Pharmaceutical Crystallization Research Articles

Machine learning analysis of rivaroxaban solubility in mixed solvents for application in pharmaceutical crystallization

This study investigates the use of machine learning models to predict solubility of rivaroxaban in binary solvents based on temperature (T), mass fraction (w), and solvent type. Using a dataset with over 250 data points and including solvents encoded with one-hot encoding, four models were compared: Gradient Boosting (GB), Light Gradient Boosting (LGB), Extra Trees (ET), and Random Forest (RF). The Jellyfish Optimizer (JO) algorithm was applied to tune hyperparameters, enhancing model performance. The LGB model achieved the best results, with an R2 of 0.988 on the test set and low error rates (RMSE of 9.1284E-05 and MAE of 5.85322E-05), surpassing other models in predictive accuracy and generalizability. Parity plots confirmed the LGB model’s close alignment between predicted and actual solubility values, highlighting its robust performance. Furthermore, 3D surface plots and partial effect plots demonstrated LGB’s capacity to model solubility across different solvent systems, capturing complex interactions between T, w, and solvent effects. Finally, the LGB model predicted maximum solubility at a temperature of 305.76 K and a mass fraction of 0.753 in a dichloromethane + methanol mixture, providing valuable insights for solubility optimization in solvent selection. This work underscores the effectiveness of the LGB model for solubility prediction, with potential applications in formulation and experimental planning.

A personal account of the history of X-ray crystallography at the University of La Plata, Argentina.

Prompted by visionary political leaders and a flowering economy, the University of La Plata was founded in 1905, the third Argentinian university after the Universities of Cordoba (1613) and Buenos Aires (1821). Differing from the older universities, more prone to professional formation, the new university was oriented towards teaching and scientific research following western European academic tradition. Along with the university was created the Institute of Physics, the first of its kind in Latin America. To pursue the foundational plan, the university recruited distinguished German physicists, some of whom became the first directors. From the start, the institute became acquainted with Röntgen rays, their generation and use, initially for radiographic images and later in occasional diffraction studies. The first dedicated crystallographic X-ray diffraction laboratory was set up in the early 1970s, when it solved the first molecular structures. Soon the fascination brought about by a methodology that afforded the visualization of atoms, molecules and crystals lured the local and national physical chemistry communities. In close partnership with an equally oriented laboratory at the University of Sao Paulo, Brazil, and in collaboration with several physical chemistry laboratories from Argentina and the Latin American region, and also from Europe, we undertook studies on the crystal structures and physicochemical and spectroscopic properties of a wide range of materials, including inorganic, organic, bioinorganic, metal-organic, organic-metal, supramolecular, pharmaceutical, organic minerals and liquid crystals. The present essay is a personal account of the origin and development of structural X-ray crystallography at the University of La Plata and its impact on the scientific research of Argentina and Latin America.

Cocrystallization Enables Ensitrelvir to Overcome Anomalous Low Solubility Caused by Strong Intermolecular Interactions between Triazine-Triazole Groups in Stable Crystal Form.

Ensitrelvir is a nonpeptide 3CL protease inhibitor used for coronavirus disease 2019 treatment. Four crystalline forms of ensitrelvir, metastable (Form I), acetonate (Form II), stable (Form III), and hydrate (Form IV), have been analyzed as pharmaceutical crystals. Their rank order of solubility is Form I > IV > III. Form III is the stable crystal with a significantly lower solubility than that predicted from its log P value of 2.7. Here, single-crystal structural analysis revealed strong intermolecular interactions between the triazine (acidic) and triazole (basic) groups of Form III not Forms I and IV. Multicomponent crystals were also designed to improve the solubility by altering the intermolecular interactions in Form III. Slurry conversion with equal molar ratios of ensitrelvir and fumaric acid successfully induced the formation of a novel cocrystal (Form V). Fumaric acid inhibited the triazine-triazole interactions, and dissolution of Form V was approximately 8- and 13-fold higher than that of Form III in pH 1.2 and 6.8 media, respectively. Furthermore, Form V exhibited an approximately 16-fold higher flux value than that of Form III. Therefore, alterations in intermolecular interactions via cocrystallization significantly enhance the dissolution and permeation of ensitrelvir.

