Phosphonate TSA-built macromatric polymer catalysts as chymotrypsin mimics for the amidolysis of amino acid p-nitroanilides: Effect of the nature and extent of crosslinker on amidase activities

Abstract

Transition state analogue-built-polymer catalysts containing l-histidine, l-aspartic acid and l-serine moieties were synthesized using a racemic transition state analogue ‘phenyl-1-(N-benzyloxycarbonylamino)-2-(phenyl)ethyl phosphonate’ for the amidolysis of p-nitroanilide of N-(benzyloxycarbonyl)-phenylalanine, Z-L-Phe-PNA. The transition state analogue imprinted and non-imprinted polymer catalysts were prepared with hydrophilic flexible dimethacrylate crosslinkers having varying alkyl chain length-ethyleneglycol dimethacrylate, 1,4-butanediol dimethacrylate and 1,6-hexanediol dimethacrylate. The substrate affinity of the polymer catalysts were evaluated in the framework of Michaelis-Menten kinetics. Among the polymer catalysts with methacrylic crosslinks, higher extreme crosslink density (90%) is found to be essential to preserve the exact geometry of the print molecule, while the increase in alkyl chain length of the crosslinker make the cavity deformed leading to poor shape-selective binding of the substrate. The maximal value of catalytic efficiency was observed with 90% ethylene glycol dimethacrylate crosslinked polymer catalyst. A comparison was also made with polymer catalysts containing hydrophobic divinylbenzene crosslinks. Among divinylbenzene crosslinked polymers, catalyst with 75% crosslinking exhibited better catalytic efficiency. The catalytic activity of the transition state analogue imprinted polymer is observed to be enantioselective, shape-selective and substrate-specific. TSA inhibition studies reveal that the phosphonate TSA is a very competitive inhibitor for Z-L-Phe-PNA.