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Specific recognition of cell-targeting systems as host-carriers modified with receptor targeting groups, is a major ambition in the application of supramolecular science to medicine and life science. Genistein (Gen), an isoflavone belonging to the class of phytoestrogens, is of great interest because it has been considered as potential remedy for many kinds of disease. In this work, Genistein in aqueous medium and in the presence of an host nanocarrier as amphiphilic cyclodextrin (CyD) modified in the upper rim with oligoethylene hydroxyl groups [(2-oligo(ethyleneoxide)-6-hexylthio)-β-CyD, SC6OH] at 1:1 molar ratio, has been firstly investigated by UV–vis measurements coupled with circular dichroism data, in order to characterize the drug/macrocycle binding affinity through the formation of the complex. Furthermore, FTIR–ATR technique has been used to detect the complex formation in solid phase and to characterize the functional groups responsible of the solid Gen/SC6OH complex stability. The infrared absorbance spectra of the complex, collected in a wide range of wavenumber and around the physiological temperature, have been analysed and compared with the spectra of the pure compounds and their physical mixture. By monitoring the most significant changes in the shape and position of the absorbance bands of the Gen functional groups, we showed that the formation and/or modification of polar bonds play the main role in the interaction of the drug with the amphiphilic CyD. From the results, Gen is shown to be entangled in SC6OH nanoaggregates, establishing hydrogen bonding with the hydrophilic PEG chains.

The inlcusion behaviour of unsubstituted β-cyclodextrin (β-CyD) and (2-hydroxypropyl)-β-cyclodextrin (HP-β-CyD), in solution and solid state was studied with regards to a poorly water-soluble bioflavonoid, coumestrol (Coum), namely 7,12-dihydroxycoumestan, well-known for its anti-oxidant, anti-inflammatory, anti-fungal and anti-viral activities. Phase-solubility measurements were performed to evaluate in solution the complexation of the two cyclodextrins, i.e. β-CyD and HP-β-CyD. The stoichiometry and stability constants of the Coum/β-CyD and Coum/HP-β-CyD complexes were calculated by the phase-solubility method, after which drug–cyclodextrin solid systems were prepared by co-precipitation. In solid phase, the formation of inclusion complexes was confirmed by Fourier transform infrared spectroscopy in attenuated total reflectance (FTIR-ATR) geometry. In particular, complexation mechanisms were explained by the significant differences revealed in the FTIR-ATR spectra of physical mixtures with respect to those of the complexes; the use of deconvolution and curve fitting was determinant.

The resolution of 1-(4-aminophenyl)-7,8-methylenedioxy-1,2,3,5-tetrahydro-4H-benzodiazepin-4-one (±)-(R,S)-2 was accomplished by chiral HPLC. The absolute configuration of (+)-2, determined by X-ray crystallographic analysis, was R. The in vivo anticonvulsant activity of the enantiomers (+)-(R)-2 and (−)-(S)-2 is reported. It has been also demonstrated that compound (±)-(R,S)-2 in vivo undergoes oxidative metabolism to derivative 1. Chirality, 2006. © 2006 Wiley-Liss, Inc.

The effect of (2-hydroxypropyl)-beta-cyclodextrin (HP-beta-CyD) on the solubility properties and spectroscopic features of hesperetin and its 7-rhamnoglucoside, hesperidin, was qualitatively and quantitatively investigated in water, by means of UV-vis absorption and fluorescence spectroscopy. The stoichiometric ratios and stability constants describing the extent of formation of the complexes have been determined by phase-solubility measurements; in both cases type-A(L) diagrams have been obtained (soluble 1:1 complexes). The higher degree of interaction showed by hesperetin may be attributed to the higher hydrophobicity and smaller size of the aglycone molecule, which therefore exhibits a greater affinity for the CyD and fits better into the cavity. The effect of molecular encapsulation on the two flavanones antioxidant activity was afterwards evaluated by means of different biological assays, concerned to the different mechanisms of in vivo action. The protection efficacy was in all cases higher for the complexed drugs, with respect to the free ones; these results are of great interest for their potential usefulness in pharmaceutics.

