| Abstract: | The collision-induced decompositions of the M – H]? and M + Li]+ ions of a few dinucleoside phenylphosphonates were studied using fast atom bombardment and linked scanning at constant B/E. Deprotonation takes place on the base or sugar moieties. The M – H]? ion decomposes mainly by cleavage on either side of the phosphonate linkage, leading to the formation of mononucleotide fragment ions and also by cleavage of the basesugar bond. Rupture of the 3′-phosphonate bond is preferred. Unlike the normal charged nucleotides, these neutral nucleotides do not eliminate a neutral base from the M – H]? ion. However, the mononucleotide fragment ions which can have the charge on the phosphorus oxygen eliminate neutral bases by charge-remote fragmentation. The 4,4′-dimethoxytrityl (DMT)-protected nucleotides show the additional fragmentation of loss of DMT. Li+ attachment can occur at several sites in the molecule. As observed for the M – H]? ion, the major cleavage occurs on either side of the phosphonate bond in the fully deprotected nucleotides, cleavage of the ester bond on C(3′) being preferred. Cleavage of the 5′-phosphonate bond is not observed in the DMT-protected nucleotides. Many of the fragmentations observed can be explained as arising from charge-remote reactions. |
