Organic salts of pharmaceutical impurity ρ-Aminophenol

The presence of impurities can drastically affect the efficacy and safety of pharmaceutical entities. ρ-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 diffi cult 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 diffi cult 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

Tailoring crystal size distributions for product performance, compaction of paracetamol

Paracetamol crystals often exhibit poor compressibility properties, which results in capping issues. The Particle Size Distribution (PSD) of paracetamol was engineered to improve the compressibility of paracetamol crystals. This was accomplished by growing paracetamol crystals in the presence of additives. The active pharmaceutical ingredient Phenacetin and impurity 4-chloroacetanalide were used to modify the crystal properties of paracetamol. In solution, the phenacetin or 4-chloroacetanalide molecules adsorb onto the paracetamol crystal faces selectively (110 or 011) and inhibit the further growth of the paracetamol crystal and consequently, the paracetamol crystal growth is reduced substantially. For controlling the PSD of crystal to improve the compressibility of paracetamol crystals, a set of cooling crystallization experiments in the presence of additive was designed. According to a statistical experimental design, the cooling rate was the most effective parameter. The PSD was reduced when paracetamol crystallized from the controlled crystallization in the presence of less than 3 mol% of both additives. These smaller particles increased almost fourfold the compressibility of paracetamol in comparison to the commercial material. Moreover, tablets were prepared for each formulation using a direct compaction method. The results illustrated that a higher tablet hardness of paracetamol was achieved by tailoring the paracetamol crystal size distribution. In addition, the tablet disintegration time was higher for the formulation increased hardness. Overall, this work presents the potential use of structurally similar compounds as additives to alter the mechanical properties of an API

Desymmetrization by asymmetric copper-catalyzed intramolecular C–H insertion reactions of α-diazo-β-oxosulfone

Effective desymmetrization in copper-catalyzed intramolecular C–H insertion reactions of α-diazo-β-oxosulfones in the formation of fused thiopyran dioxides is described for the first time. The use of a copper–bis(oxazoline)–NaBARF catalyst complex system leads to formation of the major thiopyran dioxide stereoisomer with up to 98:2 dr and up to 98% ee. The effect of varying the bis(oxazoline) ligand, copper salt, and site of C–H insertion on both diastereo- and enantioselectivities of these intramolecular C–H insertion reactions has been investigated. Similarly, desymmetrization in the formation of a fused cyclopentanone proceeds with up to 64% ee. These results represent the highest enantioselectivity reported to date in a copper-mediated desymmetrization through C–H insertion