Mass spectrometry of nucleosides related to guanosine, and codicillary research topics

A detailed examination of the gas phase ionic fragmentation behavior of guanine nucleoside base ions was accomplished in order to delineate the decompositions that are useful for trace level structure determination by mass spectrometry. This was attained by a combination of ultramicroscale chemical synthesis for the preparation of site-selective, isotopically substituted 15N- and 18O -guanosines, and by the application of low energy collision-induced dissociation tandem mass spectrometry for the detection of fragment ions produced from the protonated base ions, BH2+. An adaptation of the Hakomori" reaction was developed and used for the low level detection and structure determination of several modified nucleosides related to guanosine. The approach was shown to enhance both the low level detectability of modified nucleosides, as well as to provide an augmented amount of structurally informative fragmentation in MS/MS. In this capacity, it was used to solve the trace level structure determination of a biologically important and highly enign\atic hypermodified nucleoside of archaeal tRNA: the 7-deazapurine ribonucleoside "G*-15" - 2-amino-4,7-dihydro-4-oxo-7-(3-D-ribofuranosyl-lH-pyrrolo[2,3-ti]pyrimidine-5-carboximidamide (Archaeosine).