Stereoselectivity in deacylation of nitrophenyl acylates by poly(ethylenimine) derivatives

Deacylation of nitrophenyl acetates containing carboxyl substituents [4-acetoxy-3-nitrobenzoic acid (1), 3-acetoxy-4-nitrobenzoic acid (2), and 2-acetoxy-5-nitrobenzoic acid (3)] was studied in the presence of poly(ethylenimine) derivatives. The polymers examined contained lauryl groups (Lau₁₂PEI) or both lauryl and imidazolyl groups (Lau₁₂Im₁₀PEI). The reaction with active ester proceeds through the attack of primary amino groups of the polymers at the acyl carbons of the substrates. The reaction of Lau₁₂Im₁₀PEI with a hydrophobic ester, p-nitrophenyl caproate (NPC), however, has been reported to involve the attack by the imidazolyl group of the polymer. Thus, the anionic (carboxyl-containing) and the hydrophobic esters bind to different domains on Lau₁₂Im₁₀PEI. Among the anionic substrates, 3 has uniquely large k_cat values compared with 1 or 2. This is explained in terms of closer proximity between a nucleophile amino group of the polymer and the scissile bond of the substrate in the polymer-substrate complex.