Study of the Interaction of Dinucleotide Analogs with Alkaline Earth Metal Ions by Fast Atom Bombardment Mass Spectrometry

The fast atom bombardment (FAB)mass spectra of a series of dinucleotide analogs, compounds 1-8 with alkaline earth metal chlorides (CaCl 2 , MgCl 2 , SrCl 2 and BaCl 2 ) were studied in a thioglycerol matrix. The positive-ion FAB mass spectra of 1-8 with CaCl 2 gave [M + Ca - H] + , [M + CaCl] + and [M + Ca 2 Cl - 2H] + ions. The formulae of [M + Ca - H] + and [M + Ca 2 Cl - 2H] + ions from 2 were confirmed with high-resolution measurements. Compounds 1-8 with alkaline earth metal ions also give metal chelated dimerized species [2M + Ca 3 Cl - 4H] + , [2M + Ca 2 - 3H] + and [2M + Ca - H] + ], a process which is independent of the size of the polyether chain. The negative-ion FAB spectra also produce bimetallic ions with all substrates studied. Experiments with D 2 O addition using CaCl 2 with compounds 2 and 6 suggested the elimination of acidic protons (amide and/or amine) in the formation of [M + Met x Cl y - nH) ions in either positive or negative modes. The site of the metal chelation was the same in both positive-and negative-ion mass spectra. The collision-activated dissociation data suggest the covalent bonding of the metal to the nitrogen base and coordination with the polyether chain.