mechanism; [2H9-TMS] labelling further indicates that subsequent loss of a methyl group from [M--44]+-ions does not involve the TMS group. Corresponding ions are not observed at significant abundance in the spectra of 20beta-trimethylsilyloxy-5alpha-pregnane and 20beta-trimethylsilyloxy-4-pregnen-3-one 3-O-methyloxime. In the electron impact mass spectrum of the t-butyldimethylsilyl ether of 20beta-hydroxy-4-pregnen-3-one, an ion is observed corresponding to loss of 44 atomic mass units from the intense [M--C4H9]+ ion.

New derivatives for the analysis of sphingosine long-chain bases by gas-liquid chromatography-mass spectrometry

Cyclic derivatives formed by reaction of sphingosines with methane-, n-butane- and benzeneboronic acid have been examined by gas-liquid chromatography (GLC) and by combined GLC-mass spectrometry (MS). Analogous compounds have also been studied, in which the amino group has been protected, for example as an acetone Schiff base or N,N-dimethylaminomethylene derivative. Phytosphingosine (4D-hydroxysphinganine) yielded bis-alkaneboronates. Most of the derivatives were satisfactory for GLC. Molecular ions were apparent (1-100% relative abundance) in all electron impact mass spectra, and and (as [M+1](+)ions) were the base peaks in isobutane chemical ionisation mass spectra.

Mass spectra of delta 4- and 5 alpha-3-ketosteroids formed during the oxidation of some 3 beta-hydroxysteroids by cholesterol oxidase

Thirty-six delta5- and 5'alpha-3beta-hydroxysteroids have been oxidized with cholesterol oxidase to give the corresponding delta4- and 5alpha-3-ketosteroids, respectively. The mass spectral characteristics of the products (or their trimethylsilyl ether derivatives, in the case of 3-keto-hydroxysteroids) varied considerably, depending especially on the nature of the C-17 sidechain. The ion of m/e 124 (or its equivalent) from cleavage of ring B was frequently a major fragment from delta4-3-ketosteroids, but in some instances was of insignificant abundance. Trimethylsilylation of the product of the oxidation of neoergosterol gave neoergosterone enol-trimethylsilyl ether. Fragmentations of the sidechain predominated in the mass spectra of the 5alpha-3-ketosteroids.

Sterols of scallop. Part II. Structure of unknown sterols by combination gas-liquid chromatography and mass spectrometry

Four sterols, isolated from the scallop Pacopecten magellanicus have been identified as 24-nor-5alpha-cholest-22-en-3beta-ol; 24-norcholest-5-en-3beta-ol; 5alpha-cholest-22-en-3beta-ol; and (E) -24-propylidenecholest-5-en-3beta-ol. These bring to seventeen the total number of sterols identified in this marine mollusc. A fifth newly detected sterol, closely similar in its mass spectrometric properties is 22-cis and trans-cholesta-5, 22-dien-3beta-ol, was clearly distinguished from these by its shorter retention time by GLC.

Cholesterol oxidase. Further studies of substrate specificity in relation to the analytical characterisation of steroids

The substrate specificity of cholesterol oxidase has been further examined with respect to the size and shape of the steroid 17beta-side-chain and oxygenation of the nucleus. The relatively unreactive 17-keto-delta5-3beta-hydroxysteroids were converted to satisfactory substrates by formation of the isopentyl- or benzyloximes. The results obtained have been used to illustrate further uses of the enzyme in the gas-phase analytical characterisation and selective oxidation steroids. Oxidations were studied by kinetic experiments, gas-liquid chromatography-mass spectrometry.

The isolation of cholest-5-ene-3beta,26-diol from human brain

Cholest-5-ene-3beta,26-diol, isolated from human brain, was further characterized by oxidation to 3-oxocholest-4-en-26-ol and to 3-oxocholest-4-en-26-oic acid. Identification was achieved by comparison (by t.l.c., g.l.c. and g.l.c.-mass spectrometry) with corresponding reference compounds derived from kryptogenin.

Renal handling of calcium, magnesium, inorganic phosphate and hydrogen ions during prolonged exposure to elevated carbon dioxide concentrations

1. Fifteen healthy young men were exposed to an atmosphere of 0–7% CO2 in air for 7 weeks.

2. For 1 week before and during the exposure to CO2, serum calcium, magnesium and inorganic phosphate (Pi) levels were measured at intervals, together with 24 h urinary excretion of these three components, and net urinary acid excretion.

3. The urinary excretion of Ca2+, Mg2+ and Pi fell during exposure to CO2, whereas the serum levels of these components increased.

4. Serum levels of calcium were inversely correlated with urinary Ca2+ excretion both in control conditions and during exposure to CO2

5. An increase in urinary acid excretion in the third to fourth week of exposure to CO2 was associated with an increase in the urinary excretion of Ca2+, but not of Mg2+.

6. It is suggested that there is a difference from the normal in the renal handling of H+ and Ca2+ ions during exposure to CO2 which may lead to a retention of Ca2+ in the tissues.