Abstract
The crystal structures of the two crystalline forms (I and II) of α-[(tert-butylamino)-methyl]-2-chloro-4-hydroxybenzyl alcohol hydrochloride (HOKU-81), which is one of the metabolites of tulobuterol hydrochloride (C-78) and a potent β2-adrenergic stimulant, have been determined by X-ray structure analysis. The structures were solved by direct methods and refined by the block-diagonal least-squares method including anisotropic thermal parameters to final R values of 0.051 and 0.050 for Forms I and II, respectively. The molecular conformations in the two forms are similar, but nevertheless the crystal structures are very different. In Form I, independent hydrogen bonds of four types are formed, while three types of independent hydrogen bond are formed in Form Ii, producing characteristic molecular sheets in the crystals. Comparison of the crystal structures of the polymorphs between HOKU-81 and C-78 indicates that some of the differences of physico-chemical properties are attributable to the differences of crystal packings. Furthermore, comparison of the molecular conformations of HOKU-81 and C-78 with those of the other adrenergic agents having an ethanolamine side chain shows that these compounds have homologous conformations in the aliphatic side chain.
