DETERMINATION OF THE ANOMERIC CONFIGURATION OF GLYCOSYL ESTERS OF NUCLEOSIDE PYROPHOSPHATES AND POLYISOPRENYL PHOSPHATES BY FAST-ATOM-BOMBARDMENT TANDEM MASS-SPECTROMETRY

Collision-induced dissociation of the deprotonated molecules of glycos yl esters of nucleoside pyrophosphates and polyisoprenyl (dolichyl and polyprenyl) phosphates results in distinct fragmentation patterns tha t depend on cis-trans configuration of the phosphodiester and 2 '' (or 2', respectively)-hydroxyl groups of the glycosyl residue. At the col lision-offset voltage of 0.5 V, sugar nucleotides with cis configurati on produce only one very abundant fragment of nucleoside monophosphate , whereas compounds with trans configuration-give weak signals for nuc leoside di- and mono-phosphates and their dehydration products. These fragmentation patterns are largely preserved at higher collision energ y, with the exception that, for sugar nucleotides with trans configura tion, the characteristic signals are much more abundant and a novel di agnostic fragment of [ribosyl(deoxyribosyl)-5'-P2O5 - H](-) is generat ed. In the case of polyisoyrenyl-P-sugars, polyisoprenyl phosphate ion is the only fragment observed for compounds with trans configuration, whereas in compounds with cis configuration, this ion is accompanied by another abundant fragment, which is derived from the cleavage acros s the sugar ring and corresponds to [polyisoprenyl-PO4-(C2H3O)](-). Th e relative intensity ratio of the latter ion to the [polyisoprenyl-HPO 4](-) ion is close to 1 for compounds with cis configuration, but it i s only about 0.01 for compounds with trans configuration. This ratio m ay serve, therefore, as a diagnostic value for determination of the an omeric configuration of glycosyl esters of polyisoprenyl phosphates. I t is proposed that the observed differences in fragmentation patterns of cis-trans sugar nucleotides and polyisoprenyl-P-sugars could be exp lained in terms of kinetic stereoelectronic effect, and a speculative mechanism of fragmentation of compounds with trans configuration is pr esented. For compounds with cis configuration, formation of a hydrogen bond between the C-2 ''(2') hydroxyl and the phosphate group could pl ay a crucial role in directing the specific fragmentation reactions. C onsequently, the described empirical rules would hold only for compoun ds that have a free 2 ''(2')-hydroxyl group and no alternative charge location. Owing to its simplicity, sensitivity, and tolerance of impur ities, fast-atom bombardment-tandem mass spectrometry represents a sui table method for determination of the anomeric Linkage of glycosyl est ers of nucleoside pyrophosphates and polyisoprenyl phosphates if the a bsolute configuration of glycosyl residue is known and the compound fu lfills the above-mentioned requirements.