In the present work the feasibility of β-cyclodextrin complexation was explored, as a tool for improving the aqueous solubility and antioxidant efficacy of rutin. By means of 1 H NMR, UV–vis and circular dichroism spectroscopy the single aromatic ring of rutin was found to be inserted into the β-cyclodextrin cavity to form a 1:1 inclusion complex. The effect of β-cyclodextrin on the spectral features of rutin was quantitatively investigated, in fully aqueous medium, by holding the concentration of the guest constant and varying the host concentration. The associated binding constants were estimated to be 142 ± 20 and 153 ± 20 M −1 , respectively, on the basis of the observed UV–vis absorption and circular dichroism intensities. The antioxidant activity of rutin was also investigated, as affected by molecular encapsulation within β-cyclodextrin (batophenanthroline test; comet assay; lipid peroxidation); the inclusion complex revealed improved antioxidant efficacy that may be in part explained by an increased solubility in the biological moiety.

pH control and inclusion complex formation are commonly used as solubilization techniques in formulating ionizable drugs. Naringenin is a weakly acid compound with a low water solubility. The role of both ionized and unionized species of naringenin in solution by complexation with beta-cyclodextrin, 2-hydroxypropyl-beta-cyclodextrin and methyl-beta-cyclodextrin was investigated. This combined use of ionization and complexation increases not only the solubility of the unionized naringenin, but also that of the ionized one. This study puts on evidence the role of pH, pKa and complexation constants in increasing drug total aqueous solubility, determined by the single components in solution, as ionized and unionized naringenin both in free and complexed forms. Moreover, the presence of non-ionic surfactants in the media of complexation gives a positive contribution to the improvement of the solubility of naringenin, alone or in combination with beta-cyclodextrin.

A rapid and sensitive RP-HPLC method with UV detection for routine control of oxaliplatin in a pharmaceutical formulation (Eloxatin®) was developed. Quantitation was accomplished with the internal standard method. The procedure was validated by linearity (correlation coefficient=0.999948), accuracy, robustness and intermediate precision. Experimental design was used during validation to calculate method robustness and intermediate precision. For robustness test three factors were considered: percentage v/v of acetonitrile, flow rate and temperature; an increase in the flow rate results in a decrease of the drug found concentration, while the percentage of organic modifier and temperature have no important effect on the response. For intermediate precision measure the considered variables were: analyst, equipment and days. The RSD value (2.27%, n =24) indicated a good precision of the analytical method.

This paper describes the enantiorecognition of 1-methyl-3-hydroxy-5-aryl-2-pyrrolidinonic systems by high-performance liquid chromatography using two chiral derivatized cellulose stationary phases (CSPs) operated in the normal phase mode. According our results, the tris-(3,5-dimethylphenyl carbamate) cellulose, Chiralcel® OD, is more suitable than the tris-(4-methyl-phenylbenzoate), Chiralcel® OJ. On the first column, the resolution of the pyrrolidinonic compounds depends on the alcoholic modifier percentage.

The performance of four chiral liquid chromatographic columns (Chiralcel OA, OJ, OC, OD) was studied with respect to the enantioseparation of flavanones and some derivatives. The effect of mobile phase composition on the retention time and stereo-selectivity was studied. A good enantioseparation (alpha up to 1.45) was achieved for most of the racemates. Further, the elution order of the enantiomers from the chiral stationary phases has been determined by using a circular dichroism based detection system.

Nanoggregates of nonionic amphiphilic cyclodextrin (ACyD) modified with hydrophobic chains of intermediate length [(2-oligo-ethyleneoxide-6-hexylthio)-beta-CyD, SC6OH] were prepared by emulsification-diffusion method. They are able to entrap an isoflavone, genistein (Gen), and the complexed species are studied at different host/guest molar ratio. The increased isoflavone solubility in the presence of the aggregates of SC6OH is investigated by UV-Vis spectroscopy, whereas size, charge, and structure of aggregates and their complexes with Gen are measured by means of static and quasi-elastic light scattering, and electrophoretic mobility measurements. On the other hand, preparing samples by the conventional method used for liposomes (hydration of an organic film of SC6OH and sonication) gives rise to aggregates with different sizes and lower colloidal stability. It is shown that the improved stability in water of ACyD aggregates both in the absence and in the presence of Gen, obtained by emulsification-diffusion is due to the existence of nanodomains of organic solvent (R(H) congruent with 120 nm) which cannot be completely removed by evaporation and freeze-drying and in which host/guest complexes are contained. This result shows that residues of organic solvent from preparation step favor the colloidal stability of the aggregate, but their presence must be taken into account in designing systems for drug delivery.

