Mass spectrometry of cytokinin metabolites. Per(trimethylsilyl) and permethyl derivatives of glucosides of zeatin and 6-benzylaminopurine

The mass spectra of the Me ₃Si and permethylated derivatives of a comprehensive series of synthetic isomeric glucosides of the cytokinins zeatin and 6-benzylaminopurine (6-BAP) have been recorded by combined gas chromatography-mass spectrometry. Comparison of these spectra with those obtained for a number of glucosyl metabolites of zeatin and 6-BAP allows unambiguous structural assignments to be made. Detailed analysis of the mass spectral fragmentation patterns indicate that, a priori, it should be possible to assign the sugar ring size (furanose vs. pyranose) in such compounds on the basis of characteristic fragment ion intensities. Mass spectra of the Me ₃Si derivatives show more significant isomer differences than the corresponding permethylated compounds and their method of preparation appears less prone to multiple product formation. A thermal 1,3 migration of the sugar moiety from N ₃ to N ₉ was observed in the GC-MS of the derivatives of the 3-β-D-glucopyranoside of 6-BAP.