Determination of equilibrium solubility and apparent oil/ water partition coefficient of schizonepetin

OBJECTIVE: To determine the equilibrium solubility of schizonepetin and its partition coefficients in the n-octanol-water/buffer solution systems. METHOD: The HPLC method was established and used to detect the concentration of schizonepetin in water and different organic solvents; the partition coefficients in the n-octanol-water/buffer solution systems of schizonepetin were determined by shaking flask method. RESULT: The equilibrium solubility of schizonepetin was 910 mg x L(-1) in water at 25 degrees C. A higher equilibrium solubility of schizonepetin was reached at 93 855 mg x L(-1) in methanol. Partition coefficients in the n-octanol-water/buffer solution systems of schizonepetin was 49.35 (lnKow = 1.69) at 25 degrees C. CONCLUSION: Schizonepetin was almost insoluble in petroleum ether. It has a low solubility in water balance. Equilibrium solubility in methanol is higher than what in other solvents. It have little change in apparent distribution coefficient in neutral phosphate buffer solution and has significant decrease in apparent distribution coefficient under the alkaline conditions.