A survey of solid form landscape: Trends in occurrence and distribution of various solid forms and challenges in solid form selection

This survey provides a comprehensive analysis of solid form screens for 476 new chemical entities (NCEs) conducted at Pharmaron from 2016 to 2023. The findings from this survey reveal notable trends in polymorphism, salt formation, crystallization behavior and molecular weight (MW) distribution of the NCEs evaluated. Most solid form screens were conducted to select the preferred solid form for Investigational New Drug (IND) enabling projects, others were for candidate selection or late-stage development. Comparison to published historical data was made to show changes in occurrence of counterions/co-formers for salts/co-crystals, polymorphs, and the distribution of MWs over time. Increased complexity in the solid-form landscape and selection of the development form are discussed, including challenges in crystallization and selection of lead forms. The distribution of types of crystal forms and the observation of emerging and disappearing polymorphs are presented. These results highlight the evolving challenges and considerations in solid form screening and form selection and offer insights for future pharmaceutical development and crystallization strategies.

Crystal structure-mechanical property relationship in succinic acid and L- alanine probed by nanoindentation

Establishing structure–mechanical property relationships is crucial for understanding and engineering the performance of pharmaceutical molecular crystals. In this study, we employed nanoindentation, a powerful technique that can probe mechanical properties at the nanoscale, to investigate the hardness and elastic modulus of single crystals of succinic acid and L-alanine. Nanoindentation results reveal distinct mechanical behaviors between the two compounds, with L-alanine exhibiting significantly higher hardness and elastic modulus compared to succinic acid. These differences are attributed to the underlying variations in molecular crystal structures − the three-dimensional bonding network and high intermolecular interaction energies of L-alanine molecules leads to its stiffness compared to the layered and weakly bonded crystal structure of succinic acid. Furthermore, the anisotropic nature of succinic acid is reflected in the directional dependence of the mechanical responses where it has been found that the (111) plane is more resistant to indentation than (100). By directly correlating the nanomechanical properties obtained from nanoindentation with the detailed crystal structures, this study provides important insights into how differences in molecular arrangements can translate into different macroscopic mechanical performance. These findings have implications on the selection of molecular crystals for optimized drug manufacturability.

Advances in Pharmaceutical Crystals: Control over Nucleation and Polymorphism

Advances in Pharmaceutical Crystals: Control over Nucleation and Polymorphism

Plasticization of a stiff pharmaceutical solid for better tabletability via cocrystallization: Shape synthons as supramolecular protecting groups

Extremely high particle stiffness and very low hardness is a serious concern in various mechanical processes in pharmaceutical manufacturing. Here we report an exceptionally high Young’s modulus (E) of ∼ 18 GPa in a drug, isoniazid (INH). This is one of the highest experimentally determined values among all reported pharmaceutical molecular crystals, which we attribute to the presence of a strong three-dimensional (3D) hydrogen bonding network (HBN). Further, we successfully reduced the 3D HBN in INH to 2D in its cocrystal using a co-former, 3,4-dimethylbenzoic acid (DMBA), where its two hydrophobic groups act like protecting groups at supramolecular level and prevent the extension of HBN. This reduced the E in the 1:1 cocrystal, INH-DMBA, by many folds and markedly improved its powder tabletability. To the best of our knowledge, this is the first reliable molecular level approach to alter the stiffness of pharmaceutical crystals and tabletability improvement in a predictable manner, hence, is important in the context of crystal engineering.

Stereoselective Crystallization of Chiral Pharmaceuticals Aided by Cellulose Derivatives through Helical Pattern Matching.

Stereoselective inhibition aided by "tailor-made" polymeric additives is an efficient approach to obtain enantiopure compounds through conglomerate crystallization. The chemical and configurational match between the side groups of polymers and the molecules of undesired enantiomer is considered to be a necessary condition for successful stereoseparation. Whereas in this contribution, we present an effective resolution of chiral pharmaceuticals by using cellulose acetates as the additives, which stereoselectively reside on the specific crystal faces of one enantiomer and inhibit its crystal nucleation and growth through helical pattern and supramolecular interaction complementarity. An investigation of nimodipine serves as a case study to highlight the novelty of this strategy wherein R-crystals exhibiting an impressive enantiomeric excess value of 97 % can be attained by employing a mere 0.01 wt % cellulose acetate. Guaifenesin and phenyl lactic acid are also well-resolved by utilizing this methodology. Our work not only brings about a brand-new design strategy for "tailor-made" additives, but will also promote the further exploration of the endless potential for utilizing natural biomolecules in chiral recognition and resolution.

