Znanstveni radovi

COVID-19 infection and neurodegeneration: Computational evidence for interactions between the SARS-CoV-2 spike protein and monoamine oxidase enzymes
Lucija Hok, Hrvoje Rimac, Janez Mavri and Robert Vianello*
Computational and Structural Biotechnology Journal 2022, 20, 1254–1263

Although COVID-19 has been primarily associated with pneumonia, recent data show that its causative agent, the SARS-CoV-2 coronavirus, can infect many vital organs beyond the lungs, including the heart, kidneys and the brain. The literature agrees that COVID-19 is likely to have long-term mental health effects on infected individuals, which signifies a need to understand the role of the virus in the pathophysiology of brain disorders that is currently unknown and widely debated. Our docking and molecular dynamics simulations show that the affinity of the spike protein from the wild type (WT) and the South African B.1.351 (SA) variant towards MAO enzymes is comparable to that for its ACE2 receptor. This allows for the WT/SA∙∙∙MAO complex formation, which changes MAO affinities for their neurotransmitter substrates, thereby impacting their metabolic conversion and misbalancing their levels. Knowing that this fine regulation is strongly linked with the etiology of various brain pathologies, these results are the first to highlight the possibility that the interference with the brain MAO catalytic activity is responsible for the increased neurodegenerative illnesses following a COVID-19 infection, thus placing a neurobiological link between these two conditions in the spotlight. Since the obtained insight suggests that a more contagious SA variant causes even larger disturbances, and with new and more problematic strains likely emerging in the near future, we firmly advise that the presented prospect of the SARS-CoV-2 induced neurological complications should not be ignored, but rather requires further clinical investigations to achieve an early diagnosis and timely therapeutic interventions.

Why monoamine oxidase B preferably metabolizes N-methylhistamine over histamine: evidence from the multiscale simulation of the rate-limiting step
Aleksandra Maršavelski, Janez Mavri, Robert Vianello* and Jernej Stare*
International Journal of Molecular Sciences 2022, 23, 1910.

Histamine levels in the human brain are controlled by rather peculiar metabolic pathways. In the first step, histamine is enzymatically methylated at its imidazole Nτ atom, and the produced N-methylhistamine undergoes an oxidative deamination catalyzed by monoamine oxidase B (MAO-B), as is common with other monoaminergic neurotransmitters and neuromodulators of the central nervous system. The fact that histamine requires such a conversion prior to oxidative deamination is intriguing since MAO-B is known to be relatively promiscuous towards monoaminergic substrates; its in-vitro oxidation of N-methylhistamine is about 10 times faster than that for histamine, yet this rather subtle difference appears to be governing the decomposition pathway. This work clarifies the MAO-B selectivity toward histamine and N-methylhistamine by multiscale simulations of the rate-limiting hydride abstraction step for both compounds in the gas phase, in aqueous solution, and in the enzyme, using the established empirical valence bond methodology, assisted by gas-phase density functional theory (DFT) calculations. The computed barriers are in very good agreement with experimental kinetic data, especially for relative trends among systems, thereby reproducing the observed MAO-B selectivity. Simulations clearly demonstrate that solvation effects govern the reactivity, both in aqueous solution as well as in the enzyme although with an opposing effect on the free energy barrier. In the aqueous solution, the transition-state structure involving histamine is better solvated than its methylated analog, leading to a lower barrier for histamine oxidation. In the enzyme, the higher hydrophobicity of N-methylhistamine results in a decreased number of water molecules at the active side, leading to decreased dielectric shielding of the preorganized catalytic electrostatic environment provided by the enzyme. This renders the catalytic environment more efficient for N-methylhistamine, giving rise to a lower barrier relative to histamine. In addition, the transition state involving N-methylhistamine appears to be stabilized by the surrounding nonpolar residues to a larger extent than with unsubstituted histamine, contributing to a lower barrier with the former.

Ferrocene conjugates linked by 1,2,3-triazole and their Zn(II) and Cu(II) complexes: Synthesis, characterization and biological activity
Silvio Jakopec, Natalija Pantalon Juraj*, Anamaria Brozović*, Dijana Jadreško, Berislav Perić, Srećko I. Kirin and Silvana Raić-Malić*
Applied Organometallic Chemistry 2021, 35, e6575.

