Characterization of physico-chemical properties and pharmaceutical performance of sucrose co-freeze-dried solid nanoparticulate powders of the anti-HIV agent loviride prepared by media milling.

In order to improve the dissolution and absorption properties of loviride, a poorly soluble antiviral agent, sucrose co-freeze-dried nanopowders were prepared, characterized and evaluated. Tween 80/poloxamer 188-stabilized nanosuspensions were produced on a laboratory scale using media milling. The milling process was monitored by dynamic light scattering (DLS) and resulted in particles with a mean size of 264+/-14nm and a distribution width of 59+/-6nm after 4h of milling. Co-freeze-drying of the nanosuspensions with sucrose had an inhibiting effect on nanoparticle agglomeration and yielded solid "nanopowders" that were resuspendable and homogeneous with respect to loviride content. X-ray powder diffraction (XRPD) confirmed the presence of small loviride crystallites and indicated that sucrose and poloxamer 188 were crystalline. Differential scanning calorimetry (DSC) showed melting peaks of poloxamer 188, sucrose and loviride. Time-resolved XRPD indicated that sucrose crystallization was complete within 24h of storage. Scanning electron microscopy (SEM) suggested the formation of sheet-like matrix structures. The dissolution rate of loviride from the nanopowders was excellent. A Caco-2 experiment on the nanopowder showed a significantly higher cumulative amount transported after 120min (1.59+/-0.02microg) compared to the physical mixture (0.93+/-0.01microg) and the untreated loviride (0.74+/-0.03mcirog).

Synthesis and anti-HIV evaluation of 2',3'-dideoxyribo-5-chloropyrimidine analogues: reduced toxicity of 5-chlorinated 2',3'-dideoxynucleosides.

In view of the selective anti-HIV activity of 2',3'-dideoxy-3'-fluoro-5-chlorouridine (11), a series of eight 2',3'-dideoxy-5-chloropyrimidines were synthesized and evaluated for their inhibitory activity against human immunodeficiency virus type 1 (HIV-1) replication in MT-4 cells. A marked improvement in selectivity was noted for the 5-chlorouracil derivatives of 2,3-dideoxyribofuranose, 3-azido-2,3-dideoxyribofuranose, and 3-fluoro-2,3-dideoxyribofuranose, mainly due to decreased toxicity of the compounds for the host cells. While chlorination of 2',3'-dideoxycytidine removed the anti-HIV activity, introduction of a chlorine at the C-5 position of 3'-fluoro-, 3'-azido- or 2',3'-didehydro-2',3'-dideoxycytidine led to reduced cytotoxicity with only slightly reduced anti-HIV activity. X-ray analysis showed compound 11 to have two molecules in the asymmetric unit with chi = -168.8 (3) degrees and -131.3 (3) degrees and P = 179 (1) degree and 163 (1) degree, respectively; thus revealing no close resemblance to 3'-azido-3'-deoxythymidine (AZT).

N6-cyclopentyl-3'-substituted-xylofuranosyladenosines: a new class of non-xanthine adenosine A1 receptor antagonists.

The present study explores the C-3' site of the 3-deoxy-3-xylofuranosyl ring of nucleoside analogues with an adenine or N6-cyclopentyladenine (CPA) base moiety and evaluates the effect on adenosine receptor affinity. Two series of sugar-modified adenosines, i.e., 3'-amido-3'-deoxyadenosines and 3'-amidated 3'-deoxyxylofuranosyladenines, were synthesized and tested for their affinity at A1 and A2a receptors in rat brain cortex and rat striatum, respectively. The modest affinity found in the "xylo series" prompted us to synthesize the corresponding N6-cyclopentyl derivatives, which proved to be well accommodated by the A1 receptors with potencies in the lower nanomolar range. This represents a new perspective in the purinergic field. The absence of a GTP-induced shift, i.e., the ratio between the affinities measured in the presence and absence of 1 mM GTP indicates an antagonistic behavior of this new class of CPA analogues.

Synthesis and structure-activity relationships of analogs of 2'-deoxy-2'-(3-methoxybenzamido)adenosine, a selective inhibitor of trypanosomal glycosomal glyceraldehyde-3-phosphate dehydrogenase.

