Letters in Organic Chemistry - Volume 18, Issue 6, 2021

The composition of essential oil (EO) of E. globulus is so different all over the world. The main component of essential oil is 1,8-cineole (Compound 64), macrocarpal C (Compound 22), terpenes (Compound 23-92), oleanolic acid (Compound 21), and tannins (Compound 93-99). We searched in vitro and in vivo articles and reviewed botanical aspects, therapeutic activity, chemical composition and mechanism of action of E. globulus. Essential oils and extracts of leaves, stump, wood, root and fruits of E. globulus represented many various medicinal effects including antibacterial, antifungal, antidiabetic, anticancer, anthelmintic, antiviral, antioxidant, anti-inflammatory, protection against UV-B, wound healing effect and stimulating the immune response. Also, the leaf extract of eucalyptus is used as a food additive in the industry. Eucalyptus has so many different therapeutic effects and some of these effects were confirmed by pharmacological and clinical studies. More clinical studies are recommended to confirm the useful pharmacological activity of E. globulus.

In the present study, different derivatives of thymol (1) viz. hydrazide (2), oxadiazole thiol (3), triazole thione (4), hydrazones (5-7), and β-lactams (8-10) were synthesized. All synthesized compounds were identified and characterized using elemental analysis, UV-Visible, ¹H NMR, ¹³C NMR, and IR spectroscopic techniques. Synthesized thymol derivatives were evaluated for antifungal potential against phytopathogenic fungi Fusarium moniliforme, Rhizoctonia solani, and Dreschlera maydis of maize in comparison to recommended standards in terms of percent inhibition and ED50 values. Thymol was more effective as compared to its derivatives against all three tested fungi. Hydrazones (5-7) and β-lactams (8-10), having m-NO2 substituted phenyl ring (6, 9), were less effective as compared to o-NO2 and p-NO2 analogs against F. moniliforme and R. solani, however, the reverse trend was observed against D. maydis. Thymol and its derivatives were also tested for insecticidal activity against stored grain (chickpea) insect Callosobruchus chinensis and various parameters viz. egg laying, adult emergence, and grain damage were recorded and compared. Compounds having oxadiazole thiol (3) and triazole thione (4) moiety showed promising effects against insect C. chinensis.

In this research, the four pyrimidine derivatives have been studied by using density functional theory (DFT/B3LYP/6-31G*) in solvent water for the first time. After quantum-chemical calculations, the title compounds have been synthesized. The electronic spectra of the new derivatives in solvent water were performed by the time-dependent DFT (TD-DFT) method. The equilibrium geometry, the HOMO and LUMO orbitals, MEP, excitation energies, natural charges, oscillator strengths for the molecules have also been calculated. NBO analysis has been calculated in order to elucidate the intramolecular, rehybridization and delocalization of electron density. These molecules have high antioxidant potential due to the planarity and formation of intramolecular hydrogen bonds. Antioxidant properties of the title compounds have been investigated and discussed.

The aim of this manuscript is to give an overview of new findings in the field of thermal degradation and antimicrobial studies for copper (II) sesame and copper (II) groundnut complexes with substituted benzothiazole ligand. Solid state kinetics and thermal degradation have gained the attention of the scientific community not only due to their numerous applications in environment, energy, wastewater treatment, pollution control and green chemistry but also due to their wide range of biological activities. This work aims to explore the study of chemical steps of the investigated degradation and the evaluation of the kinetic and thermodynamic parameters of the newly synthesized biologically active complexes (CSBe and CGBe) derived from two different edible oils, i.e., sesame and groundnut and ligand containing nitrogen, oxygen and sulphur atoms, i.e., 2-amino-6-ethoxy benzothiazole. The studies include Coats-Redfern equation (CRE), Horowitz-Metzger equation (HME), Broido equation (BE) and Piloyan-Novikova equation (PNE) for the analysis of the degradation and energetics for each step using kinetic data. The observation suggests that CGBe takes a longer time and higher temperature to decompose completely than CSBe. Antimicrobial activities against Staphylococcus aureus of these compounds have also been analysed which may provide an important account of information about their industrial utilization. The TGA study reveals that CSBe and CGBe complexes undergo stepwise thermal degradation of the ligand-soap bond of complex and saturated and unsaturated fatty acid components of edible oils, i.e., sesame and groundnut. The order of antimicrobial activities of the two complexes studied is – CSBe > CGBe. These results reveal that the nature of different nitrogen, oxygen and sulphur containing ligands coordinated with copper ion plays a significant role in the inhibition activity.

A novel series of benzimidazole-5(6)-carboxamide 3a-g, carbohydrazide 5a-e and 1,3,4- oxadiazole 6a-g derivatives bearing adamantane moiety were synthesized. The synthesis of benzimidazole heterocycle was performed by direct condensation/cyclization reaction of 1- adamantanecarboxylic acid with methyl 3,4-diaminobenzoate in Trimethylsilyl Polyphosphate (PPSE). The obtained Methyl 2-(1-adamantyl)-1H-benzimidazole-5(6)-carboxylate was converted to desired carboxamide and carbohydrazide derivatives in two different ways. In the first case, the synthesized ester after hydrolysis was converted to an acid chloride and subsequently coupled with different aromatic and heterocycle amines to give carboxamide derivatives. In the second case, treatment with hydrazine hydrate gave corresponding 2-(1-adamantyl)-1H-benzimidazole-5(6)-carbohydrazide which was coupled with some acyl chlorides to give appropriate carbohydrazide derivatives and with some aromatic acids to give 1,3,4-oxadiazole derivatives.