Stereochemical aspects of the molecular pharmaceutics of ibuprofen

Quantum Chemistry and Pharmacy: Diagnostic Check of the Thermochemistry of Ibuprofen

The thermodynamic data on ibuprofen available in the literature shows that the disarray of experimental results is unacceptable for this very important drug. The data on ibuprofens available in the literature were collected, combined with our complementary experimental results and evaluated. The enthalpies of combustion and formation of the crystalline RS-(±)- and S-(+)-ibuprofens were measured using high-precision combustion calorimetry. The temperature dependence of the vapour pressure of S-(+)-ibuprofen was measured using the transpiration method and the enthalpy of vaporization was derived from this measurement. The enthalpies of fusion of both compounds were measured using DSC. The G4 calculations have been carried out to determine the enthalpy of formation in the gaseous state of the most stable conformer. Thermochemical properties of the compounds studied were evaluated and tested for consistency with the "centerpiece approach". A set of reliable and consistent values of thermodynamic properties of ibuprofens at 298.15 K is recommended for thermochemical calculations of the pharmaceutical processes. The diagnostic protocol was developed to distinguish between the "sick" or "healthy" thermodynamic data. This diagnostic is also applicable to other drugs with a different structure than ibuprofen.

Complexes of Ibuprofen Thiazolidin-4-One Derivatives with β-Cyclodextrin: Characterization and In Vivo Release Profile and Biological Evaluation

Generally, NSAIDs are weakly soluble in water and contain both hydrophilic and hydrophobic groups. One of the most widely used NSAIDs is ibuprofen, which has a poor solubility and high permeability profile. By creating dynamic, non-covalent, water-soluble inclusion complexes, cyclodextrins (CDs) can increase the dissolution rate of low aqueous solubility drugs, operating as a drug delivery vehicle, additionally contributing significantly to the chemical stability of pharmaceuticals and to reducing drug-related irritability. In order to improve the pharmacological and pharmacokinetics profile of ibuprofen, new thiazolidin-4-one derivatives of ibuprofen (4b, 4g, 4k, 4m) were complexed with β-CD, using co-precipitation and freeze-drying. The new β-CD complexes (β-CD-4b, β-CD-4g, β-CD-4k, β-CD-4m) were characterized using scanning electronic microscopy (SEM), differential scanning calorimetry (DSC), X-ray diffraction and a phase solubility test. Using the AutoDock-VINA algorithm included in YASARA-structure software, we investigated the binding conformation of ibuprofen derivatives to β-CD and measured the binding energies. We also performed an in vivo biological evaluation of the ibuprofen derivatives and corresponding β-CD complexes, using analgesic/anti-inflammatory assays, as well as a release profile. The results support the theory that β-CD complexes (β-CD-4b, β-CD-4g, β-CD-4k, β-CD-4m) have a similar effect to ibuprofen derivatives (4b, 4g, 4k, 4m). Moreover, the β-CD complexes demonstrated a delayed release profile, which provides valuable insights into the drug-delivery area, focused on ibuprofen derivatives.

Scalemic mixtures preparation for optimized composition of ibuprofen solid dosage forms

The stable and metastable phase diagrams between the sinister and the rectus ibuprofen enantiomers were established by means of thermal analysis and X-ray powder diffraction experiments as a function of temperature. The results obtained allow proving for the first time the existence, for the stable system, of a solid solution by mixing the racemic ibuprofen with one of its enantiomers for low concentration of the enantiomer. Since the rectus ibuprofen is a non-active pharmaceutical agent which can be partially bio-converted into the sinister enantiomer, the present work offers a new approach for scalemic mixtures preparation in order to improve the benefit/risk ratio related to ibuprofen solid dosage form administration.

Sila-Ibuprofen

The synthesis, characterization, biological activity, and toxicology of sila-ibuprofen, a silicon derivative of the most common nonsteroidal anti-inflammatory drug, is reported. The key improvements compared with ibuprofen are a four times higher solubility in physiological media and a lower melting enthalpy, which are attributed to the carbon-silicon switch. The improved solubility is of interest for postsurgical intravenous administration. A potential for pain relief is rationalized via inhibition experiments of cyclooxygenases I and II (COX-I and COX-II) as well as via a set of newly developed methods that combine molecular dynamics, quantum chemistry, and quantum crystallography. The binding affinity of sila-ibuprofen to COX-I and COX-II is quantified in terms of London dispersion and electrostatic interactions in the active receptor site. This study not only shows the potential of sila-ibuprofen for medicinal application but also improves our understanding of the mechanism of action of the inhibition process.

