V. Kancheva - Academia.edu (original) (raw)

Papers by V. Kancheva

Russian Chemical Bulletin, 1999

ABSTRACT The kinetics of inhibited oxidation of lipids was studied by computer simulation to eval... more ABSTRACT The kinetics of inhibited oxidation of lipids was studied by computer simulation to evaluate the contributions of the recombination/disproportionation of inhibitor radicals and chain transfer to retardation effects. The influence of inhibitor regeneration on the induction periods and inhibited oxidation rate was demonstrated.

Journal of Peptide Science, 2006

Fifteen amides of cinnamic, ferulic and sinapic acids with natural and unnatural C-protected amin... more Fifteen amides of cinnamic, ferulic and sinapic acids with natural and unnatural C-protected amino acids have been synthesized. The amides (E)-N -(feruloyl)-L-tyrosine methyl ester (10), (E)-N -(feruloyl)-L-phenylalanine t-butyl ester , (E)-N -(sinapoyl)-L-tyrosine methyl ester and (E)-N -(sinapoyl)-L-phenylalanine t-butyl ester (15) with a free carboxyl group of amino acids have been found in nature. The rest of the compounds are unknown. The hydroxycinnamoyl amino acid conjugates have been studied for their antioxidant activity (AOA) in bulk phase lipid autoxidation. The highest AOA has been found for the compounds 11 and 15, which contain the same phenylalanine moiety.

Current Medicinal Chemistry, 2013

The paradox of aerobic life is that higher eukaryotic organisms cannot exist without oxygen, yet ... more The paradox of aerobic life is that higher eukaryotic organisms cannot exist without oxygen, yet oxygen is inherently dangerous to their existence. Autoxidation of organic substances frequently occurs via free radical mechanism which generates different active radicals and peroxides OH(•), O2 (•-), LO2 (•), HOOH, LOOH, so called reactive oxygen species (ROS), which appear to be responsible for oxygen toxicity. To survive in such an unfriendly oxygen environment, living organisms generate - or obtain from food - a variety of water- and lipid-soluble antioxidant compounds. Biologically active compounds with antioxidant potential, i.e. bio-antioxidants (natural and their synthetic analogues) have a wide range of applications. They are important drugs, antibiotics, agrochemical substitutes, and food preservatives. Many of the drugs today are synthetic modifications of naturally obtained substances. This review presents information about the chemical base of antioxidant activities and beneficial effects on human health of known and new bio-antioxidants. There is abundant literature on the phenolic antioxidants and tocopherols in particular. In this review the following bio-antioxidants are considered: A) Carotenoids, B) Cathecholamines, C) Phospholipids, D) Chalcones, E) Coumarins, F) Phenolic acids, G) Flavonoids, H) Lignans, and I) Tannins.

Biochimie, 2012

Antioxidants could be promising agents for management of oxidative stress-related diseases. New b... more Antioxidants could be promising agents for management of oxidative stress-related diseases. New biologically active compounds, belonging to a rare class of natural lignans with antiangiogenic, antitumoral and DNA intercalating properties, have been recently synthesized. These compounds are benzo[kl]xanthene lignans (1,2) and dihydrobenzofuran neolignans (3,4). The radical scavenging and chain-breaking antioxidant activities of compounds 1-4 were studied by applying different methods: radical scavenging activity by DPPH rapid test, chain-breaking antioxidant activity and quantum chemical calculations. All studied compounds were found to be active as DPPH scavengers but reaction time with DPPH and compounds' concentrations influenced deeply the evaluation. The highest values of radical scavenging activity (%RSAmax) and largest rate constants for reaction with DPPH were obtained for compounds 2 and 3. Comparison of %RSAmax with that of standard antioxidants DL-α-tocopherol (TOH), caffeic acid (CA) and butylated hydroxyl toluene (BHT) give the following new order of %RSA max: TOH (61.1%) > CA (58.6%) > 3 (36.3%) > 2 (28.1%) > 4 (6.7%) > 1 (3.6%) = BHT (3.6%). Chain-breaking antioxidant activities of individual compounds (0.1-1.0 mM) and of their equimolar binary mixtures (0.1 mM) with TOH were determined from the kinetic curves of lipid autoxidation at 80 °C. On the basis of a comparable kinetic analysis with standard antioxidants a new order of the antioxidant efficiency (i.e., protection factor, PF) of compounds 1-4 were obtained: 2 (7.2) ≥ TOH (7.0) ≥ CA (6.7) > 1 (3.1) > 3 (2.2) > ferulic acid FA (1.5) > 4 (0.6); and of the antioxidant reactivity (i.e. inhibition degree, ID): 2 (44.0) > TOH (18.7) > CA (9.3) > 1 (8.4) > 3 (2.8) > FA (1.0) > 4 (0.9). The important role of the catecholic structure in these compounds, which is responsible for the high chain-breaking antioxidant activity, is discussed and a reaction mechanism is proposed. Higher oxidation stability of the lipid substrate was found in the presence of equimolar binary mixtures 2 + TOH, 3 + TOH and 4 + TOH. However, an actual synergism was only obtained for the binary mixtures with compounds 3 and 4. The geometries of compounds and all possible phenoxyl radicals were optimized using density functional theory. For description of the scavenging activity bond dissociation enthalpies (BDE), HOMO energies and spin densities were employed. The best correlation between theoretical and experimental data was obtained for compound 2, with the highest activity, and for compound 4 with the lowest activity. The BDE is the most important theoretical descriptor, which correlates with the experimentally obtained antioxidant activity of the studied benzo[kl]xanthene lignans and dihydrobenzofuran neolignans.