Ferrocene derivatives with mono- (8a–c) and bis-1,2,3-triazolyl (9 and 10a13c) chelating groups were synthesized by regioselective copper(I)-catalysed 1,3-dipolar cycloaddition of terminal alkynes with ferrocene azides. Metal complexes of the ligands were prepared with Cu(II) and Zn(II) salts. Crystal structures of ligands 9 and 11a were determined, as well as the structures of complexes [Cu(8a)2](CF3SO3)2 (8aCu) and [Cu(8c)2(CH3OH)2](BF4)2 (8cCu). In addition to NMR and UV–Vis spectroscopy, the metal complexes were characterized by cyclic voltammetry. The cytotoxic effect of ferrocene conjugates and their Zn(II) and Cu(II) complexes was explored, and cell cycle analysis was performed. The complex [Cu(8c)2](CF3SO3)2 showed the most prominent and selective cytotoxicity on cervical carcinoma (HeLa), ovarian cancer (MES-OV), non-small cell lung cancer (A549) and breast carcinoma (MDA-MB-231) cells. This complex increased cell population in the S and G2/M phase of the cell cycle, which was accompanied by an increase of the cells present in the sub-G0/G1 fraction.

Inovativna rješenja u katalitičkim proizvodnim procesima za potrebe farmaceutske industrije (CAT PHARMA)
Robert Vianello* and Srećko Kirin*
Kemija u industriji: časopis kemičara i tehnologa Hrvatske 2021, 70, 756–757.

Inorganic stereochemistry: Geometric isomerism in bis-tridentate ligand complexes
Natalija Pantalon Juraj and Srećko Kirin*
Coordination Chemistry Reviews 2021, 445, 214051.

In this review, we analyze the stereochemistry of hexacoordinated metal complexes with flexible tridentate ligands. Unlike rigid ligands, which can adopt only specific coordination modes, flexible ligands open more possibilities to fine-tuning the system for a specific application. Bis-tridentate [M(A-B-A)2] complexes of flexible ligands can form three geometric isomers: mer, trans-fac, and cis-fac. The analysis of crystallographic data for 844 structures found in the Cambridge Structural Database (CSD) elucidates influences on the formation of different isomers, such as steric and electronic properties of the ligand and metal ion, type and substitution of donor atoms, and the possibility of non-covalent interactions.


Synthesis and stereoselective catalytic transformations of 3-hydroxyisoindolinones
Nikola Topolovčan and Matija Gredičak*
Organic & Biomolecular Chemistry 2021, 19, 4637–4651.

This review focuses on the synthesis of 3-hydroxyisoindolinones, and their application as substrates in stereoselective catalytic transformations reported from 2010 to date. These compounds have attracted much attention among synthetic chemists, as they are integral structural parts of a number of natural products and biologically active compounds. The first part of this review covers methods based on electrochemical, photochemical, and thermal reactions for the synthesis of 3-hydroxyisoindolinones. The second part focuses on their employment as substrates in transition metal-catalyzed and organocatalyzed stereoselective transformations for the preparation of chiral 3-substituted isoindolinone derivatives.


Comparison of nonheme manganese- and iron-containing flavone synthase mimics
Dóra Lakk-Bogáth, Natalija Pantalon Juraj, Bashdar I. Meena, Berislav Perić, Srećko I. Kirin and József Kaizer*
Molecules 2021, 26, 3220.

Heme and nonheme-type flavone synthase enzymes, FS I and FS II are responsible for the synthesis of flavones, which play an important role in various biological processes, and have a wide range of biomedicinal properties including antitumor, antimalarial, and antioxidant activities. To get more insight into the mechanism of this curious enzyme reaction, nonheme structural and functional models were carried out by the use of mononuclear iron, [FeII(CDA-BPA*)]2+ (6) [CDA-BPA = N,N,N’,N’-tetrakis-(2-pyridylmethyl)-cyclohexanediamine], [FeII(CDA-BQA*)]2+ (5) [CDA-BQA = N,N,N’,N’-tetrakis-(2-quinolilmethyl)-cyclohexanediamine], [FeII(Bn-TPEN)(CH3CN)]2+ (3) [Bn-TPEN = N-benzyl-N,N’,N’-tris(2-pyridylmethyl)-1,2-diaminoethane], [FeIV(O)(Bn-TPEN)]2+ (9), and manganese, [MnII(N4Py*)(CH3CN)]2+ (2) [N4Py* = N,N-bis(2-pyridylmethyl)-1,2-di(2-pyridyl)ethylamine)], [MnII(Bn-TPEN)(CH3CN)]2+ (4) complexes as catalysts, where the possible reactive intermediates, high-valent FeIV(O) and MnIV(O) are known and well characterised. The results of the catalytic and stoichiometric reactions showed that the ligand framework and the nature of the metal cofactor significantly influenced the reactivity of the catalyst and its intermediate. Comparing the reactions of [FeIV(O)(Bn-TPEN)]2+ (9) and [MnIV(O)(Bn-TPEN)]2+ (10) towards flavanone under the same conditions, a 3.5-fold difference in reaction rate was observed in favor of iron, and this value is three orders of magnitude higher than was observed for the previously published [FeIV(O)(N2Py2Q*)]2+ [N,N-bis(2-quinolylmethyl)-1,2-di(2-pyridyl)ethylamine] species.

