lonization Constants of Ginkgolide B in Aqueous Solution

摘要

The thermodynamic ionization constants (pK_(a1), pK_(a2), and pK_(a3)) of ginkgolide B (9H-1,7a-(epoxymethano)-1H,6aH-cyclopenta[c]furo[2,3-6]furo-[3′,2′:3,4]cyclopenta[1,2-d]-furan-5,9,12-(4H)-trione, 3-tert-butylhexahydro-4,7b,11-trihydroxy-8-methyl-) in aqueous solution have been settled by pH-metric and NMR studies. The three macroscopic pK_a values as well as the water solubility and the water-octanol partition coefficient have been extracted from pH-metric data by means of a nonlinear regression methodology. NMR spectroscopy provided confirmation of the values of the macroscopic constants, information about the effective ionization pathways, and an estimation of the proportions of the various forms under physiologically relevant conditions.