An extensive study on isosorbide-5-mononitrate acid adducts for quantification in human plasma using liquid chromatography/electrospray ionization tandem mass spectrometry and its application to bioequivalence sample analysis

A rapid and sensitive liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) method for the determination of isosorbide-5-mononitrate (5-ISMN), used in the treatment of angina pectoris, in human plasma is described. The quantification of 5-ISMN was performed via stable acetate adduct formation with a high relative abundance. The plasma filtrate obtained after solid-phase extraction (SPE), using a polymer based, hydrophilic-lipophilic balanced (HLB) cartridge, was submitted directly to reversed-phase high-performance liquid chromatography separation followed by ESI and detection of the resulting ions using triple-quadrupole mass spectrometry in selected reaction monitoring (SRM) mode. There was no significant matrix effect on the analysis. For validation of the method, the recovery of the free analyte response was compared to that obtained from an optimized extraction method. The analyte stability was examined under conditions mimicking the sample storage, handling, and analytical procedures. The extraction procedure yielded extremely clean extracts with a recovery of 95.51% and 93.98% for iossorbide-5-mononitrate and topiramate (internal standard (IS)), respectively. The calibration curves were linear for the dynamic range of 10.0 to 1000.0 ng/mL with a correlation coefficient r > or = 0.9985. The intra-assay and inter-assay precision for the samples at the lower limit of quantification (LLOQ) were 9.02 and 13.30%, respectively. The intra-assay accuracies at LLOQ, LQC, MQC and HQC levels varied from 98.13 to 118.15, 102.34 to 105.21, 100.69 to 109.68, and 95.76 to 102.92%, respectively, while the inter-assay accuracies ranged from 93.10 to 118.15, 93.03 to 107.04, 86.97 to 109.68 and 86.18 to 105.85%, respectively, at these levels. The method is rugged and fast with a total run time of 2 min. The method was successfully applied for a bioequivalence study in 24 human subject samples after oral administration of 60 mg extended release (ER) formulations.     

High-performance liquid chromatography and thin-layer chromatography for the simultaneous quantitation of rabeprazole and mosapride in pharmaceutical products

Simple, sensitive high-performance liquid chromatography (HPLC) and thin-layer chromatography (TLC) methods are developed for the quantitative estimation of rabeprazole and mosapride in their combined pharmaceutical dosage forms. In HPLC, rabeprazole and mosapride are chromatographed using 0.01M 6.5 pH ammonium acetate buffer-methanol-acetonitrile (40:20:40, v/v, pH 5.70+/-0.02) as the mobile phase at a flow rate of 1.0 mL/min. In TLC, the mobile phase is ethyl acetate-methanol-benzene (2:0.5:2.5, v/v). Both the drugs are scanned at 276 nm. The retention times of rabeprazole and mosapride are found to be 4.93+/-0.01 and 9.79+/-0.02, respectively. The Rf values of rabeprazole and mosapride are found to be 0.42+/-0.02 and 0.61+/-0.02, respectively. The linearities of rabeprazole and mosapride are in the range of 400-2000 ng/mL and 300-1500 ng/mL, respectively, for HPLC; in TLC, the linearities of rabeprazole and mosapride are in the range of 400-1200 ng/spot and 300-900 ng/spot, respectively. The limit of detection is found to be 97.7 ng/mL for rabeprazole and 97.6 ng/mL for mosapride in HPLC; in TLC the limit of detection is found to be 132.29 ng/spot for rabeprazole and 98.25 ng/spot for mosapride. The proposed methods can be applied to the determination of rabeprazole and mosapride in combined pharmaceutical products.     

The synthesis of a [2.2]paracyclophane-derived secondary phosphine oxide and a study of its reactivity

A planar chiral secondary phosphine oxide based on [2.2]paracyclophane was synthesized and its chemistry investigated; it was shown to be a competent pre-ligand in palladium(0)-mediated reactions, and displayed promising activity in gold(I)-catalysed cyclisations. The secondary phosphine oxide could be transformed into a collection of P-stereogenic tertiary phosphine oxides. These are rare examples of the planar chirality of [2.2]paracyclophane being combined with a P-stereogenic centre. Unfortunately, epimerisation of the phosphorus stereocentre during reduction limits the use of this chemistry.     

Calix[4]arene based 1,3,4-oxadiazole and thiadiazole derivatives: design, synthesis, and biological evaluation

In the present investigation, we describe some novel calixarene based heterocyclic compounds (5a-5i) in which 1,3,4-oxadiazole and 1,3,4-thiadiazole derivatives have been coupled with 5,11,17,23-tetra-tert-butyl-25,27-bis(chlorocarbonyl-methoxy)-26,28-dihydroxy calix[4]arene. All the newly synthesized calixarene based heterocyclic compounds have been characterized by elemental analysis and various spectroscopic methods like FTIR, (1)H NMR, (13)C NMR, and FAB-MS. All the final scaffolds have been subjected to antioxidant activity, in vitro antimicrobial screening against two gram (+ve) bacteria (S. aureus, S. pyogenes), two gram (-ve) bacteria (E. coli, P. aeruginosa) and two fungal strains (C. albicans, A. clavatus) and also have been screened for their antitubercular activity against Mycobacterium tuberculosis H(37)Rv.     

