Quantitative structure-activity relationships for a series of selective estrogen receptor-beta modulators

The estrogen receptor-beta subtype (ERbeta) is an attractive drug target for the development of novel therapeutic agents for hormone replacement therapy. Hologram quantitative structure-activity relationships (HQSAR) were conducted on a series of 6-phenylnaphthalene and 2-phenylquinoline derivatives, employing values of ERbeta binding affinity. A training set of 65 compounds served to derive the models. The best statistical HQSAR model (q(2) = 0.73 and r(2) = 0.91) was generated using atoms, bonds, connections and donor and acceptor as fragment distinction parameters, and fragment size default (4-7) with hologram length of 199. The model was used to predict the binding affinity of an external test set of 16 compounds, and the predicted values were in good agreement with the experimental results. The final HQSAR model and the information obtained from 2D contribution maps should be useful for the design of novel ERbeta modulators having improved affinity.

Effects of organic solvents on the enzyme activity of Trypanosoma cruzi glyceraldehyde-3-phosphate dehydrogenase in calorimetric assays

In drug discovery programs, dimethyl sulfoxide (DMSO) is a standard solvent widely used in biochemical assays. Despite the extensive use and study of enzymes in the presence of organic solvents, for some enzymes the effect of organic solvent is unknown. Macromolecular targets may be affected by the presence of different solvents in such a way that conformational changes perturb their active site structure accompanied by dramatic variations in activity when performing biochemical screenings. To address this issue, in this work we studied the effects of two organic solvents, DMSO and methanol (MeOH), in the isothermal titration calorimetry (ITC) kinetic assays for the catalyzed reaction of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) from Trypanosoma cruzi. The solvent effects on T. cruzi GAPDH had not yet been studied. This enzyme was shown here to be affected by the organic solvents content up to 5.0% for MeOH and up to 7.5% for DMSO. The results show that when GAPDH is assayed in the presence of DMSO (5%, v/v) using the ITC experiment, the enzyme exhibits approximately twofold higher activity than that of GAPDH with no cosolvent added. When MeOH (5%, v/v) is the cosolvent, the GAPDH activity is sixfold higher. The favorable effects of the organic solvents on the Michaelis-Menten enzyme-substrate complex formation ensure the consistency of the biological assays, structural integrity of the protein, and reproducibility over the measurement time. The reaction was also kinetically monitored by standard spectrophotometric assays to establish a behavioral performance of T. cruzi GAPDH when used for screening of potential inhibitors.

The role of molecular interaction fields on enantioselective and nonselective separation of chiral sulfoxides

The separation of a series of 23 asymmetric sulfoxides, including the three proton pump inhibitors (PPI) omeprazole, lansoprazole and pantoprazole was investigated by HPLC, under reversed-phase elution with amylose tris(3,5-dimethylphenylcarbamate), amylose tris[(S)-1-phenylethylcarbamate] and amylose tris(3,5-dimethoxyphenylcarbamate) chiral stationary phases, CSP1-3, respectively. The whole set of sulfoxides showed better enantioselectivity and enantioresolution on CSP1. However, the three PPI were enantioseparated only when using CSP1 and CSP3. It was observed an improved enantioselectivity and enantioresolution on CSP3. The mechanisms of retention were evaluated by molecular interaction fields (MIF) generated via GRID force field, which yielded the geometric reasons leading to the scenario outlined. The enantioselective and nonselective interactions are discussed in terms of the reported selectivity. The steric structural outline of the CSP nonselective interaction sites is of major importance to deliver the sulfoxides to the chiral selective sites where the enantioselective interactions take place.

Specific inhibitors of Plasmodium falciparum thioredoxin reductase as potential antimalarial agents

