Acidobasic equilibria of inubosin derivatives studied by UV–Vis spectroscopy

Inubosin derivatives were suggested as compounds supporting the regeneration of neurons. For practical pharmaceutical applications their physicochemical properties need to be optimized in terms of bioavailability, possible side effects, and efficiency. We focused on four inubosin B derivatives, where acidobasic constants as key players in the biological activity were determined using the UV-Vis spectroscopy. The constants were correlated with the structure on the basis of the Hammett theory. In addition, water-organic solvent equilibria were studied for selected compounds. A software for semi-automated processing of the UV-Vis titration data was developed and tested. Time dependent density functional theory (TDDFT) was used to model and interpret the experimental spectra, which made it possible, for example, to assign the most characteristic cationic band to the S₀ → S₂ transition. For the acridine acid, both the TDDFT computations and the experimental data indicate that it forms zwitterion in the aqueous solution, whereas it is not dissociated in the organic phase.