Dissecting intermolecular interactions in the condensed phase of ibuprofen and related compounds: the specific role and quantification of hydrogen bonding and dispersion forces

Ibuprofen is a well-established non-steroidal anti-inflammatory drug, inhibiting the prostaglandin-endoperoxide synthase. One of the key features defining the ibuprofen structure is the doubly intermolecular O-HO[double bond, length as m-dash]C hydrogen bond in cyclic dimers as know from carboxylic acids and confirmed by X-ray analysis. Until now, there was neither information about the vaporization enthalpy of ibuprofen nor about how this thermal property is determined by the subtle balance between different types of intermolecular interaction. In this study we derive the vaporization enthalpy of ibuprofen from thermochemical experiments to be . We dissected the hydrogen bond energy, EHB = 45.0 kJ mol-1, exclusively from measured vaporization enthalpies of related aliphatic carboxylic acids, their homomorph methyl esters and alkyl acetates, respectively. This contribution from hydrogen bonding could be confirmed almost quantitatively from quantum chemical calculations of ibuprofen clusters, which also suggest dispersion interaction of similar order (Edisp = 47 kJ mol-1). Following the full analysis of the gas-vapor transition enthalpy, we studied the changing structural components from the solid to the liquid phase of ibuprofen by means of Attenuated Total Reflection Infrared (ATR-IR) spectroscopy. The cyclic dimers as observed in the X-ray patterns are essentially preserved in the liquid state just above the melting point. However, with increasing temperature the doubly hydrogen-bonded cyclic dimers are replaced by singly hydrogen-bonded linear dimers in the liquid ibuprofen. The transfer enthalpy from the temperature-dependent equilibria of both dimers as obtained from the IR intensity ratios of the vibrational bands quantifies for the first time the energy of the released, single hydrogen bond to be EHB = 21.0 kJ mol-1. Overall, we show that a combination of thermodynamics, infrared spectroscopy and quantum chemistry provides quantification and detailed understanding of structure and molecular interaction in ibuprofen and related compounds.

Impact of chirality on peculiar ibuprofen molecular dynamics: hydrogen bonding organization and syn vs. anti carboxylic group conformations

Impact of chirality (R and S enantiomers) on syn vs. anti carboxylic group conformations, hydrogen bond dimers and peculiar ibuprofen molecular dynamics.

Crystallization from the amorphous state: nucleation-growth decoupling, polymorphism interplay, and the role of interfaces

The physical stability of the amorphous state is governed by crystallization, which results from the complex interplay of nucleation and growth processes. These processes can be further complicated by the preferred initial nucleation of less-stable phases, and interpretation requires the evaluation of the relative roles of structure, dynamics, and thermodynamics on the kinetics of the recrystallization. As a contribution to this issue, we reanalyze data sets concerning recrystallization of two pharmaceutical compounds: L-arabitol and RS ibuprofen. These compounds share the property of being good glass formers and present monotropic polymorphism. In the present analysis, we are mainly focusing on the localization of nucleation and growth zones and the role of a transient crystallization of the metastable phase. On the basis of the elementary theories, the results offer the opportunity to discuss the impact of interfacial energies, molecular mobility, crystal disorder, liquid short-range order, and crack formation in the glass.

Overall stability for the ibuprofen racemate: experimental and topological results leading to the pressure-temperature phase relationships between its racemate and conglomerate

Enantiomer resolution is much sought after for pharmaceutical applications, because many optically active drug molecules have only one pharmaceutically active enantiomer. Although it is always possible to force separation, it will come at a cost. The present method, based on thermodynamics, provides a relatively easy approach to investigate whether separation can be thermodynamically spontaneous. A topological phase diagram of the binary enantiomer system at 0.5 mol-fraction is constructed as a function of temperature and pressure after analysis of pressure and heat related quantities. It is demonstrated that for ibuprofen, an optically active analgesic, the racemate is the only stable solid form; the phase relationship between the racemate and the conglomerate is analogous to dimorphism with overall monotropy in pure chemical compounds.