In continuation of a project aimed at the structure-based design of drugs against sleeping sickness, analogs of 2'-deoxy-2'-(3-methoxybenzamido)adenosine (1) were synthesized and tested to establish structure-activity relationships for inhibiting glycosomal glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Compound 1 was recently designed using the NAD:GAPDH complexes of the human enzyme and that of Trypanosoma brucei, the causative agent of sleeping sickness. In an effort to exploit an extra hydrophobic domain due to Val 207 of the parasite enzyme, several new 2'-amido-2'-deoxyadenosines were synthesized. Some of them displayed an interesting improvement in inhibitory activity compared to 1. Carbocyclic or acyclic analogs showed marked loss of activity, illustrating the importance of the typical (C-2'-endo) puckering of the ribose moiety. We also describe the synthesis of a pair of compounds that combine the beneficial effects of a 2- and 8-substituted adenine moiety on potency with the beneficial effect of a 2'-amido moiety on selectivity. Unfortunately, in both cases, IC50 values demonstrate the incompatibility of these combined modifications. Finally, introduction of a hydrophobic 5'-amido group on 5'-deoxyadenosine enhances the inhibition of the protozoan enzyme significantly, although the gain in selectivity is mediocre.

2'-Azido-2',3'-dideoxythymidine: synthesis and crystal structure of a 2'-substituted dideoxynucleoside.

1-(2-Azido-2,3-dideoxy-beta-D-erythro-pentofuranosyl)thymine (2'-N3ddThd) was synthesized from 1-(5-O-trityl-2,3-anhydro-beta-D-lyxofuranosyl)thymine by two different procedures. Method A prepared the title compound by opening of the oxirane ring with LiEt3BH followed by mesylation of the 2'-hydroxyl function, introduction of the 2'-azido substituent and deblocking of the 5'-function. In method B nucleophilic opening of 3'-deoxy-5'-O-(tert-butyldimethylsilyl)-5-methyl-2,2'-anhydrouridine+ ++ was carried out with sodium azide in hexamethylphosphoramide in the presence of benzoic acid. Single X-ray crystallographic studies indicated a solid state conformation (3T2), which was opposite to that of the A form of AZT (2T3) but closely resembled that of 1-(2-fluoro-2,3-dideoxy-beta-D-erythropentofuranosyl)thymine (2'-FddThd) (3T2) and of 3'-azido-2',3'-dideoxy-2,6-diaminopurine riboside (3'-N3ddDAP) (3T2). Whereas the latter displayed significant inhibitory activity against human immunodeficiency virus (HIV) replication, 2'-FddThd and 2'-N3ddThd were essentially inactive.

Physical stabilisation of amorphous ketoconazole in solid dispersions with polyvinylpyrrolidone K25.

The glass forming properties of ketoconazole were investigated using differential scanning calorimetry (DSC), by quench cooling liquid ketoconazole from T(m)+10 to 273.1 K, followed by subsequent heating at 5 K/min to T(m)+10 K. It was shown that liquid ketoconazole forms a glass which did not recrystallise following reheating, indicating its stability; T(g) was found to be 317.5+/-0.3 K. However, the presence of a small amount of crystalline ketoconazole was able to convert the amorphous drug back to the crystalline state: the addition of only 4.1% (w/w) of crystalline material converted 77.1% of the glass back to the crystalline state, and this value increased as the amount of added crystals increased. PVP K25 was found to be highly effective in the prevention of such recrystallisation, but only if the amorphous drug was formulated in a solid dispersion, since physical mixing of amorphous ketoconazole with the polymer resulted in recrystallisation of the former compound. Storage of the solid dispersions for 30 days at 298.1 K (both 0 and 52% RH) in the presence or absence of crystals did not result in recrystallisation of the amorphous drug. Solid dispersions formed compatible blends as one single T(g) was observed, which gradually increased with increasing amounts of PVP K25, indicating the anti-plasticising property of the polymer. The values of T(g) followed the Gordon-Taylor equation, indicating no significant deviation from ideality and suggesting the absence of strong and specific drug-polymer interactions, which was further confirmed with 13C NMR and FT-IR. It can be concluded therefore that the physical mechanism of the protective effect is not caused by drug-polymer interactions but due to the polymer anti-plasticising effect, thereby increasing the viscosity of the binary system and decreasing the diffusion of drug molecules necessary to form a lattice.

