Imidazoles, hydrogen bond geometry

Simple hydrolysis of substrate 36 with base in solution furnishes an essentially equal mixture of 37 and 38, since the t-butyl group is too remote to have any influence. However, catalysis by the artificial enzyme mixture 41 gave 37 only. The geometry of the catalyst-substrate complex directs the attack by water (hydrogen bonded to the imidazole) in a line perpendicular to the ring axis (cf. 42). When we moved the two imidazole groups out further, in catalyst 43, they were then able to deliver the water in a... 

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