High-throughput crystallization: polymorphs, salts, co-crystals and solvates of pharmaceutical solids

Selective manipulation of L-cysteine crystal polymorphs using focused laser beams

The selective manipulation of crystal polymorphs holds profound implications across diverse scientific and industrial fields, as distinct polymorphs exhibit unique physical and chemical properties. This study demonstrates selective polymorphic manipulation by laser trapping - a technique enabling contactless manipulation and condensation of matter at the nanometer-scale and micrometer-scale. L-cysteine, a ubiquitous amino acid employed in pharmaceuticals and food additives, was targeted. We reveal that continuous-wave laser irradiation yields single crystals of the metastable polymorph, whereas continued irradiation with high-repetition-rate femtosecond laser pulses induces poly-crystallization of the stable form. Crucially, by strategically alternating between these two laser modalities during crystal growth, we can open up new crystallization pathways, including the single crystal growth of the stable phase. These findings underscore the significant potential of focused laser beams for precision polymorphic engineering, paving the way for the development of advanced materials with tailored properties.

High-throughput encapsulated nanodroplet screening for accelerated co-crystal discovery

Co-crystals are composed of two or more chemically inequivalent molecular species, excluding solvents, generally in a stoichiometric ratio. Co-crystals are particularly important in pharmaceutical development, where a suitable co-crystal can significantly improve the physiochemical and pharmacokinetic properties of an active pharmaceutical ingredient. However, co-crystal discovery remains both practically challenging and resource intensive, requiring the extensive searching of complex experimental space. Herein, we demonstrate a high-throughput (HTP) nanoscale co-crystallisation method for the rapid screening of large areas of co-crystallisation space with minimal sample requirements, based on Encapsulated Nanodroplet Crystallisation (ENaCt). HTP co-crystallisation screening by ENaCt allowed rapid access to all 18 possible binary co-crystal combinations of 3 small molecules and 6 co-formers (A/B), through the use of 3456 individual experiments exploring solvent, encapsulating oil and stoichiometry, including 10 novel binary co-crystal structures elucidated by single crystal X-ray diffraction (SCXRD). Higher-order co-crystal (HOC) discovery, accessing co-crystals containing three or more molecules, is one of the most challenging co-crystal research areas, due to the highly complex experimental landscape that must be navigated. Herein, we further exemplify the power of ENaCt co-crystallisation by application to HOC discovery. HTP ENaCt co-crystallisation screening of three component (A/B/C) and four component (A/B/C/D) combinations gave ready access to both ternary and quaternary HOCs, each containing three or four different molecular species respectively. In total, 13 056 individual ENaCt experiments are presented resulting in 54 co-crystal structures by SCXRD, including 17 novel binary co-crystals, 8 novel ternary co-crystals and 4 novel quaternary co-crystals. ENaCt co-crystallisation is thus demonstrated to be a highly impactful and efficient tool in the search for small molecule co-crystals, through the employment of parallelised HTP nanoscale experimental workflows.

Open micro-combinatorial analysis systems of crystal growth critical points of a π-conjugated molecule in ionic liquid nanoliter droplets

Crystal engineering methodologies based on reproducible and high-throughput fabrication of high-quality single crystals have attracted much attention. Crystal formation and growth are governed by crystal growth theory. The driving force of crystallization is systematically represented with phase diagrams. However, constructing phase diagrams usually requires relatively large quantities of samples (milligrams to grams) and substantial time (weeks to months) to evaluate many conditions. Therefore, an easy and quick methodology to obtain phase diagrams, revealing critical conditions for valuable samples, is required. Here, we proposed a new method to obtain phase diagrams based on nanoliter droplet arrays of nonvolatile ionic liquids prepared by inkjet printing. Anthracene derivatives and 1-octyl-4-methylpyridinium derivatives were used as the solute and solvent, respectively. Optimization of ejection conditions, such as applied voltage, frequency, pulse width, and head temperature, enabled the formation of a 0.5 nL droplet per ejection. Inkjet printing under these conditions formed nanodroplet arrays on substrates at a droplet-patterned density of ca. 50 dots per cm2. The volume of each patterned droplet was varied from 10 to 100 nL by changing the number of ejections. The dissolution temperature of anthracene at each concentration was obtained at a heating rate of 0.2 °C min-1. This heating rate was found to be 10 times faster than the conventional technique. The same phase diagram as that prepared by the conventional technique was obtained in the range of 75-300 mM. The standard deviation of the dissolution temperatures was 0.8 °C (2.5%). This technique will facilitate the crystallization of multiple and valuable samples.

Enhancing physicochemical properties of hydrochlorothiazide with zwitterionic L-proline and 5-fluorocytosine cocrystals through mechanochemical synthesis

Hydrochlorothiazide (HTZ) is a thiazide-type diuretic drug approved by the FDA in 1959 for treatment of hypertension and peripheral edema and has been used since. HTZ exhibits low solubility and low permeability, leading to variable oral bioavailability and limited intestinal drug permeability. For this reason, several attempts to improve HTZ physicochemical properties have been made during the past decades. In the broad frame of molecular crystal engineering, significant efforts and promising results in the quest for more effective solid/dosage forms of HTZ, including studies on polymorphism and cocrystals, are being developed. As part of these efforts, we report here two new cocrystals of HTZ with the zwitterionic l-proline and the prodrug 5-Fluorocytosine. Both cocrystals show improvement in solubility and permeability, suggesting that these new solid forms could be used as new drug candidates to deliver HTZ in the antihypertensive therapy.

