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

International Journal of Molecular Sciences

Hua Zhao¹  Zhiyan Song²  Janet V. Cowins² 

[1] id="af1-ijms-09-00033">Chemistry Program, Savannah State University, Savannah, GA 31404, U

关键词: amino acid;    ionic liquid;    Mukaiyama's reagent;    microwave;    esterification;   

DOI  :  10.3390/ijms9010033

来源: mdpi

【 摘 要 】

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’.

【 授权许可】

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