An infrared study of tautomerism in acetohexamide polymorphs

International Union of Basic and Clinical Pharmacology. XCIX. Angiotensin Receptors: Interpreters of Pathophysiological Angiotensinergic Stimuli [corrected]

The renin angiotensin system (RAS) produced hormone peptides regulate many vital body functions. Dysfunctional signaling by receptors for RAS peptides leads to pathologic states. Nearly half of humanity today would likely benefit from modern drugs targeting these receptors. The receptors for RAS peptides consist of three G-protein-coupled receptors—the angiotensin II type 1 receptor (AT1 receptor), the angiotensin II type 2 receptor (AT2 receptor), the MAS receptor—and a type II trans-membrane zinc protein—the candidate angiotensin IV receptor (AngIV binding site). The prorenin receptor is a relatively new contender for consideration, but is not included here because the role of prorenin receptor as an independent endocrine mediator is presently unclear. The full spectrum of biologic characteristics of these receptors is still evolving, but there is evidence establishing unique roles of each receptor in cardiovascular, hemodynamic, neurologic, renal, and endothelial functions, as well as in cell proliferation, survival, matrix-cell interaction, and inflammation. Therapeutic agents targeted to these receptors are either in active use in clinical intervention of major common diseases or under evaluation for repurposing in many other disorders. Broad-spectrum influence these receptors produce in complex pathophysiological context in our body highlights their role as precise interpreters of distinctive angiotensinergic peptide cues. This review article summarizes findings published in the last 15 years on the structure, pharmacology, signaling, physiology, and disease states related to angiotensin receptors. We also discuss the challenges the pharmacologist presently faces in formally accepting newer members as established angiotensin receptors and emphasize necessary future developments.

Conformational polymorphism in sulfonylurea drugs: electronic structure analysis

Quantum chemical calculations have been performed using HF, B3LYP, and MP2 methods on the model sulfonylurea PhSO(2)NHC(=O)NHMe to understand the conformational and tautomeric preferences. The results indicate that a conformer with intramolecular hydrogen bond SLU-1 (hitherto not considered) is more stable than the conformer SLU-2 (which is generally considered) for sulfonylureas. The energy difference between these two conformers is about 4 kcal/mol in the gas phase; however, the energy differences between the two rotamers become negligible in the solvent phase. Iminol tautomeric forms of sulfonylurea (which were also not studied until now) are only about 5-6 kcal/mol higher in energy as per both gas-phase and solvent-phase analyses, indicating easy accessibility of tautomeric states in sulfonylureas. Quantum chemical analysis has also been carried out on the possible dimeric structures of these three important isomers of sulfonylurea, and correlations have been made to the known crystal structures of polymorphic states of sulfonylurea drugs.

The Influence of Thermal and Mechanical Preparative Techniques on the Amorphous State of Four Poorly Soluble Compounds

A number of studies in the literature have reported on the use of different preparative techniques to convert crystalline pharmaceutical compounds into the amorphous form. However, very few direct comparisons of different preparative techniques using the same drugs are available. The purpose of this study was to determine the influence of two techniques: quench cooling and ball milling on four structurally diverse pharmaceutical drugs. Dipyridamole, carbamazepine, glibenclamide, and indomethacin were converted to the amorphous form by (a) quench cooling of the drug melt and (b) ball milling. The chemical purity and physical form of the products was determined using diffractometric, spectroscopic, and thermal analytical techniques. Products were analysed immediately post preparation and after storage under different stability conditions. Quench cooling of the melt resulted in amorphous conversion of all four compounds. However with glibenclamide, quench cooling resulted in unacceptable chemical degradation whereas ball milling of glibenclamide resulted in a change in the keto-enol tautomerism at the aryl amide moiety of this drug. Ball milling resulted in predominantly amorphous products for all compounds except carbamazepine. Ball milling of carbamazepine resulted in a polymorphic transition of the starting material to form III. Physical stability studies showed that irrespective of preparative technique and storage conditions all samples showed at least partial reversion to the crystalline state after storage. Quench cooling of drug melts may be of use as a preparative technique however it can result in chemical degradation. Ball milling may also be of use as a preparative technique however its effectiveness is dependent on the unit cell structure of the compound.

A Simple Quantitative FT-IR Approach for the Study of a Polymorphic Transformation Under Crystallization Slurry Conditions

The pharmaceutical compound (2R,3S)-2-([(1R)-1-[3,5-bis(trifluoromethyl)phenyl]ethyl]oxy)-3-(4-fluorophenyl)morpholine hydrochloride (denoted here as Compound X), has been found to crystallize in at least two polymorphic forms. Using only two frequencies (1009 and 1058 cm(-1)) in the infrared, a linear (R=0.998) calibration plot, consisting of the ratio of the peak absorbances plotted against polymorph concentration, was constructed. This plot allowed the quantification of binary mixtures of polymorphs ranging from <3 to approximately 100 wt% Form II in Form I. Spectra were acquired in transmission mode using mineral oil (Nujol) mull sample preparation, for reasons of compatibility with wet cake and slurry samples. The transformation of the less thermodynamically stable polymorph (Form II) to the more stable form (Form I), in stirred methyl isobutyl ketone (MIBK) slurries, was monitored spectroscopically as a function of time. Performing the experiment at various temperatures allowed the energy of activation for the process to be estimated (42 kJ/mol).

