Effect of hydrophobic and hydrogen bonding interactions on the potency of ß-alanine analogs of G-protein coupled glucagon receptor inhibitors.

G-protein coupled glucagon receptors (GCGRs) play an important role in glucose homeostasis and pathophysiology of Type-II Diabetes Mellitus (T2DM). The allosteric pocket located at the trans-membrane domain of GCGR consists of hydrophobic (TM5) and hydrophilic (TM7) units. Hydrophobic interactions with the amino acid residues present at TM5, found to facilitate the favorable orientation of antagonist at GCGR allosteric pocket. A statistically robust and highly predictive 3D-QSAR model was developed using 58 ß-alanine based GCGR antagonists with significant variation in structure and potency profile. The correlation coefficient (R2 ) and cross-validation coefficient (Q2 ) of the developed model were found to be 0.9981 and 0.8253, respectively at the PLS factor of 8. The analysis of the favorable and unfavorable contribution of different structural features on the glucagon receptor antagonists was done by 3D-QSAR contour plots. Hydrophobic and hydrogen bonding interactions are found to be main dominating non-bonding interactions in docking studies. Presence of highest occupied molecular orbital (HOMO) in the polar part and lowest unoccupied molecular orbital (LUMO) in the hydrophobic part of antagonists leads to favorable protein-ligand interactions. Molecular mechanics/generalized born surface area (MM/GBSA) calculations showed that van der Waals and nonpolar solvation energy terms are crucial components for thermodynamically stable binding of the inhibitors. The binding free energy of highly potent compound was found to be -63.475 kcal/mol; whereas the least active compound exhibited binding energy of -41.097 kcal/mol. Further, five 100 ns molecular dynamics simulation (MD) simulations were done to confirm the stability of the inhibitor-receptor complex. Outcomes of the present study can serve as the basis for designing improved GCGR antagonists.

A robotic dissolution system with on-line fiber-optic UV analysis.

An automated, robotic system has been developed with on-line UV fiber optics for real time dissolution analysis of solid dosage forms. The system is comprised of "off-the-shelf" hardware including a UV-Vis diode array spectrophotometer, fiber optic coupler, immersion probe, robot, and dissolution apparatus. The software system is modular with the functionalities of control, data acquisition, and spectral analysis separated into three Windows applications with communications performed via Dynamic Data Exchange (DDE). The fiber optic spectrophotometer collects a full spectrum over the range of 190-810 nm. Single wavelength UV analysis is performed on dosage forms in six dissolution vessels. The robotic system automates all facets of the analyses: measuring, degassing, and dispensing of the media; thermostating the media to physiologic temperature; dropping the dosage forms into the vessels; immersing the fiber optic probe at the appropriate time intervals; initiating the data acquisition, analyses, and reporting; and emptying and washing of the vessels prior to the next automated run. As a representative dosage form, 10 mg active tablets were selected and analyzed by this method. This fiber optic system has significantly improved the throughput of the robotic systems by eliminating the need for time consuming off-line HPLC or UV analyses. In addition, with the exception of system calibration, it is no longer necessary for laboratory personnel to come in contact with samples.

Precolumn derivatization for improved detection in liquid chromatography-photolysis-electrochemistry.

Precolumn, homogeneous chemical derivatization with Sanger's reagent (2,4-dinitrofluorobenzene) is utilized to improve the chromatographic and detection properties of amino alcohols and amino acids. The 2,4-dinitrophenyl derivatives are separated using reversed-phase liquid chromatography and are detected using the hybrid photolysis-electrochemical (hv-EC) detector in tandem with UV absorbance detection. Following optimization of reaction, chromatographic, and detection variables, the derivatization-detection approach provides limits of detection in the low parts-per-billion range, with a linearity of roughly three orders of magnitude. Selectivity is based on retention times as well as dual electrode response ratios and a "lamp on/off" responsiveness criterion unique to the hv-EC detector. The method is applied to the determination of serine in beer.

Analysis for penicillins and cefoperazone by HPLC-photolysis-electrochemical detection (HPLC-hv-EC).

Continuous, post-column, on-line, real-time photolytic derivatization or degradation can now be used following HPLC separation of various penicillin derivatives prior to conventional thin-layer, amperometric electrochemical detection using oxidative working potentials. Beta-lactam derivatives are separated by conventional reversed-phase HPLC, and each separated penicillin is then photolytically degraded to form, it is presumed, stable anionic species, which are then conveyed to the on-line electrochemical detector for qualitative and quantitative determinations. These methods of trace drug analysis have been applied to four separate penicillins or prodrugs, as well as one typical cephalosporin, viz. cefoperazone. Analytical parameters of the analysis have been determined, including dual electrode response ratios, sensitivity, minimum detection limits, linearity of calibration plots and the range of linear calibration. Finally, the analysis of cefoperazone-spiked saline solutions for i.v. administration has been performed in a single-blind study, as well as the determination of bacampicillin HCl in formulations obtained from a drug manufacturer in the United States. The overall method of analysis for these drugs has been demonstrated as being reproducible, accurate, and precise for at least five beta-lactam analogs. It is suggested that other beta-lactams will be amenable to these newer methods of analysis in a wide variety of sample matrices, including solid or liquid formulations, aqueous infusion solutions, and biological media, such as blood and urine.

Glassy-carbon amperometric transducers as electrochemical detectors in liquid chromatography The influence of oxygen.

The electrochemical behaviour of oxygen on glassy-carbon electrodes and the suitability of this electrode material for electroreduction of organic compounds have been investigated. The observed oxygen overpotential on a glassy-carbon electrode was more negative than that on an amalgamated gold electrode, thus allowing the determination of easily reducible compounds such as polynitro-aromatics and quinones without the need for exhaustive removal of dissolved oxygen. The detection limits (3sigma) were about 0.2, 0.8, and 2.5 pmole for polynitro-aromatics, mononitro-aromatics and quinones, respectively. Though the glassy-carbon material has a negative-potential limit about 250 mV more positive than that for the amalgamated gold electrode, and requires a longer equilibration time before use, it is more convenient for routine use.

Determination of chlordiazepoxide, diazepam, and their major metabolites in blood or plasma by spectrophotodensitometry.

An analytical procedure was developed for the determination of chlordiazepoxide, diazepam and their major metabolites in blood or plasma. Demoxepam, a metabolite of chlordiazepoxide, is determined by spectrofluorometry after extraction. The remaining compounds are determined by spectrophotodensitometry after thin-layer chromatographic separation. The sensitivity limit of the spectrofluorometric determination of demoxepam is 0.1 to 0.2 microgram while that of the spectrophotodensitometric determination of chlordiazepoxide, diazepam and their N-desmethyl metabolites is 0.05 to 0.2 microgram. The sensitivity and specificity of the assay renders it suitable for monitoring plasma levels of chlordiazepoxide and its major metabolites following single or chronic oral administration of chlordiazepoxide hydrochloride. The sensitivity limit for diazepam and nordiazepam, its major metabolite, renders the assay useful only for the determination of plasma concentrations resulting from high dosage of diazepam. The assay was used to determine chlordiazepoxide and its metabolites following oral administration of Librium. The data showed a significant correlation to those obtained on the same specimens by differential pulse polarography and by radioimmunoassay.