Efficient Purification of an Active Pharmaceutical Ingredient via Cocrystallization: From Thermodynamics to Scale-Up

Keto-Adamantane-Based Macrocycle Crystalline Supramolecular Assemblies Showing Selective Vapochromism to Tetrahydrofuran

Here, we report the synthesis of adamantane-based macrocycle 2 by combining adamantane building blocks with π-donor 1,3-dimethoxy-benzene units. An unpredictable keto-adamantane-based macrocycle 3 was obtained by the oxidation of 2 using DDQ as an oxidant. Moreover, a new type of macrocyclic molecule-based CT cocrystal was prepared through exo-wall CT interactions between 3 and DDQ. The cocrystal material showed selective vapochromism behavior towards THF, specifically, among nine volatile organic solvents commonly used in the laboratory. Powder X-ray diffraction; UV-Vis diffuse reflectance spectroscopy; 1H NMR; and single crystal X-ray diffraction analyses revealed that color changes are attributed to the vapor-triggered decomplexation of cocrystals.

Cocrystal Synthesis through Crystal Structure Prediction

Crystal structure prediction (CSP) is an invaluable tool in the pharmaceutical industry because it allows to predict all the possible crystalline solid forms of small-molecule active pharmaceutical ingredients. We have used a CSP-based cocrystal prediction method to rank ten potential cocrystal coformers by the energy of the cocrystallization reaction with an antiviral drug candidate, MK-8876, and a triol process intermediate, 2-ethynylglyclerol. For MK-8876, the CSP-based cocrystal prediction was performed retrospectively and successfully predicted the maleic acid cocrystal as the most likely cocrystal to be observed. The triol is known to form two different cocrystals with 1,4-diazabicyclo[2.2.2]octane (DABCO), but a larger solid form landscape was desired. CSP-based cocrystal screening predicted the triol-DABCO cocrystal as rank one, while a triol-l-proline cocrystal was predicted as rank two. Computational finite-temperature corrections enabled determination of relative crystallization propensities of the triol-DABCO cocrystals with different stoichiometries and prediction of the triol-l-proline polymorphs in the free-energy landscape. The triol-l-proline cocrystal was obtained during subsequent targeted cocrystallization experiments and was found to exhibit an improved melting point and deliquescence behavior over the triol-free acid, which could be considered as an alternative solid form in the synthesis of islatravir.

Formation of ibrutinib solvates: so similar, yet so different

The transformation processes of non-solvated ibrutinib into a series of halogenated benzene solvates are explored in detail here. The transformation was studied in real time by X-ray powder diffraction in a glass capillary. Crystal structures of chlorobenzene, bromobenzene and iodobenzene solvates are isostructural, whereas the structure of fluorobenzene solvate is different. Four different mechanisms for transformation were discovered despite the similarity in the chemical nature of the solvents and crystal structures of the solvates formed. These mechanisms include direct transformations and transformations with either a crystalline or an amorphous intermediate phase. The binding preference of each solvate in the crystal structure of the solvates was examined in competitive slurry experiments and further confirmed by interaction strength calculations. Overall, the presented system and online X-ray powder diffraction measurement provide unique insights into the formation of solvates.

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.

A Review of Pharmaceutical Nano-Cocrystals: A Novel Strategy to Improve the Chemical and Physical Properties for Poorly Soluble Drugs

Nowadays, many commercial drugs have poor solubility and bioavailability. Cocrystals are formulated to modulate active pharmaceutical ingredients’ properties with improved solubility, dissolution, and bioavailability compared to their pristine individual components in the pharmaceutical industry. Nano-cocrystals, crystals in the nano range, can further enhance these properties because of not only the cocrystal structure, but also the large surface to volume ratio of nanocrystals. Even though there are many studies on cocrystals, the research of pharmaceutical nano-cocrystals is still in the initial stage. Thus, it is necessary to conduct a systematic study on pharmaceutical nano-cocrystals. In this review, the possible preparation approaches of nano-cocrystals have been reported. To have a comprehensive understanding of nano-cocrystals, some analytical techniques and characterizations will be discussed in detail. In addition, the feasible therapeutic application of nano-cocrystals will be presented. This work is expected to provide guidance to develop new nano-cocrystals with commercial value in the pharmaceutical industry.

Solution Cocrystallization: A Scalable Approach for Cocrystal Production

With an increasing interest in cocrystals due to various advantages, demand for large-scale cocrystallization techniques is rising. Solution cocrystallization is a solvent-based approach that utilizes several single-component crystallization concepts as well as equipment for generating cocrystals. Solution-based techniques can produce cocrystals with reasonable control on purity, size distribution, morphology, and polymorphic form. Many of them also offer a scalable solution for the industrial production of cocrystals. However, the complexity of the thermodynamic landscape and the kinetics of cocrystallization offers fresh challenges which are not encountered in single component crystallization. This review focuses on the recent developments in different solution cocrystallization techniques for the production of pharmaceutically relevant cocrystals. The review consists of two sections. The first section describes the various solution cocrystallization methods, highlighting their benefits and limitations. The second section emphasizes the challenges in developing these techniques to an industrial scale and identifies the major thrust areas where further research is required.