Physicochemical characterization of solid dispersions of the antiviral agent UC-781 with polyethylene glycol 6000 and Gelucire 44/14.

The purpose of this study was to prepare and characterize solid dispersions of the antiviral thiocarboxanilide UC-781 with PEG 6000 and Gelucire 44/14 with the intention of improving its dissolution properties. The solid dispersions were prepared by the fusion method. Evaluation of the properties of the dispersions was performed using dissolution studies, differential scanning calorimetry, Fourier-transform infrared spectroscopy and X-ray powder diffraction. To investigate the possible formation of solid solutions of the drug in the carriers, the lattice spacings [d] of PEG 6000 and Gelucire 44/14 were determined in different concentrations of UC-781. The results obtained showed that the rate of dissolution of UC-781 was considerably improved when formulated in solid dispersions with PEG 6000 and Gelucire 44/14 as compared to pure UC-781. From the phase diagrams of PEG 6000 and Gelucire 44/14 it could be noted that up to approximately 25% w/w of the drug was dissolved in the liquid phase in the case of PEG 6000 and Gelucire 44/14. The data from the X-ray diffraction showed that the drug was still detectable in the solid state below a concentration of 5% w/w in the presence of PEG 6000 and Gelucire 44/14, while no significant changes in the lattice spacings of PEG 6000 or Gelucire 44/14 were observed. Therefore, the possibility of UC-781 to form solid solutions with the carriers under investigation was ruled out. The results from infrared spectroscopy together with those from X-ray diffraction and differential scanning calorimetry showed the absence of well-defined drug-polymer interactions.

Mechanism of increased dissolution of diazepam and temazepam from polyethylene glycol 6000 solid dispersions.

Solid dispersion literature, describing the mechanism of dissolution of drug-polyethylene glycol dispersions, still shows some gaps; (A). only few studies include experiments evaluating solid solution formation and the particle size of the drug in the dispersion particles, two factors that can have a profound effect on the dissolution. (B). Solid dispersion preparation involves a recrystallisation process (which is known to be highly sensitive to the recrystallisation conditions) of polyethylene glycol and possibly also of the drug. Therefore, it is of extreme importance that all experiments are performed on dispersion aliquots, which can be believed to be physico-chemical identical. This is not always the case. (C). Polyethylene glycol 6000 (PEG6000) crystallises forming lamellae with chains either fully extended or folded once or twice depending on the crystallisation conditions. Recently, a high resolution differential scanning calorimetry (DSC)-method, capable of evaluating qualitatively and quantitatively the polymorphic behaviour of PEG6000, has been reported. Unraveling the relationship between the polymorphic behavior of PEG6000 in a solid dispersion and the dissolution characteristics of that dispersion, is a real gain to our knowledge of solid dispersions, since this has never been thoroughly investigated. The aim of the present study was to fill up the three above mentioned gaps in solid dispersion literature. Therefore, physical mixtures and solid dispersions were prepared and in order to unravel the relationship between their physico-chemical properties and dissolution characteristics, pure drugs (diazepam, temazepam), polymer (PEG6000), solid dispersions and physical mixtures were characterised by DSC, X-ray powder diffraction (Guinier and Bragg-Brentano method), FT-IR spectroscopy, dissolution and solubility experiments and the particle size of the drug in the dispersion particles was estimated using a newly developed method. Addition of PEG6000 improves the dissolution rate of both drugs. Mechanisms involved are solubilisation and improved wetting of the drug in the polyethylene glycol rich micro-environment formed at the surface of drug crystals after dissolution of the polymer. Formulation of solid dispersions did not further improve the dissolution rate compared with physical mixtures. X-ray spectra show that both drugs are in a highly crystalline state in the solid dispersions, while no significant changes in the lattice spacings of PEG6000 indicate the absence of solid solution formation. IR spectra show the absence of a hydrogen bonding interaction between the benzodiazepines and PEG6000. Furthermore, it was concluded that the reduction of the mean drug particle size by preparing solid dispersions with PEG6000 is limited and that the influence of the polymorphic behavior of PEG6000 (as observed by DSC) on the dissolution was negligible.

