The unexpected increase of clotrimazole apparent solubility using randomly methylated β‐cyclodextrin

Clotrimazole (CTZ) and cyclodextrin (CD) inclusion complexes having improved apparent water solubility were obtained from phase solubility diagrams. β‐CD (1.5% w/w) and hydroxypropyl‐β‐CD (40% w/w) offered poor CTZ solubility enhancements (12 and 384 times, respectively). Unexpectedly, the apparent solubility of CTZ was 9980 times increased from 0.4 µg.mL^?1 (1.42 μM) without CD to 4.89 mg.mL^?1 (14.9 mM) using randomly‐methylated β‐CD (Me‐β‐CD) (40% w/w). This is the highest apparent CTZ solubility improvement ever reported in the literature using conventional CDs. Quantitative nuclear magnetic resonance (¹H‐NMR) coupled with two‐dimensional nuclear Overhauser effect (NOESY) experiments and molecular docking calculations showed that the highest interactions with Me‐β‐CD were reported for CTZ two phenyl groups. A lower interaction was reported for chlorophenyl, while imidazole had the weakest interaction with Me‐β‐CD. Copyright © 2015 John Wiley & Sons, Ltd.     

Preparative Enantioseparation of β‐Substituted‐2‐Phenylpropionic Acids by Countercurrent Chromatography With Substituted β‐Cyclodextrin as Chiral Selectors

Preparative enantioseparation of four β‐substituted‐2‐phenylpropionic acids was performed by countercurrent chromatography with substituted β‐cyclodextrin as chiral selectors. The two‐phase solvent system was composed of n‐hexane‐ethyl acetate‐0.10 mol L‐1 of phosphate buffer solution at pH 2.67 containing 0.10 mol L^‐1 of hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD) or sulfobutylether‐β‐cyclodextrin (SBE‐β‐CD). The influence factors, including the type of substituted β‐cyclodextrin, composition of organic phase, concentration of chiral selector, pH value of the aqueous phase, and equilibrium temperature were optimized by enantioselective liquid–liquid extraction. Under the optimum separation conditions, 100 mg of 2‐phenylbutyric acid, 100 mg of tropic acid, and 50 mg of 2,3‐diphenylpropionic acid were successfully enantioseparated by high‐speed countercurrent chromatography, and the recovery of the (±)‐enantiomers was in the range of 90–91% for (±)‐2‐phenylbutyric acid, 91–92% for (±)‐tropic acid, 85–87% for (±)‐2,3‐diphenylpropionic acid with purity of over 97%, 96%, and 98%, respectively. The formation of 1:1 stoichiometric inclusion complex of β‐substituted‐2‐phenylpropionic acids with HP‐β‐CD was determined by UV spectrophotometry and the inclusion constants were calculated by a modified Benesi‐Hildebrand equation. The results showed that different enantioselectivities among different racemates were mainly caused by different enantiorecognition between each enantiomer and HP‐β‐CD, while it might be partially caused by different inclusion capacity between racemic solutes and HP‐β‐CD. Chirality 27:795–801, 2015. © 2015 Wiley Periodicals, Inc.     

Enantioseparation of ketoconazole and miconazole by capillary electrophoresis and a study on their inclusion interactions with β‐cyclodextrin and derivatives

A chiral separation method coupled with capillary electrophoresis (CE) analysis for ketoconazole and miconazole enantiomers using chiral selectors such as β‐cyclodextrin (β‐CD) and hydroxypropyl‐β‐CD (HP‐β‐CD) was developed in this study, which included the optimisation, validation and application of the method on the antifungal cream samples. The formation of inclusion complex between the hosts (β‐CD and HP‐β‐CD) and guests (ketoconazole and miconazole) were compared and analysed using ultraviolet–visible spectrophotometry, nuclear magnetic resonance (NMR) spectroscopy and molecular docking methods. Results from the study showed that in a concentration that ranged between 0.25 and 50 mg L^?1, the linear calibration curves of each enantiomer had a high coefficient of regression (R² > 0.999), low limit of detection (0.075 mg L^?1) and low limit of quantification (0.25 mg L^?1). The relative standard deviation (RSD) of the intraday and interday analyses ranged from 0.79% to 8.01% and 3.30% to 11.43%, respectively, while the recoveries ranged from 82.0% to 105.7% (RSD < 7%, n = 3). The most probable structure of the inclusion complexes was proposed based on the findings from the molecular docking studies conducted using the PatchDock server.     

