New cocrystals of heterocyclic drugs: structural,antileishmanial, larvicidal and urease inhibition studies

Many heterocycles have been developed as drugs due to their capacity to interact productively with biological systems. The present study aimed to synthesize cocrystals of the heterocyclic antitubercular agent pyrazinamide ( PYZ , 1 , BCS III) and the commercially available anticonvulsant drug carbamazepine ( CBZ , 2 , BCS class II) to study the effect of cocrystallization on the stability and biological activities of these drugs. Two new cocrystals, namely, pyrazinamide–homophthalic acid (1/1) ( PYZ:HMA , 3 ) and carbamazepine–5-chlorosalicylic acid (1/1) ( CBZ:5-SA , 4 ), were synthesized. The single-crystal X-ray diffraction-based structure of carbamazepine–trans-cinnamic acid (1/1) ( CBZ:TCA , 5 ) was also studied for the first time, along with the known cocrystal carbamazepine–nicotinamide (1/1) ( CBZ:NA , 6 ). From a combination drug perspective, these are interesting pharmaceutical cocrystals to overcome the known side effects of PYZ ( 1 ) therapy, and the poor biopharmaceutical properties of CBZ ( 2 ). The purity and homogeneity of all the synthesized cocrystals were confirmed by single-crystal X-ray diffraction, powder X-ray diffraction and FT–IR analysis, followed by thermal stability studies based on differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Detailed intermolecular interactions and the role of hydrogen bonding towards crystal stability were evaluated quantitatively via Hirshfeld surface analysis. The solubility of CBZ at pH 6.8 and 7.4 in 0.1 N HCl and H₂O were compared with the values of cocrystal CBZ:5-SA ( 4 ). The solubility of CBZ:5-SA was found to be significantly improved at pH 6.8 and 7.4 in H₂O. All the synthesized cocrystals 3 – 6 exhibited a potent urease inhibition (IC₅₀ values range from 17.32 ± 0.89 to 12.3 ± 0.8 µM), several times more potent than standard acetohydroxamic acid (IC₅₀ = 20.34 ± 0.43 µM). PYZ:HMA ( 3 ) also exhibited potent larvicidal activity against Aedes aegypti. Among the synthesized cocrystals, PYZ:HMA ( 3 ) and CBZ:TCA ( 5 ) were found to possess antileishmanial activity against the miltefosine-induced resistant strain of Leishmania major, with IC₅₀ values of 111.98 ± 0.99 and 111.90 ± 1.44 µM, respectively, in comparison with miltefosine (IC₅₀ = 169.55 ± 0.20 µM).