Theoretical and experimental study of a praziquantel and beta-cyclodextrin inclusion complex using molecular mechanic calculations and H1-nuclear magnetic resonance.

Praziquantel (PZQ) is a broadly effective anthelminthic drug available for human and veterinary use, being the drug of choice for the treatment of all forms of schistosomiasis. Nevertheless, large doses are required in order to achieve adequate concentrations at the target site due to the poor solubility of PZQ and its significant first pass metabolism. To improve it, avoiding efficiency loss, we have designed a controlled-release system, in which PZQ was encapsulated in beta-cyclodextrin (beta-CD). The inclusion complexes between PZQ/beta-CD were studied at two different stoichiometries 1:1 and 1:2, through experimental and theoretical analysis. Molecular modeling calculations were used to foresee the better stoichiometry of the complex formed as well as the possible orientations of PZQ inside the beta-CD cavity. The complexes prepared were analyzed through H1 two-dimensional nuclear magnetic resonance (H1 2D-NMR) experiments, which provide (evidences) for the 1:1 complexation of PZQ/beta-CD. H1 2D-NMR also revealed details of PZQ/beta-CD molecular interaction, in which the isoquinoline ring of praziquantel is located inside the beta-CD cavity. Finally, phase-solubility diagrams revealed a five-fold increase in praziquantel water solubility upon addition of increasing beta-CD concentrations up to 16 mM, corresponding to the solubility of beta-CD itself. The solubilization profile is consistent with 1:1 stoichiometry of the PZQ/beta-CD complex while the solubilization effect will certainly increase the pharmacological activity of praziquantel.

Comparison between neural networks (NN) and principal component analysis (PCA): structure activity relationships of 1,4-dihydropyridine calcium channel antagonists (nifedipine analogues).

The applicability of the neural network computer package PSDD (Perceptron Simulator for Drug Design/Perceptron-type Neural Network Simulator) in structure-activity relationship (SAR) studies was investigated. A group of 1,4-dihydropyridine derivatives was used in order to compare the PSDD results with those obtained previously with PCA. Calculated atomic and molecular descriptors using the semiempirical AM1 method were mainly used. It was shown that the predictive capability demonstrated by PSDD in SAR analysis were almost equivalent to that of PCA.

Structure-activity relationships (SAR) of contraceptive progestogens studied with four different methods using calculated physicochemical parameters.

Structure-activity relationships (SAR) of the contraceptive progestogens for (I) oral contraceptive activity (OCA), (II) androgenic effect, and (III) binding affinity for sex hormone binding globulin (SHBG) were studied using four different methods: principal component analysis (PCA), hierarchical cluster analysis (HCA), neural networks (NN), and electronic indices method (EIM) employing descriptors calculated by the semi-empirical Austin Model I (AM1) method. An additional set of molecules was used to check the reliability of the results obtained for OCA by PCA. Using PCA, three different sets of descriptors were found to correlate with the three different biological activities, I-III, indicating that the interaction between the receptor and the progestogen must depend on the type of biological activity. The descriptors selected by PCA were also employed for SAR analysis of the contraceptive progestogens using two other methods, HCA and NN. Both HCA and NN correctly classified high activity molecules as different from low activity ones. Thus, those descriptors selected by PCA work well in the other two methods of classification. Using the sign of p, a difference of electron densities of selected molecular orbitals in a specified region in a molecule, it was possible to discriminate high activity molecules from low activity molecules in the three different types of activities studied, I-III, with one exception.

Ionization potentials and electron affinities of nicotinic acid and nicotinamide calculated with HAM/3

Ionization potentials and electron affinities of nicotinic acid and nicotinamide were calculated by HAM/3. Observed photoelectron spectra of the molecules were analyzed with the aid of the calculated ionization potentials. Chemical reactivity of the molecules was discussed.