An Enhanced Deep Learning-Based Pharmaceutical Crystal Detection with Regional Filtering

In the process of pharmaceutical crystallization, the automatic detection of crystal shapes in images is important since controlling the morphology of the crystals improves the quality of pharmaceutical crystals. In this paper, a novel image detection method called RECDet is proposed. It leverages an automatically adapted binary image to bypass background regions, thereby reducing the detection field. In addition, the method greatly reduces the training time while improving the detection accuracy by using a specially designed detection box for the crystal shape. The performance of our model is evaluated through experimental analysis on a publicly available glutamate crystal dataset and a self-made entecavir pharmaceutical crystal dataset. Experimental results show that RECDet improves the accuracy of prediction bounding boxes by more than 2% compared to other popular models and achieves a classification accuracy of 98%. It can be used as a promising tool in the application of pharmaceutical crystallization control.

The Continuous and Reversible Transformation of the Polymorphs of an MGAT2 Inhibitor (S-309309) from the Anhydrate to the Hydrate in Response to Relative Humidity.

Polymorphic control is vital for the quality control of pharmaceutical crystals. Here, we investigated the relationship between the hydrate and anhydrate polymorphs of a monoacylglycerol acyltransferase 2 inhibitor (S-309309). Solvent evaporation and slurry conversion revealed two polymorphs, the hydrate and the solvate. The solvate was transformed into the hydrate by heating. X-ray powder diffraction demonstrated that the hydrate was transformed into an anhydrate via an intermediate state when heated. These crystal forms were confirmed under controlled humidity conditions; the presence of the anhydrate, the intermediate hydrate, or the hydrate depended on the relative humidity at 25 °C. The stoichiometry of S-309309 in water in the hydrate form was 4:1. The hydrates and anhydrates exhibited similar crystal structures and stability. The water of hydration in the intermediate hydrate was 0.1-0.15 mol according to the dynamic vapor sorption profile. The stability and dissolution profile of the anhydrate and hydrate showed no significant change due to similar crystal lattices and quick rehydration of the anhydrate. A mechanism for the reversible crystal transformation between the anhydrate and pseudo-polymorphs of the hydrate was discovered. We concluded that S-309309 causes a pseudo-polymorphic transformation; however, this is not a critical issue for pharmaceutical use.

CO2 Promoting Polymorphic Transformation of Clarithromycin: Polymorph Characterization, Pathway Design, and Mechanism Study

Carbon dioxide (CO2) has a wide range of uses such as food additives and raw materials for synthetic chemicals, while its application in the solid-state transformation of pharmaceutical crystals is rare. In this work, we report a case of using 1 atm CO2 as an accelerator to promote the polymorphic transformation of clarithromycin (CLA). Initially, crystal structures of Form 0′ and three solvates were successfully determined by single crystal X-ray diffraction (SCXRD) analysis for the first time and found to be isomorphous. Powder X-ray diffraction (PXRD) and thermal analysis indicated that the solvate desolvates and transforms into the structurally similar non-solvated Form 0′ at room temperature to ~50 °C. Form 0′ and Form II are monotropically related polymorphs with Form II being the most stable. Subsequently, the effect of CO2 on the transformation of CLA solvates to Form II was studied. The results show that CO2 can significantly facilitate the transformation of Form 0′ to Form II, despite no significant effect on the desolvation process. Finally, the molecular mechanism of CO2 promoting the polymorphic transformation was revealed by the combination of the measurement of adsorption capacity, theoretical calculations as well as crystal structure analysis. Based on the above results, a new pathway of preparing CLA Form II was designed: transform CLA solvates into Form 0′ in 1 atm air at 50 °C followed by the transformation of Form 0′ to Form II in 1 atm CO2 at 50 °C. This work provides a new idea for promoting the phase transformation of pharmaceutical crystals as well as a new scenario for the utilization of CO2.

