Coordination susceptibilities of cinnamaldehyde and cuminaldehyde derived Schiff bases towards the fac-[Re(CO)3]+ core: Formation, computational and DNA interaction studies

Synthesis and Characterization of Novel [2 + 1] Tricarbonyl Rhenium Complexes with the Hydrophilic Phosphine Ligands PTA and CAP

In the pursuit of hydrophilic model fac-[Re(CO)₃]⁺ complexes for (radio) pharmaceutical applications, six novel [2 + 1] mixed-ligand complexes of the general type fac-[Re(CO)₃(bid)P] were synthesized and characterized, where bid is a bidentate ligand bearing either (N, O) or (S, S′) donor atom sets and P is the hydrophilic phosphine 1,3,5-triaza-7-phosphoadamantane (PTA) or its macrocyclic homologue 1,4,7-triaza-9-phosphatricyclo[5.3.2.1]tridecane (CAP). The (N, O) ligands used in this study were picolinic and quinaldic acid, while the (S, S′) ligand was diethyldithiocarbamate. The complexes were synthesized in generally high yields and purity and the characterization was performed by spectroscopic methods, IR, NMR, and elemental analysis. Detailed X-ray crystallographic study of molecular packing by using Hirshfeld analysis tools revealed a plethora of intermolecular interactions such as hydrogen bond, π⋯π, C-H⋯π, and carbonyl-carbonyl interactions. To our knowledge, the CAP complexes reported herein are the first example of [2 + 1] mixed-ligand fac-[Re(CO)₃]⁺ complexes with CAP. The new complexes might have the potential to serve as platforms for the design of target-specific complexes with favorable pharmacokinetics.

Supramolecular structures of rhenium(I) complexes mediated by ligand planarity via the interplay of substituents

The crystal and molecular structures of two Re^I tricarbonyl complexes, namely fac-tricarbonylchlorido[1-(4-fluorocinnamoyl)-3-(pyridin-2-yl-κN)pyrazole-κN²]rhenium(I), [ReCl(C₁₇H₁₂FN₃O)(CO)₃], (I), and fac-tricarbonylchlorido[1-(4-nitrocinnamoyl)-3-(pyridin-2-yl-κN)pyrazole-κN²]rhenium(I) acetone monosolvate, [ReCl(C₁₇H₁₂ClN₄O₃)(CO)₃]·C₃H₆O, (II), are reported. The complexes form centrosymmetric dimers that are linked into one-dimensional columns by C-H...Cl and N-O...H interactions in (I) and (II), respectively. C-H...Cl interactions in (II) generate two R₂¹(7) loops that merge into a single R₂¹(10) loop. These interactions involve the alkene, pyrazole and benzene rings, hence restricting the ligand rotation and giving rise to a planar conformation. Unlike (II), complex (I) exhibits a twisted conformation of the ligand and a pair of molecules forms a centrosymmetric dimer with an R₂²(10) loop via C-H...O interactions. The unique supramolecular structures of (I) and (II) are determined by their planarity and weak interactions. The planar conformation of (II) provides a base for appreciable π-π stacking interactions compared to (I). In addition, an N-O...π interaction stabilizes the supramolecular structure of (II). We report herein the first n→π* interactions of Re^I tricarbonyl complexes, which account for 0.33 kJ mol^-1. Intermolecular C-H...Cl and C-H...O interactions are present in both complexes, with (II) showing a greater preference for these interactions compared to (I), with cumulative contributions of 48.7 and 41.5%, respectively. The influence of inductive (fluoro) and/or resonance (nitro) effects on the π-stacking ability was further supported by LOLIPOP (localized orbital locator-integrated π over plane) analysis. The benzene ring of (II) demonstrated a higher π-stacking ability compared to that of (I), which is supported by the intrinsic planar geometry. The HOMA (harmonic oscillator model of aromaticity) index of (I) revealed more aromaticity with respect to (II), suggesting that NO₂ greatly perturbed the aromaticity. The Hirshfeld fingerprint (FP) plots revealed the preference of (II) over (I) for π-π contacts, with contributions of 6.8 and 4.4%, respectively.

Novel organophosphorus aminopyrimidines as unique structural DNA-targeting membrane active inhibitors towards drug-resistant methicillin-resistant Staphylococcus aureus

A series of novel unique structural organophosphorus aminopyrimidines were developed as potential DNA-targeting membrane active inhibitors through an efficient one-pot procedure from aldehydes, phosphonate and aminopyrimidine. The biological assay revealed that some of the prepared compounds displayed antibacterial activities. In particular, imidazole derivative 2c exhibited more potent inhibitory activity against MRSA with an MIC value of 4 μg mL^-1 in comparison with the clinical drugs chloromycin and norfloxacin. Experiments revealed that the active molecule 2c had the ability to rapidly kill the tested strains without obviously triggering the development of bacterial resistance, showed low toxicity to L929 cells and could disturb the cell membrane. The molecular docking study discovered that compound 2c could bind with DNA gyrase via hydrogen bonds and other weak interactions. Further exploration disclosed that the active molecule 2c could also effectively intercalate into MRSA DNA and form a steady 2c-DNA supramolecular complex, which might further block DNA replication to exert powerful antibacterial effects.