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Our goals were to evaluate the effects of (i) hydrostatic pressure alone and (ii) its combined effect with shear stress during compaction, on the polymorphic transformation (form C → A) of a model drug, chlorpropamide. The powder was either subjected to hydrostatic pressure in a pressure vessel or compressed in a tablet press, at pressures ranging from 25 to 150 MPa. The overall extent of phase transformation was determined by powder X-ray diffractometry, whereas 2D-X-ray diffractometry enabled quantification of the spatial distribution of phase composition in tablets. Irrespective of the pressure, the extent of transformation following compaction was higher than that because of hydrostatic pressure alone, the difference attributed to the contribution of shear stress experienced during compaction. At a compression pressure of 25 MPa, there was a pronounced gradient in the extent of phase transformation when monitored from radial tablet surface to core. This gradient decreased with increase in compression pressure. Four approaches were attempted to minimize the effect of compression-induced phase transformation: (a) site-specific lubrication, (b) use of a viscoelastic excipient, (c) ceramic-lined die, and (d) use of cavity tablet. The ceramic-lined die coupled with site-specific lubrication was most effective in minimizing the extent of compression-induced phase transformation., (Copyright © 2019 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.)

Disproportionation propensity of salts (HCl, HBr, heminapadisylate) and adipic acid cocrystal of corticotropin releasing hormone receptor-1 antagonist was studied using model free kinetics. Using thermogravimetic weight loss profile or heat flow curves from differential scanning calorimetry, an activation energy plot for salts and cocrystal was generated based on model free kinetics. This activation energy of disproportionation provided qualitative information about the solid state salt stability. To ensure the stability throughout the shelf life, "prototype" formulations of salts and cocrystal in tablet form were stored at 40 °C and several water vapor pressures. Disproportionation kinetics were studied in these prototype tablet formulations using two-dimensional X-ray diffractometry. Formulations containing the adipic acid cocrystal or heminapadisylate salt did not show disproportionation of API when stored at 40 °C/75% RH for 300 days. On the other hand, formulations containing HCl or HBr salt disproportionated. Though isostructural, the disproportionation propensity of HBr and HCl salts was quite different. The HCl salt highlighted the important role that volatility of the counterion plays in the physical stability of the formulations. Solution state stability (i.e., in dissolution medium) of salts and cocrystal was also assessed and compared with solid state stability, by determining their solubility at different pH's, and intrinsic dissolution rate.

Transmembrane AMPA receptor regulatory proteins (TARPs) are a family of scaffolding proteins that regulate AMPA receptor trafficking and function. TARP γ-8 is one member of this family and is highly expressed within the hippocampus relative to the cerebellum. A selective TARP γ-8-dependent AMPA receptor antagonist (TDAA) is an innovative approach to modulate AMPA receptors in specific brain regions to potentially increase the therapeutic index relative to known non-TARP-dependent AMPA antagonists. We describe here, for the first time, the discovery of a noncompetitive AMPA receptor antagonist that is dependent on the presence of TARP γ-8. Three major iteration cycles were employed to improve upon potency, CYP1A2-dependent challenges, and in vivo clearance. An optimized molecule, compound (-)-25 (LY3130481), was fully protective against pentylenetetrazole-induced convulsions in rats without the motor impairment associated with non-TARP-dependent AMPA receptor antagonists. Compound (-)-25 could be utilized to provide proof of concept for antiepileptic efficacy with reduced motor side effects in patients.

Crystallization of trehalose dihydrate (C12H22O11·2H2O) was induced by storing tablets of amorphous anhydrous trehalose (C12H22O11) at 65% RH (RT). Our goal was to evaluate the advantages and limitations of two approaches of profiling spatial distribution of drug crystallization in tablets. The extent of crystallization, as a function of depth, was determined in tablets stored for different time-periods. The first approach was glancing angle X-ray diffractometry, where the penetration depth of X-rays was modulated by the incident angle. Based on the mass attenuation coefficient of the matrix, the depth of X-ray penetration was calculated as a function of incident angle, which in turn enabled us to "calculate" the extent of crystallization to different depths. In the second approach, the tablets were split into halves and the split surfaces were analyzed directly. Starting from the tablet surface and moving toward the midplane, XRD patterns were collected in 36 "regions", in increments of 0.05 mm. The results obtained by the two approaches were, in general, in good agreement. Additionally, the results obtained were validated by determining the "average" crystallization in the entire tablet by using synchrotron radiation in the transmission mode. The glancing angle method could detect crystallization up to ∼650 μm and had a "surface bias". Being a nondestructive technique, this method will permit repeated analyses of the same tablet at different time points, for example, during a stability study. However, split tablet analyses, while a "destructive" technique, provided comprehensive and unbiased depth profiling information.

