Five Cocrystal Forms of Antitumor Drug Temozolomide with p-Hydroxybenzoic Acid: Structure, Computational Analysis, Characterizations, Stability, and Transformation

Temozolomide (TMZ) is a first-line antitumor drug but suffers from troubling stability issues related to degradation during storage and processing. In this paper, cocrystallization of TMZ with p-hydroxybenzoic acid (PHBA) produced five forms including one methanolate, one hydrate, two polymorphic forms in 2:1, and one solvent-free form in 1:1 ratio, designated as TMZ/ PHBA/MeOH (1:1:1, S1), TMZ/PHBA/H2O (1:1:1, S2), TMZ/PHBA (2:1-form I, S3; 2:1-form II, S4), and TMZ/PHBA (1:1, S5). Except for S5, the other four forms were characterized and evaluated in detail by single-crystal X-ray diffraction. Powder X-ray diffraction, Fourier transform infrared spectroscopy, thermal analysis, and stability test were conducted for all five forms. The crystal form differences are mainly ascribed to the incorporation of solvent/water molecules, supramolecular synthon distinctions, and conformation flexibility of TMZ. The feeding ratio of starting components and the solvent used in the experiments both play a decisive role in the resulting form.