Study of chemical reactivity and molecular interactions of the hydrochlorothiazide-4-aminobenzoic acid cocrystal using spectroscopic and quantum chemical approaches

In this study, the molecular, electronic, and chemical properties of the drug hydrochlorothiazide (HCTZ) are determined after cocrystallization with 4-aminobenzoic acid (4-ABA). Analysis has been performed to understand how those variations lead to alteration of physical properties and chemical reactivity in the cocrystal HCTZ-4ABA. IR and Raman characterizations were performed along with quantum chemical calculations. A theoretical investigation of hydrogen bonding interactions in HCTZ-4ABA has been conducted using two functionals: B3LYP and wB97X-D. The results obtained by B3LYP and wB97X-D are compared which leads to the conclusion that B3LYP is the best applied function (density functional theory) to obtain suitable results for spectroscopy. The chemical reactivity descriptors are used to understand various aspects of pharmaceutical properties. Natural bond orbital (NBO) analysis and quantum theory of atoms (QTAIM) are used to analyze nature and strength of hydrogen bonding in HCTZ-4ABA. QTAIM analyzed moderate role of hydrogen bonding interactions in HCTZ-4ABA. The calculated HOMO-LUMO energy gap shows that HCTZ-4ABA is chemically more active than HCTZ drug. These chemical parameters suggest that HCTZ-4ABA is chemically more reactive and softer than HCTZ. The results of this study suggest that cocrystals can be a good alternative for enhancing physicochemical properties of a drug without altering its therapeutic properties.

Premix technologies for drug delivery: manufacturing, applications, and opportunities in regulatory filing

Active pharmaceutical ingredients (APIs) and excipients can be carefully combined in premix-based materials before being added to dosage forms, providing a flexible platform for the improvement of drug bioavailability, stability, and patient compliance. This is a promising and transformative approach in novel and generic product development, offering both the potential to overcome challenges in the delivery of complex APIs and viable solutions for bypassing patent hurdles in generic product filing. We discuss the different types of premixes; manufacturing technologies such as spray drying, hot melt extrusion, wet granulation, co-crystal, co-milling, co-precipitation; regulatory filing opportunities; and major bottlenecks in the use of premix materials in different aspects of pharmaceutical product development.

Polymorphic Structure Determination of the Macrocyclic Drug Paritaprevir by MicroED

Paritaprevir is an orally bioavailable, macrocyclic drug used for treating chronic Hepatitis C virus (HCV) infection. Its structures have been elusive to the public until recently when one of the crystal forms is solved by microcrystal electron diffraction (MicroED). In this work, the MicroED structures of two distinct polymorphic crystal forms of paritaprevir are reported from the same experiment. The different polymorphs show conformational changes in the macrocyclic core, as well as the cyclopropyl sulfonamide and methyl pyrazinamide substituents. Molecular docking shows that one of the conformations fits well into the active site pocket of the HCV non-structural 3/4A (NS3/4A) serine protease target, and can interact with the pocket and catalytic triad via hydrophobic interactions and hydrogen bonds. These results can provide further insight for optimization of the binding of acyl sulfonamide inhibitors to the HCV NS3/4A serine protease. In addition, this also demonstrates the opportunity to derive different polymorphs and distinct macrocycle conformations from the same experiments using MicroED.

Third Generation Solid Dispersion-Based Formulation of Novel Anti-Tubercular Agent Exhibited Improvement in Solubility, Dissolution and Biological Activity

The long treatment period and development of drug resistance in tuberculosis (TB) necessitates the discovery of new anti-tubercular agents. The drug discovery program of the institute leads to the development of an anti-tubercular lead (IIIM-019), which is an analogue of nitrodihydroimidazooxazole and exhibited promising anti-tubercular action. However, IIIM-019 displays poor aqueous solubility (1.2 µg/mL), which demands suitable dosage form for its efficient oral administration. In the present study, third generation solid dispersion-based formulation was developed to increase the solubility and dissolution of IIIM-019. The solubility profile of IIIM-019 using various polymeric carriers was determined and subsequently, PVP K-30 and P-407 were selected for preparation of binary and ternary solid dispersion. The third-generation ternary solid dispersion comprising PVP K-30 and P-407 revealed a remarkable enhancement in the aqueous solubility of IIIM-019. Physicochemical characterization of the developed formulations was done by employing FTIR spectroscopy, scanning electron microscopy, X-ray diffraction analysis, differential scanning calorimetry, and dynamic light scattering analysis. The dissolution study indicated an impressive release profile with the optimized formulation. The optimized formulation was further examined for cytotoxicity, cellular uptake, and hemolytic activity. The results indicated that the formulation had no apparent cytotoxicity on Caco-2 cells and was non-hemolytic in nature. Moreover, the optimized formulation showed significantly improved anti-tubercular activity compared to the native molecule. These findings showed that the developed third generation ternary solid dispersion could be a promising option for the oral delivery of investigated anti-tubercular molecule.

Modular, multi-robot integration of laboratories: an autonomous workflow for solid-state chemistry

Automation can transform productivity in research activities that use liquid handling, such as organic synthesis, but it has made less impact in materials laboratories, which require sample preparation steps and a range of solid-state characterization techniques. For example, powder X-ray diffraction (PXRD) is a key method in materials and pharmaceutical chemistry, but its end-to-end automation is challenging because it involves solid powder handling and sample processing. Here we present a fully autonomous solid-state workflow for PXRD experiments that can match or even surpass manual data quality, encompassing crystal growth, sample preparation, and automated data capture. The workflow involves 12 steps performed by a team of three multipurpose robots, illustrating the power of flexible, modular automation to integrate complex, multitask laboratories.

High-throughput nanoscale crystallization of dihydropyridine active pharmaceutical ingredients

Single-crystal X-ray diffraction analysis of small molecule active pharmaceutical ingredients is a key technique in the confirmation of molecular connectivity, including absolute stereochemistry, as well as the solid-state form. However, accessing single crystals suitable for X-ray diffraction analysis of an active pharmaceutical ingredient can be experimentally laborious, especially considering the potential for multiple solid-state forms (solvates, hydrates and polymorphs). In recent years, methods for the exploration of experimental crystallization space of small molecules have undergone a `step-change', resulting in new high-throughput techniques becoming available. Here, the application of high-throughput encapsulated nanodroplet crystallization to a series of six dihydropyridines, calcium channel blockers used in the treatment of hypertension related diseases, is described. This approach allowed 288 individual crystallization experiments to be performed in parallel on each molecule, resulting in rapid access to crystals and subsequent crystal structures for all six dihydropyridines, as well as revealing a new solvate polymorph of nifedipine (1,4-dioxane solvate) and the first known solvate of nimodipine (DMSO solvate). This work further demonstrates the power of modern high-throughput crystallization methods in the exploration of the solid-state landscape of active pharmaceutical ingredients to facilitate crystal form discovery and structural analysis by single-crystal X-ray diffraction.

