Catalysis

Biocatalysis

Biocatalysis, specifically the use of enzymes for organic synthesis, has been replacing various chemical processes for decades. In recent times, enzymes have been increasingly employed in synthesising complex molecules like pharmaceuticals, offering advantages such as high chemo- and stereo-selectivity, as noted by Young et al. (2022). Limitations in reactivity and selectivity can be addressed by tapping into large metagenomic databases for new enzymes and leveraging protein engineering (Lubberink et al., 2023).

The benefits of employing biocatalysis are numerous and contribute to several economic and environmental advantages over traditional chemical synthesis.

• Sustainability: Enzymes used in biocatalysis are biodegradable and derived from renewable resources, aligning with sustainable practices.

• Aqueous conditions: Enzymatic reactions can be performed in water, reducing the need for environmentally harmful solvents and promoting greener practices.

• Mild reaction temperatures: The use of enzymes allows for reactions to take place at milder temperatures, decreasing energy consumption and promoting energy efficiency.

• Elimination of protection/deprotection strategies: The selectivity of biocatalytic methods frequently eliminates the need for protection/deprotection strategies or functional group activation, simplifying synthetic routes and reducing the use of additional chemicals.

• Reduced waste: Biocatalysis generally leads to less hazardous (e.g. metal) waste compared to conventional organic synthesis, contributing to more sustainable and environmentally friendly processes.

• Cost-effectiveness: The efficiency of biocatalytic methods, combined with reduced waste and lower energy consumption, results in cost-effective processes, making it an economically viable option.

These benefits collectively position biocatalysis as a promising and sustainable approach in the field of organic synthesis (Sheldon and Woodley, 2018).

Classification of enzymes

The classification of enzymes is based on the reactions they catalyse and is organised into six main categories:

• Oxidoreductases: These enzymes catalyse oxidation-reduction reactions, where one molecule is oxidised (loses electrons) and another is reduced (gains electrons). Examples include dehydrogenases and oxidases.

• Transferases: These enzymes transfer functional groups (like methyl or phosphate groups) from one molecule to another. Examples include kinases (transfer phosphate groups) and transaminases (transfer amino groups).

• Hydrolases: These enzymes catalyse the hydrolytic cleavage of C-O, C-N, and C-C bonds, including the digestion of food molecules. Examples include lipases, proteases, and nucleases.

• Lyases: These enzymes cleave C-C, C-O, C-N, and other bonds by means other than hydrolysis and oxidation, often forming a new double bond or a new ring structure. Examples include decarboxylases and aldolases.

• Isomerases: These enzymes catalyse the rearrangement of atoms within a molecule, converting one isomer to another. Examples include racemases, which convert one optical isomer into another, and cis-trans isomerases.

• Ligases: Also known as synthetases, these enzymes catalyse the joining of two molecules with the simultaneous hydrolysis of a diphosphate bond in ATP or a similar triphosphate. Examples include DNA ligase, which joins DNA strands together.

This classification system is based on the Enzyme Commission (EC) numbers, a numerical classification scheme for enzymes, based on the chemical reactions they catalyse. Each enzyme is described by a four-number code, where the first number refers to the main class (as listed above), and the following numbers provide further details about the specific substrate, type of reaction, and sequence of the reaction it catalyses.