Biocatalyseurs artificiels à deux composantes – BiCAB

The obtention of optically pure compounds for the production of pharmaceuticals, agrochemicals, and fine chemicals is one of the most active fields in organic synthesis. For example, the worldwide sales of chiral drugs is estimated to reach more than 200 billion Euros by 2008. Organometallic complexes, enzymes and their tailored version (through molecular evolution) have been successively used as catalysts with different level of success. Laccases have long been thought to be a perfect candidate for many industrial processes including bio-bleaching, bio-remediation of polluted effluents, wood composites, phenolic glues, food additives or in health-care products, as dyes, drugs or antibiotics etc.. This large panel of potential industrial applications is linked to the plasticity of the enzyme, to its broad susbtrate specificity and to the nature of the primary product of the reaction they catalyse. Laccases associate a mono electronic oxidation of phenolics to a four electrons reduction of friendly dioxygen into water, primarily generating phenoxi radicals that can evolve towards the formation of quinones, ring cleavage and polymers. Organic compounds derived from radical coupling of phenols have important biological roles as cell structural polymers (lignin), wound healing agent, defense molecules etc.. Coupled phenol derivatives posses interesting pharmaceutical properties as antibiotics, antiviral and antitumorals (e.g. phenoxazinones, lignans, etc.). However, unlike most biological oxidation, the bimolecular phenoxy radical coupling reaction is not under a strictly regio- and stereospecific control. This considerably reduces the potential of radical generating oxidases as biocatalysts for the synthesis of chemical goods. Chiral promoting factors naturally exist in plants. Indeed, although the new stereogenic centres which arise from in vitro oxidative phenol coupling (e. g. laccase mediated) are racemic, naturally occurring plant lignans are homochiral. A protein factor, called Dirigent Protein (DP), has been shown to promote the formation of enantiopure pinoresinol from achiral coniferyl alcohol. More generally, the existence of a broad class of coupling proteins responsible of distinctive coupling mode in lignans synthesis is postulated.On the other hand, the existence of a fungal heterodimeric laccase has been recently reported. In this complex, the small subunit, called interactant, seems to influence both the stability of the laccase unit and its activity (the activity is higher in the complex than in laccase alone). On the other hand, cyclodextrins (CDs) have emerged as powerful tools in enzyme biocatalysis mainly due to their ability to form stable inclusion complexes with a wide variety of hydrophobic compounds. CDs are good auxiliaries for enantioselective catalysis. CDs are functionalizable and can be attached to proteins by different chemical means (e.g. click-chemistry). With the recent advances in their design, artificial enzymes appear as highly promising sustainable alternatives to traditional catalysts. The interaction of a non chiral catalytic moiety, which ensures activity, with a chiral template is expected to produce active and (enantio)selective hybrids. In this context, the overall aim of BiCAB is to develop eco-friendly catalysts that allow efficient stereoselective coupling of phenols moiety as building blocks in the synthesis of drugs and fine chemicals. Two component bio-based hybrid catalysts that associate the oxidative power of an oxidase to organic (CDs) or proteinaceous (DPs) substrate dirigent modules will be built to replace harmful traditional synthesis. To this end, the core enzyme (dioxygen reducing laccases) and enzyme interacting modules will be tailor-adapted to each other and the efficiency of two-component biocompatible heterogeneous catalysts will be tested.