Urease inhibition studies of six Ni(II), Co(II) and Cu(II) complexes with two sexidentate N2O4-donor bis-Schiff base ligands: An experimental and DFT computational study

Synthesis, Urease Inhibition, Molecular Docking, and Optical Analysis of a Symmetrical Schiff Base and Its Selected Metal Complexes

Designing and developing small organic molecules for use as urease inhibitors is challenging due to the need for ecosystem sustainability and the requirement to prevent health risks related to the human stomach and urinary tract. Moreover, imaging analysis is widely utilized for tracking infections in intracellular and in vivo systems, which requires drug molecules with emissive potential, specifically in the low-energy region. This study comprises the synthesis of a Schiff base ligand and its selected transition metals to evaluate their UV/fluorescence properties, inhibitory activity against urease, and molecular docking. Screening of the symmetrical cage-like ligand and its metal complexes with various eco-friendly transition metals revealed significant urease inhibition potential. The IC50 value of the ligand for urease inhibition was 21.80 ± 1.88 µM, comparable to that of thiourea. Notably, upon coordination with transition metals, the ligand-nickel and ligand-copper complexes exhibited even greater potency than the reference compound, with IC50 values of 11.8 ± 1.14 and 9.31 ± 1.31 µM, respectively. The ligand-cobalt complex exhibited an enzyme inhibitory potential comparable with thiourea, while the zinc and iron complexes demonstrated the least activity, which might be due to weaker interactions with the investigated protein. Meanwhile, all the metal complexes demonstrated a pronounced optical response, which could be utilized for fluorescence-guided targeted drug delivery applications in the future. Molecular docking analysis and IC50 values from in vitro urease inhibition screening showed a trend of increasing activity from compounds 7d to 7c to 7b. Enzyme kinetics studies using the Lineweaver-Burk plot indicated mixed-type inhibition against 7c and non-competitive inhibition against 7d.

Fabrication of metal-organic salts with heterogeneous conformations of a ligand as dual-functional urease and nitrification inhibitors

Urease inhibitors (UIs) and nitrification inhibitors (NIs) can greatly reduce nitrogen loss in agriculture soil. However, design and synthesis of an efficient and environmentally friendly dual-functional inhibitor is still a great challenge. Herein, four metal-organic salts (MOSs) based on heterogeneous conformations of the ligand N1,N1,N2,N2-tetrakis(2-fluorobenzyl)ethane-1,2-diamine (L), namely, [2HL]2+·[MCl4]2- (M = Cu, Zn, Cd, and Co), have been synthesized by the "second sphere" coordination method and structurally characterized in detail. Single crystal X-ray diffraction (SCXRD) analyses reveal that the four MOSs are 0D supramolecular structures containing [2HL]2+ and [MCl4]2-, which are connected through non-covalent bonds. Furthermore, the urease and nitrification inhibitory activities of MOSs are evaluated, showing excellent nitrification inhibitory activity with the nitrification inhibitory rate as high as 70.57% on the 28th day in soil cultivation experiment. In particular, MOS 1 shows significant urease inhibitory activity with half maximal inhibitory concentration (IC50) values of 0.89 ± 0.01 μM (0.5 h) and 1.87 ± 0.01 μM (3 h), which can serve as a dual-functional inhibitor.

Recent Efforts in the Discovery of Urease Inhibitor Identifications

Urease is an attractive drug target for designing anti-infective agents against pathogens such as Helicobacter pylori, Proteus mirabilis, and Ureaplasma urealyticum. In the past century, hundreds of medicinal chemists focused their efforts on explorations of urease inhibitors. Despite the FDA's approval of acetohydroxamic acid as a urease inhibitor for the treatment of struvite nephrolithiasis and the widespread use of N-(n-butyl)thiophosphoric triamide as a soil urease inhibitor as nitrogen fertilizer synergists in agriculture, urease inhibitors with high potency and safety are urgently needed. Exploration of novel urease inhibitors has therefore become a hot research topic recently. Herein, inhibitors identified worldwide from 2016 to 2021 have been reviewed. They structurally belong to more than 20 classes of compounds such as urea/thioure analogues, hydroxamic acids, sulfonamides, metal complexes, and triazoles. Some inhibitors showed excellent potency with IC50 values lower than 10 nM, having 10000-fold higher potency than the positive control thiourea.

Discovery of metal-based complexes as promising antimicrobial agents

The antimicrobial resistance (AMR) is an intractable problem for the world. Metal ions are essential for the cell process and biological function in microorganisms. Many metal-based complexes with the potential for releasing ions are more likely to be absorbed for their higher lipid solubility. Hence, this review highlights the clinical potential of organometallic compounds for the treatment of infections caused by bacteria or fungi in recent five years. The common scaffolds, including antimicrobial peptides, N-heterocyclic carbenes, Schiff bases, photosensitive-grand-cycle skeleton structures, aliphatic amines-based ligands, and special metal-based complexes are summarized here. We also discuss their therapeutic targets and the risks that should be paid attention to in the future studies, aiming to provide information for researchers on metal-based complexes as antimicrobial agents and inspire the design and synthesis of new antimicrobial drugs.

Therapeutic potential of N4-substituted thiosemicarbazones as new urease inhibitors: Biochemical and in silico approach

Urease enzyme plays a key role in pathogenesis of gastritis and peptic ulcers. Its inhibition averts our bodies from many disorders including formation of urinary calculi. In agriculture, the high urease content causes severe environmental and hence economic problems. Due to deficiency of effective and safer drugs to tackle the aforementioned disorders, the quest for new scaffolds becomes mandatory in the field of medicinal chemistry. In this regard, we herein report a new series of N⁴-substituted thiosemicarbazones 3a-v as potential candidates for urease inhibition. These new N⁴-substituted thiosemicarbazones 3a-v of distant chemical scaffolds were characterized by advanced spectroscopic techniques, such as FTIR, ¹HNMR, ¹³CNMR, ESI-MS and in the case of compound 3g by single crystal X-ray analysis. The compounds were evaluated for their urease inhibitory potential. All newly synthesized compounds showed significant urease inhibitions with IC₅₀ values in range of 2.7 ± 0.320-109.2 ± 3.217 μM. Molecular docking studies were used for interactions pattern and structure-activity relationship for all compounds, which demonstrated excellent binding interactions with the active site residues, such as hydrogen bonding, π-π interactions, π-H and nickel atom coordination.