Separation of Selected Imidazole Enantiomers Using Dual Cyclodextrin System in Micellar Electrokinetic Chromatography

Cyclodextrin‐modified micellar electrokinetic chromatography (CD‐MEKC) method was developed for simultaneous enantioseparation of three imidazole drugs namely tioconazole, isoconazole and fenticonazole. Three easily available and inexpensive cyclodextrins namely 2‐hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD), 2‐hydroxypropyl‐γ‐cyclodextrin (HP‐γ‐CD) and heptakis(2,6‐di‐O‐methyl)‐β‐cyclodextrin (DM‐β‐CD) were evaluated to discriminate the six stereoisomers of the drugs. However, none of the three CDs gave a complete enantioseparation of the drugs. Effective enantioseparation of tioconazole, isoconazole and fenticonazole was achieved using a combination of 35 mM HP‐γ‐CD and 10 mM DM‐β‐CD as chiral selectors. The best separation using both HP‐γ‐CD and DM‐β‐CD (35 mM:10 mM) as chiral selectors were accomplished in background electrolyte (BGE) containing 35 mM phosphate buffer (pH 7.0), 50 mM sodium dodecyl sulfate (SDS) and 15% (v/v) acetonitrile at 27 kV and 30 °C with all peaks resolved in less than 15 min with resolutions, R_s 1.90‐27.22 and peak efficiencies, N > 180 000. The developed method was linear over the concentration range of 25–200 mg l^‐1 (r² > 0.998) and the detection limits (S/N = 3) of the three imidazole drugs were found to be 2.7‐7.7 mg l^‐1. The CD‐MEKC method was successfully applied to the determination of the three imidazole drugs in spiked human urine sample and commercial cream formulation of tioconazole and isoconazole with good recovery (93.6‐106.2%) and good RSDs ranging from 2.30‐6.8%. Chirality 25:328–335, 2013. © 2013 Wiley Periodicals, Inc.     

Structural insights into the inclusion complexes between clomiphene citrate and β‐cyclodextrin: The mechanism of preferential isomeric selection

A major challenge in pharmaceuticals for clinical applications is to alter the solubility, stability, and toxicity of drug molecules in living systems. Cyclodextrins (CDs) have the ability to form host–guest inclusion complexes with pharmaceuticals for further development of new drug formulations. The inclusion complex of clomiphene citrate (CL), a poorly water‐soluble drug, with native β‐cyclodextrin (β‐CD) was characterized by a one and two‐dimensional nuclear magnetic resonance (NMR) spectroscopic approach and also by molecular docking techniques. Here we report NMR and a computational approach in preferential isomeric selection of CL, which exists in two stereochemical isomers, enclomiphene citrate (ENC; E isomer) and zuclomiphene citrate (ZNC; Z isomer) with β‐CD. β‐CD cavity protons, namely, H‐3′ and H‐5′, experienced shielding in the presence of CL. The aromatic ring protons of the CL molecule were observed to be deshielded in the presence of β‐CD. The stoichiometric ratio of the β‐CD:CL inclusion complex was observed by NMR and found to be 1:1. The overall binding constant of β‐CD:CL inclusion complexes was based on NMR chemical shifts and was calculated to be 50.21 M⁻¹. The change in Gibb's free energy (∆G) was calculated to be −9.80 KJ mol⁻¹. The orientation and structure of the β‐CD:CL inclusion complexes are proposed on the basis of NMR and molecular docking studies. 2D ¹H‐¹H ROESY confirmed the involvement of all three aromatic rings of CL in the inclusion complexation with β‐CD in the solution, confirming the multiple equilibria between β‐CD and CL. Molecular docking and 2D ¹H‐¹H ROESY provide insight into the inclusion complexation of two isomers of CL into the β‐CD cavity. A molecular docking technique further provided the different binding affinities of the E and Z isomers of CL with β‐CD and confirmed the preference of the Z isomer binding for β‐CD:CL inclusion complexes. The study indicates that the formation of a hydrogen bond between –O– of CL and the hydrogen atom of the hydroxyl group of β‐CD was the main factor for noncovalent β‐CD:CL inclusion complex formation and stabilization in the aqueous phase.     