Mitochondriotropic agents conjugated with NSAIDs through metal ions against breast cancer cells

Two copper(I) polymorphs of formula [Cu(SALH)(TPP)3] (1a and 1b) were prepared by the conjugation of the Non-Steroidal Anti-Inflammatory Drug (NSAID) salicylic acid (SALH2) with the mitochondriotropic agent triphenylphosphine (TPP) via metal ion. For comparison, the isomorph [Ag(SALH)(TPP)3] (2) was prepared. The conjugates 1a, 1b and 2 were characterized by melting point (m.p.), Attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy, Ultraviolet-Visible (UV-Vis) spectroscopy and nuclear magnetic resonance (1H NMR). The crystal structures of 1a, 1b and 2 were confirmed by X-ray diffraction crystallography (XRD). The ex vivo binding affinity of 1-2 towards CT (calf thymus)-DNA was studied by UV, fluorescence, viscosity and DNA Thermal Denaturation studies. Their inhibitory activity against lipoxygenase (LOX) (an enzyme which is mainly located in the mitochondrion) was determined. The in vitro activity of 1-2 was evaluated against human breast cancer cell lines MCF-7 (hormone depended (HD)) and MDA-MB 281 (hormone independent (HI)) cells. Compounds 1-2 inhibit stronger than cisplatin the cancerous cells. The molecular mechanism of action of 1-2 was suspected by the MCF-7 cells morphology and confirmed by DNA fragmentation, Acridine Orange/Ethidium Bromide (AO/EB) Staining and mitochondrial membrane permeabilization tests.

Polymorph screening at surfaces of a benzothienobenzothiophene derivative: discovering new solvate forms

The discovery of new polymorphs opens up unique applications for molecular materials since their physical properties are predominantly influenced by the crystal structure type. The deposition of molecules at surfaces offers great potential in the variation of the crystallization conditions, thereby allowing access to unknown polymorphs. With our surface crystallization approach, four new phases are found for an oligoethylene glycol-benzothienobenzothiophene molecule, and none of these phases could be identified via classical polymorph screening. The corresponding crystal lattices of three of the new phases were obtained via X-ray diffraction (XRD). Based on the volumetric considerations together with X-ray fluorescence and Raman spectroscopy data, the phases are identified as solvates containing one, two or three solvent molecules per molecule. The strong interaction of dichloromethane with the oligoethylene glycol side chains of the molecules may be responsible for the formation of the solvates. Temperature-dependent XRD reveals the low thermal stability of the new phases, contrary to the thermodynamically stable bulk form. Nevertheless, the four solvates are stable under ambient conditions for at least two years. This work illustrates that defined crystallization at surfaces enables access to multiple solvates of a given material through precise and controlled variations in the crystallization kinetics.

Polymorphic Structure Determination of the Macrocyclic Drug Paritaprevir by MicroED

Paritaprevir is an orally bioavailable, macrocyclic drug used for treating chronic Hepatitis C virus infection. Its structures had been elusive to the public until recently when one of the crystal forms was solved by MicroED. In this work, we report the MicroED structures of two distinct polymorphic crystal forms of paritaprevir from the same experiment. The different polymorphs show conformational changes in the macrocyclic core, as well as the cyclopropylsulfonamide and methylpyrazinamide substituents. Molecular docking shows that one of the conformations fits well into the active site pocket of the NS3/4A serine protease target, and can interact with the pocket and catalytic triad via hydrophobic interactions and hydrogen bonds. These results can provide further insight for optimization of the binding of acylsulfonamide inhibitors to the NS3/4A serine protease. In addition, this also demonstrate the opportunity of deriving different polymorphs and distinct macrocycle conformations from the same experiments using MicroED.

Transnasal-brain delivery of nanomedicines for neurodegenerative diseases

Neurodegenerative diseases (NDs) have become a serious global health problem as the population ages. Traditionally, treatment strategies for NDs have included oral and intravenous administration; however, the blood–brain barrier (BBB) can prevent drugs from reaching the brain, rendering the treatment incomplete and the effect unsatisfactory. Additionally, the prolonged or excessive use of drugs that can cross the BBB can damage liver and kidney function. Recent studies have shown that nose-to-brain drug delivery can noninvasively bypass the BBB, allowing drugs to enter the brain through the olfactory or trigeminal nerve pathways; additionally, nanoparticle carriers can enhance drug delivery. This review introduces drug carrier nanoparticles for nose-to-brain delivery systems, compares the advantages and disadvantages of different nanoparticles, and discusses the factors influencing nose-to-brain nanomedicine delivery and enhancement strategies. We also summarize nose-to-brain delivery and nanomedicines for treating NDs, the current challenges of this approach, and the future promise of nanomedicine-based ND treatment.

Quantitative matching of crystal structures to experimental powder diffractograms

The identification and classification of crystal structures is fundamental in materials science, as the crystal structure is an inherent factor of what gives solid materials their properties. Being able to identify the same crystallographic form from unique origins (e.g. different temperatures, pressures, or in silico-generated) is a complex challenge. While our previous work has focused on comparison of simulated powder diffractograms from known crystal structures, herein is presented the variable-cell experimental powder difference (VC-xPWDF) method to match collected powder diffractograms of unknown polymorphs to both experimental crystal structures from the Cambridge Structural Database and in silico-generated structures from the Control and Prediction of the Organic Solid State database. The VC-xPWDF method is shown to correctly identify the most similar crystal structure to both moderate and "low" quality experimental powder diffractograms for a set of 7 representative organic compounds. Features of the powder diffractograms that are more challenging for the VC-xPWDF method are discussed (i.e. preferred orientation), and comparison with the FIDEL method showcases the advantage of VC-xPWDF provided the experimental powder diffractogram can be indexed. The VC-xPWDF method should allow rapid identification of new polymorphs from solid-form screening studies, without requiring single-crystal analysis.