Kinetics and Catalysis, 2010

Six antioxidants from the class of chalcones (ArOH), compounds from which flavonoids are obtained... more Six antioxidants from the class of chalcones (ArOH), compounds from which flavonoids are obtained in nature, were studied. The antiradical activity of chalcones and a number of related compounds was determined by a chemiluminescence method using the scavenging of peroxide radicals ROO • + ArOH → ROOH + OAr • (with the rate constant k 7 ) in a model reaction of diphenylmethane (RH) oxidation. The structures and energies of the reagents and intermediates were determined by semiempirical quantum chem ical (PM3, PM6) calculations. 3,4 Dihydroxychalcone and caffeic acid, which have a catechol structure, that is, two neighboring OH groups in phenyl ring B, exhibited high antioxidant activity (k 7 ≈ 10 7 l mol -1 s -1 ); this is consistent with the lowest bond strengths D(ArO-H) of 79.2 and 76.6 kcal/mol, respectively. The abstrac tion of a hydrogen atom by the ROO • radical is the main reaction path of these compounds; however, the low stoichiometric coefficients of inhibition (f = 0.3-0.7) suggest a contribution of secondary and/or side reac tions of ArOH and OAr • . In the other chalcones, the ArO-H bond is stronger (D(ArO-H) = 83-88 kcal/mol) and the antioxidant activity is lower (k 7 = 10 4 -10 5 l mol -1 s -1 ).

Russian Chemical Bulletin, 1999

ABSTRACT The kinetics of inhibited oxidation of lipids was studied by computer simulation to eval... more ABSTRACT The kinetics of inhibited oxidation of lipids was studied by computer simulation to evaluate the contributions of the recombination/disproportionation of inhibitor radicals and chain transfer to retardation effects. The influence of inhibitor regeneration on the induction periods and inhibited oxidation rate was demonstrated.

Journal of Peptide Science, 2006

Fifteen amides of cinnamic, ferulic and sinapic acids with natural and unnatural C-protected amin... more Fifteen amides of cinnamic, ferulic and sinapic acids with natural and unnatural C-protected amino acids have been synthesized. The amides (E)-N -(feruloyl)-L-tyrosine methyl ester (10), (E)-N -(feruloyl)-L-phenylalanine t-butyl ester , (E)-N -(sinapoyl)-L-tyrosine methyl ester and (E)-N -(sinapoyl)-L-phenylalanine t-butyl ester (15) with a free carboxyl group of amino acids have been found in nature. The rest of the compounds are unknown. The hydroxycinnamoyl amino acid conjugates have been studied for their antioxidant activity (AOA) in bulk phase lipid autoxidation. The highest AOA has been found for the compounds 11 and 15, which contain the same phenylalanine moiety.

Current Medicinal Chemistry, 2013

The paradox of aerobic life is that higher eukaryotic organisms cannot exist without oxygen, yet ... more The paradox of aerobic life is that higher eukaryotic organisms cannot exist without oxygen, yet oxygen is inherently dangerous to their existence. Autoxidation of organic substances frequently occurs via free radical mechanism which generates different active radicals and peroxides OH(•), O2 (•-), LO2 (•), HOOH, LOOH, so called reactive oxygen species (ROS), which appear to be responsible for oxygen toxicity. To survive in such an unfriendly oxygen environment, living organisms generate - or obtain from food - a variety of water- and lipid-soluble antioxidant compounds. Biologically active compounds with antioxidant potential, i.e. bio-antioxidants (natural and their synthetic analogues) have a wide range of applications. They are important drugs, antibiotics, agrochemical substitutes, and food preservatives. Many of the drugs today are synthetic modifications of naturally obtained substances. This review presents information about the chemical base of antioxidant activities and beneficial effects on human health of known and new bio-antioxidants. There is abundant literature on the phenolic antioxidants and tocopherols in particular. In this review the following bio-antioxidants are considered: A) Carotenoids, B) Cathecholamines, C) Phospholipids, D) Chalcones, E) Coumarins, F) Phenolic acids, G) Flavonoids, H) Lignans, and I) Tannins.

