Estudos teórico e experimental da reatividade de compostos carbonílicos frente a reação de Pictet-Spengler catalisada pela enzima TfNCS

Abstract

The enzyme (S)–NCS, from the organism Thalictrum Flavum (TfNCS), has been studied in the last years, revealing the great potential for different applications, such as the production of intermediaries in biosynthetic paths and the production of tetrahydroisoquinoline. This enzyme is involved in the enantioselective catalysis of a reaction of Pictet-Spengler, between dopamine and carbonyl compounds. Searching to explore the potential of the enzymes of (S)-NCS, the work purpose was: by literature research, molecular modeling and computational chemistry techniques, make investigations to understand which parameters could be associated with reactivity of the carbonyl compound in the biocatalysis. For this study, the enzyme TfNCS was expressed, and a protocol to determine the reactivity of the carbonyl compounds by nuclear magnetic resonance (NMR) was implemented. By a literature research of compounds tested on Pictet-Spengler reactions catalyzed by TfNCS, were founded 49 carbonyl compounds with activity known. This library was added to the experimental activities determinated in this work and were modeled. This library was used in the construction of a QSAR model (Quantitative Structure-Activity Relationship) to find molecular parameters that could be associated with a carbonyl group activity. From the library composed of 53 compounds, some representative compounds were selected and separated into six study groups. These study groups were used in molecular docking, molecular dynamics, and calculation of Fukui functions. From the molecular dockings, the carbonyl approximation to the catalytic site was evaluated; from molecular dynamics, the carbonyl's behavior on the enzyme's catalytic site was studied; and by calculating Fukui functions, the electronic nature of the carbonyl was studied. The results showed that the effects of conjugation, size, and different substituents could be associated with the experimental activity of a carbonyl compounds, explaning the difference betwen reactive and non reactive compounds. The classification protocol proposed in this work could help predict active compounds for TfNCS catalysis of Pictet-Spengler reactions, and with some adaptations, could be used to study other promiscuous enzymes.