The resolution of 1-(4-aminophenyl)-3,5-dihydro-3-N-ethylcarbamoyl-5-methyl-7,8-methylenedioxy-4H-2,3-benzodiazepin-4-one (R,S)-(+/-)-5 by chiral HPLC and assignment of the absolute configuration of the two enantiomers was carried out. Compound (R,S)-(+/-)-5 and its enantiomers were tested in a binding assay to evaluate their affinity for AMPA receptors. Enantiomer (S)-(-)-5 appears to be more potent than its optical antipode (R)-(+)-5. In a primary culture of rat cerebellar granule cells, which express AMPA receptors, (R,S)-(+/-)-5 and (S)-(-)-5 inhibited kainate- induced [Ca(2+)](i) increase, thus confirming the antagonism at the AMPA receptor.

The ( R , S )-2-acetyl-1-(4′-chlorophenyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline (( R , S )- 1 ) was previously identified as a potent non-competitive AMPA receptor antagonist able to prevent epileptic seizures and reduce AMPA-induced current in electrophysiological experiments. Through the enantiomeric resolution of racemate by chiral HPLC we already demonstrated that the ( R )- 1 enantiomer was the eutomer. Considering the poor water solubility, these compounds have been complexed with β-cyclodextrin (β-CyD). The effect of β-cyclodextrin on the spectral features of molecules was quantitatively investigated, in fully aqueous medium by phase-solubility study and the obtained diagrams suggested that it forms complexes with a molar ratio 1:1. The binding constant ( K ( R )- 1 = 15889 M −1 , K ( R , S )- 1 = 1079 M −1 ) and the complexation efficiency (CE) were calculated. Then the solid complexes in 1:1 molar ratio were prepared by the co-precipitation method and the FTIR-ATR measurements were carried out in order to confirm the host–guest interactions that drive the complexation process, by monitoring the significant differences of the spectra of the complexes with respect to those of the corresponding physical mixtures in the same molar ratio. The experimental data have been compared with molecular modelling studies and we confirmed our hypothesis.

The improvement of isoflavones bioavailability by complexation with chemically modified cyclodextrins (CyDs) has been exploited to analyse the drug/macrocycle binding affinity by a conventional method with new useful measures. Genistein (Gen) and daidzein (Daidz) were investigated in aqueous medium and in presence an amount of (2-hydroxypropyl)-beta-cyclodextrin (HP-beta-CyD) at different host/guest molar ratios. The solubility in pure water, approximately 3 x 10(-6)M for Gen and approximately 10 x 10(-6)M for Daidz, was obtained by distributing the of guest molecule between water and the organic solvent. The stoichiometric ratios and stability constants describing the extent of formation of the complexes have been determined by phase-solubility UV-vis measurements and confirmed by circular dichroism data. These results have implications in the determination of the carrier's capacity for the complexation of the drug in water solution.

The aim of this work was to obtain the direct optical resolution of a new glutamate receptor antagonist (( p -chloro)1-aryl-6,7,-dimethoxy-1,2,3,4-tetrahydroisoquinoline, PS3), by liquid chromatography on Chiralcel ® OD column. A response surface methodology (RSM) was employed to optimize the enantiomeric separation of the racemate with the lowest number of experiments; in particular, a face-centred design (FCD) was applied to evaluate the influence of critical parameters on the experimental response. Furthermore, in order to find the best compromise between several responses, a multicriteria decision-making approach, the Derringer's desirability function, was successful to simultaneously optimize the responses resolution and migration times of the two enantiomers. The proposed LC method provided the baseline enantioseparation of the investigated drug. 9.3% (v/v) ethanol added to n -hexane as mobile phase, 1.0 mL min −1 flow rate, and 18 °C column temperature were the optimum experimental conditions allowing to achieve the highest enantioresolution of PS3 in less than 17 min.

