Exploring the Potential of Diels—Alderases as Biocatalysts

Abstract

The Diels–Alder reaction is widely used in organic chemistry to construct molecules containing a cyclohexene core. However, it often requires the use of harsh conditions such as elevated temperature and pressure or the use of catalysts. An attractive alternative would be to use enzymes to catalyse such [4+2] cycloadditions at room temperature. Hence, significant effort has been dedicated to the development of artificial Diels–Alderases as well as to the study of biosynthetic pathways proposed to involve a Diels-Alder reaction. However, the field is in its infancy and significant effort is required to develop such biocatalytic carbon-carbon bond-forming reactions for use on a synthetically valuable scale. The antibiotic abyssomicin C is a notable spirotetronate formed via a Diels-Alder reaction catalysed by AbyU. Using a combination of organic synthesis, X-ray crystallography and molecular modelling, we have provided insights into the mechanism of AbyU, which involves the intramolecular cycloaddition between a conjugated diene and the exo-methylene group in the linear precursor. We have prepared an analogue and shown that it is also a substrate for AbyU giving cyclohexane core. This work is focused on identifying the key residues that are involved in substrate-folding within the AbyU active site. This work is also focused on investigating the substrate specificity of AbyU. The synthesis of analogues of the native substrate and their biotransformations are described laying the foundation towards potential future applications of an engineered enzyme as a biocatalyst for use in synthesis.