The supersaturation potential of poorly water-soluble compounds is of interest in the context of solubility enhancing formulations for enhanced bioavailability. In this regard, the amorphous "solubility", i.e., the maximum increase in solution concentration that can be obtained relative to the crystalline form, is an important parameter, albeit a very difficult one to evaluate experimentally. The goal of the current study was to develop new approaches to determine the amorphous "solubility" and to compare the experimental values to theoretical predictions. A group of six diverse model compounds was evaluated using the solvent exchange method to generate an amorphous phase in situ, determining the concentration at which the amorphous material was formed. The theoretical estimation of the amorphous "solubility" was based on the thermal properties of the crystalline and amorphous phases, the crystalline solubility, and the estimated concentration of water in the water-saturated amorphous phase. The formation of an amorphous precipitate could be captured transiently for all six compounds and hence the amorphous "solubility" determined experimentally. A comparison of the experimental amorphous "solubility" values to those calculated theoretically showed excellent agreement, in particular when the theoretical estimate method treated the precipitated phase as a supercooled liquid, and took into account heat capacity differences between the two forms. The maximum supersaturation ratio in water was found to be highly compound dependent, varying between 4 for ibuprofen and 54 for sorafenib. This information may be useful to predict improvements in biological exposure for poorly water-soluble compounds formulated as amorphous solid dispersions or other formulations that rely on supersaturation.

Tablets of amorphous indomethacin were compressed at 10, 25, 50, or 100 MPa using either an unlubricated or a lubricated die and stored individually at 35 °C in sealed Mylar pouches. At selected time points, tablets were analyzed by two-dimensional X-ray diffractometry (2D-XRD), which enabled us to profile the extent of drug crystallization in tablets, in both the radial and axial directions. To evaluate the role of lubricant, magnesium stearate was used as "internal" and/or "external" lubricant. Indomethacin crystallization propensity increased as a function of compression pressure, with 100 MPa pressure causing crystallization immediately after compression (detected using synchrotron radiation). However, the drug crystallization was not uniform throughout the tablets. In unlubricated systems, pronounced crystallization at the radial surface could be attributed to die wall friction. The tablet core remained substantially amorphous, irrespective of the compression pressure. Lubrication of the die wall with magnesium stearate, as external lubricant, dramatically decreased drug crystallization at the radial surface. The spatial heterogeneity in drug crystallization, as a function of formulation composition and compression pressure, was systematically investigated. When formulating amorphous systems as tablets, the potential for compression induced crystallization warrants careful consideration. Very low levels of crystallization on the tablet surface, while profoundly affecting product performance (decrease in dissolution rate), may not be readily detected by conventional analytical techniques. Early detection of crystallization could be pivotal in the successful design of a dosage form where, in order to obtain the desired bioavailability, the drug may be in a high energy state. Specialized X-ray diffractometric techniques (2D; use of high intensity synchrotron radiation) enabled detection of very low levels of drug crystallization and revealed the heterogeneity in crystallization within the tablet.