Physical stability of solid dispersions of the antiviral agent UC-781 with PEG 6000, Gelucire 44/14 and PVP K30.

This paper describes the physical stability of solid dispersions of UC-781 with PEG 6000, Gelucire 44/14 and PVP K30 prepared by the solvent and melting methods. The concentration of the drug in the solid dispersions ranged from 5 to 80% w/w. The solid dispersions were stored at 4-8 and 25 degrees C (25% RH), then their physicochemical properties were analysed by differential scanning calorimetry (DSC), X-ray powder diffraction and dissolution studies as a function of storage time. The DSC curves of solid dispersions of UC-781 with PVP K30 did not show any melting peaks corresponding to UC-781 after storage, indicating no recrystallization of the drug. The DSC data obtained from PEG 6000 and Gelucire 44/14 showed some variations in melting peak temperatures and enthalpy of fusion of the carriers. It was shown that the enthalpy of fusion of PEG 6000 in the dispersions increased after storage; it was more pronounced for samples stored at 25 degrees C compared to those at 4-8 degrees C indicating the reorganization of the crystalline domains of the polymer. Similarly, the enthalpy of fusion of Gelucire 44/14 in the solid dispersions increased as a function of time. Dissolution of UC-781 from all solid dispersions decreased as a function of storage time. While these observations concurred with the DSC data for all solid dispersions, they were not reflected by X-ray powder diffraction data. It was concluded that it is the change of the physical state of the carriers and not that of the drug, which is responsible for the decreased dissolution properties of the solid dispersions investigated.

Improvement of the dissolution rate of artemisinin by means of supercritical fluid technology and solid dispersions.

The purpose of this study was to enhance the dissolution rate of artemisinin in order to improve the intestinal absorption characteristics. The effect of: (1) micronisation and (2) formation of solid dispersions with PVPK25 was assessed in an in vitro dissolution system [dissolution medium: water (90%), ethanol (10%) and sodium lauryl sulphate (0.1%)]. Coulter counter analysis was used to measure particle size. X-ray diffraction and DSC were used to analyse the physical state of the powders. Micronisation by means of a jet mill and supercritical fluid technology resulted in a significant decrease in particle size as compared to untreated artemisinin. All powders appeared to be crystalline. The dissolution rate of the micronised forms improved in comparison to the untreated form, but showed no difference in comparison to mechanically ground artemisinin. Solid dispersions of artemisinin with PVPK25 as a carrier were prepared by the solvent method. Both X-ray diffraction and DSC showed that the amorphous state was reached when the amount of PVPK25 was increased to 67%. The dissolution rate of solid dispersions with at least 67% of PVPK25 was significantly improved in comparison to untreated and mechanically ground artemisinin. Modulation of the dissolution rate of artemisinin was obtained by both particle size reduction and formation of solid dispersions. The effect of particle size reduction on the dissolution rate was limited. Solid dispersions could be prepared by using a relatively small amount of PVPK25. The formation of solid dispersions with PVPK25 as a carrier appears to be a promising method to improve the intestinal absorption characteristics of artemisinin.

Solid state properties of pure UC-781 and solid dispersions with polyvinylpyrrolidone (PVP K30).

