180264-40-8Relevant academic research and scientific papers
Isomer differentiation via collision-induced dissociation: The case of protonated a-, β2- and β3-phenylalanines and their derivatives
Lam, Adrian K. Y.,O'Hair, Richard A. J.
, p. 1779 - 1790 (2011/11/05)
A combination of electrospray ionisation (ESI), multistage and high-resolution mass spectrometry experiments is used to examine the gas-phase fragmentation reactions of the three isomeric phenylalanine derivatives, a-phenylalanine, b2-phenylalanine and b3-phenylalanine. Under collision-induced dissociation (CID) conditions, each of the protonated phenylalanine isomers fragmented differently, allowing for differentiation. For example, protonated b3-phenylalanine fragments almost exclusively via the loss of NH3, only b2-phenylalanine via the loss of H2O, while a- and b2- phenylalanine fragment mainly via the combined losses of H2ORCO. Density functional theory (DFT) calculations were performed to examine the competition between NH3 loss and the combined losses of H2O and CO for each of the protonated phenylalanine isomers. Three potential NH3 loss pathways were studied: (i) an aryl-assisted neighbouring group; (ii) 1,2 hydride migration; and (iii) neighbouring group participation by the carboxyl group. Finally, we have shown that isomer differentiation is also possible when CID is performed on the protonated methyl ester and methyl amide derivatives of a-, b2- and b3-phenylalanines.
X-ray crystallographic study of substituted perhydropyrimidinones. Extreme changes in ring conformation
Ramirez-Quiros, Yara,Balderas, Margarita,Escalante, Jaime,Quintana, Delia,Gallardo, Itzell,Madrigal, Domingo,Molins, Elies,Juaristi, Eusebio
, p. 8668 - 8680 (2007/10/03)
X-ray crystal structures of 20 differently substituted perhydropyrimidin-4-ones are presented. Analysis of these data reveal a remarkable conformational sensitivity of a six-membered ring to substitution. Thus half-chair, envelope, boat, twist-boat, and intermediate conformations are found for the six-membered heterocycle, providing evidence for a relatively fiat conformational energy surface in this ring. Interpretation of the preferred conformations is advanced in terms of steric interactions among substituents and, in some cases, as the result of particular conformational (A1.3 strain, anomeric) effects.
