Gas chromatography chemical ionization mass spectrometry of prostaglandin Fα cyclic boronate derivatives

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Abstract
The electron impact mass spectra of prostaglandins F1α, F2α and F3α methyl ester cyclic 9,11-methane-, n-butane-, cyclohexane- and benzeneboronate 15-trimethylsilyl ethers show base peaks corresponding to [M – (C-16—C-20)]+, i.e. [M - 71]+ for prostaglandins F1α and F2α but [M - 69]+ for prostaglandin F3α yielding identical ions in the latter two cases. Derivatives of prostaglandin F2α and F3α are difficult to separate by gas chromatography, so that the use of this ion type for single ion monitoring of either prostaglandin (as has been reported) is ambiguous. The chemical ionization mass spectra of these cyclic boronates, however, show distinctive base peaks for prostaglandins F1α, F2α and F3α at m/e 317, 315 and 313 respectively, corresponding to [M - RBO2H2 - TMSO]+. Fragmentation patterns have been investigated by the use of [3,3,4,4-2H4]prostaglandin F2α and by the formation of [2H9]trimethylsilyl ethers and a [2H3]methyl ester. Cleavage of the C-15—C-16 bond is of minor importance under chemical ionization conditions. The possible value of the [M - RBO2H2 – TMSO]+ ions for single ion monitoring is explored: specificity is aided by the formation of the same ions from a series of boronates of characteristic retention indices.