Heterogeneous crystallization of Chlorzoxazone for modulating the physicochemical properties of crystals

The polymer on modulating the crystal's habit is an evolving research in pharmaceutical crystallization. This study demonstrates the crystal habit modification of chlorzoxazone (CHZ) by heterogeneous crystallization (HC) in the binary solvent acetonitrile-ethanol (A-E (1:1)) in the presence of polyvinylpyrrolidine (PVP) at concentrations of 0.50, 0.75, and 1.00 wt%. The A-E (1:1) and PVP in HC experiments influenced to change the shape of crystals from needle to plate shape and reduced the crystal size producing a lower aspect ratio (in the range of 1.5–2.3). In the presence of PVP, the CHZ size distribution is 65–78 μm which tends to enhance the powder flow-ability of CHZ crystals and as the PVP concentration increases, the nucleation rate decreases. The solubility of size-reduced CHZ crystals at different pH is found to be improved by 1.2–1.4 times. Hence, HC is deemed effective in modifying the physicochemical attributes of CHZ.

Recent Progress in Antisolvent Crystallization of Pharmaceuticals with a Focus on the Membrane‐Based Technologies

AbstractContinuous crystallization of pharmaceuticals has been in the center of attention during the past two decades, with a more focus on the large‐scale production of active pharmaceutical ingredients. The increasing demand for pharmaceuticals requires high‐throughput production of drug crystals with different solubilities, stabilities, shapes, habits, polymorphs, and size distributions. With numerous advantages including low cost, ease of scale‐up, and superior control over polymorph and size distribution of drug crystals, antisolvent crystallization is one of the most promising crystallization methods recently attempted. However, it fails to deliver the required characteristic where the crystal systems tend to grow and for the preparation of metastable polymorphs. This review focuses on the most recent efforts to tackle these drawbacks by coupling antisolvent crystallization with cooling, supercritical‐assisted, microfluidics‐assisted, and membrane‐assisted crystallization. This systematic review aims to provide a concise summary of each coupled antisolvent technique and their positive and negative aspects. This review can be used as a guideline for pharmacist, biologists, and chemists, who are interested in the crystal engineering of pharmaceuticals to pave the way for further developments in this field.

Scrolling in Supramolecular Gels: A Designer's Guide.

Gelation by small molecules is a topic of enormous importance in catalysis, nanomaterials, drug delivery, and pharmaceutical crystallization. The mechanism by which gelators self-organize into a fibrous gel network is poorly understood. Herein, we describe the crystal structures and gelation properties of a library of bis(urea) compounds and show, via molecular dynamics simulations, how gelator aggregation progresses from a continuous pattern of supramolecular motifs to a homogeneous fiber network. Our model suggests that lamellae with asymmetric surfaces scroll into uniform unbranched fibrils, while sheets with symmetric surfaces undergo stacking to form crystals. The self-assembly of asymmetric lamellae is associated with specific molecular features, such as the presence of narrow and flexible end groups with high packing densities, and likely represents a general mechanism for the formation of small-molecule gels.

Medium-chain dicarboxylic acids: chemistry, pharmacological properties, and applications in modern pharmaceutical and cosmetics industries.

Succinic (SUA), glutaric (GLA), pimelic (PA), suberic (SUBA), adipic (ADA), azelaic (AZA), and sebacic acids (SA) make up the majority of medium-chain dicarboxylic acids (MCDAs) with chain lengths of C4-C10, and are widely utilised in the chemical, food, textile, pesticide, pharmaceutical, and liquid crystal sectors. The MCDAs' two carboxyl groups provide them with an incredibly broad variety of applications. The focus of significant scientific research now is on the increasingly varied pharmacological effects of MCDAs. However, only a few studies have compared the biological characteristics of MCDAs in the contemporary pharmaceutical and cosmetic sectors and thoroughly examined the most recent research and marketing initiatives for MCDAs. This review's objective is to offer a thorough analysis of academic works on MCDAs, to assess the usefulness of these substances' chemical-pharmacological properties for use in the contemporary pharmaceutical and cosmetic industries, and to investigate the direction of their possible applications in these two disciplines. In addition, this review investigates how these compounds are metabolised in the human body.

Population balance model enabled digital design and uncertainty analysis framework for continuous crystallization of pharmaceuticals using an automated platform with full recycle and minimal material use

A systematic digital design framework for the development of a digital twin of a continuous crystallization process was presented using the model compound, diphenhydramine hydrochloride (DPH). The key features of the framework include operating space investigations, kinetic parameter estimation using population balance modeling, and systematic batch-to-continuous crystallization translation of the estimated parameters. An approach that compares experimental uncertainties with model-prediction uncertainties was used to justify the robustness of the parameter estimation procedure. For continuous crystallization development, a continuous configuration with full recycle and dissolution was developed, which enabled rapid process design with minimal material use. The results demonstrated successful model development for both batch and mixed-suspension-mixed-product-removal (MSMPR) crystallization configurations. This experimentally validated model, along with quantified uncertainty space of the kinetic parameters, serves as a digital twin of the process, which was later used to optimize the multistage MSMPR process to produce larger crystals with narrower distributions.

