Pentacycloundecane lactam vs lactone norstatine type protease HIV inhibitors: binding energy calculations and DFT study

Background

Novel pentacycloundecane (PCU)-lactone-CO-EAIS peptide inhibitors were designed, synthesized, and evaluated against wild-type C-South African (C-SA) HIV-1 protease. Three compounds are reported herein, two of which displayed IC₅₀ values of less than 1.00 μM. A comparative MM-PB(GB)SA binding free energy of solvation values of PCU-lactam and lactone models and their enantiomers as well as the PCU-lactam-NH-EAIS and lactone-CO-EAIS peptide inhibitors and their corresponding diastereomers complexed with South African HIV protease (C-SA) was performed. This will enable us to rationalize the considerable difference between inhibitory concentration (IC₅₀) of PCU-lactam-NH-EAIS and PCU-lactone-CO-EAIS peptides.

Results

The PCU-lactam model exhibited more negative calculated binding free energies of solvation than the PCU-lactone model. The same trend was observed for the PCU-peptide inhibitors, which correspond to the experimental activities for the PCU-lactam-NH-EAIS peptide (IC₅₀ = 0.076 μM) and the PCU-lactone-CO-EAIS peptide inhibitors (IC₅₀ = 0.850 μM). Furthermore, a density functional theory (DFT) study on the natural atomic charges of the nitrogen and oxygen atoms of the three PCU-lactam, PCU-lactim and PCU-lactone models were performed using natural bond orbital (NBO) analysis. Electrostatic potential maps were also used to visualize the electron density around electron-rich regions. The asymmetry parameter (η) and quadrupole coupling constant (χ) values of the nitrogen and oxygen nuclei of the model compounds were calculated at the same level of theory. Electronic molecular properties including polarizability and electric dipole moments were also calculated and compared. The Gibbs theoretical free solvation energies of solvation (∆G_solv) were also considered.

Conclusions

A general trend is observed that the lactam species appears to have a larger negative charge distribution around the heteroatoms, larger quadrupole constant, dipole moment and better solvation energy, in comparison to the PCU-lactone model. It can be argued that these characteristics will ensure better eletronic interaction between the lactam and the receptor, corresponding to the observed HIV protease activities in terms of experimental IC₅₀ data.

Electronic supplementary material

The online version of this article (doi:10.1186/s12929-015-0115-5) contains supplementary material, which is available to authorized users.     

Sublethal effects of imidacloprid and pymetrozine on the life table parameters of Aphis gossypii Glover (Homoptera: Aphididae)

In this study we report the sublethal effects of recommended concentrations of imidacloprid and pymetrozine on cotton aphid's reproduction. Fecundity life table parameters for AG were studied on cucumber under conditions of 25+/-1 degrees C, 70+/-5% RH and photoperiod of 16:8 (L:D). Leaf discs of cucumber immersed in the recommended concentrations of the above mentioned insecticides and controls and the new born female was released on the lower surface of leaf discs. Values of parameters such as adult longevity and daily fecundity rate were recorded. Standard error of population growth parameter was calculated using the Jacknife method. The results show that these two insecticides significantly reduce life table parameters compared with control.     

High-performance liquid chromatographic determination of lamivudine in human serum using liquid-liquid extraction; application to pharmacokinetic studies

A simple, fast, and sensitive high performance liquid chromatographic (HPLC) assay was developed for quantitation of lamivudine in human serum. Lamivudine is polar compound and its extraction from the human serum in previously published HPLC methods involved either protein precipitation or solid phase extraction techniques. However, existence of endogenous peaks which interfere with the drug or appeared as late eluting peaks and lead to long run time of analysis has been reported. Application of either an ion pairing agent in the mobile phase or time consuming column purge has been used in the published methods. Present paper describes liquid - liquid extraction of lamivudine and internal standard (famotidine) using dichloromethane-isopropyl alcohol (1:1, v/v) as an extracting solvent and salting out approach. The mobile phase was a mixture of phosphate buffer (0.05 M) containing triethylamine (1 mL/L, v/v; pH 3.5) and methanol (91:9, v/v) at a flow rate of 2.2 mL/min. The analysis was performed on a column (150 mm x 6 mm i.d.) which was packed with 5 microm particles of ODS packing material. Under these conditions no interference in the assay from any endogenous substance was observed. The limit of quantification was evaluated to be 5 ng/mL. Accuracy and precision of the method were also studied and the technique was shown to be selective and linear into the concentration range of 5-2500 ng/mL. This method has been used in two randomized crossover bioequivalence studies of 100 and 150 mg lamivudine preparations in 12 and 24 healthy volunteers, respectively.     

Phloridzin reduces blood glucose levels and improves lipids metabolism in streptozotocin-induced diabetic rats

Phloridzin is the specific and competitive inhibition of sodium/glucose cotransporters in the intestine (SGLT1) and kidney (SGLT2). This property which could be useful in the management of postprandial hyperglycemia in diabetes and related disorders. Phloridzin is one of the dihydrochalcones typically contained in apples and in apple-derived products. The effect of phloridzin orally doses 5, 10, 20 and 40 mg/kg body weight on diabetes was tested in a streptozotocin-induced rat model of diabetes type 1. From beneficial effect of this compound is significant reduction of blood glucose levels and improve dyslipidemia in diabetic rats. As a well-known consequence of becoming diabetic, urine volume and water intake were significantly increased. Administration of phloridzin reduced urine volume and water intake in a dose-dependent manner. Phloretin decreases of food consumption, as well as a marked lowering in the weight. In conclusion, this compound could be proposed as an antihyperglycemic and antihyperlipidemic agent in diabetes and potential therapeutic in obesity.     

