1 Setup and validation of shake-flask procedures for the 2 determination of partition coefficients (log D) from low drug 3 amounts 4 5 Axel Andrésa, Martí Rosésa, Clara Ràfolsa, Elisabeth Boscha, Sonia Espinosab, Víctor 6 Segarrab, Josep M. Huertab 7 aDepartament de Química Analítica and Institut de Biomedicina (IBUB), Universitat de Barcelona 8 Martí i Franquès 1-11, 08028 Barcelona (Spain) 9 b Computational and Structural Drug Discovery Department, R&D Centre, Almirall S.A. 10 Laureà Miró 408-410, 08980 Sant Feliu de Llobregat, Barcelona (Spain) 11 12 13 14 15 16 17 18 Correspondence to: 19 Clara Ràfols 20 Departament de Química Analítica 21 Universitat de Barcelona 22 Martí i Franquès 1-11 23 E-08028 Barcelona (Spain) 24 Tel: +34 93 403 48 12 25 Fax: +34 93 402 12 33 26 E-mail:
[email protected] 27 28 ABSTRACT 29 Several procedures based on the shake-flask method and designed to require a 30 minimum amount of drug for octanol-water partition coefficient determination have 31 been established and developed. The procedures have been validated by a 28 32 substance set with a lipophilicity range from -2.0 to 4.5 (log D7.4). 33 The experimental partition is carried out using aqueous phases buffered with 34 phosphate (pH 7.4) and n-octanol saturated with buffered water and the analysis is 35 performed by liquid chromatography. In order to have accurate results, four 36 procedures and eight different ratios between phase volumes are proposed. Each 37 procedure has been designed and optimized (for partition ratios) for a specific range of 38 drug lipophilicity (low, regular and high lipophilicity) and solubility (high and low 39 aqueous solubility).