Microwave-Assisted Esterification of N-Acetyl-L-Phenylalanine Using Modified Mukaiyama's Reagents: A New Approach Involving Ionic Liquids

Inspired by the concept of ionic liquids (ILs), this study modified the original Mukaiyama's reagent, 2-chloro-1-methylpyridinium iodide (m.p. 200-dec), from ionic solid into liquids by changing its anion. The esterification of N-acetyl-L-phenylalanine was investigated as a model reaction. The microwave irradiation was more effective in esterifying N-acetyl-L-phenylalanine than the conventional reflux method. The original Mukaiyama's reagent was modified into ILs through manipulating its anion. However, only non-nucleophilic anions (such as EtSO4– and Tf2N–) were favorable since nucleophilic ones (such as CF3COO– and CH3COO–) could exchange with chlorine resulting in non-reactive coupling reagents. Two modified Mukaiyama's compounds (i.e. hydrophilic [2-ClMePy][EtSO4] and hydrophobic [2-ClMePy][Tf2N]) have been identified as the best ILtype coupling reagents. The esterification reaction was greatly enhanced by using 1- methylimidazole as the base instead of conventional toxic tertiary amines, and by using excess amount of alcohols as solvents instead of dichloromethane. Overall, the method reported is effective and ‘greener’

31P NMR Study of GTP-Cation Interactions

Guanosine 5\u27-triphosphate (GTP) plays a pivotal role in many biologi­cal processes. The interactions of cations with GTP are essential to the stabilization of this nucleotide and the regulation of its functions. In this study, we present solution 31P NMR data on GTP samples in varied salt concentrations or pHs. From chemical shifts and T1 , T2 relaxations, it is concluded that the interaction strengths of cations with GTP are in the order of Ca2+ \u3e Mg2+ \u3e Li+ \u3e Na+ for the cations, and in the order of beta \u3e gamma \u3e alpha for the phosphate groups. An increased sample pH causes deprotonation of the beta and gamma phosphates with enhanced cations\u27 affinities, as indicated by significant chemical shift changes, while the chemical shift of alpha phosphate is essentially unaf­fected by varying pH. These results will aid in exploring the mecha­nism of GTP-cation interactions, and fully understanding the effects of cations on GTP\u27s stabilization and its biological activities

Microwave-Assisted Esterification of N-Acetyl-L-Phenylalanine Using Modified Mukaiyama’s Reagents: A New Approach Involving Ionic Liquids

Inspired by the concept of ionic liquids (ILs), this study modified the original Mukaiyama’s reagent, 2-chloro-1-methylpyridinium iodide (m.p. 200-dec), from ionic solid into liquids by changing its anion. The esterification of N-acetyl-L-phenylalanine was investigated as a model reaction. The microwave irradiation was more effective in esterifying N-acetyl-L-phenylalanine than the conventional reflux method. The original Mukaiyama’s reagent was modified into ILs through manipulating its anion. However, only non-nucleophilic anions (such as EtSO4- and Tf2N-) were favorable since nucleophilic ones (such as CF3COO- and CH3COO-) could exchange with chlorine resulting in non-reactive coupling reagents. Two modified Mukaiyama’s compounds (i.e. hydrophilic [2- ClMePy][EtSO4] and hydrophobic [2-ClMePy][Tf2N]) have been identified as the best ILtype coupling reagents. The esterification reaction was greatly enhanced by using 1- methylimidazole as the base instead of conventional toxic tertiary amines, and by using excess amount of alcohols as solvents instead of dichloromethane. Overall, the method reported is effective and ‘greener’