Drago Bešlo

SAR and QSAR of the Antioxidant Activity of Flavonoids

Flavonoids are a group of naturally occurring phytochemicals abundantly present in fruits, vegetables, and beverages such as wine and tea. In the past two decades, flavonoids have gained enormous interest because of their beneficial health effects such as anti-inflammatory, cardio-protective and anticancer activities. These findings have contributed to the dramatic increase in the consumption and use of dietary supplements containing high concentrations of plant flavonoids. The pharmacological effect of flavonoids is mainly due to their antioxidant activity and their inhibition of certain enzymes. In spite of abundant data, structural requirements and mechanisms underlying these effects have not been fully understood. This review presents the current knowledge about structure-activity relationships (SARs) and quantitative structure-activity relationships (QSARs) of the antioxidant activity of flavonoids. SAR and QSAR can provide useful tools for revealing the nature of flavonoid antioxidant action. They may also help in the design of new and efficient flavonoids, which could be used as potential therapeutic agents.

THE VERTEX-CONNECTIVITY INDEX REVISITED

We report a search for optimum molecular descriptors based on the connectivity index. A suggestion made by several authors that the exponent -0.5 used in the standard formula for computing the connectivity index may not be the optimum for modeling some molecular properties was reexamined. We considered several molecular properties and found that in most cases the optimum value of the exponent is indeed different from -0.5. We suggest that a modified version of the (valence) vertex-connectivity index should be routinely employed in the structure-property modeling instead of the standard version of the index.

THE USE OF THE ORDERED ORTHOGONALIZED MULTIVARIATE LINEAR REGRESSION IN A STRUCTURE-ACTIVITY STUDY OF COUMARIN AND FLAVONOID DERIVATIVES AS INHIBITORS OF ALDOSE REDUCTASE

The relationship between molecular descriptors and the inhibitory activity of aldose reductase (AR) for a series of coumarin and flavonoid derivatives has been investigated using a novel multivariate linear regression based on the ordered orthogonalized descriptor set. First, starting from the set of 31 descriptors we produced absolutely the best nonorthogonalized QSAR models with I descriptors (I = 1−7). These models are always better than the models that the most authors achieve by the use of the stepwise inclusion-exclusion procedure. In the next step we realized all possible orthogonalization orderings of a given set of N descriptors (there are N! of these). The key result is that some orthogonalization orderings lead to QSAR models with I ordered orthogonalized descriptors that have higher values of both the correlation coefficient R and cross-validated correlation coefficient Rcv than the corresponding models with the same number of nonorthogonalized descriptors. In order to achieve the highest poss...

Two-dimensional quantitative structure–activity relationship study on polyphenols as inhibitors of α-glucosidase

Polyphenols and their derivates have been reported to exhibit inhibitory activity against α-glucosidase. The relationship between structure and inhibitory activity of polyphenols was studied by means of multiple linear regression analysis with use of various descriptors derived from the 2D and 3D representations of molecules and physicochemical parameters calculated by DRAGON. The best model for the prediction of inhibitory activity was obtained using combination of topological charge index (JGI2), information index (CIC2) and number of exo-conjugated C atoms (nCconjR). This study revealed that an enhanced inhibitory activity of polyphenols is mainly conditioned by stabilization of molecule due to intramolecular electron and charge delocalization.

Prediction of pK Values, half-lives and electronic spectra of flavylium salts from molecular structure

Simple QSAR/QSPR models have been developed which enable the prediction of the pK values and half-lives of flavylium salts as a function of their molecular descriptors. On the basis of these results, as well as calculated UV−vis spectra, flavylium salt model structures are proposed, which are expected to be useful as potential food dyes.

The Sum-Connectivity Index - An Additive Variant of the Randić Connectivity Index

This review discusses structure-property modeling applications of a novel variant of the Randic connectivity index that is called the sum-connectivity index. We compare published one-descriptor quantitative structure-property relationship (QSPR) models obtained with the new sum-connectivity index and with the Randic connectivity index, called here the product-connectivity index. Additionally, the efficiency of both variants of connectivity indices in QSPR modeling is tested on five datasets of alkanes and two datasets of polycyclic hydrocarbons. Several physicochemical properties of alkanes (i.e. boiling and melting points, retention index, molar volume, molar refraction, heat of vaporization, standard Gibbs energy of formation, critical temperature, critical pressure, surface tension, density) and π- electronic energies of two sets of polycyclic hydrocarbons were correlated with the product- and sum-connectivity indices. A comparison of these QSPR models shows that both variants of connectivity indices are equivalent, and only slightly (but not significantly) better results are obtained with the sum-connectivity index. Inter-correlations between the product- and sum-connectivity indices are mostly linear with a slope very close to 1.0 for alkanes, and with a slope more different from 1.0 (0.88) for polycyclic compounds. The comparative analysis presented here supports the use of the sumconnectivity index in QSPR/QSAR studies together with the product-connectivity index. Further studies on larger and more heterogeneous datasets should test the sum-connectivity index in QSPR/QSAR models.

QSAR OF FLAVYLIUM SALTS AS INHIBITORS OF XANTHINE OXIDASE

A simple QSAR model of xanthine oxidase (XO) inhibitory flavylium salts, which enables prediction of the inhibitory potency of anthocyanidins as a function of their molecular properties, has been developed. The results obtained in the present work help to understand which of the several tautomeric anhydrobase species present in nearly neutral solution are mainly responsible for the inhibition of XO.

Validation of flavonoids as potential dipeptidyl peptidase III inhibitors: Experimental and computational approach.

Fifteen flavonoids were studied for their inhibitory activity against human dipeptidyl peptidase III (hDPP III) combining an in vitro assay with an in silico molecular modeling study. All analyzed flavonoids showed inhibitory effects against hDPP III with the IC50 values ranging from 22.0 to 437.2 μm. Our 3D QSAR studies indicate that the presence of hydrophilic regions at a flavonoid molecule increases its inhibitory activity, while the higher percentage of hydrophobic surfaces has negative impact on enzyme inhibition. Furthermore, molecular dynamics (MD) simulations of the complex of hDPP III with one of the most potent inhibitors, luteolin, were performed, and binding mode analysis revealed that the 3′ and 4′ hydroxyl group on B‐ring as well as 5 and 7 hydroxyl group on A‐ring helps luteolin to interact with the Asn391, Asn406, Tyr417, His450, Glu451, Val447, Glu512, Asn545, Gln566, and Arg572 residues. The MD results clearly provide valuable information explaining the importance of flavonoid hydroxyl groups in the mechanism for the binding pattern at the active site of hDPP III.