Synthesis, Characterization, Stereogenic and Antibacterial Properties of New Macrocyclic Boronates with 4-SH Phenyl, Boraxan and Boroxin Groups

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Thesis Type: Postgraduate

Institution Of The Thesis: Ankara University, Fen Fakültesi, Kimya Bölümü, Turkey

Approval Date: 2023

Thesis Language: Turkish

Student: Blessing Kusena Zvikomborero

Supervisor: Selen Bilge Koçak

Abstract:

Within the context of this thesis, 4 salenH₂ type ligand (1a-1d), and 8 original macrocyclic boronates (boron complexes) (2a-2d and 3a-3d) were synthesized. Firstly, salenH₂ ligands (1a-1c) were prepared from the reaction of salicylaldehyde with 1,2-diaminoethane, 1,3-diaminopropane and 1,4-diaminobutane in MeOH, respectively. salenH₂ ligand (1d) was obtained from the reaction of salicylaldehyde with cystamine dihydrochloride in EtOH. 4-Mercaptophenylboronic acid and salenH₂ ligands (1a-1d) were brought to condensation reactions in a 2:1 stoichiometry in toluene to obtain macrocyclic boronates with a boraxane group (RB-O-BR) (dinuclear boron complexes) (2a-2d). Macrocyclic boronates with a boroxine group (B-O-B)-(O2BPh) were synthesized through the combination of boric acid/4-mercaptophenylboronic acid and salenH₂ ligands (1a-1d) in CH₃CN. Dinuclear macrocyclic boronates (2a-2d) have two four-coordinated boron atoms, while trinuclear macrocyclic boronates (3a-3d) contain two four-coordinated and one three-coordinated boron atoms. All of the boron complexes synthesized in this thesis contain a central 7- (2a and 3a), 8- (2b and 3b), 9- (2c and 3c) and 11- (2d and 3d) membered heterocycle with an oxygen atom bridging two boron atoms. Due to its four-coordination, the two boron atoms are stereogenic centers that lead to the formation of diastereoisomers. The structures of macrocyclic boronates (2 and 3) were characterized by MS, FTIR, one-dimensional (1D) and two-dimensional (2D) NMR techniques. CD and UV spectra of macrocyclic boronates (2 and 3) were recorded and their stereogenic properties were examined by evaluating the NMR and CD spectra together. Accordingly, it was determined that dinuclear macrocyclic boronates (2a and 2d) contained a mixture of diastereoisomers, while the other boronates contained only one of the diastereoisomers. Dinuclear (2) and trinuclear (3) macrocyclic boronates were subjected to anti-bacterial activity against two bacteria [Escherichia coli (ATCC 35218) and Staphylococcus aureus (MRSA)]. It was observed that dinuclear macrocyclic boronates (2a and 2c) were found to have anti-bacterial effect on Staphylococcus aureus.