The Study of the Enzymatic Synthesis Mechanism of 4,6-Disubstituted 3-cyano-2-pyridones

Abstract

In this thesis, the mechanism of lipase catalyzed synthesis of 4,6-disubstituted-3-cyano-2-pyridones was studied, and for that purpose the simplest molecule, 4,6-dimethyl-3-cyano-2-pyridone, and vitamin B6 precursor, 4-ethoxymethyl-6-methyl-3-cyano-2-pyridone, were synthesized. In order to find the optimal conditions for their synthesis a response surface methodology (RSM) was applied, and the influence of three reaction factors (temperature, enzyme concentration and substrate molar ratio) was investigated. After that, at determined optimal conditions, the kinetic study was performed and the obtained results showed that these reactions can be described with ping–pong bi–ter model with inhibition by cyanoacetamide. The second part of the thesis was focused on the development of the immobilized enzyme with the best catalytic properties. Lipase was adsorbed or covalently bonded on different supports, and the highest enzyme loading, of 1.4 mg per 1 mg of support, was achieved with amino functionalized carbon nanotubes. It was found that immobilized preparations with the highest percentage of retained activity were obtained when lipase was adsorbed on unmodified carbon nanotubes in a high ionic strength buffer (up to 85 %). Immobilized enzymes with the highest total activity were obtained by binding lipase on oxidized carbon nanotubes under condtions that promote covalent binding. Immobilized preparations with the best properties showed high catalytic activity in the synthesis of 4,6-dimethyl-3-cyano-2-pyridone

U okviru ove teze, pomoću lipaze iz Candida rugosa, sintetisani su 4,6-disupstituisani-3-cijano-2-piridoni. Najpre je, kao najprostiji molekul, sintetisan 4,6-dimetil-3-cijano-2-piridon, a zatim i 4-etoksimetil-6-metil-3-cijano-2-piridon, koji predstavlja prekursor vitamina B6. U cilju određivanja optimalnih uslova za njihovu sintezu metodom odzivnih površina (RSM) ispitan je uticaj tri reakciona faktora i to: temperature, molskog odnosa supstrata i koncentracije enzima. Nakon toga je, na utvrđenim optimalnim uslovima, ispitivana enzimska kinetika i na osnovu dobijenih rezultata, modelovanjem regresionim modelom drugog reda, utvrđeno da se ove reakcije mogu opisati ping–pong bi–ter modelom sa inhibicijom cijanoacetamidom. U drugom delu disertacije ispitana je imobilizacija lipaze adsorpcijom ili kovalentnim vezivanjem na različite nosače. Imobilizacijom na višeslojne ugljenične nanocevi postignute su izuzetno velike količine vezanog enzima od čak 1,4 mg po 1 mg nosača. Ustanovljeno je da se adsorpcijom na nemodifikovane ugljenične nanocevi dobijaju imobilizati kod kojih je lipaza zadržala najveći procenat aktivnosti, i pri imobilizaciji u puferu veće jonske jačine iznosi i do 85 %. Imobilizati najveće ukupne aktivnosti dobijaju se vezivanjem na oksidovane nanocevi u uslovima koji promovišu kovalentno vezivanje. Ispitivanjem imobilizata najboljih svojstava u reakciji sinteze 4,6-dimetil-3-cijano-2-piridona ustanovljeno je da se mogu postići visoki prinosi, a najveći s postižu sa lipazom imobilisanom na oksidovane nanocevi