Abstract
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 EtSO 4 - and Tf 2N -) were favorable since nucleophilic ones (such as CF 3COO - and CH 3COO -) could exchange with chlorine resulting in non-reactive coupling reagents. Two modified Mukaiyama's compounds (i.e. hydrophilic [2-ClMePy][EtSO 4] and hydrophobic [2-ClMePy][Tf 2N]) have been identified as the best IL-type 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'.
Original language | English (US) |
---|---|
Pages (from-to) | 33-44 |
Number of pages | 12 |
Journal | International journal of molecular sciences |
Volume | 9 |
Issue number | 1 |
DOIs | |
State | Published - Jan 2008 |
Externally published | Yes |
Keywords
- Amino acid
- Esterification
- Ionic liquid
- Microwave
- Mukaiyama's reagent