Comparative molecular field analysis and comparative molecular similarity indices analysis of hydroxyethylamine derivatives as selective human BACE-1 inhibitor

Three-dimensional quantitative structure–activity relationship (3D-QSAR) models were developed based on comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA), on a series of 43 hydroxyethylamine derivatives, acting as potent inhibitors of β-site amyloid precursor protein (APP) cleavage enzyme (BACE-1). The crystal structure of the BACE-1 enzyme (PDB ID: 2HM1) with one of the most active compound 28 was available, and we assumed it to be the bioactive conformation of the studied series, for 3D-QSAR analysis. Statistically significant 3D-QSAR model was established on a training set of 34 compounds, which were validated by a test set of 9 compounds. For the best CoMFA model, the statistics are, r ² =  0.998, r²_cv = 0.810{r^{2}_{\rm cv} = 0.810} , n =  34 for the training set and r²_pred = 0.934{r^{2}_{\rm pred} = 0.934} , n = 9 for the test set. For the best CoMSIA model (combined steric, electrostatic, hydrophobic, and hydrogen bond donor fields), the statistics are r ² =  0.978, r²_cv = 0.754{r^{2}_{\rm cv} = 0.754} , n =  34 for the training set and r²_pred = 0.750{r^{2}_{\rm pred} = 0.750} , n =  9 for the test set. The resulting contour maps, produced by the best CoMFA and CoMSIA models, were used to identify the structural features relevant to the biological activity in this series of analogs. The data generated from the present study will further help to design novel, potent, and selective BACE-1 inhibitors.     

BER performance enhancement for secure wireless optical communication systems based on chaotic MIMO techniques

There has been a growing interest in the use of chaotic techniques for enabling secure communication in recent years. This need has been motivated by the emergence of a number of wireless services which require the channel to provide low bit error rates (BER) along with information security. The aim of such activity is to steal or distort the information being conveyed. Optical Wireless Systems (basically Free Space Optic Systems, FSO) are no exception to this trend. Thus, there is an urgent necessity to design techniques that can secure privileged information against unauthorized eavesdroppers while simultaneously protecting information against channel-induced perturbations and errors. Conventional cryptographic techniques are not designed for protecting information integrity when data is being transferred over a harsh communication medium. Hence, a separate channel coding protocol is often necessary to achieve this goal. Our work indicates that the use of a suitable Chaotic Shift Keying (CSK) map combined with an appropriate Space-Time Code (STC) can allow both requirements to be met. In this paper, we have concentrated on investigating the error rate performance of chaotic-wireless optical communication links operating over atmospheric channel, where the turbulence-induced fading is described by the Gamma–Gamma and log–normal distributions. The main aim of the paper is to assess the feasibility of employing Space-Time Coded chaotic communications over Multiple Input Multiple Output (MIMO) communication channels. Our simulations indicate that the combination of the STC and tent map provides the best BER performance in addition to security when compared to the choice of other maps.     

Synthesis and characterization of double –SO3H functionalized Brönsted acidic hydrogensulfate ionic liquid confined with silica through sol-gel method

Imidazolium-based metal and halogen-free Brönsted acidic ionic liquid (BAIL) (3,3′-(hexane-1,6-diyl)bis(2-methyl-1-(3-sulfopropyl)-1H-benzimidazolium) hydrogensulfate [HbMBIM-PS][HSO₄] was synthesized. The physicochemical properties of this BAIL were investigated using a variety of different analytical and spectroscopic techniques such as ¹H and¹³C-NMR, FT-IR, mass, UV–vis and TGA spectra. A porous silica matrix has been synthesized using BAIL and tetraethoxysilane (TEOS) as silica source by nonhydrolytic sol–gel method. The properties of IL confined silica gel matrix have been studied using FTIR, TGA, SEM, N₂-sorption measurement (BET characterization for determining pore parameters), and NH₃-TPD techniques. From the N₂-sorption measurement, it has been found that BET surface area decreased while pore volume, average pore size and porosity decreased. The thermal stability of the IL has been found to increase upon confinement in silica gel matrix. The results suggested that IL had been successfully confined on silica gel. This IL confined silica gel catalyst is environment friendly and useful for alkane isomerization and esterification reactions.     

Design,synthesis,in vitro evaluation of tetrahydropyrimidine-isatin hybrids as potential antibacterial,antifungal and anti-tubercular agents

A series of 5-substitued-3-(5-(4-(furan-2-yl)-6-methyl-2-oxo/thioxo-1,2,3,4-tetrahydropyrimidin-5-yl)-1,3,4-thiadiazol-2- ylimino)indolin-2-one derivatives were synthesized,characterized and were screened for anti-bacterial,anti-fungal and antitubercular activity.     

Design,synthesis and in vitro evaluation of tetrahydropyrimidine-isatin hybrids as potential antitubercular and antimalarial agents

A series of 5-substituted-3-[{5-(6-methyl-2-oxo/thioxo-4-phenyl-1,2,3,4-tetrahydropyrimidin-5-yl)-1,3,4-oxadiazol-2-yl}-imino] -1,3-dihydro-2H-indol-2-one were synthesized,characterized and screened for their anti-tubercular and antimalarial activity.     

Regioselective Functionalization of 7‐Azaindole by Controlled Annular Isomerism: The Directed Metalation‐Group Dance

The regioselective functionalization of 7‐azaindole by controlled annular isomerism employing a directed metalation‐group migration is reported. The N7 carbamoyl azaindoles undergo regioselective metalation and quenching with an electrophile to furnish C6‐substituted derivatives which, in the presence of a catalytic amount of ClCONR₂ promotes a carbamoyl group shift or dance from N7 to N1. A second directed metalation/electrophile quench sequence leads to 2,6‐substituted azaindoles. Optimization of the metalation conditions for C2 and C6, separately and iteratively, is presented. Using the directed metalation group dance strategy, a late‐stage deuteration of an antipsychotic drug is described. Overall, the controlled migration of the carbamoyl directing group allows multiple functionalization events of the bioactive azaindole scaffold.