The purpose of this study was to elucidate the physical structure of solid dispersions of the antiviral agent UC-781 (N-[4-chloro-3-(3-methyl-2-butenyloxy)phenyl]-2-methyl-3-furancarbothioamide) with polyvinylpyrrolidone (PVP K30). Solid dispersions were prepared by coevaporating UC-781 with PVP K30 from dichloromethane. The physicochemical properties of the dispersions were evaluated in comparison with the physical mixtures by differential scanning calorimetry (DSC), X-ray powder diffraction, and FT-IR spectroscopy. We investigated the single crystal structure of pure UC-781. The data from single crystal analysis showed that UC-781 crystallized with orthorhombic symmetry in the space group Pcab. Its cell parameters were found to be; a = 8.1556(7) A,b = 17.658(2) A and c = 23.609(2) A; the unit cell was made up of eight molecules of UC-781. The molecules formed intermolecular hydrogen bonds between NH and thio groups, and were packed in a herringbone-like structure. The data from X-ray powder diffraction showed that crystalline UC-781 was changed into the amorphous state by co-evaporating it with PVP K30. From differential scanning calorimetry analysis, UC-781 peaks were observed in the DSC curves of all physical mixtures, while no peaks corresponding to the drug could be observed in the solid dispersions with the same drug composition up to the concentration of 50% w/w. The data from FT-IR spectroscopy showed the distortions and disappearance of some bands from the drug, while other bands were too broad or significantly less intense compared with the physical mixtures of the crystalline drug in PVP K30. Furthermore, the results from IR spectroscopy demonstrated that UC-781 interacted with PVP K30 in solid dispersions through intermolecular H-bonding.

Vibrational characterization of the peptide bond.

This article describes the complete vibrational analysis of N,N'-dimethyloxamide, CH3HNCOCONHCH3, on basis of the infrared and Raman spectra of four isotopes (H, D, CH3, CD3). Force field calculations on the monomers and multimers (n = 5) combined with solid state spectra in the -196 to +100 degrees C temperature range have been used to obtain a better understanding of the influence of hydrogen bonding on the typical amide fundamentals. The cooperative effect in de series monomer --> multimers --> solid state at decreasing temperatures has been demonstrated. Nine typical so-called 'amide bands' have been further characterized and special attention has been given to the Amide IV mode. The influence of the CH and CD vibrations on the amide fundamentals, has been studied by comparison with the calculated and experimental fundamentals and P.E.D. values of the CH3 and CD3 isotopes. The most important amide bands have further been assigned in X-CONHCH3 molecules where X = methyl, amide, thioamide, ester, salt, cyanide and acid functional groups.

Vibrational study of the secondary thioamide function, the intramolecular resonance assisted and intermolecular hydrogen bonding in NN'-hydroxyalkyl dithiooxamides.

The article describes the vibrational characterization of the secondary thioamide formation and especially a spectroscopical interesting study of different types of hydrogen bonding in NN'-dihydroxyalkyldithiooxamides.

The effect of pressure and temperature on the vibrational spectra of different hydrogen bonded systems.

The effect of pressure and temperature on the vibrational spectra of hydrogen bonded systems has been studied on amides, thioamides, carboxylic acids and urea. The compounds under investigation are indicative for the kind of hydrogen bonding changing from pure intermolecular to intramolecular and dimeric forms. The discussion of the temperature dependence on the fundamentals involved in the hydrogen bonding is straightforward but the pressure data are much more complicated and only if the changes in the crystalline state at different pressures are known, we will have a better understanding of the dependence of some fundamentals in the hydrogen bonded systems. A clear example of this approach is given for urea.

Tribenzylphosphine oxide.

The title compound, (C(6)H(5)CH(2))(3)PO, is an organic tertiary phosphine oxide. The molecule has threefold symmetry, with the P-O bond along the threefold axis. Main dimensions include P-O 1.488 (4), P-C 1.823 (3) A and O-P-C 114.7 (1) degrees. The crystals were accidentally obtained when preparing complexes of nickel(II) with dibenzylphosphine.

Synthesis, structural studies and pharmacological activity of novel bicyclic compounds derived from 3,4-dihydropyridones: 4-aryl-7,7-dimethyl-2,5-dioxo-1,2,3,4,5,6,7,8-octahydroquinolines.

The purpose of this research is to characterize the possible vascular selectivity of a series of novel bicyclic compounds derived from 3,4-dihydropyridones. We describe the synthesis, structural study by X-ray analysis and quantum chemical calculations at semiempirical (AMI) and ab initio (HF/321G) levels and pharmacological activity of these 4-aryl-7,7-dimethyl-2,5-dioxo-1,2,3,4,5,6,7,8-octahydroquinolines. In addition, the more favoured conformation for compounds 4a-c in solution was determined from the calculated and experimental proton coupling constants. We report the first computational study on the structure of octahydroquinolines. The results of ab initio (HF/3-21G) and semiempirical molecular orbital calculations (AMI) are compared with the data obtained by X-ray crystallographic study for 4a.