A chiral enantioseparation generic strategy for anti‐Alzheimer and antifungal drugs by short end injection capillary electrophoresis using an experimental design approach

The present study describes a generic strategy using capillary electrophoretic (CE) method for chiral enantioseparation of anti‐Alzheimer drugs, namely, donepezil (DON), rivastigmine (RIV), and antifungal drugs, namely, ketoconazole (KET), Itraconazole (ITR), fluconazole (FLU), and sertaconazole (SRT) in which these drugs have different basic and acidic properties. Several modified cyclodextrins (CDs) were applied for enantioseparation of racemates such as highly sulfated α, γ CDs, hydroxyl propyl‐β‐CD, and Sulfobutyl ether‐β‐CD. The starting screening conditions consist of 50‐mM phosphate‐triethanolamine buffer at pH 2.5, an applied voltage of 15 kV, and a temperature of 25°C. The CE strategy implemented in the separation starts by screening prior to the optimization stage in which an experimental design is applied. The design of experiment (DOE) was based on a full factorial design of the crucial two factors (pH and %CD) at three levels, to make a total of nine (3²) experiments with high, intermediate, and low values for both factors. Evaluation of the proposed strategy pointed out that best resolution was obtained at pH 2.5 for five racemates using low percentages of HS‐γ‐CD, while SBE‐β‐CD was the most successful chiral selector offering acceptable resolution for all the six racemates, with the best separation at low pH values and at higher %CD within 10‐min runtime. Regression study showed that the linear model shows a significant lack of fit for all chiral selectors, anticipating that higher orders of the factors are most likely to be present in the equation with possible interactions.     

Revealing interaction between sulfobutylether‐β‐cyclodextrin and reserpine by chemiluminescence and site‐directed molecular docking

The host–guest interaction between sulfobutylether‐β‐cyclodextrin (SBE‐β‐CD) and reserpine (RSP) is described using flow injection‐chemiluminescence (FI‐CL) and site‐directed molecular docking methods. It was found that RSP could inhibit the CL intensity produced by a luminol/SBE‐β‐CD system. The decrease in CL intensity was logarithmic over an RSP concentration range of 0.03 to 700.0 nM, giving a regression equation of ?I = 107.1lgC_RES + 186.1 with a detection limit of 10 pM (3σ). The CL assay was successfully applied in the determination of RSP in injection, saliva and urine samples with recoveries in the range 93.5–106.1%. Using the proposed CL model, the binding constant (K_CD‐R) and the stoichiometric ratio of SBE‐β‐CD/RSP were calculated to be 7.4 × 10⁶ M^‐1 and 1 : 1, respectively. Using molecular docking, it was confirmed that luminol binds to the small cavity of SBE‐β‐CD with a nonpolar interaction, while RSP targeted the larger cavity of SBE‐β‐CD and formed a 1 : 1 complex with hydrogen bonds. The proposed new CL method has the potential to become a powerful tool for revealing the host–guest interaction between CDs and drugs, as well as monitoring drugs with high sensitivity. Copyright © 2013 John Wiley & Sons, Ltd.     

Targeting human telomeric G‐quadruplex DNA with antitumour natural alkaloid aristololactam‐β‐D‐glucoside and its comparison with daunomycin

Study on anticancer agents that act via stabilization of telomeric G‐quadruplex DNA has emerged as novel and exciting field for anticancer drug discovery. The interaction of carbohydrate containing anticancer alkaloid aristololactam‐β‐D‐glucoside (ADG) with human telomeric G‐quadruplex DNA sequence was characterized by different biophysical techniques. The binding parameters were compared with daunomycin (DAN), a well‐known chemotherapeutic drug. The Scatchard binding isotherms revealed noncooperative binding for both with the binding affinity values of (1.01 ± 0.05) × 10⁶ and (1.78 ± 0.18) × 10⁶ M⁻¹ for ADG and DAN, respectively. Circular dichroism, ferrocyanide quenching study, anisotropy study, thiazole orange displacement, optical melting, differential scanning calorimetry study, and molecular docking study suggest significant stacking and stabilizing efficiency of ADG with comparison to DAN. The energetics of the interaction for ADG and DAN revealed that both reactions were predominantly entropy driven. Negative heat capacity values were obtained from the temperature dependence of the enthalpy change. The standard molar Gibbs energy change exhibited only marginal alterations with temperature suggesting the occurrence of enthalpy‐entropy compensation. These findings indicate that ADG can act as a stabilizer of telomeric G‐quadruplex DNA and thereby can be considered as a potential telomerase inhibitor.     

