Large hydrophobic interactions with clearly defined geometry. A dimeric steroid with catalytic properties

Abstract

The steroid dimer α,α′-bis(17β-(4'-imidazolyl)-11-keto-5α- androstan-3β-amino)-p-xylene, 3, has been synthesized by reductive animation of 17β-(4′-imidazolyl)-5α- androstane-3,11-dione by p-xylenediamine in the presence of sodium cyanoborohydride, and by reductive amination of terephthalaidehyde by 3β-amino-17β-(4′-imidazolyl)-5α- androstan-11-one. The second method is stereochemically unambiguous; the first is not. Compound 3 acts as a catalyst for the hydrolysis of 3-arylpropionate esters of 3-hydroxy-4-nitrobenzoic acid. For the phenanthryl propionate the rate enhancement relative to imidazole is 200-fold, and the rate enhancement relative to the hypothetical rate for the propionate reacting with the steroid by the same transition state geometry is 3000-fold. The slope of a plot of log kcorr vs. π for the reaction of 3b with aryl propionate esters was 0.83; the corresponding slope for 12 was 0.39. This provides a design parameter for the construction of artificial enzymes.