Hydrolytic kinetics of lithospermic acid B extracted from roots of Salvia miltiorrhiza.

The hydrolytic kinetics of lithospermic acid B (LAB) extracted from the roots of Salvia miltiorrhiza (Chinese herb: danshen) was investigated by using reversed-phase high-performance liquid chromatography (HPLC) with UV-vis detection. The influences of initial drug concentration, pH and temperature on hydrolysis of LAB were studied in aqueous solutions. The results showed that initial concentration of LAB has no effect on the degradation rate at pH 2.0. The hydrolysis followed pseudo-first-order kinetics at 90 degrees C. The log k(obs)-pH profile indicated that the optimal stability range was at pH 2.0-5.0. The rate constant of overall hydrolysis as a function of temperature under the given conditions obeyed the Arrhenius equation. Analysis of the acid-induced degraded solution of LAB by liquid chromatography-mass spectrometry (LC-MS) revealed at least four degradation products [M-H](-) ion at m/z 197, 137, 537 and 537, respectively. Three of these degradation products, i.e. danshensu (DSU), protocatechuic aldehyde (PRO), and lithospermic acid, were further identified by comparing the retention times with standard samples. According to the structure of LAB and its hydrolysis behavior in solution, the other product was proposed to be the isomer of lithospermic acid.