Mitosis inhibitor (R)-litronesib (LY2523355) is a 1,3,4-thiadiazoline-bearing phenyl and N-(2-ethylamino)ethanesulfonamido-methyl substituents on tetrahedral C5. Chiral instability has been observed at pH 6 and above with the rate of racemization increasing with pH. A positively charged trigonal intermediate is inferred from the fact that p-methoxy substituent on the phenyl accelerated racemization, whereas a p-trifluoromethyl substituent had the opposite effect. Racemization is proposed to occur through a relay mechanism involving intramolecular deprotonation of the sulfonamide by the side chain amino group and attack of the sulfonamide anion on C5, cleaving the C5S bond, to form an aziridine; heterolytic dissociation of the aziridine yields an ylide. This pathway is supported by (1) a crystal structure providing evidence for a hydrogen bond between the sulfonamide NH and the amino group, (2) effects of substituents on the rate of racemization, and (3) computational studies. This racemization mechanism results from neighboring group effects in this densely functionalized molecule. Of particular novelty is the involvement of the side-chain secondary amino group, which overcomes the weak acidity of the sulfonamide by anchimeric assistance., (© 2014 Wiley Periodicals, Inc. and the American Pharmacists Association.)

As part of our ongoing interest in identifying novel agonists acting at metabotropic glutamate (mGlu) 2/3 receptors, we have explored the effect of structural modifications of 1S,2S,5R,6S-2-aminobicyclo[3.1.0]hexane-2,6-dicarboxylate (LY354740), a potent and pharmacologically balanced mGlu2/3 receptor agonist. Incorporation of relatively small substituents (e.g., F, O) at the C4 position of this molecule resulted in additional highly potent mGlu2/3 agonists that demonstrate excellent selectivity over the other mGlu receptor subtypes, while addition of larger C4-substituents (e.g., SPh) led to a loss of agonist potency and/or the appearance of weak mGlu2/3 receptor antagonist activity. Further characterization of the α-fluoro-substituted analogue (LY459477) in vivo revealed that this molecule possesses good oral bioavailability in rats and effectively suppresses phencyclidine-evoked locomotor activity at doses that do not impair neuromuscular coordination. This molecule therefore represents a valuable new addition to the arsenal of pharmacological tools competent to investigate mGlu2/3 receptor function both in vitro and in vivo.

Serotonin norepinephrine reuptake inhibitor (SNRI) pyrrolidinyl ether 2 was synthesized by employing a dynamic kinetic resolution (DKR) with enantio- and diastereoselective hydogenation on β-keto-γ-lactam 8 to afford β-hydroxy-γ-lactam 9 with 96% ee and 94% de. Reduction of 9 and purification via the dibenzoyl-(L)-tartaric acid diastereomeric salt 16 enriched the ee and de to 100%. While screening hydrogenation reaction systems with ruthenium-BINAP catalysts to prepare 9, it was found that adding catalytic HCl and LiCl enabled higher yields. In addition, the rate and equilibrium of the DKR-hydrogenation of 8 to give 9 was studied by online NMR and chiral HPLC, which indicated that one of the enantiomers of 8 was reducing faster to 9 than the equilibration of the stereocenter of 8.

The objective of the described research effort was to identify a novel serotonin and norepinephrine reuptake inhibitor (SNRI) with improved norepinephrine transporter activity and acceptable metabolic stability and exhibiting minimal drug-drug interaction. We describe herein the discovery of a series of 3-substituted pyrrolidines, exemplified by compound 1. Compound 1 is a selective SNRI in vitro and in vivo, has favorable ADME properties, and retains inhibitory activity in the formalin model of pain behavior. Compound 1 thus represents a potential new probe to explore utility of SNRIs in central nervous system disorders, including chronic pain conditions.

Purpose: Salts of active pharmaceutical ingredients are often used to enhance solubility, dissolution rate, or take advantage of other improved solid-state properties. The selected form must be maintained during processing and shelf-life to ensure quality. We aimed to develop a model to quantify risk of disproportionation, where the salt dissociates back to the freebase form., Methods: A mechanistic model based on thermodynamics was built to predict disproportionation. Stress testing of molecules in combination with excipients was used to benchmark model predictions. X-ray powder diffraction and solid-state NMR were used to quantify the formation of freebase experimentally., Results: 13 pharmaceutical compounds were screened in 4 formulations containing different combinations of excipients. The test set spanned molecules which did and did not disproportionate and also formulations which did and did not induce disproportionation. Model predictions were in qualitative agreement with the experimental data, recovering trends of how disproportionation varies with humidity, formulation excipients, base pK(a) and solubility of the API., Conclusions: The model can predict the balance between different driving forces for disproportionation with limited experimental data resulting in a tool to aid in early-phase risk assessment and formulation design with respect to disproportionation.