Enhancing the Stability of Nicotine via Crystallization Using Enantiopure Tartaric Acid Salt Formers

Crystallization of nicotine, an oil prone to degradation at room temperature, has been demonstrated to be an effective means of creating nicotine-based materials with tunable thermal properties and improved resistance to photo-induced degradation. Herein, we show that both isomers of enantiomerically pure tartaric acid are highly effective salt formers when combined with nicotine. Both salts exhibit enhanced photostability, and with a melting point of 143.1 °C, the salt prepared using d-(-)-tartaric acid possesses one of the highest melting points for a crystalline nicotine solid reported to date.

Advanced crystallisation methods for small organic molecules

Molecular materials based on small organic molecules often require advanced structural analysis, beyond the capability of spectroscopic techniques, to fully characterise them. In such cases, diffraction methods such as single crystal X-ray diffraction (SCXRD), are one of the most powerful tools available to researchers, providing molecular and structural elucidation at atomic level resolution, including absolute stereochemistry. However SCXRD, and related diffraction methods, are heavily dependent on the availability of suitable, high-quality crystals, thus crystallisation often becomes the major bottleneck in preparing samples. Following a summary of classical methods for the crystallisation of small organic molecules, this review will focus on a number of recently developed advanced methods for crystalline material sample preparation for SCXRD. This review will cover two main areas of modern small organic molecule crystallisation, namely the inclusion of molecules within host complexes (e.g., "crystalline sponge" and tetraaryladamantane based inclusion chaperones) and the use of high-throughput crystallisation, employing "under-oil" approaches (e.g., microbatch under-oil and ENaCt). Representative examples have been included for each technique, together with a discussion of their relative advantages and limitations to aid the reader in selecting the most appropriate technique to overcome a specific analytical challenge.

Cocrystals; basic concepts, properties and formation strategies

Cocrystallization is an old technique and remains the focus of several research groups working in the field of Chemistry and Pharmacy. This technique is basically in field for improving physicochemical properties of material which can be active pharmaceutical ingredients (APIs) or other chemicals with poor profile. So this review article has been presented in order to combine various concepts for scientists working in the field of chemistry, pharmacy or crystal engineering, also it was attempt to elaborate concepts belonging to crystal designing, their structures and applications. A handsome efforts have been made to bring scientists together working in different fields and to make chemistry easier for a pharmacist and pharmacy for chemists pertaining to cocrystals. Various aspects of chemicals being used as co-formers have been explored which predict the formation of co-crystals or molecular salts and even inorganic cocrystals.

Baloxavir Marboxil Shows Anomalous Conversion of Crystal Forms from Stable to Metastable through Formation of Specific Solvate Form

Baloxavir marboxil is a novel cap-dependent endonuclease inhibitor of influenza. This study aimed to identify its polymorphs and their relationship with crystal engineering. Polymorph screening by evaporation gave forms I-III and solvate forms IV and V. Heating enabled the conversion of form III to form II, but did not enable that of forms I and II. The solvent-mediated transformation of the forms I-III by magnetic stirring in various solvents resulted in the formation of form I. These results indicate that form I is the stable form. However, all crystal forms transformed to form II after magnetic stirring in a 50% acetonitrile aqueous solution, which was not obtained from water or acetonitrile. The suspension in a 50% acetonitrile aqueous solution exhibited a novel X-ray diffraction pattern as shown in form VI. The measurement of the suspension by solid-state ¹³C-nuclear magnetic resonance revealed that the spectra of forms II and VI were similar. From these results, we conclude that the drug forms a solvate with both water and acetonitrile and spontaneously transforms to form II upon rapid desolvation under ambient conditions. This study elucidates the mechanism of unexpected convergence to a metastable form in a specific solvent and contributes to the crystal engineering of baloxavir marboxil.

The surface site interaction point approach to non-covalent interactions

The functional properties of molecular systems are generally determined by the sum of many weak non-covalent interactions, and therefore methods for predicting the relative magnitudes of these interactions is fundamental to understanding the relationship between function and structure in chemistry, biology and materials science. This review focuses on the Surface Site Interaction Point (SSIP) approach which describes molecules as a set of points that capture the properties of all possible non-covalent interactions that the molecule might make with another molecule. The first half of the review focuses on the empirical non-covalent interaction parameters, α and β, and provides simple rules of thumb to estimate free energy changes for interactions between different types of functional group. These parameters have been used to have been used to establish a quantitative understanding of the role of solvent in solution phase equilibria, and to describe non-covalent interactions at the interface between macroscopic surfaces as well as in the solid state. The second half of the review focuses on a computational approach for obtaining SSIPs and applications in multi-component systems where many different interactions compete. Ab initio calculation of the Molecular Electrostatic Potential (MEP) surface is used to derive an SSIP description of a molecule, where each SSIP is assigned a value equivalent to the corresponding empirical parameter, α or β. By considering the free energies of all possible pairing interactions between all SSIPs in a molecular ensemble, it is possible to calculate the speciation of all intermolecular interactions and hence predict thermodynamic properties using the SSIMPLE algorithm. SSIPs have been used to describe both the solution phase and the solid state and provide accurate predictions of partition coefficients, solvent effects on association constants for formation of intermolecular complexes, and the probability of cocrystal formation. SSIPs represent a simple and intuitive tool for describing the relationship between chemical structure and non-covalent interactions with sufficient accuracy to understand and predict the properties of complex molecular ensembles without the need for computationally expensive simulations.