Serum Iron,Zinc, and Copper Concentration in Premature Graying of Hair

Premature graying of hair with unclear etiology, which is known as premature canities, is a common cause of referrals to the dermatologists. We assessed the relationship between serum iron, copper, and zinc concentrations with premature canities. This study was conducted on patients under 20 years old suffering from premature canities, having a minimum of ten gray hair fibers, and referring to university hospitals of Isfahan (Iran). The results were compared with age–sex-matched controls. Demographic data and disease characteristics were recorded for two groups. We studied serum iron, copper, and zinc concentrations of 66 patients and 66 controls using atomic absorption and Ferrozine methods. The mean age of studied cases was 17.8 ± 2.0 years, and the mean age of the onset of canities was 15.5 ± 3.2 years with no significant difference between males and females (P > 0.05). Serum copper concentration was significantly lower in patients compared with controls (90.7 ± 37.4 vs. 105.3 ± 50.2 μg/dL, P = 0.048), but serum iron concentration was significantly lower in controls compared to patients (88.8 ± 39.5 vs. 108.3 ± 48.4 μg/dL, P = 0.008). Also, there was no significant difference between patients and controls in serum zinc concentration (114.8 ± 67.8 vs. 108.2 ± 49.9 μg/dL, P = 0.285). According to these results, among copper, zinc, and iron, a low serum copper concentration may play a role in premature graying of hairs in our society. Further studies are needed to find the underlying mechanism of this relationship.     

Emulsifying Activity, Particle Uniformity and Rheological Properties of a Natural Polysaccharide-Protein Biopolymer from Durian Seed

Polysaccharide-protein gums are complex polymers with many applications in emulsion and emulsion-based products. It is crucial to enclose a concept on understanding of functional properties of polysaccharide-protein biopolymer in order to select the appropriate one based on the application scope. The main objective of the current study was to investigate the effect of three extraction variables on the surface activity, particle uniformity, apparent viscosity, and protein content of a natural polysaccharide-protein biopolymer from durian fruit seed. Three extraction variables namely water: seed (W/S) ratio (20:1?C60:1), temperature (25.0?C85.0?°C) and pH (4.0?C10.0) were considered as independent variables. The results indicated that durian seed gum induced very low viscosity (0.93?C4.98?mPa.s) with pseudoplastic rheological behavior in the aqueous system. The current study revealed that the extraction variables had the most significant (p?<?0.05) effect on the emulsifying surface activity of the natural biopolymer from durian fruit seed. This might be due to the significant (p?<?0.05) effect of the proteineous constituent present in the chemical structure of the biopolymer from durian fruit seed. The aqueous extraction variables showed the most and least significant (p?<?0.05) effect on the specific surface area and protein content, respectively. Among all extraction variables, W/S ratio and pH exhibited the highest and lowest significant (p?<?0.05) effect on the physicochemical and functional properties of the natural biopolymer from durian fruit seed.     

High-performance liquid chromatographic determination of inactive carboxylic acid metabolite of clopidogrel in human serum: Application to a bioequivalence study

A sensitive and rapid method is described for determination of clopidogrel carboxylic acid (CCA), the inactive metabolite of anti platelet agent, clopidogrel, in human serum. The analytical procedure involves liquid-liquid extraction of the analyte and an internal standard (phenytoin) with ethyl acetate. A mobile phase consisting of 0.05 M phosphate buffer containing triethylamine (0.5 mL/L; pH 5.7) and acetonitrile (56:44 v/v) was used and chromatographic separation was achieved using C18 analytical column at detector wavelength of 220 nm. The calibration curves were linear over a concentration range of 0.05-10 microg/mL of CCA in human serum. The total run time of analysis was 5.5 min and the lower limits of detection (LOD) and quantification (LOQ) were 0.02 and 0.05 microg/mL, respectively. The method validation was carried out in terms of specificity, sensitivity, linearity, precision, accuracy and stability. The validated method was applied in a randomized cross-over bioequivalence study of two different clopidogrel preparations in 24 healthy volunteers.     

Determination of oseltamivir carboxylic acid in human serum by solid phase extraction and high performance liquid chromatography with UV detection

A new straightforward method based on cloud-point extraction (CPE) has been developed, optimized and validated for the determination of venlafaxine in human plasma by reversed-phase high-performance liquid chromatography with fluorescence detection. The non-ionic surfactant Triton X-114 (polyethylene glycol tert-octylphenyl ether) was chosen as the extract solvent. Separation was obtained using a reversed-phase Diamonsil column (C(18), 250mmx4.6mm I.D., 5mum) and a mobile phase composed of acetonitrile-phosphate buffer solution (pH 3.0)-triethylamine (33.5:66.5:0.4). Fluorescence detection was used (lambda(ex) 276nm, lambda(em) 598nm). Maprotiline was used as the internal standard. Under the optimum conditions, the linear range of venlafaxine in human plasma was 10-800ngmL(-1) (r(2)=0.9995). The limit of detection (LOD) was less than 2ngmL(-1) (S/N=3) and the limit of quantification (LOQ) was less than 10ngmL(-1) (S/N=10). The method was successfully applied for the evaluation of pharmacokinetic profiles of venlafaxine capsules in nine healthy volunteers.