Characterization of glass solutions of poorly water-soluble drugs produced by melt extrusion with hydrophilic amorphous polymers

Indomethacin, lacidipine, nifedipine and tolbutamide are poorly soluble in water and may show dissolution-related low oral bioavailability. This study describes the formulation and characterization of these drugs as glass solutions with the amorphous polymers polyvinylpyrrolidone (PVP) and polyvinylpyrrolidone-co-vinyl acetate by melt extrusion. The extrudates were compared with physical mixtures of drug and polymer. X-ray powder diffraction, thermal analysis, infrared spectroscopy, scanning electron microscopy, HPLC, moisture analysis and dissolution were used to examine the physicochemical properties and chemical stability of the glass solutions prepared by melt extrusion at a 1:1 drug/polymer ratio. Depending on the temperature used, melt extrusion produced amorphous glass solutions, with markedly improved dissolution rates compared with crystalline drug. A significant physico-chemical interaction between drug and polymer was found for all extrudates. This interaction was caused by hydrogen bonding (H-bonding) between the carbonyl group of the pyrrole ring of the polymer and a H-donor group of the drug. Indomethacin also showed evidence of H-bonding when physical mixtures of amorphous drug and PVP were prepared. After storage of the extrudates for 4-8 weeks at 25 degrees C/75% relative humidity (RH) only indomethacin/polymer (1:1) extrudate remained totally amorphous. All extrudates remained amorphous when stored at 25 degrees C/< 10% RH. Differences in the physical stability of drug/polymer extrudates may be due to differences in H-bonding between the components.

Structure determination from conventional powder diffraction data: application to hydrates, hydrochloride salts, and metastable polymorphs

Recent advances in crystallographic computing have made it possible to solve by powder diffraction methods structures that have not been possible to solve by single-crystal methods. Although there is vast improvement in the quality of data obtained from high-intensity synchrotron radiation, we found that surprisingly reliable results can be obtained from conventional laboratory sources. In this article we examine the application of Monte Carlo/simulated annealing methods for the determination of structures ranging in complexity from 9 to 15 degrees of freedom. We re-determine the structures of papaverine hydrochloride and erythromycin A dihydrate by the powder diffraction method and compare the structures to those determined by single-crystal diffraction methods. The structure of a metastable polymorphic form of acetohexamide, form B, is solved and examined spectroscopically. Its structure has not previously been solved by single-crystal techniques because of the small size of its crystals.

From genotype to phenotype--behavior of the transgenic rat TGR(mRen2)27 as an example

Transgenic techniques provide a tool to generate animals that differ from the wild-type by one or more genes, either by introducing foreign genes (transgenic animals) or by specific mutations of genes (knock-out animals). Most transgenic and knock-out animals are mice and not rats. The frequent use of rat models in the behavioral laboratory, however, will require the increasing application of transgenic techniques in this species. This paper reviews behavioral data from our laboratory as an example of characterizing the behavioral phenotype of a particular transgenic rat, the TGR(mRen2)27 rat. By describing the anxiogenic profile of this rat we also consider some problems associated with such an analysis, with the intention to raise issues that may also apply to studies of behavior in transgenic animals in general.

Preparation and characterisation of a new insoluble polymorphic form of glibenclamide

A crystalline form of glibenclamide, with higher melting point (218 degrees C) and lower solubility in simulated gastric and intestinal fluids, was arisen during an attempt to elucidate transitional phases by melting, cooling and reheating. The new form was obtained from the glassy state, by applying sublimation at 130-160 degrees C and was characterised by differential scanning calorimetry (DSC), infrared (IR) spectroscopy, scanning electron microscopy (SEM), hot-stage microscopy (HSM), X-ray powder diffraction (XRD) and solubility studies. Formation of the new crystal form is considered as reason of reduction in dissolution and bioavailability of tablets.

Effects of palmatine on isometric force and intracellular calcium levels of arterial smooth muscle

The effects of palmatine on isometric force and intracellular free calcium levels ([Ca2+]i) were determined in isolated rat arterial strips. Palmatine dose-dependently relaxed the contractile responses stimulated by phenylephrine (PE) in aortic strips. In contrast, it only partially relaxed aortic strips contracted by 51 mM KCl. Pretreatment with palmatine shifted the dose-response curves of PE both rightwards and downwards in a dose-dependent manner. When Ca2+-free solution and re-addition of Ca2+ were applied to assess PE-induced phasic and tonic contractions, palmatine was found to be effective in inhibiting both contractions. The effects of palmatine on intracellular calcium levels were measured with the bioluminescent calcium indicator aequorin in rat tail artery strips. Palmatine caused a concomitant, dose-dependent decrease in PE-activated isometric force and [Ca2+]i, resulting in small changes in the [Ca2+]i-force relationship. These results suggest that vasodilatory effect of palmatine was mediated by reducing [Ca2+]i as well as affecting [Ca2+]i sensitivity of the contractile apparatus. Palmatine-induced [Ca2+]i decreases appeared to involve decreases in both Ca2+ release from intracellular stores and Ca2+ influx through calcium channels.

Use of silica gel with reversed-phase eluents for the separation and determination of alkaloids in Corydalis Yanhusuo W. T. Wang and its preparations

An HPLC method using unmodified silica with reversed-phase eluents was developed for the determination of DL-tetrahydropalmatine in Corydalis Yanhusuo W. T. Wang and its set prescription preparations. The mobile phase was a mixture of methanol and 2 mmol/L phosphate buffer (75:25, v/v). The result was calculated by external standardization. The method is simple, rapid and precise, and could also be used for the separation and determination of alkaloids in other crude drugs and preparations.