Int. J. Mol. Sci. 2008, 9(1), 33-44; doi:10.3390/ijms9010033
Article

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

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Received: 30 November 2007; Accepted: 10 January 2008 / Published: 16 January 2008
(This article belongs to the Special Issue Ionic Liquids)
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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 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’.
Keywords: amino acid; ionic liquid; Mukaiyama’s reagent; microwave; esterification.
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MDPI and ACS Style

Zhao, H.; Song, Z.; Cowins, J.V.; Olubajo, O. Microwave-Assisted Esterification of N-Acetyl-L-Phenylalanine Using Modified Mukaiyama’s Reagents: A New Approach Involving Ionic Liquids. Int. J. Mol. Sci. 2008, 9, 33-44.

AMA Style

Zhao H, Song Z, Cowins JV, Olubajo O. Microwave-Assisted Esterification of N-Acetyl-L-Phenylalanine Using Modified Mukaiyama’s Reagents: A New Approach Involving Ionic Liquids. International Journal of Molecular Sciences. 2008; 9(1):33-44.

Chicago/Turabian Style

Zhao, Hua; Song, Zhiyan; Cowins, Janet V.; Olubajo, Olarongbe. 2008. "Microwave-Assisted Esterification of N-Acetyl-L-Phenylalanine Using Modified Mukaiyama’s Reagents: A New Approach Involving Ionic Liquids." Int. J. Mol. Sci. 9, no. 1: 33-44.

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