Cocrystal: A Review on the Design and Preparation of Pharmaceutical Cocrystals

The majority of the active pharmaceutical components have issues with poor solubility, bioavailability, chemical stability, and moisture absorption. Pharmaceutical crystals are a reliable way to change the aforementioned physicochemical properties of drugs without changing their pharmacological behaviour. However, the success of these approaches depends on the physical and chemical properties of the molecules being developed. The development of drug products with superior physicochemical characteristics, such as melting point, tablet ability, solubility, stability, bioavailability, and permeability, while preserving the pharmacological properties of the active pharmaceutical ingredient is greatly facilitated by co-crystallization of drug substances. All the components of a cocrystal, which is a stoichiometric homogeneous multicomponent system connected by non-covalent interactions, are solid under ambient conditions.

Review of the Application of PAT in the Pharmaceutical Continuous Crystallization Process.

As an important pharmaceutical process, crystallization greatly impacts the final product. In recent years, the continuous crystallization process has attracted more attention from researchers, with the promotion of continuous manufacturing (CM) by the Food and Drug Administration (FDA). The continuous crystallization process has the advantages of high economic benefit, stable and uniform quality, a short production cycle, and personalization. To carry out continuous crystallization, some related process analytical technology (PAT) tools have become the focus of breakthroughs. Infrared (IR) spectroscopy, Raman spectroscopy, and focused beam reflection measurement (FBRM) tools have gradually become research hotspots due to their fast, non-destructive, and real-time monitoring characteristics. This review compared the advantages and disadvantages of the three technologies. Their applications in the upstream mixed continuous crystallization process, the middle reaches of crystal nucleation and growth, and the process of the downstream refining were discussed to provide corresponding guidance for the practice and further development of these three technologies in the continuous crystallization process and promote the development of CM in the pharmaceutical industry.

Preparation, characterization, and stability enhancement of metoprolol pharmaceutical multicomponent crystals

Crystal engineering is a crucial technology in improving the physicochemical properties of active pharmaceutical ingredients (APIs). To address the drawback of the instability and low melting point of metoprolol (MET), multi-component compounds of metoprolol were designed and synthesized to enhance their stability. Six stable multi-component crystals with dihydrocaffeic acid (DA), p-hydroxybenzoic acid (p-HA), 4-chlorobenzoic acid (4-CA), 3,5-dinitrobenzoic acid (3,5-DA), cinnamic acid (CA) and oxalic acid (OA) were obtained for the first time. Single crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) and thermogravimetric analysis (TG) techniques were used to characterize the novel multicomponent crystals. In addition, the stability of the solid drug forms was evaluated. The results indicate that the stability of all six multicomponent crystals was significantly higher than that of the raw materials.

Case Studies in the Application of a Workflow-Based Crystallization Design for Optimized Impurity Rejection in Pharmaceutical Development

Crystallization is an important unit operation in pharmaceutical drug substance manufacturing for the isolation of organic products. Impurity control is a recurring critical quality attribute in most commercial pharmaceutical crystallization processes. A systematic workflow that can reveal the incorporation mechanism of various impurities during crystallization and guide us to understand impurity rejection is useful for crystallization process design. Such a workflow was recently published by Urwin et al. Herein, we present three case studies implementing this workflow, covering surface deposition, conglomerate formation, and agglomeration as principal routes for impurity incorporation during crystallization of a drug substance’s active pharmaceutical ingredient and its intermediates. We demonstrate the experimental steps to identify various impurity incorporation mechanisms and discuss the strategy for impurity rejection in each case. We built upon the previous approach to demonstrate a material sparing approach through our case studies. We highlight the value of stepwise dissolution and show the importance of doing it early in the impurity incorporation identification stage. At this stage, we introduce a missing incorporation mechanism in prior work, namely, conglomerate systems. We show how to identify and resolve this mode of incorporation mechanism through stepwise dissolution and solubility-limited rejection maps.