The retention behaviour of racemic 1-(4-aminophenyl)-1,2,3,5-tetrahydro-7,8-methylendioxy-4H-2,3-benzodiazepin-4-one derivatives with anticonvulsant activity on several chiral stationary phases was investigated. The selective performances of six polysaccharide phases, namely, Chiralcel OA, OD, OF, OG, OJ and Chiralpak AD were studied and normal phase HPLC methods were optimized to separate the enantiomeric forms of this class of compounds. The chiral recognition mechanism between the analytes and the chiral selectors was discussed. A molecular modeling study was carried out with the aim to explore the enantioselective molecular recognition process with the Chiralcel OG stationary phase.

A reversed-phase high-performance liquid chromatographic (HPLC) separation with photo-diode array detection was developed for the simultaneous determination of flavonoids extracted from Citrus bergamia juice. It employs a C18 reversed-phase column and a linear gradient elution system with methanol/water with 5% acetic acid (v/v), as mobile phase. The method was validated in terms of detection limits (LOD), quantitation limits (LOQ), linearity, precision and accuracy. Limits of detection ranged from a low of 0.007 mg ml(-1) (narirutin) to a high of 0.018 mg ml(-1) (didymin). The limits of quantitation were between a low of 0.011 mg ml(-1) (7-OH flavanone) and a high of 0.024 mg ml(-1) (didymin). An excellent linear response was observed over the range specified for all analytes, as confirmed by the correlation coefficient with ranged from 0.9982 and 0.9999. The intra-day R.S.D.% ranged from 0.11 to 3.64%. The intermediate precision R.S.D.% were not higher than 7.62%. The accuracy of the method was confirmed with an average recovery ranging, except for neoeriocitrin, between 88.07% and 102.45%. Since the extraction conditions can affect analyte recovery, a suitable optimization strategy of the procedure was needed. The experimental parameters optimized were extraction time, temperature, and solvents. A multivariate approach was used to provide direct evaluation of the selected variables and related interactions. The D-optimal design was constructed by applying the exchange algorithm. All experimental results were computed by NEMROD-W software. This methodology led us to obtain the best recovery for all the flavonoids in the least number of experiments.

Anti-HIV enantiomeric 1H, 3H-thiazolo[3, 4-a] benzimidazoles have been stereospecifically analyzed by elution on a column of cellulose tris-(4-methyl-phenylbenzoate)ester adsorbed on macroporous silica (ChiralcelR OJ).

This paper reports a fast and accurate RP-HPLC chromatographic method for the simultaneous determination of 3-hydroxyflavone (3-OH F) and its photodegradation products. Solutions (5 x 10(-5) M) in acetonitrile (ACN) of the molecule were subjected to forced degradation by exposure to artificial UV-A light source (black-light, lambda(max) 354 nm) and the changes appearing in chromatograms were monitored at selected irradiation times. A multistep gradient was optimised to achieve complete elution of all photoproducts in the shortest analysis time. UV spectra recorded by the diode array detector system (285 and 340 nm) clearly showed the structural changes in the new species formed, with respect to the parent compound. The analytical method was subjected to a validation procedure in which linearity and range, as well as specificity, precision and accuracy were determined according to ICH guidelines. Quantitative evaluation of the photochemical process was performed on the basis of the calculated kinetic parameters: photodegradation rate constant k, half-life time t(0.5), time degradation of 10% of the drug t(0.1).

3-Hydroxyflavone (3-OH-F) photochemistry in solution has been rationalized in terms of an excited state intramolecular proton transfer (ESIPT), which involves the free 3-hydroxy group interacting with the ortho-carbonyl. This photo-rearrangement occurs rapidly and is strongly influenced by the physico-chemical properties of the solvent, which plays an essential role in determining whether a photo-oxidation or a photo-induced molecular rearrangement takes place. 3-OH-F photoreactivity has been deeply investigated and the related mechanisms elucidated, as affected by various solvents, pH values and irradiation wavelengths, leading to different photodegradation rates and pathways. Moreover, the influence of molecular encapsulation upon alpha- and beta-cyclodextrins (alpha- and beta-CyD) on the molecule photoreactivity has been examined, as a potential tool for increasing molecule photostability as well as minimizing photoinduced toxic effects on biosubstrates.

