Two crystalline forms of α-[(tert-butylamino) methyl]-2-chloro-4-hydroxybenzyl alcohol hydrochloride (HOKU-81) were found by X-ray powder diffraction and infrared spectroscopic analyses. By means of differential scanning calorimetry (DSC), the melting points of forms I and II were found to be 179 and 181°C, respectively. It was found by simultaneous DSC and thermogravimetry that the two polymorphs of HOKU-81 decomposed upon further heating. Both polymorphs of HOKU-81 were very stable to humidity, heating and mechanical treatments such as grinding or compressing. These physicochemical properties of HOKU-81 are very different from those of tulobuterol hydrochloride, a pre-metabolite form of HOKU-81 in humans and an excellent bronchodilator.
