Pyrazolyl-phthalazine-dione derivatives (PPDs) were synthetized in the ionic liquid catalyzed one-pot multicomponent reaction of acetylacetone, 2,3-dihydrophthalazine-1,4-dione, and different aldehydes in moderate to good yields. Six new PPDs were obtained, and the crystal structure of 2-acetyl-1-(4-fluorophenyl)-3-methyl-1H-pyrazolo[1,2-b]phthalazine-5,10-dione (PPD-4) was determined. The most interesting structural features of the novel PPD-4 is the formation of a rather short intermolecular distance between the F atom of one molecule and the midpoint of the neighbouring six-membered heterocyclic ring. This interaction arranges all molecules into parallel supramolecular chains. UV-Vis spectra of all PPDs were acquired and compared to the simulated ones obtained with TD-DFT. All synthetized compounds were subjected to evaluation of their in vitro antioxidative activity using a stable DPPH radical. It was shown that PPD-7, with a catechol motive, is the most active antioxidant, while PPD-9, with two neighbouring methoxy groups to the phenolic OH, exerted a somewhat lower, but significant antioxidative potential. The results of DFT thermodynamical study are in agreement with experimental findings that PPD-7 and PPD-9 should be considered as powerful radical scavengers. In addition, the obtained theoretical results (bond dissociation and proton abstraction energies) specify SPLET as a prevailing radical scavenging mechanism in polar solvents, and HAT in solvents with lower polarity. On the other hand, the obtained reaction enthalpies for inactivation of free radicals suggest competition between HAT and SPLET mechanisms, except in the case of the ˙OH radical in polar solvents, where HAT is labeled as prefered.

The pyrazolone class comprises a variety of hybrid compounds displaying diverse biological actions. Although studied for decades, these compounds are still of interest due to their facile chemical transformations. In our previous work, we presented the synthetic route of functionalised pyrazolone derivatives. The presence of pyrazolone structural motif in many drugs, such as edaravone, prompted us to investigate the antioxidant features of the selected compounds. In this paper, we provide an extensive in vitro and in silico description of the antioxidant properties of selected pyrazolone analogues. The obtained in vitro results revealed their great antiradical potency against the DPPH radical (IC₅₀ values in the 2.6–7.8 μM range), where the best results were obtained for analogues bearing a catechol moiety. Density functional theory (DFT) was used to assess their antioxidant capacity from the thermodynamic aspect. Here, good agreement with in vitro results was achieved. DFT was employed for the prediction of the most preferable radical scavenging pathway, also. In polar solvents, the SPLET mechanism is a favourable scavenging route, whereas in nonpolar solvents the HAT is slightly predominant. Furthermore, antioxidant mechanisms were studied in the presence of relevant reactive oxygen species. The obtained values of the reaction enthalpies with the selected radicals revealed that HAT is slightly prevailing in polar solvents, while the SPLET mechanism is dominant in nonpolar solvents. Regarding the well-known antioxidant features of the drug edaravone, these findings represent valuable data for this pyrazolone class and could be used as the basis for further investigations.

A one-pot, oxidative Ugi-azide multicomponent reaction mediated by oxoammonium salts is presented. This method provides a direct access to α-tetrazoloN-heterocycles in excellent yields employing simple NaN₃as azide source.

Three-component Mannich reaction of acetophenone or 4-iodoacetophenone with a variety of substituted anilines and benzaldehyde, catalysed with diethanolammonium chloroacetate, was performed under mild conditions. Mannich bases ( MBs ), of which five are new, were obtained in good to excellent yields. All compounds were characterized using elemental analysis, NMR and IR. In addition, detailed experimental and simulated UV–Vis spectral characterization of these compounds is presented here for the first time. In vitro antioxidative potential of synthetized MBs was evaluated using 2,2-diphenyl-1-picryl-hydrazyl radical and density functional theory (DFT) thermodynamical study. It was shown that compounds with anisidine moiety express moderate antioxidative activity. Mechanism of the organocatalysed Mannich reaction was thoroughly inspected by means of DFT. The reaction undergoes the hydrogen bonding-assisted mechanism. Moreover, the proposed rate determining step of the overall reaction is water elimination in the process of iminium ion formation. To the extent of our knowledge, this is the first detailed report on the influence of this type of catalyst on the formation of iminium ion, as a crucial intermediate for the whole reaction.