Impurity Occurrence and Removal in Crystalline Products from Process Reactions

Effects of structurally – related impurities on the crystal growth of curcumin spherulites

The crystal growth of curcumin in pure 2-propanol containing two structurally related impurities, demethoxycurcumin (DMC) and bisdemethoxycurcumin (BDMC), has been investigated by seeded isothermal desupersaturation experiments at 283, 293 and 308 K.

Impurity incorporation in solution crystallization: diagnosis, prevention, and control

This work highlights recent advances in the diagnosis, prevention, and control of impurity incorporation during solution crystallization.

29th Annual GP2A Medicinal Chemistry Conference

The 29th Annual GP₂A (Group for the Promotion of Pharmaceutical chemistry in Academia) Conference was a virtual event this year due to the COVID-19 pandemic and spanned three days from Wednesday 25 to Friday 27 August 2021. The meeting brought together an international delegation of researchers with interests in medicinal chemistry and interfacing disciplines. Abstracts of keynote lectures given by the 10 invited speakers, along with those of the 8 young researcher talks and the 50 flash presentation posters, are included in this report. Like previous editions, the conference was a real success, with high-level scientific discussions on cutting-edge advances in the fields of pharmaceutical chemistry.

Impact of Impurities on Crystallization and Product Quality: A Case Study with Paracetamol

A thorough, systematic study into the effect that structurally related impurities have on both the process and product quality during the crystallization of an active pharmaceutical ingredient is presented. The presence of acetanilide and metacetamol influences the crystallization and product quality of paracetamol. Where high concentrations of either impurity were present in the crystallization feed, product recovery decreased by up to 15%. Acetanilide is included in the final product through adsorption onto the particle surface in concentrations up to 0.79 mol%, which can be reduced to acceptable levels through product reslurrying. The presence of metacetamol results in much higher concentrations—up to 6.78 mol% in the final product, of which approximately 1 mol% is incorporated into the crystal lattice, resulting in the perturbation of the unit-cell dimensions. The incidental crystallization and subsequent isolation of metastable Form II paracetamol increased product purity in the presence of a low metacetamol concentration. This metastable product converts to stable paracetamol Form I through reslurrying, offering an efficient metacetamol impurity rejection route. The morphology of the product is modified consistently by both impurities. An elongation of the normal prismatic shape is observed, which in the extreme case of high metacetamol contamination results in the isolation of fine, fragile needles. This problematic morphology is also improved by a reslurrying of the crystallization product to give a more equilateral shape. This systematic study of the influence of acetanilide and metacetamol on the crystallization of paracetamol builds a well-rounded picture of the concomitant impact of impurities on the principal quality attributes of a crystallization product.

A Structured Approach To Cope with Impurities during Industrial Crystallization Development

The perfect separation with optimal productivity, yield, and purity is very difficult to achieve. Despite its high selectivity, in crystallization unwanted impurities routinely contaminate a crystallization product. Awareness of the mechanism by which the impurity incorporates is key to understanding how to achieve crystals of higher purity. Here, we present a general workflow which can rapidly identify the mechanism of impurity incorporation responsible for poor impurity rejection during a crystallization. A series of four general experiments using standard laboratory instrumentation is required for successful discrimination between incorporation mechanisms. The workflow is demonstrated using four examples of active pharmaceutical ingredients contaminated with structurally related organic impurities. Application of this workflow allows a targeted problem-solving approach to the management of impurities during industrial crystallization development, while also decreasing resources expended on process development.

One-Pot, Tandem Wittig Hydrogenation: Formal C(sp3)-C(sp3) Bond Formation with Extensive Scope

A one-pot, tandem Wittig hydrogenation of aldehydes with stabilized ylides is reported, representing a formal C(sp³)-C(sp³) bond construction. The tandem reaction operates under mild conditions, is high yielding, and is broad in scope. Chemoselectivity for olefin reduction is observed, and the methodology is demonstrated in the synthesis of lapatinib analogues and a formal synthesis of (±)-cuspareine. Early insights suggest that the chemoselectivity observed in the reduction step is due to partial poisoning of the catalyst, after step one, thus adding to the power of the one-pot procedure.

Effect of Solution Composition on Impurity Profile of the Crystallized Product in Oiling-Out Crystallization

Oiling-out is a unique phenomenon that the liquid phase is separated into two parts during crystallization. The emergence of new liquid phase changes the environment where crystals nucleate and grow, we call "mother phase," because target material and impurities become distributed to each phase according to their own particular distribution ratios. In our previous study on crystallization of an intermediate compound with impurities (denoted Imp-A, -B, and -C), we found that when oiling-out was formed, incorporation of Imp-C was inhibited, because Imp-C was distributed to the mother phase less than Imp-A and -B. In this study, we explored the effect of EtOH solution composition on impurity profile of the crystallized product in oiling-out crystallization, and found that the low content of Imp-B in the EtOH solution, the higher content of Imp-C in the crystallized product. Our finding revealed that not only oiling-out but also Imp-B played a key role in inhibiting the incorporation of Imp-C into the crystals.

Stepwise dissolution and composition determination of samples of multiple crystals using a dissolution medium containing aqueous alcohol and fluorocarbon phases

A biphasic medium gave controlled partial dissolution of crystals in multi-particle samples allowing the distribution of impurities to be determined.

Determination of composition distributions of multi-particle crystalline samples by sequential dissolution with concomitant particle sizing and solution analysis

Sequential dissolution of multi-particle samples with before-and-after sizing gave composition data that can be assigned to defined sample particle regions.

Amplification of impurity upon complex formation: how a 2% ligand impurity lowers the corresponding complex purity to 50%

Statistical incorporation of small amounts of ligand impurities has devastating consequences on the purity of metal–organic complexes derived from the respective ligands.