The inclusion into the beta-cyclodextrin is used to improve pharmacokinetic characteristics of hesperetin and naringenin. Solubility of hesperetin and naringenin with increasing concentrations of beta-cyclodextrin grows as long as the temperature increased. Stability constants were determined by the solubility method by Higuchi and Connors at different temperatures, and the thermodynamic parameters were calculated for inclusion complex formation in aqueous solution. The solid complexes were obtained in a molar ratio of 1:1 and their dissolution behavior at different pH was examined.

Flavonoids are natural substances with a lot of biological activities, including the antioxidant one. Their use in pharmaceutical field is, however, limited by their aqueous insolubility. As the formation of the inclusion complexes can improve their solubility in water, the flavonoids hesperetin, hesperidin, naringenin and naringin have been complexed with beta-cyclodextrin (beta-CD) by the coprecipitation method and studied in solution and in solid state by NMR, FT-IR, differential scanning calorimetry and X-ray techniques. The effects of complexation on the chemical shifts of the internal and external protons of beta-CD in the presence of each flavonoid were observed.

The racemization of (-)-adrenaline was followed by polarimetric variable-temperature kinetic experiments obtaining activation parameters and k(0bs)(T) profile in one tenth of the time usually spent for traditional kinetic runs. A polarimeter connected to a computer for the acquisition and processing of the analytical data was used. The kinetic profiles were processed by both an integral method and a differential method. The results are in good agreement with each other and with those obtained by constant-temperature kinetics. (C) 2002 Elsevier Science B.V. All rights reserved.

An experimental design methodology has been applied to the enantioseparation of a new synthesized aryl propionic acid of pharmaceutical interest, namely 2-[(4'-benzoyloxy-2'-hydroxy)phenyl-propionic acid] (DF-1770y) by chiral capillary zone electrophoresis (CCZE). The chiral separation of the studied compound has been achieved employing vancomycin as the chiral selector. The partial filling-counter current method has been used in order to avoid the presence of the absorbing chiral selector in the path length of the detector and to increase the method sensitivity. A central composite design has been employed to optimize the experimental conditions for a fast separation of the enantiomers of the new synthesized aryl propionic acid. Critical parameters such as chiral selector concentration, pH and temperature have been studied to evaluate how they affected responses such as resolution and migration times. The desirability function approach has been employed in order to find the best compromise between the different experimental responses. The proposed CCZE method provided the baseline enantioseparation of the investigated drug. A Britton-Robinson buffer at pH 6.4 supplemented with 7 mM of vancomycin at 22 degrees C and -20 kV were the optimum experimental conditions allowing to achieve the highest enantioresolution of DF-1770y in less than 8.5 min.

Racemic reboxetine, (R,S)-2[(R,S)-α-(2-ethoxyphenoxybenzyl] morpholine methane sulfonate, is a mixture of the (R,R) and (S,S) enantiomers. Separation of the enantiomers of reboxetine by liquid chromatography has been investigated on three chiral stationary phases—cellulose tris-(3,5-dimethylphenylcarbamate) (Chiralcel OD), cellulose tris-(phenylcarbamate) (Chiralcel OC), and amylose tris-(3,5-dimethylphenylcarbamate) (Chiralpak AD). On these stationary phases the resolution of the (R,R) and (S,S) enantiomers was highly dependent on mobile-phase composition. When Chiralcel OD and OC were used, addition of diethylamine to the mobile phase greatly improved the separation of the enantiomers. On Chiralpak AD enantio-separation was achieved without the use of additives. Solute-mobile phase-stationary phase interactions which might participate in the mechanism of enantiorecognition are discussed.