Direct metal-free transformation of alkynes to nitriles: Computational evidence for the precise reaction mechanism
Lucija Hok and Robert Vianello*
International Journal of Molecular Sciences 2021, 22, 3193.

Density functional theory calculations elucidated the precise reaction mechanism for the conversion of diphenylacetylenes into benzonitriles involving the cleavage of the triple C≡C bond, with N-iodosuccinimide (NIS) as an oxidant and trimethylsilyl azide (TMSN3) as a nitrogen donor. The reaction requires six steps with the activation barrier ΔG = 33.5 kcal mol−1 and a highly exergonic reaction free-energy ΔG= −191.9 kcal mol−1 in MeCN. Reaction profiles agree with several experimental observations, offering evidence for the formation of molecular I2, interpreting the necessity to increase the temperature to finalize the reaction, and revealing thermodynamic aspects allowing higher yields for alkynes with para-electron-donating groups. In addition, the proposed mechanism indicates usefulness of this concept for both internal and terminal alkynes, eliminates the option to replace NIS by its Cl- or Br-analogues, and strongly promotes NaN3 as an alternative to TMSN3. Lastly, our results advise increasing the solvent polarity as another route to advance this metal-free strategy towards more efficient processes.

A ferrocene-based pseudopeptide chiroptical switch
Saša Opačak, Darko Babić, Berislav Perić, Željko Marinić, Vilko Smrečki, Barbara Pem, Ivana Vinković Vrček and Srećko I. Kirin*
Dalton Transactions 2021, 50, 4504-4511.

We present a double-stranded ferrocene pseudopeptide 2b which exhibits stimuli responsive chirality inversion triggered by solvent exchange or acid addition. Compound 2b exists as a mixture of self-assembled fast exchanging oligomers which macroscopically behave as a chiroptical switch with two stable states. The ferrocene group inversion results in a distinct CD signal in the visible part of the spectrum. The inversion is accomplished through a conformational change due to a rearrangement of hydrogen bonding forcing the rotation of ferrocene rings.



Halohydrin dehalogenases and their potential in industrial application – A viewpoint of enzyme reaction engineering
Zvjezdana Findrik Blažević,* Nevena Milčić, Martina Sudar and Maja Majerić Elenkov
Advanced Synthesis & Catalysis 2021, 363, 388-410.

At the moment, there are approx. 100 published papers investigating halohydrin dehalogenases from different aspects; enzymology, molecular biology and reactions they can catalyse. Unquestionably, these enzymes are of great importance and hold an immense potential due to the wide spectrum of different compounds that can be synthesized by their action. These compounds, such as chiral epoxides, β‐substituted alcohols, oxazolidinones etc., significantly enrich the chemist’s toolbox and, moreover, open the possibility for the synthesis of even more complex compounds. Still, there are many unknowns, and it is the purpose of this work to demonstrate the possibilities and bottlenecks, in scientific sense, that could further help in broadening the applicative potential of these fascinating enzymes.



Synthesis and biological evaluations of mono- and bis-ferrocene uracil derivatives
Senka Djaković, Ljubica Glavaš-Obrovac, Jasmina Lapić, Silvija Maračić, Juraj Kirchofer, Marija Knežević, Marijana Jukić
and Silvana Raić-Malić*
Applied Organometallic Chemistry 2021, 35, e6052.

Mono- (3a–3e and 4a–4e) and bis-ferrocene (5a–5e and 6a–6e) conjugated 5-substituted uracil derivatives that are bridged by 1,2,3-triazole linker were synthesized. The impact of ferrocene unit and spacer between ferrocene and triazole on radical scavenging potency was observed. Bis-ferrocenyl uracil derivatives exhibited better antiproliferative activities than their monoferrocenyl analogs. Bis-ferrocenyl methyl- (5b) and halogen-substituted (5e, 6c, and 6d) uracil derivatives showed pronounced and selective cytostatic activities on colon adenocarcinoma (CaCo-2) and Burkitt lymphoma (Raji) cells, with higher potency and selectivity than the reference drug 5-fluorouracil. Generation of reactive oxygen species (ROS) in CaCo-2 and Raji cells when treated with compounds 5b, 5e, and 6d was observed. Bisferrocenyl 5-chlorouracil 6c induced significant disruption in mitochondrial membrane potential that is accompanied by activation of apoptosis in CaCo-2, Raji, and acute lymphoblastic leukemia (CCRF-CEM) cells, while 6d caused mitochondrial dysfunction and apoptosis induction in CaCo-2 and Raji cells. Potent antiproliferative activity of 6c and 6d could be associated with mitochondrial membrane potential disruption accompanied by apoptosis induction. Our findings highlighted 6c and 6d with potent and selective antiproliferative activity on CaCo-2, Raji, and CCRF-CEM cells that may be associated with targeting cancer cell mitochondria, as a molecular target.