Xin-Cheng Liao

ESI-MSn study on the fragmentation of protonated cyclic-dipeptides

Cyclic dipeptides are relatively simple compounds that can exhibit a great variety of important biological activities. The fragmentation pathways of protonated cyclic dipeptides have been studied by electrospray ionization multistage mass spectrometry (ESI-MS n ). The mass spectra studies of the cyclic dipeptides showed that the cyclic dipeptides with the similar substituents, the side chains of amino acid residues at the diketopiperazine ring, followed the same fragmentation pathway. In the fragmentation spectra of protonated cyclic dipeptides, some characteristic fragment ions were observed and could be used to distinguish the cyclic dipeptides. The hydrogen/deuterium (H/D) exchange experiment and the high-resolution mass spectrometry (Q-TOF) were used to verify and rationalize the proposed fragmentation pathways. These observations may have some potential applications in the structural elucidation and interpretation of the mass spectra of homologous compounds.

Synthesis and Characterization of Chloropentaaryloxycyclotriphosphazene Derivatives

Five chloropentaaryloxycyclotriphosphazene derivatives were synthesized by the reaction of hexachlorocyclotriphosphazene with potassium phenoxide in tetrahydrofuran. A satisfactory yield could be obtained when a 5.1 : 1(KOC 6 H 4 R : P 3 N 3 Cl 6 ) molar ratio was used. The new compounds were characterized by IR, 1H NMR, 31P NMR, 13C NMR, and ESI-MS, and for two of them by HR-MS.

The Investigation of Interaction Competition Between ATP and DIPP-Ala, Boc-Ala, or Ala by ESI-MS/MS and Theoretical Calculation

The interactions between ATP and N-(O,O-diisopropyl) phosphoryl-L-alanine (DIPP-Ala), N-(tert-butoxycarbonyl)-L-alanine (Boc-Ala), or L-alanine (Ala) were investigated by electrospray ionization tandem mass spectrometry (ESI-MS/MS). The non-covalent complexes between ATP and Boc-Ala or DIPP-Ala were observed, while the complex between ATP and Ala was not found in the mass spectra. The affinity of DIPP-Ala for ATP was confirmed to be stronger than that of Boc-Ala by competition experiment. Through molecular modeling calculations, it was found that the non-covalent complexes were stabilized by intermolecular hydrogen bonds, and the affinity sequence for ATP was DIPP-Ala > Boc-Ala > Ala by comparing their binding energy, −35.407 kcal/mol, −15.634 kcal/mol, −6.555 kcal/mol, respectively. The results implied that a phosphoryl group was a very important functional group to provide an interaction site between amino acids and ATP, and that N-phosphoryl amino acids can be used as a good model of protein in the studies of molecular recognition of ATP.

CCDC 624205: Experimental Crystal Structure Determination

Related Article: Shu-Xia Cao, Jin-Ming Liu, Xie Ya-Li, Xin-Cheng Liao, Yu-Fen Zhao|2006|Acta Crystallogr.,Sect.E:Struct.Rep.Online|62|o4642|doi:10.1107/S1600536806037792

Studies on Fragmentation Pathways of N-Ethoxy (phenyl) phosphoryl Amino Acids by Electrospray Ionization Tandem Mass Spectrometry

The positive and negative ESI-MS/MS spectra of N-ethoxy(phenyl) phosphoryl amino acids (EPP-AA) were investigated by electrospray ionization (ESI) ion trap mass spectrometry. The fragmentation pathways of [M + Na]+ and [M − H]− ions are proposed and rationalized. The observation may have some potential applications in the interpretation of the MS/MS spectra of novel N-phosphoryl compounds. The complexity of MS/MS spectra of EPP-AA [M + Na]+ ions is decreased compared with that of N-dialkyloxyphosphoryl amino acid. Therefore, the new phosphonamidate method may be considered one of the superior methods that can be used in sequencing peptides and proteins extensively.