On the Specificity of Reactions Catalysed by the Antibody H11

The substrate specificity and the stereochemical course of the reactions catalysed by the antibody H11 (which was raised to a protein conjugated derivative of the adduct of 1-acetoxy-buta-1,3-diene 1) have been investigated. The antibody shows high selectivity for acetoxybutadiene which it hydrolyses to the corresponding dienol, the major diene component of the cycloaddition reactions observed. However, it tolerates a range of N-alkylmaleimides. The stereochemical course of cycloaddition is shown to produce a significant enantiomeric excess of the 3aR, 4S, 7aR-endo-diastereoisomer by analysis with Mosherʹs ester derivatives. This study also revealed that H11 is capable of slowly catalysing the hydrolysis of N-alkylmaleimide substrates. The implications for the mechanism of action of H11 are discussed.