The formation of inclusion complexes between beta-cyclodextrin with the two beta-blockers, atenolol and celiprolol, have been studied in the aqueous environment and in the solid state by nuclear magnetic resonance (NMR) spectroscopy, X-ray, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) techniques. The magnitude of the chemical shifts of the interior and exterior beta-cyclodextrin protons in the presence of each beta-blocker indicated that these are included within the beta-cyclodextrin cavity. In aqueous solution they form 1:1 complexes. In the solid state the formation of the beta-cyclodextrin/atenolol (celiprolol) complexes is confirmed by X-ray, DSC and SEM, also employed to characterize pure substances and their physical mixtures.

A reversed-phase high-performance liquid chromatographic (HPLC) method was developed and validated for estimation of zafirlukast in a pharmaceutical formulation. Assay samples were extracted utilizing acetonitrile. Drug and internal standard were chromatographed on reversed-phase C18 columns, using mixtures of acetonitrile/water and the eluents were monitored at different wavelengths. The method was validated statistically for its linearity, accuracy, robustness and precision. Experimental design was used during validation to evaluate method robustness and for the determination of intermediate precision. Factors examined for statistical approaches include laboratory, day, analyst, instrument, different percentage of organic modifier, temperature, wavelength and flow-rate. Due to its simplicity and accuracy, the method may be used for routine quality control analysis.

A high-performance liquid chromatographic method is reported for the resolution of the enantiomers of a series of fused γ-lactams (2,7-diaza-3-oxo[3.3.0]octan-6-ones) with probable anti-HIV and anticancer activity. Resolution was achieved on a Chiralcel® OD column, cellulose tris-(3,5-dimethylphenyl carbamate) adsorbed on macroporous silica gel; mixtures ofn-hexane and isopropyl alcohol in different proportions were used as the mobile phase. The analysis was studied at different temperatures.

The crystal structure of the title complex has been determined from single crystal X-ray data. The palladium atom is in the usual square planar arrangement with 7-bromo- 1,3-dihydro-5-(2-pyridyl)-2H-1,4-benzodiazepine-2-one (bromazepam) coordinated with the two α-diimine nitrogen atoms of bromazepam and two cis-chlorine atoms. The geometry of the molecule and its crystal packing are similar to the corresponding platinum(II) complex, where the usual boat conformation of bromazepam is retained. The kinetics of displacement of coordinated bromazepam, by 1,10-phenanthroline and 2,2′-bipyridine, in [Pd(bromazepam)Cl2] have been studied by stopped-flow spectrophotometry in dimethylsulphoxide at 25°C. The data have been interpreted in terms of a mechanism implying two reacting forms, the complex and a solvo-species with mono-coordinated bromazepam. In the case of the less reactive bipyridine, ring closure of bromazepam and entry of the nucelophile compete for the reaction centre.

1,4-Benzodiazepines cleave the halide-bridged complexes [Pd2X4(PPrn3)2](X = Cl or l) to give monomeric complexes in which the benzodiazepine is presumably co-ordinated through N(4) of the heterocyclic ring. The reaction between [Pd2I4(PPrn3)2] and 7-chloro-1,3-dihydro-1-methyl-5-phenyl-, 5-(2-chlorophenyl)-1,3-dihydro-7-nitro-, 1,3-dihydro-7-nitro-5-phenyl-, and 7-bromo-1,3-dihydro-5-(2-pyridyl)-2H-1,4-benzodiazepin-2-one and 7-chloro-2,3-dihydro-1-methyl-5-phenyl-1,4-benzodiazepine has been studied kinetically and thermodynamically in CHCl3. The stability of the monomeric complexes formed varies considerably throughout the series of ligands and is much lower when the benzodiazepine is in the 2-keto form. The nucleophilic activities of these substances, as expressed by the second-order rate constants k2 corresponding to direct attack at palladium in the cleavage reaction, are similar but much lower, for steric reasons, than that of pyridine. The difference in stability of the various complexes is attributed mainly to the difference in the rate constants corresponding to the reverse reaction, i.e. the release of the co-ordinated ligand.