Design, Preparation, Characterization and Evaluation of Five Cocrystal Hydrates of Fluconazole with Hydroxybenzoic Acids

To modulate the physicochemical properties of fluconazole (FLZ), a multifunctional antifungal drug, the crystal engineering technique was employed. In this paper, five novel cocrystal hydrates of FLZ with a range of phenolic acids from the GRAS list, namely, 2,4-dihydroxybenzoic acid (24DHB), 3,4-dihydroxybenzoic acid (34DHB, form I and form II), 3,5-dihydroxybenzoic acid (35DHB), and 3,4,5-trihydroxybenzoic acid (345THB) were disclosed and reported for the first time. Crystals of these five hydrates were all obtained for single-crystal X-ray diffraction (SCXRD) analysis. Robust (hydroxyl/carboxyl) O-H. . . N_arom hydrogen bonds between acids and FLZ triazolyl moiety were observed to be dominant in guiding these crystal forms. The water molecule plays the role of supramolecular "linkage" in the strengthening and stabilization of these hydrates by interacting with FLZ and acids through O-H. . . O hydrogen bonds. In particular, the formation of FLZ-34DHB-H₂O (1:1:1) significantly reduces hygroscopicity and hence improves the stability of FLZ, the latter of which is unstable and easily transforms into its monohydrate form. Increased initial dissolution rates were observed in the obtained cocrystal forms, and an enhanced intrinsic dissolution rate was obtained in FLZ-35DHB-H₂O (1:1:1) in comparison with commercialized FLZ form II.

Conformational Trimorphism in an Ionic Cocrystal of Hesperetin

We report the existence of conformational polymorphism in an ionic cocrystal (ICC) of the nutraceutical compound hesperetin (HES) in which its tetraethylammonium (TEA⁺) salt serves as a coformer. Three polymorphs, HESTEA-α, HESTEA-β and HESTEA-γ, were characterized by single-crystal X-ray diffraction (SCXRD). Each polymorph was found to be sustained by phenol···phenolate supramolecular heterosynthons that self-assemble with phenol···phenol supramolecular homosynthons into C ₃ ²(7) H-bonded motifs. Conformational variability in HES moieties and different relative orientations of the H-bonded motifs resulted in distinct crystal packing patterns: HESTEA-α and HESTEA-β exhibit H-bonded sheets; HESTEA-γ is sustained by bilayers of H-bonded tapes. All three polymorphs were found to be stable upon exposure to humidity under accelerated stability conditions for 2 weeks. Under competitive slurry conditions, HESTEA-α was observed to transform to the β or γ forms. Solvent selection impacted the relationship between HESTEA-β (favored in EtOH) and HESTEA-γ (favored in MeOH). A mixture of the β and γ forms was found to be present following H₂O slurry.

Glibenclamide - Malonic Acid Cocrystal with an Enhanced Solubility and Bioavailability

OBJECTIVE

The objective of the work is to enhance the solubility, dissolution and pharmacokinetic properties of Glibenclamide (GLB) via cocrystallization technique. Significance: Glibenclamide (GLB) is an oral hypoglycemic agent used for treating non-insulin-dependent (type II) diabetes mellitus. It exhibits poor aqueous solubility and oral bioavailability, thereby compromising its therapeutic effect. Therefore, utilizing cocrystal approach for enhancing the solubility will modulate the physicochemical properties of GLB without altering its molecular structure.

METHODS

Cocrystal was prepared by solution crystallization method using coformer malonic acid. The cocrystal was characterized by Differential Scanning Calorimetry (DSC), Powder X-ray Diffraction (PXRD) and Fourier Transform Infrared (FT-IR) studies. The prepared cocrystal was subjected to solubility, in vitro dissolution, and pharmacokinetic studies.

RESULTS

The DSC endotherms, PXRD patterns and the FT-IR spectra of the cocrystal established the formation of a cocrystal. The formation of eutectic mixture was refuted upon comparing the DSC endotherm and PXRD pattern of the cocrystal with that of the physical mixture. GLB showed a two-fold enhancement in solubility and a significant improvement in the rate of dissolution (p < 0.05, Independent t-test) after cocrystallization. The pharmacokinetic parameters on male Sprague Drawly rats showed 1.45 enhancement in AUC _0-24 and 1.36 -fold enhancement in the C_max of GLB as compared to the pure drug.

CONCLUSION

These findings demonstrate that cocrystallization technique was able to tailor the solubility and dissolution profile of GLB leading to an enhanced pharmacokinetic property.

Applications of Artificial Intelligence and Machine Learning Algorithms to Crystallization

Artificial intelligence and specifically machine learning applications are nowadays used in a variety of scientific applications and cutting-edge technologies, where they have a transformative impact. Such an assembly of statistical and linear algebra methods making use of large data sets is becoming more and more integrated into chemistry and crystallization research workflows. This review aims to present, for the first time, a holistic overview of machine learning and cheminformatics applications as a novel, powerful means to accelerate the discovery of new crystal structures, predict key properties of organic crystalline materials, simulate, understand, and control the dynamics of complex crystallization process systems, as well as contribute to high throughput automation of chemical process development involving crystalline materials. We critically review the advances in these new, rapidly emerging research areas, raising awareness in issues such as the bridging of machine learning models with first-principles mechanistic models, data set size, structure, and quality, as well as the selection of appropriate descriptors. At the same time, we propose future research at the interface of applied mathematics, chemistry, and crystallography. Overall, this review aims to increase the adoption of such methods and tools by chemists and scientists across industry and academia.

Polymorphism in Ionic Cocrystals Comprising Lithium Salts and l-Proline

The occurrence of polymorphism in ionic cocrystals formed by two lithium salts, lithium salicylate (LIS) and lithium 4-methoxybenzoate (L4M), and l-proline (PRO) has been investigated. The previously reported monoclinic form of the 1:1 cocrystal of LIS and PRO, LISPRO(α), and a new thermodynamically stable orthorhombic polymorph, LISPRO(β), were prepared and characterized. The two polymorphs form square grid, sql, topology coordination networks and differ mainly in the conformation of the salicylate ions and positioning of the sql nets. LISPRO(α) was observed to transform to LISPRO(β) under slurry conditions. The 1:1 ionic cocrystal of L4M and PRO (L4MPRO) was found to form three polymorphs. Apart from the previously reported orthorhombic crystal form, L4MPRO(α), two new monoclinic crystal forms, L4MPRO(β) and L4MPRO(γ), were obtained by modifying crystallization conditions. The new polymorphs were found to be metastable, undergoing transformations to L4MPRO(α) upon exposure to humidity. Experimental conditions that induce transformations between the polymorphs of LISPRO and L4MPRO are detailed, and the structural differences between the polymorphs are discussed in the broader context of polymorphism.