Effect of 2‐hydroxypropyl‐β‐cyclodextrin on thermal stability and aggregation of glycogen phosphorylase b from rabbit skeletal muscle

The study of the kinetics of thermal aggregation of glycogen phosphorylase b (Phb) from rabbit skeletal muscles by dynamic light scattering at 48°C showed that 2‐hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD) accelerated the aggregation process and induced the formation of the larger protein aggregates. The reason of the accelerating effect of HP‐β‐CD is destabilization of the protein molecule under action of HP‐β‐CD. This conclusion was supported by the data on differential scanning calorimetry and the kinetic data on thermal inactivation of Phb. It is assumed that destabilization of the Phb molecule is due to preferential binding of HP‐β‐CD to intermediates of protein unfolding in comparison with the original native state. The conclusion regarding the ability of the native Phb for binding of HP‐β‐CD was substantiated by the data on the enzyme inhibition by HP‐β‐CD. © 2010 Wiley Periodicals, Inc. Biopolymers 93: 986–993, 2010.     

Diversity in the supramolecular interactions of 5,6-dichloro-2-(trifluoromethyl)-1H-benzimidazole with modified cyclodextrins: Implications for physicochemical properties and antiparasitic activity

The molecular interactions of 5,6-dichloro-2-(trifluoromethyl)-1H-benzimidazole (G2), an antiprotozoa with poor aqueous solubility, with 2-hydroxypropyl-α-cyclodextrin (HPαCD), methyl-β-cyclodextrin (MβCD) and 2-hydroxypropyl-β-cyclodextrin (HPβCD) were examined. The aqueous solubility enhancement by cyclodextrins (CDs) was evidenced in phase-solubility diagrams, and the stoichiometry of G2/CD systems was determined by Job's plots. Two-dimensional NMR spectroscopic data revealed that a different mode of interaction took place between G2 and CDs in solution. With HPαCD, a non-inclusion complex was generated. In the case of MβCD, a typical host-guest system was obtained and with HPβCD a partial inclusion complex through the narrow side of the macrocycle was formed. ESI-mass spectrometric data confirmed the stoichiometry and mode of interaction of these systems in solution. Solid-state characterization (scanning calorimetry and powder X-ray diffraction) supported the inclusion complex formation. The leishmanicidal activity, trypanocidal activity and non-toxic profile of G2/MβCD showed the advantages of using this inclusion complex to promote the biological assays extension of G2.     

Stereoselectivity in β-cyclodextrin complexation of 1,4-dihydropyridine derivatives

Structure–interaction relationships, stereoselectivity, and solubility enhancement in inclusion compexation of β-cyclodextrins (CDs) with some racemic and enantiomerically pure 1,4-dihydropyridine derivatives (DHPs) were investigated. 1:1 and 1:2 (mole ratio) complexes were prepared and characterized by X-ray powder diffraction, differential scanning calorimetry (DSC), MS-FAB spectrometry, ¹H-NMR spectroscopy, water and phase solubility. The solubility studies have revealed different complexation equilibria for optically pure DHP enantiomers, and corresponding racemic mixtures in water solutions. By means of ¹H-NMR chemical shift measurements, the inclusion of aromatic fragments of racemic and enantiomerically pure DHP molecules within the cavities of different CDs was elucidated. Considerable stereoselectivity in complexation interactions was observed. The results indicate the potential use of cyclodextrins as chiral selectors for enantiomeric resolution of 1,4-DHP calcium antagonists. © 1993 Wiley-Liss, Inc.     

