Microwave-assisted esterification of N-acetyl-L-phenylalanine using modified Mukaiyama's reagents: A new approach involving ionic liquids

Hua Zhao, Zhiyan Song, Janet V. Cowins, Olarongbe Olubajo

Research output: Contribution to journalArticlepeer-review

19 Scopus citations

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 languageEnglish (US)
Pages (from-to)33-44
Number of pages12
JournalInternational journal of molecular sciences
Volume9
Issue number1
DOIs
StatePublished - Jan 2008
Externally publishedYes

Keywords

  • Amino acid
  • Esterification
  • Ionic liquid
  • Microwave
  • Mukaiyama's reagent

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