Collisionally induced dissociation in the study of A-ring hydroxylated vitamin D type compounds

Article abstract of DOI:10.1021/ac00032a004

Colllslonally Induced dissociation (CID) is often used to determine the structure of ions based on comparison with the CID spectra of known ions. The latter are generated from Judiciously selected compounds taking into account basic principles of Ion chemistry. We report here on the use of this approach toward determination of the site of A-ring hydroxylation of vitamin D. Although not Intrinsically an aromatic compound, vitamin D gives rise in its mass spectrum to an aromatic methytstyryl cation at mlz 118. A-ring hydroxylated metabolites of vitamin D would thus Incorporate the extra OH group on the ion at mlz 118, shifting it to mlz 134. The position of substitution of the extra OH group on a metabolite could then be ascertained by comparing the CID spectrum of its mlz 134 fragment to those of the four possible (hydroxymethyl)styryl cations generated from synthesized authentic compounds. Because of their propensity to polymerize, these cations were generated in situ via the McLafferty rearrangement of the corresponding (hydroxyphenyl)ethanols. For optimum differentiation of Isomeric Ions, preparation of permethylated derivatives of vitamin D was necessary. The validity of the hypothesis was verified using 1,25-dihydroxy-vitamin D₃ as a test compound. This method provides a viable approach for the characterization of A-ring hydroxylated metabolites of vitamin D as well as for related aromatic compounds.