A new approach for the efficient and convenient synthesis of novel aminoalkyl-functionalized 4-arylquinolines via the Friedländer reaction of differently substituted 2-(3,4-dihydroisoquinolin-1-yl)anilines with various α-methylene ketones in acetic acid was developed. The reaction allows easy access to a diversity of 4-arylquinoline derivatives in moderate to excellent yields under mild conditions.

Fe(II)/2OG-dependent dioxygenases of the AlkB family catalyze a direct removal of alkylated damages in the course of DNA and RNA repair. A human homolog of the E. coli AlkB ALKBH3 protein is able to hydroxylate N1-methyladenine, N3-methylcytosine, and N1-methylguanine in single-stranded DNA and RNA. Due to its contribution to an antitumor drug resistance, this enzyme is considered a promising therapeutic target. The elucidation of ALKBH3’s structural peculiarities is important to establish a detailed mechanism of damaged DNA recognition and processing, as well as to the development of specific inhibitors. This work presents new data on the wild type ALKBH3 protein and its four mutant forms (Y143F, Y143A, L177A, and H191A) obtained by circular dichroism (CD) spectroscopy. The dataset includes the CD spectra of proteins measured at different temperatures and a 3D visualization of the ALKBH3–DNA complex where the mutated amino acid residues are marked. These results show how substitution of the key amino acids influences a secondary structure content of the protein.

Non-heme dioxygenases of the AlkB family hold a unique position among enzymes that repair alkyl lesions in nucleic acids. These enzymes activate the Fe(II) ion and molecular oxygen through the coupled decarboxylation of the 2-oxoglutarate co-substrate to subsequently oxidize the substrate. ALKBH3 is a human homolog of E. coli AlkB, which displays a specific activity toward N1-methyladenine and N3-methylcytosine bases in single-stranded DNA. Due to the lack of a DNA-bound structure of ALKBH3, the basis of its substrate specificity and structure–function relationships requires further exploration. Here we have combined biochemical and biophysical approaches with site-directed mutational analysis to elucidate the role of key amino acids in maintaining the secondary structure and catalytic activity of ALKBH3. Using stopped-flow fluorescence spectroscopy we have shown that conformational dynamics play a crucial role in the catalytic repair process catalyzed by ALKBH3. A transient kinetic mechanism, which comprises the steps of the specific substrate binding, eversion, and anchoring within the DNA-binding cleft, has been described quantitatively by rate and equilibrium constants. Through CD spectroscopy, we demonstrated that replacing side chains of Tyr143, Leu177, and His191 with alanine results in significant alterations in the secondary structure content of ALKBH3 and decreases the stability of mutant proteins. The bulky side chain of Tyr143 is critical for binding the methylated base and stabilizing its flipped-out conformation, while its hydroxyl group is likely involved in facilitating the product release. The removal of the Leu177 and His191 side chains substantially affects the secondary structure content and conformational flexibility, leading to the complete inactivation of the protein. The mutants lacking enzymatic activity exhibit a marked decrease in antiparallel β-strands, offset by an increase in the helical component.