Enzyme‐triggered fluorescence turn‐off/turn‐on of carbon dots for monitoring β‐glucosidase and its inhibitor in living cells

Energy transfer engineering based on fluorescent probes for directly sensing enzyme activities are in great demand as enzyme‐mediated transformations, which are central to all biological processes. Here, a fluorescence carbon dot (CD)‐based assay exhibiting selective responses to the quantitation of β‐glucosidase and the effect of its inhibitor was developed. The most common substrate, para‐nitrophenyl‐β‐d ‐glucopyranoside (pNPG) was hydrolyzed by β‐glucosidase to release p‐nitrophenol (pNP), which can efficiently quench fluorescence of CDs via an inner filter effect and electron transfer. However, in the presence of inhibitors of β‐glucosidase, the fluorescence intensity gradually recovered as the concentration of inhibitors increased. Therefore, the enzyme‐triggered fluorescence turn‐off/turn‐on of specific CDs successfully achieved sensitive detection of β‐glucosidase and monitored the effect of its inhibitors. This new strategy was applied to detect β‐glucosidase and monitor β‐glucosidase inhibitor in hepatoma cells using cell imaging. All results suggest that the new method is sensitive and promising for use in cancer diagnosis and treatment.     

Chiral separation of catechin by capillary electrophoresis using mono‐, di‐, tri‐succinyl‐β‐cyclodextrin as chiral selectors

The chiral separation of (±)‐catechin was investigated by capillary electrophoresis using characterized succinyl‐β‐cyclodextrins (Suc‐β‐CDs) with one to three degree of substitution values. The effects of nature and concentration of Suc‐β‐CDs and running buffer pH on the migration time and resolution of (±)‐catechin are discussed. All three kinds of Suc‐β‐CDs show a clear baseline separation of (±)‐catechin in capillary electrophoresis. Mono‐Suc‐β‐CD effectively separated (±)‐catechin, and additional substituted CDs (di‐ and tri‐Suc‐β‐CD) were capable of chiral separation at a broad pH range. The optimum running conditions were found to be 100 mM borate buffer (pH 9.8) containing 5 mM mono‐Suc‐β‐CD with no methanol organic modifier. Chirality, 2009. © 2009 Wiley‐Liss, Inc.     

Comparison of three S‐β‐CDs with different degrees of substitution for the chiral separation of 12 drugs in capillary electrophoresis

Three kinds of sulfated β‐cyclodextrin (S‐β‐CD), including a single isomer, heptakis‐6‐sulfato‐β‐cyclodextrin (HS‐β‐CD), degree of substitution (DS) of 7, which was synthesized in our laboratory and another two commercialized randomly substituted mixtures, a sulfated β‐cyclodextrin with DS of 7 to 11, as well as a highly sulfated‐β‐cyclodextrin with DS of 12 to 15, were used for the enantioresolution of 12 drugs (the β‐blockers, phenethylamines, and anticholinergic agents) in capillary electrophoresis. The enantioseparation under varying concentrations of S‐β‐CD and background electrolyte pH were systematically investigated and compared. Based on the experimental results, the effect of the nature of S‐β‐CD and analyte structure on the enantioseparation is discussed.     

Chiral recognition of verapamil by cyclodextrins studied with capillary electrophoresis,NMR spectroscopy,and electrospray ionization mass spectrometry

Capillary electrophoresis (CE) allows the observation of the opposite affinities of the enantiomers of (±)‐verapamil [2‐isopropyl‐2,8‐bis(3,4‐dimethoxyphenyl)‐6‐methyl‐6‐azaoctannitrile, VP] toward β‐cyclodextrin (β‐CD) and heptakis(2,3,6‐tri‐O‐methyl)‐β‐CD (TM‐β‐CD). In addition, in the presence of β‐CD in the background electrolyte, longer migration times and lower separation factors were observed compared to TM‐β‐CD. The binding constants of (+)‐ and (−)‐VP with β‐CD and TM‐β‐CD determined using ¹³C NMR spectroscopy explain the results observed in CE. Electrospray ionization mass spectrometry (ESI‐MS) was used as an alternative technique for the characterization of VP‐CD complexes. Chirality 11:635–644, 1999. © 1999 Wiley‐Liss, Inc.     

