Multiwavelength UV-metric and pH-metric determination of the dissociation constants of the hypoxia-inducible factor prolyl hydroxylase inhibitor Roxadustat

Abstract

UV-VIS spectra, molar absorption coefficients and protonation equilibriaRoxadustat is an orally bioavailable, hypoxia-inducible factor prolyl hydroxylase inhibitor with potential anti-anemic activity. It is one of the Active Pharmacenutical Ingredients possessing acidic/basic functionalities their ionization state is controlled by solution pH and acid dissociation constants. Nonlinear regression of the pH-spectra with programs REACTLAB and SQUAD84 and of the pH-titration curve with ESAB determined four multiple consecutive dissociation constants with the protonation scheme. A sparingly soluble neutral molecule LH 3 of Roxadustat was dissociated to the soluble anions LH 2-, LH 2-and L 3-or protonated to the cation LH 4 + in an aqueous medium. The graph of molar absorption coefficients of variously protonated species according to wavelength shows that the spectra of two anions LH 2-and LH 2-are nearly the same in colour. The Roxadustat spectrum exhibited five sharp isosbestic points related to the LH 2-/L 3-equilibrium. Four consecutive thermodynamic dissociation constants were estimated using UV-metric data pK T a1 = 3.60(04), pK T a2 = 5.62(14), pK T a3 = 7.66(16), pK T a4 = 9.08(02) at 25°C and pK T a1 = 3.60(04), pK T a2 = 5.73(10), pK T a3 = 7.52(10), pK T a4 = 8.99(02) at 37°C and using pH-metric data pK T a1 = 4.33(09), pK T a2 = 6.57(11), pK T a3 = 8.88(05), pK T a4 = 9.03(04) at 25°C and pK T a1 = 4.25(09), pK T a2 = 6.49(10), pK T a3 = 8.80(06), pK T a4 = 9.00(05) at 37°C The positive values of the enthalpy ΔH 0 showed that the dissociation process is endothermic and the positive values of the Gibbs free energy ΔG 0 at 25°C indicated that the dissociation process was not spontaneous, which also was confirmed by a negative value of the entropy ΔS 0. Four macrodissociation constants of Roxadustat and six protonation locations were predicted by MARVIN.

A critical review of Roxadustat formulations, solid state studies, and analytical methodology

“…Roxadustat pKa parameter has been analyzed by two analytical techniques potentiometric pH-metric titration and Spectrophotometric-UV method. Meloun et al described the spectrophotometric analysis method as more sensitive among the methods, with a detection range between 10 −5 to 10 −6 M concentration [ 47 ]. A GC-MS method is also described in the literature to study the effect of Roxadustat on retinopathy treatment under hypoxia conditions.…”

Hydrolytic Degradation Study of Roxadustat by Rp-HPLC and HPTLC

“…As per the literature survey for Roxadustat Liquid chromatographytandem mass spectrometry, UPLC-MS method and UV method were reported, but no stability indicating HPLC and HPTLC method is reported [11,13].…”

Isoquinoline‐based intrinsic fluorescence assessment of erythropoiesis‐stimulating agent, Roxadustat (FG‐4592), in tablets: applications to content uniformity and human plasma evaluation

“…They do, however, require a few extras and safeguards in addition to the straightforwardness of the suggested analytical techniques. Furthermore, chromatographic [27], potentiometric [27][28][29] and ultraviolet (UV) spectroscopic [27,30] approaches were used to determine the pKa of ROX as part of the reported method. These papers, however, omitted information regarding the analytical performance of the used approaches.…”