Approach of Cocrystallization to Improve the Solubility and Photostability of Tranilast

The
cocrystals and salts of an antiallergic drug, tranilast, were synthesized
to improve its solubility and photostability. Two tranilast cocrystals
with urea (1) and nicotinamide (2), as well
as two salts with cytosine (3) and sodium ion (4), were obtained and characterized by infrared spectra, thermogravimetric
analyses, differential scanning calorimetry, and powder and single
crystal X-ray diffractions. The results of single crystal structure
analyses of 1–3 indicate that tranilast
combines amide groups in coformers via R22(8) synthon, resulting in a 1:1 stoichiometry.
The complexes showed advantages in terms of solubility and photostability
in comparison to pure tranilast. The maximum solubility values of 1–3 in phosphate buffer of pH 6.8 are
approximately 1.6, 1.9, and 2.0 times as large as that of tranilast,
and the residual of tranilast is 79.5, 92.9, 88.5, 86.2, and 87.4%
for tranilast and 1–4, respectively,
under the fluorescent lamp irradiation for 96 h.