Biochimie, 2012

Antioxidants could be promising agents for management of oxidative stress-related diseases. New b... more Antioxidants could be promising agents for management of oxidative stress-related diseases. New biologically active compounds, belonging to a rare class of natural lignans with antiangiogenic, antitumoral and DNA intercalating properties, have been recently synthesized. These compounds are benzo[kl]xanthene lignans (1,2) and dihydrobenzofuran neolignans (3,4). The radical scavenging and chain-breaking antioxidant activities of compounds 1-4 were studied by applying different methods: radical scavenging activity by DPPH rapid test, chain-breaking antioxidant activity and quantum chemical calculations. All studied compounds were found to be active as DPPH scavengers but reaction time with DPPH and compounds' concentrations influenced deeply the evaluation. The highest values of radical scavenging activity (%RSAmax) and largest rate constants for reaction with DPPH were obtained for compounds 2 and 3. Comparison of %RSAmax with that of standard antioxidants DL-α-tocopherol (TOH), caffeic acid (CA) and butylated hydroxyl toluene (BHT) give the following new order of %RSA max: TOH (61.1%) > CA (58.6%) > 3 (36.3%) > 2 (28.1%) > 4 (6.7%) > 1 (3.6%) = BHT (3.6%). Chain-breaking antioxidant activities of individual compounds (0.1-1.0 mM) and of their equimolar binary mixtures (0.1 mM) with TOH were determined from the kinetic curves of lipid autoxidation at 80 °C. On the basis of a comparable kinetic analysis with standard antioxidants a new order of the antioxidant efficiency (i.e., protection factor, PF) of compounds 1-4 were obtained: 2 (7.2) ≥ TOH (7.0) ≥ CA (6.7) > 1 (3.1) > 3 (2.2) > ferulic acid FA (1.5) > 4 (0.6); and of the antioxidant reactivity (i.e. inhibition degree, ID): 2 (44.0) > TOH (18.7) > CA (9.3) > 1 (8.4) > 3 (2.8) > FA (1.0) > 4 (0.9). The important role of the catecholic structure in these compounds, which is responsible for the high chain-breaking antioxidant activity, is discussed and a reaction mechanism is proposed. Higher oxidation stability of the lipid substrate was found in the presence of equimolar binary mixtures 2 + TOH, 3 + TOH and 4 + TOH. However, an actual synergism was only obtained for the binary mixtures with compounds 3 and 4. The geometries of compounds and all possible phenoxyl radicals were optimized using density functional theory. For description of the scavenging activity bond dissociation enthalpies (BDE), HOMO energies and spin densities were employed. The best correlation between theoretical and experimental data was obtained for compound 2, with the highest activity, and for compound 4 with the lowest activity. The BDE is the most important theoretical descriptor, which correlates with the experimentally obtained antioxidant activity of the studied benzo[kl]xanthene lignans and dihydrobenzofuran neolignans.

Kinetics and Catalysis, 2010

Six antioxidants from the class of chalcones (ArOH), compounds from which flavonoids are obtained... more Six antioxidants from the class of chalcones (ArOH), compounds from which flavonoids are obtained in nature, were studied. The antiradical activity of chalcones and a number of related compounds was determined by a chemiluminescence method using the scavenging of peroxide radicals ROO • + ArOH → ROOH + OAr • (with the rate constant k 7 ) in a model reaction of diphenylmethane (RH) oxidation. The structures and energies of the reagents and intermediates were determined by semiempirical quantum chem ical (PM3, PM6) calculations. 3,4 Dihydroxychalcone and caffeic acid, which have a catechol structure, that is, two neighboring OH groups in phenyl ring B, exhibited high antioxidant activity (k 7 ≈ 10 7 l mol -1 s -1 ); this is consistent with the lowest bond strengths D(ArO-H) of 79.2 and 76.6 kcal/mol, respectively. The abstrac tion of a hydrogen atom by the ROO • radical is the main reaction path of these compounds; however, the low stoichiometric coefficients of inhibition (f = 0.3-0.7) suggest a contribution of secondary and/or side reac tions of ArOH and OAr • . In the other chalcones, the ArO-H bond is stronger (D(ArO-H) = 83-88 kcal/mol) and the antioxidant activity is lower (k 7 = 10 4 -10 5 l mol -1 s -1 ).