Low- versus Mid-frequency Raman Spectroscopy for in Situ Analysis of Crystallization in Slurries

Slurry studies are useful for exhaustive polymorph and solid-state stability screening of drug compounds. Raman spectroscopy is convenient for monitoring crystallization in such slurries, as the measurements can be performed in situ even in aqueous environments. While the mid-frequency region (400–4000 cm^–1) is dominated by intramolecular vibrations and has traditionally been used for such studies, the low-frequency spectral region (<200 cm^–1) probes solid-state related lattice vibrations and is potentially more valuable for understanding subtle and/or complex crystallization behavior. The aim of the study was to investigate low-frequency Raman spectroscopy for in situ monitoring of crystallization of an amorphous pharmaceutical in slurries for the first time and directly compare the results with those simultaneously obtained with mid-frequency Raman spectroscopy. Amorphous indomethacin (IND) slurries were prepared at pH 1.2 and continuously monitored in situ at 5 and 25 °C with both low- and mid-frequency Raman spectroscopy. At 25 °C, both spectral regions profiled amorphous IND in slurries as converting directly from the amorphous form toward the α crystalline form. In contrast, at 5 °C, principal component analysis revealed a divergence in the detected conversion profiles: the mid-frequency Raman suggested a direct conversion to the α crystalline form, but the low-frequency region showed additional transition points. These were attributed to the appearance of minor amounts of the ε-form. The additional solid-state sensitivity of the low-frequency region was attributed to the better signal-to-noise ratio and more consistent spectra in this region. Finally, the low-frequency Raman spectrum of the ε-form of IND is reported for the first time.

Foundations of gastrointestinal-based drug delivery and future developments

Gastrointestinal-based drug delivery is considered the preferred mode of drug administration owing to its convenience for patients, which improves adherence. However, unique characteristics of the gastrointestinal tract (such as the digestive environment and constraints on transport across the gastrointestinal mucosa) limit the absorption of drugs. As a result, many medications, in particular biologics, still exist only or predominantly in injectable form. In this Review, we examine the fundamentals of gastrointestinal drug delivery to inform clinicians and pharmaceutical scientists. We discuss general principles, including the challenges that need to be overcome for successful drug formulation, and describe the unique features to consider for each gastrointestinal compartment when designing drug formulations for topical and systemic applications. We then discuss emerging technologies that seek to address remaining obstacles to successful gastrointestinal-based drug delivery.

A complete description of thermodynamic stabilities of molecular crystals

Predicting stable polymorphs of molecular crystals remains one of the grand challenges of computational science. Current methods invoke approximations to electronic structure and statistical mechanics and thus fail to consistently reproduce the delicate balance of physical effects determining thermodynamic stability. We compute the rigorous ab initio Gibbs free energies for competing polymorphs of paradigmatic compounds, using machine learning to mitigate costs. The accurate description of electronic structure and full treatment of quantum statistical mechanics allow us to predict the experimentally observed phase behavior. This constitutes a key step toward the first-principles design of functional materials for applications from photovoltaics to pharmaceuticals.

Predictions of relative stabilities of (competing) molecular crystals are of great technological relevance, most notably for the pharmaceutical industry. However, they present a long-standing challenge for modeling, as often minuscule free energy differences are sensitively affected by the description of electronic structure, the statistical mechanics of the nuclei and the cell, and thermal expansion. The importance of these effects has been individually established, but rigorous free energy calculations for general molecular compounds, which simultaneously account for all effects, have hitherto not been computationally viable. Here we present an efficient “end to end” framework that seamlessly combines state-of-the art electronic structure calculations, machine-learning potentials, and advanced free energy methods to calculate ab initio Gibbs free energies for general organic molecular materials. The facile generation of machine-learning potentials for a diverse set of polymorphic compounds—benzene, glycine, and succinic acid—and predictions of thermodynamic stabilities in qualitative and quantitative agreement with experiments highlight that predictive thermodynamic studies of industrially relevant molecular materials are no longer a daunting task.

Hydrogen Bonding and Polymorphism of Amino Alcohol Salts with Quinaldinate: Structural Study

Three amino alcohols, 3-amino-1-propanol (abbreviated as 3a1pOH), 2-amino-1-butanol (2a1bOH), and 2-amino-2-methyl-1-propanol (2a2m1pOH), were reacted with quinoline-2-carboxylic acid, known as quinaldinic acid. This combination yielded three salts, (3a1pOHH)quin (1, 3a1pOHH⁺ = protonated 3-amino-1-propanol, quin⁻ = anion of quinaldinic acid), (2a1bOHH)quin (2, 2a1bOHH⁺ = protonated 2-amino-1-butanol), and (2a2m1pOHH)quin (3, 2a2m1pOHH⁺ = protonated 2-amino-2-methyl-1-propanol). The 2-amino-1-butanol and 2-amino-2-methyl-1-propanol systems produced two polymorphs each, labeled 2a/2b and 3a/3b, respectively. The compounds were characterized by X-ray structure analysis on single-crystal. The crystal structures of all consisted of protonated amino alcohols with NH₃⁺ moiety and quinaldinate anions with carboxylate moiety. The used amino alcohols contained one OH and one NH₂ functional group, both prone to participate in hydrogen bonding. Therefore, similar connectivity patterns were expected. This proved to be true to some extent as all structures contained the NH₃⁺∙∙∙⁻OOC heterosynthon. Nevertheless, different hydrogen bonding and π∙∙∙π stacking interactions were observed, leading to distinct connectivity motifs. The largest difference in hydrogen bonding occurred between polymorphs 3a and 3b, as they had only one heterosynton in common.