When selecting the physical form of an active pharmaceutical substance, there is often a question of when a molecule's pKa renders it too low for salt formation and formulation into a product that will be sufficiently physically stable to provide adequate shelf life. In the paper, a graph is provided that tabulates pKa values of active pharmaceuticals versus the salt or free base form that was chosen to be developed as an orally administered drug product. Tabulation of the data provides insight into where, if any, practical cutoff exists, under which salt formation should not be considered. Specific examples of disproportionation reactions are reviewed and are described in light of the concepts of pH maximum, pH microenvironment, and Gibbs free energy to gain further insight into when such reactions become favorable. The driving force for disproportionation reactions is substantially greater than that for polymorphic form conversion, and as a consequence, its probability of occurring in the solid-state is much greater when formulated in favorable microenvironments. Factors that influence the reaction rate are examined. It is concluded that each salt should be evaluated on the merit of its physical properties and often the most soluble salt will not be one's best choice. Unfortunately, compounds that stand to benefit the most from salt formation due to their exceptionally low intrinsic solubility are the ones that will be most likely to disproportionate if their pKa is relatively low., (Copyright © 2010 Wiley-Liss, Inc.)

The design, synthesis, and biological characterization of an orally active prodrug (3) of gemcitabine are described. Additionally, the identification of a novel co-crystal solid form of the compound is presented. Valproate amide 3 is orally bioavailable and releases gemcitabine into the systemic circulation after passing through the intestinal mucosa. The compound has entered clinical trials and is being evaluated as a potential new anticancer agent.

A novel, potent series of indole analogs were recently developed as MR antagonists, culminating in 14. This compound represents the first MR antagonist in this class of molecules, exhibiting picomolar binding affinity and in vivo blood pressure lowering at pharmaceutically relevant doses.

(-)-4-Amino-2-thiabicyclo-[3.1.0]hexane-4,6-dicarboxylate (LY389795, (-)-3) is a highly potent and selective agonist of metabotropic glutamate receptors 2 (mGlu2) and 3 (mGlu3). As part of our ongoing research program, we have prepared S-oxidized variants of (-)-3, compounds (-)-10, (+)-11 (LY404040), and (-)-12 (LY404039). Each of these chiral heterobicyclic amino acids displaced specific binding of the mGlu2/3 receptor antagonist 3H-2S-2-amino-2-(1S,2S-2-carboxycycloprop-1-yl)-3-(xanth-9-yl)propanoic acid (3H-LY341495) from membranes expressing recombinant human mGlu2 or mGlu3 and acted as potent agonists in cells expressing these receptor subtypes. Docking of the most potent of these derivatives, (+)-11, to mGlu2 revealed the possibility of an additional H-bond interaction between the sulfoxide oxygen of (+)-11 with tyrosine residue Y236. Pharmacokinetic analysis of mGlu active enantiomers (+)-11 and (-)-12 in rats showed each to be well absorbed following oral administration. Consistent with their mGlu2/3 agonist potency and pharmacokinetic properties, both (+)-11 and (-)-12 blocked phencyclidine-evoked ambulations in a dose-dependent manner, indicating their potential as nonclassical antipsychotic agents.

Stratteratrade mark is the first FDA-approved nonstimulant medication for the treatment of Attention Deficit Hyperactivity Disorder (ADHD) in children, adolescents, and adults. Two polymorphic forms and an amorphous form of the active pharmaceutical ingredient, atomoxetine HCl, were discovered during drug development. The thermodynamically stable polymorphic form was selected for the commercial product. The stable form readily grows as crystals suitable for single crystal diffraction. The meta-stable crystal form is isolated by rapid crystallization, providing crystals that are too small for routine single crystal methods; consequently its structure was determined by X-ray powder diffraction., (Copyright 2006 Wiley-Liss, Inc.)