Plasmodium falciparum thioredoxin reductase (PfTrxR: NADPH+Trx(S)2+H+<-->NADP++Trx(SH)2) is a high Mr flavin-dependent TrxR that reduces thioredoxin (Trx) via a CysXXXXCys pair located penultimately to the C-terminal Gly. In this respect, PfTrxR differs significantly from its human counterpart which bears a Cys-Sec redox pair at the same position. PfTrxR is essentially involved in antioxidant defense and redox regulation of the parasite and has been previously validated by knock-out studies as a potential drug target for malaria chemotherapy. Moreover, human TrxR is present in most cancer cells at levels tenfold higher than in normal cells. Here we report the discovery of a series of potent inhibitors of PfTrxR. The three most promising inhibitors, 3(IC50(PfTrxR)=2 microM and IC50(hTrxR)=50 microM), 7(IC50(PfTrxR)=2 microM and IC50(hTrxR)=140 microM), and 11(IC50(PfTrxR)=0.5 microM and IC50(hTrxR)=4 microM) were selective for the parasite enzyme. Detailed mechanistic characterization of the effects of these compounds on the PfTrxR-catalyzed reaction showed clear uncompetitive inhibition with respect to both substrate and cofactor. For the most specific PfTrxR inhibitor 7, an alkylation mechanism study based on a thiol conjugation model was performed. Furthermore, all three compounds were active in the lower micromolar range on the chloroquine-resistant P. falciparum strain K1 in vitro.

Structure-activity relationships for a collection of structurally diverse inhibitors of purine nucleoside phosphorylase

Values of inhibition constants, Ki, and concentrations required for 50% inhibition, IC50, for a collection of structurally diverse competitive inhibitors of calf spleen purine nucleoside phosphorylase have been determined employing inosine as substrate. These values have been employed to create predictive quantitative structure-activity relationships (QSAR) which link structure to values of Ki and IC50. These QSAR models have substantial power to predict values and the associated uncertainties for Ki and IC50 for unknown, structurally diverse inhibitors of purine nucleoside phosphorylase.

Structure-activity relationships for the analgesic activity of gallic acid derivatives

Values of ID50 for a collection of structurally-related gallic acid derivatives have been employed to create a predictive quantitative structure-activity relationship (QSAR) which links structure to values of analgesic activity. The QSAR model developed has substantial predictive power for the design of novel gallic acid derivatives having improved analgesic potency.

Analgesic activity of cyclic imides: 1,8-naphthalimide and 1,4,5,8-naphthalenediimide derivatives

In early studies, we have reported the synthesis and biological activities of several cyclic imides. The present study describes the analgesic activity of 1,8-naphthalimide and 1,4,5,8-naphthalenediimide derivatives in a standard murine model of analgesia. The pharmacological results show that all compounds studied, given intraperitoneally, produced significant inhibition of acetic acid-induced abdominal constrictions. At the ID50 (micromol/kg) level, these cyclic imide derivatives were about 40-270-fold more potent in this assay than aspirin and acetaminophen, two well-known and widely used analgesics. These results extend previous studies on the analgesic activity of cyclic imides.

Development of a predictive statistical model for the analgesic activity of a family of imides

Quantitative structure-activity relationship (QSAR) studies were done with a family of cyclic imides. Promising efforts to create a QSAR model with substantial predictive power for the design of novel cyclic imides with improved analgesic activity are reported.

Structure-activity relationships for a class of inhibitors of purine nucleoside phosphorylase

Values of inhibition constants, Ki, for a family of structurally related, competitive inhibitors of calf spleen purine nucleoside phosphorylase (PNP) have been determined employing both inosine as substrate and a manual assay and 2-amino-6-mercapto-7-methylpurine ribonucleoside (MESG) as substrate and a robot-based enzyme kinetics facility. Several of the values determined robotically were confirmed employing the same substrate and a manual assay. Surprisingly, for many of the inhibitors examined, values of Ki determined with MESG as substrate are smaller than those obtained employing inosine as substrate by a factor that varies from less than 2 to 10. Values of concentrations required for 50% inhibition of PNP, IC50, have also been determined for the same family of inhibitors employing inosine as substrate. Values of IC50ino and those for Kiino and Kimesg for subsets of the inhibitors have been employed as training sets to create quantitative structure-activity relationships (QSAR) which have substantial power to predict values of IC50 and Ki for inhibitors outside the training set. These QSAR models should be useful in guiding future medicinal chemistry efforts designed to discover inhibitors of PNP having increased potency.

Further studies on analgesic activity of cyclic imides

As part of our research programme to obtain pharmacologically active compounds structurally related to cyclic imides, we have synthesized different compounds and examined their analgesic activities using the abdominal constriction test in mice. The results showed that some of the compounds studied, given intraperitoneally, exhibited graded and significant analgesia against acetic acid-induced abdominal constriction, being several times more potent than aspirin and paracetamol, two standard drugs used for comparison.