Biocatalysis and organocatalysis
Dott.ssa Nicoletta Gaggero
Biotrasformations (or biocatalysis) employ natural and/or ingegnerized isolate enzymes or microorganisms for the synthesis of chiral enantiomerically enriched molecules with farmacological interest or building blocks (synthons) of wide employment in the organic synthesis (es. sulfoxides, epoxides).
The enzymes offer the advantage of a highest catalytic efficiency to a highest selectivity (chemo-, regio, diastero- and enantio-selectivity).
The mild experimental conditions (pH 7 aqueous phase, room temperature) minimized undesired side- reactions such as decompositions, racemizations and rearrangments which often plague traditional methodologies of organic synthesis and moreover, it is possible to carry out sequential processes by means of multi-enzyme systems.
In my search, I employ enzymes (monooxygenases, hydrolases) but also enzymatic models such as cyclodextrins and microperoxidase 11 and proteins (bovine serum albumin).
The organocatalisys is a branch of catalysis that uses small organic molecules for the synthesis of enantiomerically enriched biologically active molecules and chiral building blocks.
Its increasing importance in the panorama of the synthetic methodologies depends on versatility of the organocatalysts, which are able to work in mild experimental conditions, in the presence of oxygen and water in the reaction mixture and to their remarkable eco-compatibility due to the fact that they do not contain transition metals.
The fact not to contain metals is particularly important with regard the synthesis of all those products that do not tolerate metal contamination, such as drugs.
There are a lot of natural products that possess variously functionalized chiral scaffolds which can be further modified and that are the starting materials to easily obtain chiral ligands and organocatalysts.
For example proline, a natural aminoacid, is able to catalyze organic reactions with amazing results, considering the simplicity of its structure.
The starting materials for many of these reactions are simple carbonyl compounds.
From the studies in order to clear the mechanism to the base of the stereoselection, new catalysts are developed which are able to face specific problems concerning the synthesis.
The catalytic species carry out their activity through multiple, non-covalent, weak interactions (electrostatic, hydrogen-bond) with their substrates just like to enzymatic catalysis mechanisms which are based on the concept of the cooperation.
Part of the reactions that I perform within the organocatalytic subject is carried out in phase transfer catalysis (PTC) conditions, that is, in bifasic solid/organic solvent systems in which reactive anions are generated in situ by means of starting material deprotonation thanks to the employment of economic, inorganic bases (NaOH, K2CO3). The catalyst (often a quaternary ammonium salt), via ionic exchange, participates in the formation and in the transport of anionic intermediates in the organic phase where the reaction happens.