Every chemical element is special, but some elements are more special than others! Carbon, the sixth element of the periodic table, is unique with respect to its versatility and impact on our lives. Carbon is the foundational element of all organic molecules including for example, materials, pharmaceuticals and fuels. No other element has shaped the world around us more than carbon. For this reason, the development of innovative methods to link carbon atoms together in desirable structures is of tremendous importance and is an overarching ambition in the field of organic chemistry. An important example of a reaction that can be used to link carbon atoms together is the Diels-Alder reaction, which since its discovery has been used to construct the complex carbon skeletons of numerous important molecules including pharmaceuticals, vitamins, hormones, agrochemicals and a raft of fragrance and flavour compounds. Historically, the Diels-Alder reaction has been performed using either chemical catalysts or high temperatures and pressures. Unfortunately, these approaches can give a mixture of products and have detrimental sustainability issues (use of energy and metal catalysts). However, biological catalysts for this reaction, so called 'Diels-Alderases', offer an attractive alternative, circumventing many of the complexities associated with chemical catalysis, and thus enabling Diels-Alder reactions to be performed under ambient conditions, with exquisite regio- and stereochemical control, and in an inherently 'greener' way. In this academic-industrial project, which builds on a strong foundation of interdisciplinary collaborative research by the applicants in the study of natural Diels-Alderases, the researchers will: i) Develop flow systems using immobilised enzymes to catalyse Diels-Alder reactions on gram scales; ii) investigate the ability of natural Diels-Alderases and rationally-engineered variants to catalyse both intramolecular (with both reactive groups within the same molecule) and intermolecular (with reactive groups in different molecules) cycloaddition reactions; iii) study hitherto uncharacterised natural Diels-Alderases and their associated natural products from cryptic biosynthetic gene clusters; iv) Deploy our portfolio of natural and engineered Diels-Alderases, in combination with auxiliary enzymes, to undertake chemoenzymatic total syntheses of high-value target compounds.