2,3-Substituted 5-methyl-4-thiazolidinones (1) and 3-substituted 5-methyl-2,4-thiazolidine-diones (II) were prepared by reacting some carbodiimides with α-mercaptopropionic acid, with the purpose of obtaining potentially chemotherapeutic agents. It is noteworthy that 3-cyclohexyl-5-methyl-2,4-thiazolidinedione (IId) was obtained in three different crystalline structures. Some secondary compounds were also obtained: the N,N-disubstituted ureas (III) and thioureas (IV) in all cases, the dianilides (V) and the tri-substituted guanidines (VI) from the arylcarbodiimides, and the dithiolactide (VII) from the isopropyl- and cyclohexylcarbodiimides.

The conformational analysis of biologically active lofendazam (7-chloro-5-phenyl-1,3,4,5-tetrahydro-2H-1,5-benzodiazepin-2-one) is carried out by means of lanthanide shift reagent assisted 1H NMR spectroscopy: the lanthanide induced shift computer simulation suggests that in deuteriochloroform the heterocyclic ring of lofendazam assumes a cycloheptene-like chair conformation, where 1-N moves away from trigonal stereochemistry to a very flattened pyramidal structure. At room temperature the conformational equilibrium is markedly shifted (85%) towards the conformer showing pseudoaxial H-1 and 5-Ph. The remarkable influence of steric requirements in controlling conformation, and the importance of 3- and/or 4-methyl groups in hindering the ring inversion at room temperature, have been verified by conformational analysis of suitable analogous 1,3,4,5-tetraydro-2H-1,5-benzodiazepin-2-ones.

The stereochemistry of some 1-methyl-5-phenyl-2,3,4,5-tetrahydro-1H-1,5-benzodiazepine-2,4-diones was determined by proton magnetic resonance using the paramagnetic shift reagent tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato)europium [Eu(fod)3] two of these compounds, clobazam and triflubazam, are clinically used as psychotherapeutic agents. Several model structures, with intermediate stereochemistry in the range of the possible limit situations of benzocycloheptene, -cycloheptadiene or -cycloheptatriene type, are considered; LIS (3) are computer simulated on the basis of proton geometric parameters. It was found that at room temperature, these derivatives exist in only one pseudo-boat cycloheptadiene-like conformation, showing the 5-phenyl group directed pseudo-axially. This conformational preference is interpreted in terms of a balance between the steric requirements of the bulky substituent and electronic repulsion in the ring π-system.

The sterochemistry of some 1,3-dihydro-2H-1,4-benxodiazepin-2-ones, employed as psychotherapeutic agents, is deduced by proton magnetic resonance using the paramagnetic shift reagent Eu(fod)3. the lanthanide induced shifts are computer simulated on the basis of the geometric parameters of the protons in different model structures, having intermediate conformations between a cycloheptadiene- and a cyclohepatatriene-like system. N-Desmethyldiazepam shows a conformational equilibrium between two pseudoboat forms, while the 1-alkyl substituted derivatives exist, at room temperature, in olny one boat cycloheptatriene-like conformation.

The lanthanide shift reagent (LSR)/1H NMR study of some 7-chloro-5-phenyl-2,3-dihydro-1 H-1, 4-benzodiazepines shows that these compounds exist in CDCI3 solution as two pseudo-boat conformers, rapidly interconverting at room temperature. Computer simulated lanthanide induced shifts (LIS) are consistent with LSR complexation by the imine nitrogen atom. The lanthanide shifts the conformational equilibrium towards conformer (a), with a pseudoequatorial 1-substituent: this effect may be the result of the greater basicity of 4-N when the 1-N lone pair is pseudoaxially directed, thus permitting an extended electron delocalization from 1- to 4-N through the fused benzene ring. The detection of H-9/1-Me through space spin-spin coupling in medazepam (7-chloro-1-methyl-5-phenyl-2,3-dihydro-1H-1,4-benzodiazepine) supports the observed higher availability of conformer (a) to LSR. A LIS computer calculation to predict the population ratio results in reasonable agreement with the conformational changes based on the response of 3J(HH) to lanthanide addition. The electronic and steric effects which determine the greater stability of conformer (a) may be effective in the drug-receptor interaction.