1977 Volume 50 Issue 12 Pages 3276-3280
As models for acetyl-α-chymotrypsin, 4-acetoxymethylbenzimidazole (2), its 5-methyl derivative 3 and 2,5-dimethyl derivative 4 were synthesized from o-toluidine in moderate yields. Their hydrolytic reactivities were determined in water at 50 °C in comparison with their open-chain analog, 4-(acetoxyethyl)imidazole(1). The rate constant (k1) for intramolecular general base catalysis by the imidazolyl group of 2 was 1.6 times larger than k1 for 1. 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 3 enhances the k1 value 1.4 times as large as that for 2. The enhancement can be attributed to restriction of the second internal rotation. The hydrolytic reactivity of 4 is discussed.
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