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Identifier 000456425
Title α) Μελέτη για την ανάπτυξη νέας φωτο-βιοκαταλυτικής μεθόδου για τη σύνθεση οπτικά ενεργών αλκοολών και υποκατεστημένων κετονών β) Χημειοενζυμική σύνθεση οπτικά καθαρών α,α-διχλωρο-β-υδρόξυ εστέρων
Alternative Title a) Study for the development of a new photo-biocatalytic method for the synthesis of optically active alcohols and substituted ketones b) Chemoenzymatic synthesis of optically pure α,α-dichloro-β-hydroxy esters
Author Γιαννόπουλος, Βασίλειος Π
Thesis advisor Σμόνου, Ιουλία
Reviewer Στρατάκης, Εμμανουήλ
Κατερινόπουλος, Χαράλαμπος
Βασιλικογιαννάκης, Γεώργιος
Νεοχωρίτης, Κωνσταντίνος
Σπύρος, Απόστολος
Παυλίδης, Ιωάννης
Abstract The subject of this thesis falls in the field of biocatalysis and photocatalysis, and mainly includes efforts to develop and study a new synthetic methodology that combines these two fields. The combination of chemocatalysis and biocatalysis in multistep synthetic processes is a very dynamic and rapidly developing research field for the synthesis of high added value chemical products such as optically pure alcohols and substituted ketones. More specifically, the first section presents the study on the synthesis of optically pure alcohols and substituted ketones in a single step (one-pot) through a combination of the non-metallic carbon nitride photocatalyst enriched on its surface with carbon nanoparticles (CD-C3N4) and different bioreductive enzymes. The overall strategy is based on a three-step sequence at ambient temperature and pressure. The original idea is that starting from an alkene by photooxygenation with excited oxygen οξυγόνο (1O2) an allylic hydroperoxide intermediate is formed, which is then reduced to racemic allyl alcohol. The reaction involves the use of either a classical photosensitizer such as tetraphenylporphyrin TPP or CD-C3N4 as a photosensitizer (prepared in our laboratory). Upon further photooxidation under visible light using CD-C3N4 or an aqueous-compatible photocatalyst such as sodium anthraquinone (SAS), the material is converted to the corresponding α,β-unsaturated ketone. The final step is the asymmetric biocatalytic reduction of the ketone’s double bond leading to the stereoselective formation of the optically pure ketone or a stereoselective carbonyl bioreduction to the optically pure allylic alcohol. This section includes the synthesis of different α,β-unsaturated ketone substrates, the study of their biocatalytic reduction with enzymes of different specificity including ketoreductases and ene reductases (EReds), as well as the combination experiments in a sequence of photocatalytic (with different photocatalysts) and biocatalytic reactions. Enzymatic reduction of the double bonds of the racemic enones was completely successful and different EReds were identified with excellent activity (>99% conv.) yielding the corresponding optically active α-substituted ketones with excellent enantioselectivity (99% ee.). Although the results of these enzymatic reductions using ene reductases were very satisfactory, the extensive investigation of the photooxidation of racemic allylic alcohol precursors with the above-mentioned photocatalysts did not have the corresponding expected results even after numerous attempts and tests and for this reason it was not finally feasible to develop the originally proposed one-pot process. The second section presents the photooxidations of aryl alcohols using CD-C3N4 as well as mechanistic studies for the specific reactions. CD-C3N4 was shown to act as a fairly efficient non-metallic photocatalyst for the photooxidation of different aryl alcohols in the presence of molecular oxygen. The experiments carried out highlight the photoinduced electron transfer in the valence band and conduction band of the material as well as a hydrogen abstraction in the product determining step of the reaction. The kinetic study of the photooxidations of different p-substituted aryl alcohols was carried out as well as a study of the kinetic isotope effects, which clearly demonstrated the hydrogen abstraction in the reaction-determining step. In the third section, a novel, and highly efficient one-step method for the dichlorination of β-keto esters and 1,3-diketones via the Oxone/AlCl3 system was developed. Inexpensive, relatively non-toxic and safe reagents in aqueous medium were used in this process. The exclusive formation of dichlorinated compounds in high yields and the short reaction times make this method very attractive. The possible mechanistic aspects of this reaction were also reported. This specific methodology constitutes a new powerful synthetic tool for the dichlorination of β-dicarbonyl substrates. In the last section, a fairly efficient chemoenzymatic methodology was developed for the synthesis of seven optically pure α,α-dichloro-β-hydroxy esters in two steps, starting from β-keto esters, with the key step being the enantioselective bioreduction of α,α-dichloro-β -keto esters using NADPH-dependent ketoreductases. This novel biotransformation affords, in a single synthetic step, seven different (S)-α,α-dichloro-β-hydroxy esters with excellent conversion rates, quite high yields and most importantly with excellent enantioselectivities (>99% ee).
Language Greek
Subject Aryl alcohols
Biocatalysis
Biocatalytic reduction
CD-C3N4
Dichlorination
Ene reductases
Ketoreductases
Mechanistic studies
NADPH
One-pot
Oxone/AlCl3
Photocatalysis
Αρυλο αλκοόλες
Βιοκατάλυση
Βιοκαταλυτική αναγωγή
Διχλωρίωση
Κετορεδουκτάσες
Μηχανιστικές μελέτες
Ρεδουκτάσες ενίου
Φωτοκατάλυση
α,α-dichloro-β-ketoesters
α,α-διχλωρο-β-κετοεστέρες
Issue date 2023-06-14
Collection   School/Department--School of Sciences and Engineering--Department of Chemistry--Doctoral theses
  Type of Work--Doctoral theses
Permanent Link https://elocus.lib.uoc.gr//dlib/3/1/9/metadata-dlib-1687244171-639233-15709.tkl Bookmark and Share
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