Characterization of the interaction of a mono‐6‐thio‐β‐cyclodextrin‐capped CdTe quantum dots–methylene blue/methylene green system with herring sperm DNA using a spectroscopic approach

Novel, water‐soluble CdTe quantum dots (QDs) capped with β‐cyclodextrin (β‐CD) and ~ 4.0 nm in diameter were synthesized in aqueous solution, and characterized using transmission electron microscopy (TEM). A fluorescence‐sensing system based on the photoinduced electron transfer (PET) of (mono‐6‐thio‐β‐CD)–CdTe QDs was then designed to measure the interaction of phenothiazine dyes [methylene blue (MB) and methylene green (MG)] with herring sperm DNA (hsDNA). This fluorescence‐sensing system was based on a fluorescence “OFF–ON” mode. First, MB/MG adsorbed on the surface of (mono‐6‐thio‐β‐CD)–CdTe QDs effectively quenches the fluorescence of (mono‐6‐thio‐β‐CD)–CdTe QDs through PET. Then, addition of hsDNA restores the fluorescence intensity of (mono‐6‐thio‐β‐CD)–CdTe QDs, because hsDNA can bind with MB/MG and remove it from the as‐prepared (mono‐6‐thio‐β‐CD)–CdTe QDs. In addition, detailed reaction mechanisms of the (mono‐6‐thio‐β‐CD)–CdTe QDs–MB/MG–hsDNA solution system were studied using optical methods, by comparison with the TGA–CdTe QDs–MB/MG–hsDNA solution system. Copyright © 2014 John Wiley & Sons, Ltd.     

SN-38-Cyclodextrin Complexation and Its Influence on the Solubility,Stability, and In Vitro Anticancer Activity Against Ovarian Cancer

SN-38, an active metabolite of irinotecan, is up to 1,000-fold more potent than irinotecan. But the clinical use of SN-38 is limited by its extreme hydrophobicity and instability at physiological pH. To enhance solubility and stability, SN-38 was complexed with different cyclodextrins (CDs), namely, sodium sulfobutylether β-cyclodextrin (SBEβCD), hydroxypropyl β-cyclodextrin, randomly methylated β-cyclodextrin, and methyl β-cyclodextrin, and their influence on SN-38 solubility, stability, and in vitro cytotoxicity was studied against ovarian cancer cell lines (A2780 and 2008). Phase solubility studies were conducted to understand the pattern of SN-38 solubilization. SN-38-βCD complexes were characterized by differential scanning calorimetry (DSC), X-ray powder diffraction analysis (XRPD), and Fourier transform infrared (FTIR). Stability of SN-38-SBEβCD complex in pH 7.4 phosphate-buffered saline was evaluated and compared against free SN-38. Phase solubility studies revealed that SN-38 solubility increased linearly as a function of CD concentration and the linearity was characteristic of an A_P-type system. Aqueous solubility of SN-38 was enhanced by about 30–1,400 times by CD complexation. DSC, XRPD, and FTIR studies confirmed the formation of inclusion complexes, and stability studies revealed that cyclodextrin complexation significantly increased the hydrolytic stability of SN-38 at physiological pH 7.4. Cytotoxicity of SN-38-SBEβCD complex was significantly higher than SN-38 and irinotecan in both A2780 and 2008 cell lines. Results suggest that SBEβCD encapsulated SN-38 deep into the cavity forming stable inclusion complex and as a result increased the solubility, stability, and cytotoxicity of SN-38. It may be concluded that preparation of inclusion complexes with SBEβCD is a suitable approach to overcome the solubility and stability problems of SN-38 for future clinical applications.     