The following article examines the influence of thermal expansion on X-ray powder diffraction patterns. With the increasing percentages of structures that are being solved using low-temperature data sets and the nearly exclusive collection of room-temperature experimental datasets by X-ray powder diffraction, considerable discrepancies are observed when comparing calculated powder diffraction patterns to experimental patterns. Such comparisons are extremely valuable to solid-state pharmaceutical scientists attempting to identify crystal forms of active pharmaceutical ingredients and excipient components of formulations. In this study, fluoxetine HCl, raloxifene HCl, and olanzapine are examined and serve as practical laboratory examples. The observations are supported through analysis of data presented in the Cambridge Structural Database to help assess the extent and potential impact of this problem.

The stereospecific synthesis of the PPAR alpha/gamma agonist 1 was accomplished via ethylation of the optically pure trihydroxy derivative 6, itself derived via an enzymatic resolution. The ethylation can be accomplished without epimerization only under strict control of the reaction conditions and the choice of base (sodium tert-amylate), temperature (-30 degrees C), order of addition, and solvent (DMF). The key diastereospecific SN2 reaction of the phenol 4 with S-2-chloropropionic acid is best achieved via the sodium phenoxide of 4 derived from Na0 as the reagent of choice. The structure elucidation and key purification protocols to achieve pharmaceutical purity will also be described.

The design and synthesis of the dual peroxisome proliferator activated receptor (PPAR) alpha/gamma agonist (S)-2-methyl-3-[4-[2-(5-methyl-2-thiophen-2-yl-oxazol-4-yl)ethoxy]phenyl]-2-phenoxypropionic acid (2) for the treatment of type 2 diabetes and associated dyslipidemia are described. 2 possesses a potent dual hPPAR alpha/gamma agonist profile (IC(50) = 28 and 10 nM; EC(50) = 9 and 4 nM, respectively, for hPPARalpha and hPPARgamma). In preclinical models, 2 substantially improves insulin sensitivity and potently reverses diabetic hyperglycemia while significantly improving overall lipid homeostasis.

Residual dipolar couplings (RDCs), in combination with molecular order matrix calculations, were used to unambiguously determine the complete relative stereochemistry of an organic compound with five stereocenters. Three simple one-dimensional experiments were utilized for the measurements of (13)C-(1)H, (13)C-(19)F, (19)F-(1)H, and (1)H-(1)H RDCs. The order matrix calculation was performed on each chiral isomer independently. The fits were evaluated by the comparison of the root-mean-square deviation (rmsd) of calculated and measured RDCs. The order tensor simulations based on two different sets of RDC data collected with phage and bicelles are consistent. The resulting stereochemical assignments of the stereocenters obtained from using only RDCs are in perfect agreement with those obtained from the single-crystal X-ray structure. Six RDCs are found to be necessary to run the simulation, and seven are the minimum to get an acceptable result for the investigated compound. It was also shown that (13)C-(1)H and (1)H-(1)H RDCs, which are the easiest to measure, are also the most important and information-rich data for the order matrix calculation. The effect of each RDC on the calculation depends on the location of the corresponding vector in the structure. The direct RDC of a stereocenter is important to the configuration determination, but the configuration of stereocenters devoid of protons can also be obtained from analysis of nearby RDCs.

2-Amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl)propanoic acid (AMPA) potentiators are ligands that act as positive allosteric modulators at the AMPA receptors. We recently disclosed a novel series of 2-arylpropylsulfonamides that were potent potentiators of responses mediated through AMPA receptors. To further define the structural requirements for activity in this series, new ring-constrained analogues were prepared and a new stereocenter was introduced. The potentiating activity was highly dependent on the stereochemistry at the 2-position of the disubstituted cyclopentane and was independent of the relative stereochemistry at the 1-position. Compound (R,R)-10 represents a potent, novel potentiator of iGluR4 flip receptors (EC(50) = 22.6 nM).

Quantitative analysis of solid state composition is often used to ensure the safety and efficacy of drug substances or to establish and validate the control of the pharmaceutical production process. There are a number of common techniques that can be applied to quantify the phase composition and numerous different methods for each technique. Each quantitative option presents its own issues in ensuring accuracy and precision of the solid state method. The following article describes many of the common techniques that are used for quantitative phase analysis and many of the considerations that are necessary for the development of such methods.