Structure and conformational analysis of the opioid antagonist (-)-(1R,5R,9R)-5,9-diethyl-2-(3-furylmethyl)-2'-hydroxy-6,7-benzomorpha n (Mr2266).

C21H27NO2, Mr = 325.449, monoclinic, P2(1), a = 16.3916 (7), b = 12.7460 (5), c = 8.9806 (5) A, beta = 107.191 (4) degrees, V = 1792.5 (2) A3, Z = 4, Dm = 1.22 (2), D chi = 1.206 Mg m-3, lambda(Cu K alpha) = 1.54178 A, mu(Cu K alpha) = 0.566 mm-1, F(000) = 704, T = 291 K, final R = 0.048 for 4225 observed reflections. The two molecules present in the asymmetric unit adopt a different conformation with respect to the N-side chain. Starting from the asymmetric carbon and proceeding along the allyl moiety the conformations are antiperiplanar/(-)-anticlinal for molecule 1 and antiperiplanar/(+)-synclinal for molecule 2. The furyl rings engage in aromatic-aromatic interactions which are compared with results from a theoretical study from the literature. Finally, the 3-furyl geometry is evaluated through a Cambridge Structural Database search and CNDO/2 calculations.

Structure of a kappa-opioid receptor misfit: (1S,5R,8R,9R)-2'-hydroxy-5,9-dimethyl-8,2-epoxyethano-6,7-benzomorphan hydrochloride.

C16H22NO+2.Cl-, Mr = 295.808, monoclinic, P2(1), a = 11.967 (1), b = 12.529 (1), c = 9.9369 (9) A, beta = 93.00 (1) degrees, V = 1487.8 (2) A3, Z = 4, Dm = 1.32 (2), Dx = 1.321 Mg m-3, lambda(Cu K alpha) = 1.54178 A, mu(Cu K alpha) = 2.289 mm-1, F(000) = 632, T = 291 K, final R = 0.040 for 2448 observed reflections. The two molecules present in the asymmetric unit are linked by an extensive network of hydrogen bonds, including several of the less common (C-)H...O and (C-)-H...Cl types. This interpretation is substantiated by a Mulliken population analysis resulting from CNDO/2 calculations. The major effect of the presence of the epoxyethano bridge is a marked flattening about the N atom of the piperidinium ring. Whether this is sufficient to explain the inactivity of the compound at the opioid kappa receptor is not clear.

Structure and absolute configuration of two stereoisomers of alpha,alpha'-[iminobis-(methylene)]bis(3,4-dihydro-2H-1-benzopyran-2- methanol) hydrobromide.

alpha,alpha'-1,1'-Bis(3,4-dihydro-2H-benzopyran-2-yl)-2,2'-iminodieth anol hydrobromide. (I) C22H28NO4+.Br-, Mr = 450.37, orthorhombic, P2(1)2(1)2(1), a = 5.1278(1), b = 13.1699(6), c = 30.858(2) A, V = 2083.9(2)A3, Z = 4, Dm = 1.44, D chi = 1.436 Mg m-3, lambda(Cu K alpha) = 1.54178 A, mu(Cu K alpha) = 2.915 mm-1, F(000) = 936, room temperature, final R = 0.054 for 2086 observed reflections. (II) C22H28NO4+.Br-, Mr = 450.37, orthorhombic, P2(1)2(1)2(1), a = 5.1292(2), b = 13.1764(9), c = 30.847(3) A, V = 2084.8(3)A3 lambda(Cu K alpha) = 1.54178A, mu(Cu K alpha) = 2.915 mm-1, F(000) = 936, room temperature, final R = 0.054 for 2676 observed reflections. The two structures are mirror images and the central C--C--N--C--C chain adopts the anti-periplanar-synclinal conformation. The active beta 1-selective adrenergic receptor blocker [isomer (I)] has the S,R,R,S absolute configuration while the inactive isomer (II) has the R,S,S,R configuration. Endless chains are formed by (N-)H...Br hydrogen bonds in the a direction and by (O-)H...Br hydrogen bonds in the b direction.