Electrospray ionization mass spectrometry of serine/alanine conjugated 5'-UMP and 3',5'-dithymidine phosphoramidates

A novel methyl migration to the phosphoryl group with the formation of cyclic aminoacylphosphoramidates in electrospray ionization tandem mass spectra of amino acid ester phosphoramidates of antiviral nucleosides

The mass spectral behavior of amino acid methyl ester phosphoramidate derivatives have been investigated using electrospray ionization multistage mass spectrometry (ESI-MS(n)) and moderate theoretical calculations at the B3LYP/6-31G(d) level. A novel methyl group migration to the phosphoryl group with the formation of the intermediate cyclic aminoacylphosphoramidate was found. The proposed structures of the rearrangement ions were confirmed by high-resolution tandem mass spectrometry. A possible mechanism involving the pentacoordinate phosphoric-carboxylic phosphate anhydride was proposed, in which the metal ion coordination with the phosphoryl and carbonyl groups and the intrinsic properties of phosphoryl group might be the key factors responsible for this novel migration.

Amino acid homochirality may be linked to the origin of phosphate-based life

Phosphorylation has to have been one of the key events in prebiotic evolution on earth. In this article, the emergence of phosphoryl amino acid 5'-nucleosides having a P-N bond is described as a model of the origin of amino acid homochirality and Genetic Code. It is proposed that the intramolecular interaction between the nucleotide base and the amino acid side-chain influences the stability of particular amino acid 5'-nucleotides, and the interaction also selects for the chirality of amino acids. The differences between L: - and D: -conformation energies (DeltaE (conf)) are evaluated by DFT methods at the B3LYP/6-31G(d) level. Although, as expected, these DeltaE (conf) values are not large, they do give differences in energy that can distinguish the chirality of amino acids. Based on our calculations, the chiral selection of the earliest amino acids for L: -enantiomers seems to be determined by a clear stereochemical/physicochemical relationship. As later amino acids developed from the earliest amino acids, we deduce that the chirality of these late amino acids was inherited from that of the early amino acids. This idea reaches far back into evolution, and we hope that it will guide further experiments in this area.

Identification of phosphorylcholine substituted peptides by their characteristic mass spectrometric fragmentation

Phosphorylcholine (PC) substituted biomolecules are wide-spread, highly relevant antigens of parasites, since this small hapten has been found to be a potent immunomodulatory component which allows the establishment of long lasting infections of the host. Structural data, especially of protein bound PC-substituents, are still rare due to the observation that mass spectrometric analyses are mostly hampered by this zwitterionic substituent resulting in low sensitivities and unusual but characteristic fragmentation patterns. Here we investigated the fragmentation behaviour of synthetic PC-substituted peptides by matrix-assisted laser desorption/ionization mass spectrometry and electrospray ionization ion trap mass spectrometry. We could show that the predominant neutral loss of a trimethylamine unit (Hoffmann elimination) leads to cyclic phosphate derivatives which prevent further fragmentation of the peptide backbone by stabilizing the positive charge at this particular side chain. Knowledge of this PC-specific fragmentation might help to identify PC-substituted biomolecules and facilitate their structural analysis.

Synthesis of serine/alanine conjugated 3',5'-TpT

Serine and alanine phosphoramidates conjugates of 3',5'-TpT 4, 5 were synthesized. The corresponding serine phosphoamidate possesses some unique properties due to the presence of the side chain hydroxyl group.