THE [M-H-CO2](-) ANION FROM GLYCYL GLYCINE UNDERGOES REARRANGEMENT INTHE GAS-PHASE

The [M-H-CO2](-) anion derived from collision induced loss of CO2 from the [M-H](-) ion of glycyl glycine has been examined using various ta ndem mass spectrometry (MS/MS) experiments. Using N-15 isotopically la belled glycyl glycine, these MS/MS experiments reveal that the initial ly formed carbanion [H2NCH2C(O)NHCH2](-) (A) undergoes rearrangement t o the nitrogen anion [HNCH2C(O)NHCH3](-) (B), The latter ion is respon sible for the subsequent fragmentation reactions. In addition, high le vel ab initio calculations (at the MP2/6-311+G level of theory) have been carried out on the rearrangement of A to B, which reveal that thi s intramolecular rearrangement process proceeds via a six centred tran sition state with a modest activation energy (11.1 kcal mol(-1)) and i s overall exothermic by 3.2 kcal mol(-1) thereby favouring the formati on of the product B, (C) 1998 John Wiley & Sons, Ltd.