An examination of the thermodynamics of fusion, vaporization, and sublimation of ibuprofen and naproxen by correlation gas chromatography

The vaporization enthalpies of (S)-ibuprofen and (S)-naproxen measured by correlation gas chromatography at T = 298.15 K are reported and compared with literature values. Adjustment of the fusion enthalpies of (RS)- and (S)-ibuprofen and (S)-naproxen to T = 298.15 K and combined with the vaporization enthalpy of the (S)-enantiomer of both ibuprofen and naproxen also at T = 298.15 K resulted in the sublimation enthalpies of both (S)-enantiomers. On the assumption that the vaporization enthalpy of the racemic form of ibuprofen is within the experimental uncertainty of the chiral form, the sublimation enthalpy of racemic ibuprofen was also evaluated. The vaporization and sublimation enthalpies compare favorably to the most of the literature values for the racemic form of ibuprofen but differ from the value reported for chiral ibuprofen. The literature values of (S)-naproxen are somewhat smaller than the values measured in this work. The following vaporization enthalpies were measured for (S)-ibuprofen and (S)-naproxen, respectively: ΔH(vap) (298.15 K), 106.0 ± 5.5, 132.2 ± 5.0 kJ·mol(-1) . Sublimation enthalpies of 122.7 ± 5.6 and 155.2 ± 7.1 kJ·mol(-1) were calculated for the (S)-enantiomers of ibuprofen and naproxen and a value of 128.9 ± 5.8 kJ·mol(-1) was estimated for the racemic form of ibuprofen.

Dielectric Relaxation and Crystallization of Ultraviscous Melt and Glassy States of Aspirin, Ibuprofen, Progesterone, and Quinidine

Molecular relaxation in ultraviscous melt and glassy states of aspirin, ibuprofen, progesterone, and quinidine has been studied by dielectric spectroscopy. The asymmetric relaxation spectra is characterized by the Kohlrausch distribution parameter of 0.46 +/- 0.02 for aspirin to 0.67 +/- 0.02 for progesterone. The dielectric relaxation time varies with the temperature, T, according to the Vogel-Fulcher-Tammann Equation, log(10)(tau(0)) = A(VFT) + [B(VFT)/(T - T(0))], where A(VFT), B(VFT), and T(0) are empirical constants. The extrapolated tau(0) at calorimetric glass-softening temperature is close to the value expected. The equilibrium permittivity, epsilon(0), is lowest for ibuprofen which indicates an antiparallel orientation of dipoles in its liquid's hydrogen-bonded structure. A decrease in epsilon(0) with time shows that ultraviscous aspirin, progesterone, and quinidine begin to cold-crystallize at a relatively lower temperature than ibuprofen. epsilon(0) of the cold-crystallized phases are, 4.7 for aspirin at 290 K, 2.55 for ibuprofen at 287 K, 2.6 for progesterone at 320 K, and 3.2 for quinidine at 375 K. It is argued that hydrogen-bonding, the Kohlrausch parameter, extent of localized motions and the long-range diffusion times all determine the physical and chemical stability of an amorphous pharmaceutical during storage.

Recent progress in the computational prediction of aqueous solubility and absorption

The computational prediction of aqueous solubility and/or human absorption has been the goal of many researchers in recent years. Such an in silico counterpart to the biopharmaceutical classification system (BCS) would have great utility. This review focuses on recent developments in the computational prediction of aqueous solubility, P-glycoprotein transport, and passive absorption. We find that, while great progress has been achieved, models that can reliably affect chemistry and development are still lacking. We briefly discuss aspects of emerging scientific understanding that may lead to breakthroughs in the computational modeling of these properties.

Solubility of (+/-)-ibuprofen and S (+)-ibuprofen in the presence of cosolvents and cyclodextrins

Aqueous solubility is an important parameter for the development of liquid formulations and in the determination of bioavailability of oral dosage forms. Ibuprofen (IB), a nonsteroidal anti-inflammatory drug, is a chiral molecule and is currently used clinically as a racemate (racIB). However, the S form of ibuprofen or S(+)-ibuprofen (SIB) is the biologically active isomer and is primarily responsible for the antiinflammatory activity. Phase solubility studies were carried out to compare the saturation solubilities of racIB and SIB in the presence of common pharmaceutical solvents such as glycerol, sorbitol solution, propylene glycol (PG), and polyethylene glycol (PEG 300) over the range of 20% to 80% v/v in aqueous based systems. The solubilities of the two compounds were also compared in the presence of cyclodextrins such as beta cyclodextrin (CD), hydroxypropyl beta cyclodextrin (HPCD), and beta cyclodextrin sulfobutyl ether sodium salt (CDSB) over the range of 5% to 25% w/v. Solubility determinations were carried at 25 degrees C and 37 degrees C. Cosolvents exponentially increased the solubility of both SIB and racIB, especially in the presence of PG and PEG 300. Glycerol was not very effective in increasing the aqueous solubilities of both compounds, whereas sorbitol solution had a minimal effect on their solubility. PG and PEG 300 increased the solubility of SIB by 400-fold and 1500-fold, respectively, whereas the rise in solubility for racIB was 193-fold and 700-fold, respectively, at 25 degrees C for the highest concentration of the cosolvents used (80% v/v). Of the two compounds studied, higher equilibrium solubilities were observed for SIB as compared with racIB. The derivatized cyclodextrins increased the aqueous solubility of racIB and SIB in a concentration-dependent manner giving AL type of phase diagrams. The phase solubility diagrams indicated the formation of soluble inclusion complexes between the drugs and HPCD and CDSB, which was of 1:1 stoichiometry. The addition of underivatized CD reduced the solubility of racIB and SIB via the formation of an insoluble complex. The S form formed more stable complexes with HPCD and CDSB as compared with raclB. The solubilization process is discussed in terms of solvent polarity and differential solid-state structure of raclB and SIB. The thermodynamic parameters for the solubilization process are presented.