Recent advances in crystallographic computing have made it possible to solve by powder diffraction methods structures that have not been possible to solve by single-crystal methods. Although there is vast improvement in the quality of data obtained from high-intensity synchrotron radiation, we found that surprisingly reliable results can be obtained from conventional laboratory sources. In this article we examine the application of Monte Carlo/simulated annealing methods for the determination of structures ranging in complexity from 9 to 15 degrees of freedom. We re-determine the structures of papaverine hydrochloride and erythromycin A dihydrate by the powder diffraction method and compare the structures to those determined by single-crystal diffraction methods. The structure of a metastable polymorphic form of acetohexamide, form B, is solved and examined spectroscopically. Its structure has not previously been solved by single-crystal techniques because of the small size of its crystals.

The hydrated crystal structures of cromolyn, cefazolin, and fenoprofen sodium salts are reported. The former two compounds are non-stoichiometric hydrates, whereas the fenoprofen lattice maintains its stoichiometry over a broad range of relative humidity. The relationship between composition, lattice parameters, and relative humidity is studied using a combination of moisture sorption isotherms and variable humidity X-ray powder diffraction. The dehydration properties of the sodium salts are related to the ion coordination and hydrogen bonding of the water molecules in the structures. Anisotropic lattice contraction is observed during dehydration of the cromolyn and cefazolin sodium and is related to the closeness of intermolecular contacts in the hydrated structures.

The synthesis and biological evaluation of trans-2,3-dihydroraloxifene, 2, is described. The synthesis proceeds in 8 steps in 20% overall yield. Relative trans 2,3-stereochemistry is definitively established in ester 6, which is converted to the title compound via derivatization, Grignard addition, and deprotection. Evaluation in vitro shows the compound to be a potent selective estrogen receptor modulator (SERM).

The objective of this work was to investigate a common but poorly understood category of crystalline organic substances: isomorphic desolvates. When solvent is lost from a crystal lattice but the lattice retains its three-dimensional order, a lattice is created which is in a high-energy state relative to the original solvate structure. The desolvated lattice can reduce its internal energy by either resorbing solvent or by relaxation processes which increase the packing efficiency of the solid by reducing the unit cell volume. In the following paper, solid-state properties of isomorphic desolvates of cephalexin, cefaclor, erythromycin A, and spirapril hydrochloride hydrates are investigated. The hygroscopicity of the compounds are evaluated using a vacuum moisture balance, and structural relaxation is measured using a combination of X-ray powder diffraction and isothermal microcalorimetry. The study results are explained in terms of Kitaigorodski's close packing principle.

The crystal structures of the commercially available form of erythromycin A dihydrate and clarithromycin anhydrate, in addition to the structure of erythromycin B dihydrate, are reported in this paper. In light of the crystallographic data, analysis of the structural information provides insight into the physical properties of these pharmaceuticals. The propensity of these pharmaceuticals to form solvated structures is discussed and the hygroscopicity of erythromycin A dihydrate is investigated. Solid-state 13C NMR was used to monitor changes that occur when the dihydrate form of erythromycin A is stored under conditions of low relative humidity. Although erythromycin A dihydrate retains its crystallographic order at low humidity, as indicated by its X-ray powder diffraction pattern, the local chemical environment is dramatically influenced by the loss of the water molecules and results in dramatic changes in its solid-state 13C NMR spectrum.

The aqueous acidic degradation of the oral cephalosporin cefaclor was investigated. A number of degradation products were isolated and characterized. The degradation products can be loosely classified into three categories: thiazole derivatives, pyrazine derivatives, and simple hydrolysis or rearrangement products. Degradation pathways are proposed that involve (1) hydrolysis of the beta-lactam carbonyl with subsequent rearrangement, (2) ring contraction of the six-membered cephem nucleus to five-membered thiazole derivatives through an episulfonium ion intermediate, and (3) attack of the primary amine of the phenylglycyl side chain on the "masked aldehyde" at carbon-6 to form fluorescent substituted pyrazines.