Synthesis and Pharmacokinetic Study of Three Gemfibrozil Salts: An Exploration of the Structure-Property Relationship

Three salts, [H₃N(CH₂)₂NH₃)][gem]₂ (1), [H₃N(CH₂)₃NH₃)][gem]₂·2H₂O (2), and [H₃N(CH₂)₄NH₃)][gem]₂·2H₂O (3) of the minimally soluble drug gmfibrozil (Hgem), used for the treatment of hyperlipidemia have been synthesized by using a series of diamine with different carbon chain lengths and characterized by single crystal/powder X-ray diffraction, Fourier transform infrared spectroscopy, and ¹H nuclear magnetic resonance. In the three salts, two protons of two gmfibrozil molecules transfer to one diamine, and the resulting organic diammonium cation and gmfibrozil anion are assembled by hydrogen bond interactions into a two-dimensional layer. Although the apparent solubility of salts 1-3 is obviously improved compared to that of the original gemfibrozil, pharmacokinetic studies in rats indicate the enhancement of absorption is limited with the relative bioavailability of 104% for 1, 154% for 2, and 108% for 3. It is notable that the rapid dissolution behavior of salt 1-3 leads to the increase of maximal plasma concentration (C_max) and the dramatic shortening of the time required to reach the C_max. The investigation of the structure-property relationship shows that there is little correlation of solubility with the carbon chain length of cation which is different from previous observations, and we speculate that both electrostatic attraction and hydrogen bond interaction contribute to the solubility order (2 > 1 > 3).