Organic Salts of Pharmaceutical Impurity p-Aminophenol

The presence of impurities can drastically affect the efficacy and safety of pharmaceutical entities. p-Aminophenol (PAP) is one of the main impurities of paracetamol (PA) that can potentially show toxic effects such as maternal toxicity and nephrotoxicity. The removal of PAP from PA is challenging and difficult to achieve through regular crystallization approaches. In this regard, we report four new salts of PAP with salicylic acid (SA), oxalic acid (OX), l-tartaric acid (TA), and (1S)-(+)-10-camphorsulfonic acid (CSA). All the PAP salts were analyzed using single-crystal X-ray diffraction, powder X-ray diffraction, infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. The presence of minute amounts of PAP in paracetamol solids gives a dark color to the product that was difficult to remove through crystallization. In our study, we found that the addition of small quantities of the aforementioned acids helps to remove PAP from PA during the filtration and washings. This shows that salt formation could be used to efficiently remove challenging impurities.

Structural motifs in salts of sulfathiazole: implications for design of salt forms in pharmaceuticals APIs

The creation of salts is a frequently used approach to modify physicochemical properties of active pharmaceutical ingredients. This work prepares a collection of sulfathiazole salts to probe the influence of counterion structure on crystal packing.

Experimental cocrystal screening and solution based scale-up cocrystallization methods

Cocrystals are crystalline single phase materials composed of two or more different molecular and/or ionic compounds generally in a stoichiometric ratio which are neither solvates nor simple salts. If one of the components is an active pharmaceutical ingredient (API), the term pharmaceutical cocrystal is often used. There is a growing interest among drug development scientists in exploring cocrystals, as means to address physicochemical, biopharmaceutical and mechanical properties and expand solid form diversity of the API. Conventionally, coformers are selected based on crystal engineering principles, and the equimolar mixtures of API and coformers are subjected to solution-based crystallization that are commonly employed in polymorph and salt screening. However, the availability of new knowledge on cocrystal phase behaviour in solid state and solutions has spurred the development and implementation of more rational experimental cocrystal screening as well as scale-up methods. This review aims to provide overview of commonly employed solid form screening techniques in drug development with an emphasis on cocrystal screening methodologies. The latest developments in understanding and the use of cocrystal phase diagrams in both screening and solution based scale-up methods are also presented. Final section is devoted to reviewing the state of the art research covering solution based scale-up cocrystallization process for different cocrystals besides more recent continuous crystallization methods.

Pharmaceutical cocrystals: along the path to improved medicines

Cocrystals, a long known but understudied class of crystalline solids, have attracted interest from crystal engineers and pharmaceutical scientists in the past decade and are now an integral part of the preformulation stage of drug development.

Direct co-crystal assembly from synthesis to co-crystallization

The ternary phase diagram for the direct assembly of a 2 : 1 co-crystal of benzoic acid–sodium benzoate was illustrated. Benzoic acid acted as a reactant and underwent neutralization to produce sodium benzoate. The excessive amount of benzoic acid as an API can interact with the product, sodium benzoate as another API, to undertake API–API co-crystallization by cooling.

The solid-state continuum: a perspective on the interrelationships between different solid-state forms in drug substance and drug product

Objective

The objective of the review is to provide an overview of the nomenclature used in the solid-state continuum and relate these to the development of drug substances and drug products.

Key findings

The importance of a rational approach to solid-state form selection, including integrated decision making (ensuring equal weight is given to the needs of the drug substance and the drug product), is vital for the effective development of a drug candidate. For example, how do secondary processing considerations influence the selection of drug substance solid-state form and resulting formulation, and how can drug substance solid-state form be used to optimise secondary processing? Further, the potential use of ‘crystal’ engineering to optimise stability, purity and optical resolutions, and the linked regulatory requirements, will be discussed.

Summary

The nomenclature used in the solid-state continuum, which contains a large number of different crystalline and non-crystalline forms, for example, amorphous systems, was reviewed. Further, the significant role of the drug substance within the solid oral dose form from a physicochemical perspective was covered.

From discovery to scale-up: α-lipoic acid : nicotinamide co-crystals in a continuous oscillatory baffled crystalliser

Discovery, characterisation and scale-up of novel α-lipoic acid co-crystals using continuous crystallisation in a COBC is demonstrated.