Development of P450 and BVMO biocatalysts for the stereocontrolled production of the garlic sulfoxide components

Garlic (Allium sativum Linn.) and garlic extracts had important dietary and therapeutic roles for centuries, and their beneficial effects on the cardiovascular system, as well as their antimicrobial, anti-inflammatory and hypoglycemic effects, were known since the time of the Roman Empire. Garlic extracts have been found to possess antibacterial activity against a number of Gram-positive and Gram-negative bacteria resistant to standard antibiotics, including methicillin-resistant Staphilococcus aurus (MRSA) and multidrug-resistant enterotoxicogenic Escherichia coli, as well as synergistic effect when combined with streptomycin in the treatment of Gram-negative bacterial infections. The main components of garlic responsible for the antibacterial properties, and for the strong and characteristic smell, are the sulphur-containing molecules allicin, S-allyl-cycteine (alliin) and ajoene. From a chemical point of view alliin, allicin and ajoene are chiral sulfoxides and their biological properties are associated with only one of the two possible enantiomeric forms. The synthesis of the sulfoxide garlic components can be carried out through sulphur-oxidation of the easily accessible sulphide precursors. Practically, the oxidation of a sulphide into an enantiopure sulfoxide may represent a challenge in chemistry, mainly due to the low stereoselectivity of the reaction and the formation of over-oxidised inactive side products. Moreover, the harsh reaction conditions can lead to the racemization of the labile sulfoxide stereocentres. As a consequence, the development of new, sustainable and stereoselective approaches for the efficient production of enantiomerically pure sulfoxide, analogues of the garlic components, may look highly appealing from a chemical manufacturing point of view as well as for pharmaceutical industries.

The proposed project aims at the development of new oxidising biocatalysts, namely P450 and BVMO enzymes, for the sustainable and stereoselective production of sulfoxide analogues of the garlic components alliin, allicin and ajoene. Within this project, new sulphur-oxidising enzymes will be developed, produced and optimised in collaboration with the industrial partner, Almac Group, that has world leading experience in this area. Analogues of the garlic components will be produced using purified or cell-free extract (CFE) of P450 and/or BVMO enzymes. Improvements of the lead enzymes (i.e. rate, yield, selectivity of biotransformations, process robustness, etc), will be carried out by advanced genome mining or protein direct evolution, as appropriate, in order to develop optimised biocatalysts for selected substrates. Finally, a library of garlic sulfoxide analogues will be produced during the project and assessed for their antimicrobial properties against a wide panel of wild type and drug resistant Gram positive and Gram negative bacteria.