Preparation and Characterization of Inclusion Complexes of a Hemisuccinate Ester Prodrug of Δ<Superscript>9</Superscript>-Tetrahydrocannabinol with Modified Beta-Cyclodextrins

Δ⁹-Tetrahydrocannabinol hemisuccinate (THC-HS), an ester prodrug of Δ⁹-tetrahydrocannabinol (THC) has been investigated for its potential to form inclusion complexes with modified synthetic beta-cyclodextrins (CDs). Phase solubility studies were performed to determine the stoichiometric ratio of complexation of THC-HS with random methylated beta-cyclodextrin (RAMEB) and 2-hydroxypropyl beta-cyclodextrin (HPBCD). THC-HS/RAMEB and THC-HS/HPBCD solid systems were prepared by lyophilization and the lyophilized complexes were characterized by Fourier transform infrared (FT-IR) spectroscopy, proton nuclear magnetic spectroscopy, and molecular modeling techniques. The formation of inclusion complexes of THC-HS/RAMEB and THC-HS/HPBCD was demonstrated by an A_L type curve with the slopes less than unity by the phase solubility method. The association constants for THC-HS/RAMEB and THC-HS/HPBCD were found to be 562.48 and 238.83 M⁻¹, respectively. The stoichiometry of both of the complexes was found to be 1:1 as determined from the Job's plot. This was confirmed by ¹H NMR and FT-IR techniques. The results obtained from the molecular modeling studies were in accordance with the data obtained from nuclear magnetic resonance and FT-IR. The docking studies revealed the most probable mode of binding of THC-HS with RAMEB in which the alkyl chain was submerged in the hydrophobic pocket of the CD molecule and hydrogen bonding interactions were observed between the hemisuccinate ester side chain of THC-HS and the rim hydroxy groups of RAMEB. The solubility of THC-HS was significantly higher in RAMEB compared to HPBCD. Solid dispersions of THC-HS with CDs will be further utilized to develop oral formulations of THC-HS with enhanced bioavailability.     

The impact of β‐azido(or 1‐piperidinyl)methylamino acids in position 2 or 3 on biological activity and conformation of dermorphin analogues

The synthesis of new dermorphin analogues is described. The (R)‐alanine or phenylalanine residues of natural dermorphin were substituted by the corresponding α‐methyl‐β‐azidoalanine or α‐benzyl‐β‐azido(1‐piperidinyl)alanine residues. The potency and selectivity of the new analogues were evaluated by a competitive receptor binding assay in rat brain using [³H]DAMGO (a μ ligand) and [³H]DELT (a δ ligand). The most active analogue in this series, Tyr‐(R)‐Ala‐(R)‐α‐benzyl‐β‐azidoAla‐Gly‐Tyr‐Pro‐Ser‐NH₂ and its epimer were analysed by ¹H and ¹³C NMR spectroscopy and restrained molecular dynamics simulations. The dominant conformation of the investigated peptides depended on the absolute configuration around C^α in the α‐benzyl‐β‐azidoAla residue in position 3. The (R) configuration led to the formation of a type I β‐turn, whilst switching to the (S) configuration gave rise to an inverse β‐turn of type I′, followed by the formation of a very short β‐sheet. The selectivity of Tyr‐(R)‐Ala‐(R) and (S)‐α‐benzyl‐β‐azidoAla‐Gly‐Tyr‐Pro‐Ser‐NH₂ was shown to be very similar; nevertheless, the two analogues exhibited different conformational preferences. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.     

Fluorescence enhancement of warfarin induced by interaction with β‐cyclodextrin

Warfarin is the most common agent used for control and prevention of venous as well as arterial thromboembolism (blood clots). In aqueous media, warfarin forms inclusion complexes with a family of cyclic oligosaccharides, α, β, γ‐cyclodextrins (CD). The formation of these complexes results in enhancement of the fluorescence of warfarin. Such spectroscopic changes offer a venue for the development of bioanalytical methodologies for warfarin quantification in biological liquids. We characterized the photophysical properties of warfarin in solvents with varying polarity and viscosity. The fluorescence quantum yield of warfarin correlated: (1) strongly with the solvent viscosity (R = 0.979) and (2) weakly with the solvent polarity (R = 0.118). These findings indicate that it is the change of the viscosity, rather than polarity, of the microenvironment that causes the fluorescence enhancement of warfarin upon binding to β‐CD. Utilizing the observed fluorescence enhancement in fluorescence titration measurements, the binding constants of warfarin to β‐CD were obtained (2.6 × 10² M^?1–3.7 × 10² M^?1). Using multivariable linear analysis, we extracted the stoichiometry of warfarin‐β‐CD interaction (1:1). © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009