Polymorphism and cocrystal salt formation of 2-((2,6-dichlorophenyl)amino)benzoic acid, harvest of a second form of 2-((2,6-dimethylphenyl)amino)benzoic acid, and isomorphism between the two systems

Isomorphism and isostructurality were observed between form I of 2-((2,6-dimethylphenyl)amino)benzoic acid and its analog 2-((2,6-dichlorophenyl)amino)benzoic acid, which suggests double Cl–CH3 exchange also leads to structural similarity.

Transforming liquid nicotine into a stable solid through crystallization with orotic acid

The volatile liquid active pharmaceutical ingredient, nicotine, is stabilized in the solid-state through crystallization with orotic acid. The structure, thermal properties and bonding environment are characterized and compared with previous examples.

New solvates and a salt of the anti-HIV compound etravirine

Four new solvates of the anti-HIV compound etravirine [systematic name: 4-({6-amino-5-bromo-2-[(4-cyanophenyl)amino]pyrimidin-4-yl}oxy)-3,5-dimethylbenzonitrile, C₂₀H₁₅BrN₆O] with dimethyl sulfoxide (C₂H₆OS, two distinct monosolvates), 1,4-dioxane (C₄H₈O₂, the 0.75-solvate) and N,N-dimethylacetamide (C₄H₉NO, the monosolvate), which exhibit conversion to the same anhydrous etravirine phase upon desolvation, and a stable etravirinium oxalate salt {6-amino-5-bromo-4-(4-cyano-2,6-dimethylphenoxy)-2-[(4-cyanophenyl)amino]pyrimidin-1-ium hemioxalate, C₂₀H₁₆BrN₆O⁺·0.5C₂O₄^2-} were obtained. The crystal structures were solved by single-crystal X-ray diffraction and analyzed by powder X-ray diffraction, and the intermolecular interactions were explored by Hirshfeld surface analysis. Lattice energies were evaluated using the atom-atom force field Coulomb-London-Pauli (AA CLP) approximation, which distributes the total energy as four separate contributions: Coulombic, polarization, dispersion and repulsion. The formation of the solvates and the oxalate salt was further characterized by thermal analysis and IR spectroscopy.

Multiwell Raman plate reader for high-throughput biochemical screening

Although Raman spectroscopy has been used for the quantitative analysis of samples in many fields, including material science, biomedical, and pharmaceutical research, its low sensitivity hindered the application of the analytical capability for high-throughput screening. Here, we developed a high-throughput Raman screening system that can analyze hundreds of specimens in a multiwell plate simultaneously. Multiple high numerical aperture (NA) lenses are assembled under each well in the multiwell plate to detect Raman scattering simultaneously with high sensitivity. The Raman spectrum of 192 samples loaded on a standard 384-well plate can be analyzed simultaneously. With the developed system, the throughput of Raman measurement was significantly improved (about 100 times) compared to conventional Raman instruments based on a single-point measurement. By using the developed system, we demonstrated high-throughput Raman screening to investigate drug polymorphism and identify a small-molecule binding site in a protein. Furthermore, the same system was used to demonstrate high-speed chemical mapping of a centimeter-sized pork slice.

Quantitation of Commercially Available API Solid Forms by Application of the NMR-qSRC Approach: An Optimization Strategy Based on In Silico Simulations

Physical forms of active pharmaceutical ingredients (APIs) play a crucial role in drug discovery since 85% of API molecules exhibit polymorphism and sometimes complicated phase behavior, often resulting in important differences in the respective biochemical and physical properties. Characterization and quantitation of the different forms are becoming more and more essential in the pharmaceutical industry: once these characteristics are known, it is easier to choose the best solid form for development, formulation, manufacturing, and storage. Time domain-nuclear magnetic resonance (TD-NMR) has recently been used to develop a quantitation protocol for solid mixtures, named qSRC, based on the linear combination of T₁ saturation recovery curves (SRCs) collected on a bench-top instrument. Despite its potentials and ease of use, a limited number of application cases have been reported in the literature since its development and many aspects remain to be clarified for the technique to be adopted as a robust routinely industrial analytical tool. In the present work, the reliability of the qSRC approach has been studied by focusing on the role played by key experimental variables, including mixture composition, signal-to-noise ratio, and T₁ differences. In silico simulations were carried out for a wide range of theoretical cases to predict the expected level of accuracy obtainable for a given sample-parameter acquisition set and to clearly define the range of applicability of the method. Results of the simulation are presented alongside a comparison with three real-case studies of commercially available APIs: piroxicam, naproxen sodium, and benzocaine.

An industrial perspective on co-crystals: Screening, identification and development of the less utilised solid form in drug discovery and development

Active pharmaceutical ingredients are commonly marketed as a solid form due to ease of transport, storage and administration. In the design of a drug formulation, the selection of the solid form is incredibly important and is traditionally based on what polymorphs, hydrates or salts are available for that compound. Co-crystals, another potential solid form available, are currently not as readily considered as a viable solid form for the development process. Even though co-crystals are gaining an ever-increasing level of interest within the pharmaceutical community, their acceptance and application is still not as standard as other solid forms such as the ubiquitous pharmaceutical salt and stabilised amorphous formulations. Presented in this chapter is information that would allow for a co-crystal screen to be planned and conducted as well as scaled up using solution and mechanochemistry based methods commonly employed in both the literature and industry. Also presented are methods for identifying the formation of a co-crystal using a variety of analytical techniques as well as the importance of confirming the formation of co-crystals from a legal perspective and demonstrating the legal precedent by looking at co-crystalline products already on the market. The benefits of co-crystals have been well established, and presented in this chapter are a selection of examples which best exemplify their potential. The goal of this chapter is to increase the understanding of co-crystals and how they may be successfully exploited in early stage development.

