Synthesis and hydrolysis of 4-acetoxymethylbenzimidazoles. Effects of freezing an internal rotation on intramolecular catalysis by a benzimidazolyl group.

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概要

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• As models for acetyl-α-chymotrypsin, 4-acetoxymethylbenzimidazole (<B>2</B>), its 5-methyl derivative <B>3</B> and 2,5-dimethyl derivative <B>4</B> were synthesized from <I>o</I>-toluidine in moderate yields. Their hydrolytic reactivities were determined in water at 50 °C in comparison with their open-chain analog, 4-(acetoxyethyl)imidazole(<B>1</B>). The rate constant (<I>k</I><SUB>1</SUB>) for intramolecular general base catalysis by the imidazolyl group of <B>2</B> was 1.6 times larger than <I>k</I><SUB>1</SUB> for <B>1</B>. A corrected relative rate of 4.1 is obtained by correcting the basicity difference and the polar substituent effect. The value of 4.1 is an expected magnitude of the effect of freezing an internal rotation as reported for 4,5-(1-acetoxymethyltetramethylene)imidazole. The 5-methyl group of <B>3</B> enhances the <I>k</I><SUB>1</SUB> value 1.4 times as large as that for <B>2</B>. The enhancement can be attributed to restriction of the second internal rotation. The hydrolytic reactivity of <B>4</B> is discussed.

• 公益社団法人 日本化学会の論文

著者

• Utaka Masanori

  Department Of Applied Chemistry Faculty Of Engineering Okayama University

• Takeda Akira

  Department Of Gastroenterology Osaka General Medical Center

• Takatsu Masahisa

  Department of Synthetics Chemistry, School of Engineering, Okayama University

• Takeda Akira

  Department of Applied Chemistry, Faculty of Engineering, Okayama University

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