Ten 9-aryl substituted hydroxylated xanthen-3-ones, including three new compounds (III) are synthesized using a reliable one-pot synthesis.

Oxidative stress is directly related to several diseases and symptoms, where antioxidant compounds, such as xanthenes, may become important in prevention and/or treatmant. Ten biologically active 9-aryl substituted 2, 6, 7-trihydroxyxanthen-3-one derivatives were synthesized using reliable one-pot synthesis and their structures were confirmed by IR, 1H and 13C NMR spectroscopy and mass spectrometry. Some of the synthesized compounds were scanned for their antioxidant potency using electrochemical method cyclic voltammetry of immobilized microparticles. Substitution of hydrogen at the phenyl ring of 2, 6, 7-trihydroxy-9-phenylxanthen-3-one with an electron-donating group affected the reducing power of the compounds by lowering the biological oxidation potential. These results signify the importance of xanthen-3-one derivatives as antioxidant agents and their further biological evaluation.

For some synthesized coumarin derivatives, 1H and 13C NMR isotropic chemical shifts and some other molecular properties were calculated using density functional theory. The calculations yield reliable results, that are in good correlation with experimental data. This is a good basis for the collaboration between experimentalists and quantum chemists.

In the present investigation, a series of coumarin-based compounds containing a chalcone moiety were studied for their in vitro and in silico pro- perties. The DFT global chemical reactivity descriptors (chemical hardness, total energy, electronic chemical potential and electrophilicity) were calculated for four synthesized compounds and used to predict their relative stability and reactivity. The antibacterial activities of all compounds were screened against Bacillus subtilis (ATCC 6633) and Bacillus cereus (ATCC 11778). The quantum-chemical calculations indicated that the antibacterial activity correlates well with chemical reactivity descriptors of the molecules.

Series of synthesized xanthen-3-one derivatives were analyzed for thermal characteristics by differential scanning calorimetry (DSC), as well as for crystallinity using X-ray powder diffraction. Xanthen-3-one derivatives are prepared according to the well known procedure which includes two-fold Friedel-Crafts alkylation. The aim of this research was to determine purity and crystallinity of synthesized xanthen-3-one derivatives. Thermograms of synthesized compounds showed that compounds have purity above 98%, while crystallographic analysis of powder showed that the compounds have a 10-30% crystalline form.

Purpose – The purpose of this paper is to test absorption characteristics of some newly synthesised 4‐hidroxycoumarins, containing phenyl‐prop‐2‐enoyl group at the 3‐position. Change in spectral characteristics in solvents of different polarity (chloroform and acetonitrile) was followed in regard to the influence of the substitution at the phenyl ring and influence of concentration H+ ions. Effectiveness of tested substances was compared with well‐known UV absorbers such as benzophenone‐3 and butyl methoxydibenzoylmethane (BMDM).Design/methodology/approach – All the tested substances were dissolved in chloroform and acetonitrile, with 10‐3 mmol concentration range. The pH was adjusted using 0.1 mol/l HCl, glacial acetic acid, 0.1 mol/l NaOH (aqueous solution) and 0.1 mol/l NaOH (methanolic solution). Spectrophotometric measurement was recorded in the range of 200‐800 nm, using 1‐cm quartz cells.Findings – The tested 4‐hydroxycoumarin derivatives showed good UV absorption properties in the range 280‐380 nm...

Background and purpose: Having in mind the results of our previous work, which suggested antimicrobial activity of some 3-cynnamoyl-4-hydroxycoumarins, we carried out the synthesis of several new derivatives of this group. The microbiological activity of compounds was tested by the diffusion and dilution methods on various species of bacteria. The aim of the study was to evaluate the influence of the substituents on antimicrobial activity. Material and methods: A series of new 3-cynnamoyl-4-hydroxycoumarins was prepared by the reaction of nucleophylic addition from 3-acetyl-4-hydroxycoumarin acting on appropriate aromatic aldehydes. The microbiological activity of compounds was tested by the diffusion and dilution methods on species of bacteria Pseudomonas aeruginosa, Echerichia coli, Salmonella typhimurium, Bordatella bronchiseptica, Bacillus subtilis, and Staphyloccocus aureus. Results: The synthesis of new 3-cynnamoyl-4-hydroxycoumarins was carried out. The elementary content of the synthesized compounds was confirmed by elementary analysis, and structures were confirmed with IR-spectrophotometry and 1 H-NMR spectrophotometry.

Coumarin-based compounds containing a chalcone moiety exhibit antimicrobial activity. These substances are potential drugs and it is important to determine their pKa values. However, they are almost insoluble in water. The dissociation constant was experimentally determined by potentiometric titration for 3-[3-(2-nitrophenyl)prop-2-enoyl]-2H-1-benzopyran-2-one because this compound shows good activity and solubility. A number of different computer programs for the calculation of the dissociation constant of chemical compounds have been developed. The pKa value of the target compound was calculated using three different computer programs, i.e., the ACD/pKa, CSpKaPredictor and ADME/ToxWEB programs, which are based on different theoretical approaches. The analysis demonstrated good agreement between the experimentally observed pKa value of 3-[3-(2-nitrophenyl)prop-2-enoyl]-2H-1-benzopyran- 2-one and the value calculated using the computer program CSpKa.