*Article* **Crystal Structure of Novel Terephthalate Salt of Antiarrhythmic Drug Disopyramide**

**Majid Ismail Tamboli † , Yohei Utusmi † , Takayuki Furuishi \*, Kaori Fukuzawa and Etsuo Yonemochi \***

> Department of Physical Chemistry, School of Pharmacy and Pharmaceutical Sciences, Hoshi University, 2-4-41 Ebara, Shinagawa-ku, Tokyo 142-8501, Japan; t-majid@hoshi.ac.jp (M.I.T.); s172504@hoshi.ac.jp (Y.U.); k-fukuzawa@hoshi.ac.jp (K.F.)

> **\*** Correspondence: t-furuishi@hoshi.ac.jp (T.F.); e-yonemochi@hoshi.ac.jp (E.Y.); Tel.: +81-3-5498-5159 (T.F.); +81-3-5498-5048 (E.Y.)

† Co-first author, these authors contributed equally to this work.

**Abstract:** 1:1 salt of Disopyramide (DPA) with Terephthalic acid (TA) was obtained by the slow solvent evaporation and the slurry crystallization methods. X-ray single crystal diffraction of DPA:TA confirmed the formation of salt by the transfer of an acidic proton from one of the carboxylic acidic groups of TA to the tertiary amino group of the chain moiety (N3-nitrogen atom) of the DPA molecules. DPA:TA salt crystals crystalize in the triclinic system with space group *P*-1. The asymmetric unit, comprising one protonated DPA and one TA anion, are linked by a strong charge assisted N+–H···O¯ hydrogen bond and a C–H···O¯ hydrogen bond. Moreover, structural characterization of DPA:TA salt was carried out using Fourier transform infrared spectroscopy, differential scanning calorimeter, thermogravimetric analysis, and powder X-ray diffraction techniques

**Keywords:** Disopyramide; Terephthalic acid; salt; crystal structure; molecular packing; slurry crystallization
