Intensive efforts have been made to develop effectively chemotherapeutic agents against the human immunodeficiencv virus(HIV).[1]Nucleoside analogues are widelv used as antiviral agents in the treatments of AIDS and the AIDS related complex.
Electrospray ionization mass spectrometry (ESI-MS) is a powerful method for sequencing peptides. A novel fragmentation pattern with the loss of a neutral fragment of 45 Da was observed with the dipeptides, tripeptides, tetrapeptides and pentapeptides containing phenylalanine or histidine residues. A novel rearrangement reaction with the extrusion of a formamide piece was studied and the rearrangement mechanism was proposed and confirmed by deuterium labeling experiments with ESI-MSn and high-resolution mass spectrometry. These findings are poten-tially helpful in identifying the specific sequence pattern in the peptide sequencing.
Dinucleotide (TpAZT) phosphoramidates were synthesized by Todd reaction of dinucleoside H-phosphonates and amino acid methyl esters, and their diastereomers (Rp and Sp) were separated by crystallization, and the results showed that natural and cheap methyl esters of alanine and phenylalanine can be used for large-scale synthesis of dinucleotide analogs.
Mass spectroscopic characteristics of phosphoryl amino acids were studied in detail by positive and negative electrospray ionization mass spectrometry (ESI-MS) in conjunction with tandem mass spectrometry (MS/MS). Be- sides N-diisopropyloxyphosphoryl amino acids (N-DIPP-AA), O-phospho- and O-diisopropyloxyphosphoryl amino acids (O-DIPP-AA) were studied and compared to N-DIPP-AA. The fragmentation pathways of [M+H]+, [M+Na]+ and [M-H]- ions of phosphoryl amino acids were summarized. In addition to several similar patterns, each of them showed its characteristic fragmention.
The peptide formation of N-phosphoryl aminoacids with amino acids proceeds in aqueous solution withoutany coupling reagents. After being separated in sephadex gelcolumn, the phosphoryl dipeptides were analyzed by theelectrospray ionization tandem mass spectrometry (ESIMS/MS). The result demonstrates that phosphoryl dipeptideswere datected in all the reaction systems. It is found tkat theformation of N-phosphoryl dipeptides is oriented: theN-terminal amino acid residues of the N-phosphoryl dipep-tides are from N-phosphoryl amino acids, and the peptideelongation happened at the C-terminal. Only adipeptide, noβ-dipeptide, is formed in the N-phosphoryl dipeptides,showing that α-carboxylic group is activated selectively byN-pbosphorylation. Theoretical calculation shows that thepeptide formation of N-phosphoryl amino acids might hap-pen through a pentu-coordinate carboxylic-phosphoric in-termediate in solution. These results might give some clues tothe stlidy on the origin of proteins and protein
With introduction of a diisopropyloxy phosphoryl group into the N terminal of amino acids, it was found that proton affinity (PA) of amino acid was enhanced in mass spectrometry. Density functional theory calculations showed that the energy for protonation of DIPP-amino acid is lower than that of amino acid, which means PA of DIPP-AA is higher than that of corresponding amino acid. These results, coincident with our empirical results, offer a useful interpretation of experimental observations.