Obtaining Cocrystals by Reaction Crystallization Method: Pharmaceutical Applications

Cocrystals have gained attention in the pharmaceutical industry due to their ability to improve solubility, stability, in vitro dissolution rate, and bioavailability of poorly soluble drugs. Conceptually, cocrystals are multicomponent solids that contain two or more neutral molecules in stoichiometric amounts within the same crystal lattice. There are several techniques for obtaining cocrystals described in the literature; however, the focus of this article is the Reaction Crystallization Method (RCM). This method is based on the generation of a supersaturated solution with respect to the cocrystal, while this same solution is saturated or unsaturated with respect to the components of the cocrystal individually. The advantages of the RCM compared with other cocrystallization techniques include the ability to form cocrystals without crystallization of individual components, applicability to the development of in situ techniques for the screening of high quality cocrystals, possibility of large-scale production, and lower cost in both time and materials. An increasing number of scientific studies have demonstrated the use of RCM to synthesize cocrystals, mainly for drugs belonging to class II of the Biopharmaceutics Classification System. The promising results obtained by RCM have demonstrated the applicability of the method for obtaining pharmaceutical cocrystals that improve the biopharmaceutical characteristics of drugs.

Solid-State Overview of R-Baclofen: Relative Stability of Forms A, B and C and Characterization of a New Heterosolvate

A new polymorphic form (Form C) of enantiopure Baclofen was isolated and characterized. Crystal structures of R-Baclofen Form A and Form C were resolved from powder diffraction data, and cell parameters by profile matching for Form B. The relative stability of these three forms is proposed based on structural data, thermal analyses and solvent-mediated conversions. The experiments highlight the stability order A < C < B at 25 °C (A is the most stable form), whereas above 180 °C it would likely be: C < A < B (C being the stable modification). Moreover, a new heterosolvate of the molecule is observed in N,N-DMF/water mixture. This heterosolvate offers a new pathway to isolate pure R-Baclofen Form B provided the lactam impurity does not exceed 3%. Upon mechanical stress Form B tends to evolve to Form C.

Challenges and opportunities of pharmaceutical cocrystals: a focused review on non-steroidal anti-inflammatory drugs

The focus of the review is to discuss the relevant and essential aspects of pharmaceutical cocrystals in both academia and industry with an emphasis on non-steroidal anti-inflammatory drugs (NSAIDs). Although cocrystals have been prepared for a plethora of drugs, NSAID cocrystals are focused due to their humongous application in different fields of medication such as antipyretic, anti-inflammatory, analgesic, antiplatelet, antitumor, and anti-carcinogenic drugs. The highlights of the review are (a) background of cocrystals and other solid forms of an active pharmaceutical ingredient (API) based on the principles of crystal engineering, (b) why cocrystals are an excellent opportunity in the pharma industry, (c) common methods of preparation of cocrystals from the lab scale to bulk quantity, (d) some latest case studies of NSAIDs which have shown better physicochemical properties for example; mechanical properties (tabletability), hydration, solubility, bioavailability, and permeability, and (e) latest guidelines of the US FDA and EMA opening new opportunities and challenges.

Mechanochemistry: A Green Approach in the Preparation of Pharmaceutical Cocrystals

Mechanochemistry is considered an alternative attractive greener approach to prepare diverse molecular compounds and has become an important synthetic tool in different fields (e.g., physics, chemistry, and material science) since is considered an ecofriendly procedure that can be carried out under solvent free conditions or in the presence of minimal quantities of solvent (catalytic amounts). Being able to substitute, in many cases, classical solution reactions often requiring significant amounts of solvents. These sustainable methods have had an enormous impact on a great variety of chemistry fields, including catalysis, organic synthesis, metal complexes formation, preparation of multicomponent pharmaceutical solid forms, etc. In this sense, we are interested in highlighting the advantages of mechanochemical methods on the obtaining of pharmaceutical cocrystals. Hence, in this review, we describe and discuss the relevance of mechanochemical procedures in the formation of multicomponent solid forms focusing on pharmaceutical cocrystals. Additionally, at the end of this paper, we collect a chronological survey of the most representative scientific papers reporting the mechanochemical synthesis of cocrystals.

Polymorphic forms of antiandrogenic drug nilutamide: structural and thermodynamic aspects

Attempts to obtain new cocrystals of nonsteroidal antiandrogenic drug nilutamide produced alternative polymorphic forms of the compound (Form II and Form III) and their crystal structures were elucidated by single-crystal X-ray diffraction. Apart from the cocrystallization technique, lyophilization was found to be an effective strategy for achieving polymorph control of nilutamide, which was difficult to obtain by other methods. The physicochemical properties and relative stability of the commercial Form I and newly obtained Form II were comprehensively investigated by a variety of analytical methods (thermal analysis, solution calorimetry, solubility, and sublimation), whereas for Form III, only a handful of experimental parameters were obtained due to the elusive nature of the polymorph. Form I and Form II were found to be monotropically related, with Form I being confirmed as the thermodynamically most stable solid phase. In addition, the performance of different DFT-D and semi-empirical schemes for lattice energy calculation and polymorph energy ranking was compared and analysed. Lattice energy calculations using periodic DFT at B3LYP-D3/6-31(F+)G(d,p) and PBEh-3c/def2-mSVP levels of theory were found to provide the most accurate lattice energy values for Form I against experimental data, while PIXEL and PBEh-3c/def2-mSVP were the only methods that predicted the correct order of stability of Forms I and II.

Polymorphic Characterization, Pharmacokinetics, and Anti-Inflammatory Activity of Ginsenoside Compound K Polymorphs

Polymorphism exhibits different physicochemical properties, which can impact the bioavailability and bioactivity of solid drugs. This study focused on identifying the polymorphs of ginsenoside compound K (CK) and studying their different behaviors in pharmacokinetics (PK) and pharmacodynamics (PD). Four CK polymorphs (form I, II, III, and IV) from organic solvents were characterized by scanning electron microscope (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and powder X-ray diffraction (PXRD). A feasible LC-MS/MS method was exploited to determine the PK parameters. Form II displayed the most exposure, followed by form I, III, and IV. Notably, all forms showed sex dimorphism, and the bioavailability in the female group was about two-fold higher than in the male group. The PD properties were investigated in carrageenan-induced acute paw inflammation, and form II at 20 mg/kg showed significant inhibition of edema by 42.7%. This study clarified the polymorphic, PK, and PD characters of four crystal forms of CK, and the data suggested that form II had the best efficacy for drug development.