Shoji Atsushi, Yanagida Akio, Shindo Heisaburo, Ito Yoichiro, Shibusawa Yoichi
Division of Structural Biology and Analytical Science, School of Pharmacy, Tokyo University of Pharmacy and Life Science, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan.
J Chromatogr A. 2007 Jul 20;1157(1-2):101-7. doi: 10.1016/j.chroma.2007.04.027. Epub 2007 Apr 19.
The kinetics of Z-(cis)/E-(trans) isomerization of enalapril was investigated by reversed phase high-performance liquid chromatography (RP-HPLC) using a monolith ODS column under a series of different temperature and pH conditions. At a neutral pH 7, the rate (k(obs)) of Z-(cis)/E-(trans) isomerization of enalapril at 4 degrees C (9.4 x 10(-3)min(-1)) is much lower than at 23 degrees C (1.8 x 10(-1)min(-1)), while the fractional concentration of Z-(cis) isomer is always higher than that of E-(trans) isomer in the pH range 2-7. The fractional concentration of the E-(trans) isomer becomes a maximum (about 40%) in the pH range 3-6, where enalapril exists as a zwitterion. The hydrophobicity (logP(O/W)) of both isomers was estimated by high-speed counter-current chromatography (HSCCC). Normal phase HSCCC separation using a tert-butyl methyl ether-acetonitrile-20mM potassium phosphate buffer (pH 5) two-phase solvent system (2:2:3, v/v/v) at 4 degrees C was effective in partially separating the isomers, and the partition coefficient (K) of each isomer was directly calculated from the retention volume (V(R)). The logP(O/W) values of Z-(cis) and E-(trans) isomers were -0.46 and -0.65, respectively.
采用整体式ODS柱，通过反相高效液相色谱法（RP-HPLC）在一系列不同温度和pH条件下研究了依那普利Z-（顺式）/E-（反式）异构化的动力学。在中性pH 7条件下，依那普利在4℃时Z-（顺式）/E-（反式）异构化速率（k(obs)）（9.4×10⁻³ min⁻¹）远低于23℃时（1.8×10⁻¹ min⁻¹），而在pH 2-7范围内，Z-（顺式）异构体的分数浓度始终高于E-（反式）异构体。在pH 3-6范围内，E-（反式）异构体的分数浓度达到最大值（约40%），此时依那普利以两性离子形式存在。通过高速逆流色谱法（HSCCC）估算了两种异构体的疏水性（logP(O/W)）。在4℃下，使用叔丁基甲基醚-乙腈-20mM磷酸钾缓冲液（pH 5）两相溶剂体系（2:2:3，v/v/v）进行正相HSCCC分离，可有效部分分离异构体，并根据保留体积（V(R)）直接计算每种异构体的分配系数（K）。Z-（顺式）和E-（反式）异构体的logP(O/W)值分别为-0.46和-0.65。