Interactions of Poly(vinylpyrrolidone) with Ibuprofen and Naproxen: Experimental and Modeling Studies

PURPOSE

To elucidate the differences in the interaction of chiralic ibuprofen (IBP) and naproxen (NAP) with poly(vinylpyrrolidone) (PVP) in a solid state.

METHODS

Drugs/PVP physical mixtures and solid dispersions were characterized by scanning electron microscope (SEM), Fourier transform infrared spectrometry (FT-IR), solid state (13)C NMR spectroscopy, and x-ray diffractometry. Molecular modeling study of the crystal structures and PVP was performed.

RESULTS

A spontaneous conversion of IBP/PVP physical mixtures in a stable glasslike form (solid dispersion) was observed after storage. The enantiomer reacted more strongly than the racemate. NAP did not interact with PVP. The crystal structures of drugs showed differences in the hydrogen bonding, aromatic interactions, molecular energies, and distances inside the crystals. The trimer structure of PVP was built and optimized. It was proposed that each PVP monomer could interact with one IBP dimmer in contrast to NAP, where two out of three PVP monomers faced the catemer carboxylic groups.

CONCLUSIONS

The differences in the interaction of PVP with racemic IBP, enantiomer IBP, and NAP can be related to the differences in their crystal structures. The correlation between the experimental data and the results of the molecular modeling analysis suggest that the IBP dimmer structures are likely to perform HB and aromatic interactions with PVP.

Thermodynamics of sublimation, crystal lattice energies, and crystal structures of racemates and enantiomers: (+)- and (+/-)-ibuprofen

Thermodynamic differences between ibuprofen (IBP) racemate and the (+)-enantiomer were studied by X-ray diffraction, thermoanalysis, and crystal energy calculations. The thermodynamic functions of sublimation (as a measure of crystal lattice energy) were obtained by the transpiration method. The sublimation enthalpies (DeltaH(sub)) of (+/-)-IBP and (+)-IBP are 115.8 +/- 0.6 and 107.4 +/- 0.5 kJ. mol(-1), respectively. Using the temperature dependency of the saturated vapor pressure, the relative fractions of enthalpy and entropy of the sublimation process were calculated, and the sublimation process for both the racemate and the enantiomer was found to be enthalpy driven (62%). Two different force fields, Mayo et al. (M) and Gavezzotti (G), were used for comparative analysis of crystal lattice energies. Both force fields revealed that the van der Waals term contributes more to the packing energy in (+)-IBP than in (+/-)-IBP. The hydrogen bonding energy, however, contributes at 29.7 and 32.3% to the total crystal lattice energy in (+)-IBP and (+/-)-IBP (M), respectively. Furthermore, different structure fragments of the IBP molecule were analyzed with respect to their contribution to nonbonded van der Waals interactions. The effect of the C-H distance on the van der Waals term of the crystal lattice energy was also studied.

Racemic species of sodium ibuprofen: characterization and polymorphic relationships

Racemic and homochiral sodium ibuprofen were characterized by thermal analysis and powder X-ray diffractometry. The melting point phase diagram was constructed and thermodynamic calculation was performed. In contrast to racemic ibuprofen, which is a racemic compound, racemic sodium ibuprofen forms both a racemic conglomerate (termed the gamma-form) as well as two polymorphic racemic compounds, alpha and beta, which are less stable monotropes. From the supercooled liquid, alpha and beta crystallized along with the original gamma-form. Forms alpha and beta are "enantiotropically related" with a transition temperature between 75 degrees and 113 degrees C, but can be considered to be metastable monotropes of the racemic conglomerate, the stable gamma-form.