title: The dissociation constants of the cytostatic bosutinib by nonlinear least-squares regression of multiwavelength spectrophotometric and potentiometric pH-titration data.
abstract: Potentiometric and spectrophotometric pH-titration of the multiprotic cytostatics bosutinib for dissociation constants determination were compared. Bosutinib treats patients with positive chronic myeloid leukemia. Bosutinib exhibits four protonatable sites in a pH range from 2 to 11, where two pK are well separated (ΔpK>3), while the other two are near dissociation constants. In the neutral medium, bosutinib occurs in the slightly water soluble form LH that can be protonated to the soluble cation LH4(3+). The molecule LH can be dissociated to still difficultly soluble anion L(-). The set of spectra upon pH from 2 to 11 in the 239.3-375.0nm was divided into two absorption bands: the first one from 239.3 to 290.5nm and the second from 312.3 to 375.0nm, which differ in sensitivity of chromophores to a pH change. Estimates of pK of the entire set of spectra were compared with those of both absorption bands. Due to limited solubility of bosutinib the protonation in a mixed aqueous-methanolic medium was studied. In low methanol content of 3-6% three dissociation constants can be reliably determined with SPECFIT/32 and SQUAD(84) and after extrapolation to zero content of methanol they lead to pKc1=3.43(12), pKc2=4.54(10), pKc3=7.56(07) and pKc4=11.04(05) at 25°C and pKc1=3.44(06), pKc2=5.03(08) pKc3=7.33(05) and pKc4=10.92(06) at 37°C. With an increasing content of methanol in solvent the dissociation of bosutinib is suppressed and the percentage of LH3(2+) decreases and LH prevails. From the potentiometric pH-titration at 25°C the concentration dissociation constants were estimated with ESAB pKc1=3.51(02), pKc2=4.37(02), pKc3=7.97(02) and pKc4=11.05(03) and with HYPERQUAD: pKc1=3.29(12), pKc2=4.24(10), pKc3=7.95(07) and pKc4=11.29(05).
authors.affiliation: Department of Analytical Chemistry, University of Pardubice, CZ 532 10 Pardubice, Czech Republic. Electronic address: milan.meloun@upce.cz.
authors.forename: Milan
authors.initials: M
authors.lastname: Meloun
authors.affiliation: Department of Analytical Chemistry, University of Pardubice, CZ 532 10 Pardubice, Czech Republic.
authors.forename: Veronika
authors.initials: V
authors.lastname: Nečasová
authors.affiliation: Department of Process Control, University of Pardubice, CZ 532 10 Pardubice, Czech Republic.
authors.forename: Milan
authors.initials: M
authors.lastname: Javůrek
authors.affiliation: Zentiva k.s., U kabelovny 130, CZ 102 37 Prague, Czech Republic.
authors.forename: Tomáš
authors.initials: T
authors.lastname: Pekárek
mesh_terms: D000814:Aniline Compounds / Q000032:analysis* / Q000737:chemistry*; D054697:Cytostatic Agents / Q000032:analysis* / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D016018:Least-Squares Analysis; D009570:Nitriles / Q000032:analysis* / Q000737:chemistry*; D017711:Nonlinear Dynamics; D011199:Potentiometry; D011804:Quinolines / Q000032:analysis* / Q000737:chemistry*; D013053:Spectrophotometry / Q000379:methods
chemical_list: D000814:Aniline Compounds; D054697:Cytostatic Agents; D009570:Nitriles; D011804:Quinolines; C471992:bosutinib
keywords: Bosutinib; Dissociation constants; ESAB2M; HYPERQUAD; INDICES; PALLAS; Potentiometric Titration; SQUAD(84) SPECFIT/32; Spectrophotometric titration