Four new non-symmetrical derivatives based on central naphthalene moiety, 4-((4–(alkoxy)phenyl) diazenyl)naphthalen–1–yl 4–substitutedbenzoate (In/x), were prepared, and their properties were investigated experimentally and theoretically. The synthesized materials bear two wing groups: an alkoxy chain of differing proportionate length (n = 6 and 16 carbons) and one terminal attached to a polar group, X. Their molecular structures were elucidated via elemental analyses and FT-IR and NMR spectroscopy. Differential scanning calorimetry (DSC) and polarized optical microscopy (POM) were carried out to evaluate their mesomorphic properties. The results of the experimental investigations revealed that all the synthesized analogues possess only an enantiotropic nematic (N) mesophase with a high thermal stability and broad range. Density functional theory (DFT) calculations were in accordance with the experimental investigations and revealed that all prepared materials are to be linear and planar. Moreover, the rigidity of the molecule increased when an extra fused ring was inserted into the center of the structural shape, so its thermal and geometrical parameters were affected. Energy gap predictions confirmed that the I16/c derivative is more reactive than other compounds.

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A number of new symmetrically and asymmetrically 2,3-disubstituted quinoxalines were synthesized through functionalization of 2,3-dichloroquinoxaline (2,3-DCQ) with a variety of sulfur and/or nitrogen nucleophiles. The structures of the obtained compounds were established based on their spectral data and elemental analysis. The antimicrobial activity for the prepared compounds was investigated against four bacterial species and two fungal strains. The symmetrically disubstituted quinoxalines 2, 3, 4, and 5 displayed the most significant antibacterial activity, while compounds 6a, 6b, and the pentacyclic compound 10 showed considerable antifungal activity. Furthermore, compounds 3f, 6b showed broad antimicrobial spectrum against most of the tested strains.

Structurally diverse piperazine-based compounds hybrid with thiadiazole, isatin or with sulfur/nitrogen, functionalities were synthesized. The structures of the new compounds were established based on their spectral data and elemental analysis. The physicochemical, bioactivity scores and pharmacokinetic behavior of all the prepared ligands were evaluated using in silico computational tools. The new piperazine ligands have been screened for their inhibition activity against SARS-CoV-2 protease enzyme using molecular docking analysis. The docking studies showed that all the ligands have been docked with negative dock energy onto the target protease protein. Moreover, Molecular interaction studies revealed that SARS-CoV-2 protease enzyme had strong hydrogen bonding interactions with piperazine ligands. The present in silico study thus, provided some guidance to facilitate drug design targeting the SARS-CoV-2 main protease.

A series of arylidene thiosemicarbazides have been prepared by a new method, which was titled as transalkylidation. This method is an effective, fast, green and clean method. The mechanism of this reaction has been discussed. Moreover, we clarified the divergences of the structural assignments reported in the literature for the reaction of thiosemicarbazide and aldehydes or ketones in the presence of different catalysts. Where 1,2,4-triazolidine-3-thiones were incorrectly reported as sole product of such reaction, based on occurance of intramolecular cycloaddition of thiosemicarbazones formed in situ. Our findings proved that the reaction stops at earlier stage of thiosemicarbazone and neither cyclization to 1,2,4-triazolidine-3-thiones nor 2-amino-1,3,4-thiadiazoline take place. We have removed the confusion of the NMR interpretation of thiosemicarbazone and their cycloaddition product by carrying out 1 H-NMR, 13 C-NMR, 15 N-NMR and 1 H-15 N HSQC experiments with temperature gradient. Furthermore, DFT-NMR calculations have been done to make structural distinguish between the three possible structural isomers for this reaction, namely, 1,2,4triazolidene-3-thione, 2-amino-1,3,4-thiadiazoline and thiosemicarbazone.

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A new series of laterally fluorinated mesomorphic compounds, namely 2-fluoro-4-((4-(alkyloxy)phenyl)diazenyl)phenyl 4-substitutedbenzoate (Inx) were prepared and evaluated for their mesophase behavior. The synthesized series constitutes five members that possess different terminally attached polar groups (X). Their molecular structures were confirmed by elemental analyses and both FT-IR and NMR spectroscopy. Examination of the prepared derivatives was conducted via experimental and theoretical tools. Mesomorphic investigations were carried by polarized optical microscopy (POM) and differential scanning calorimetry (DSC). DSC and POM measurements indicated that except for the un-substituted analogue, all other derivatives were purely nematogenic, possessing their nematic (N) mesophase enantiotropically. This is to say that insertions of terminal polar substituents on their mesogenic structures induced the N phase. In addition, the location of lateral and terminal polar moieties played a considerable role in achieving good thermal N stability. Computational calculations were investigated to determine the deduced optimized molecular structures. Theoretical data indicated that both size and polarity of the terminal substituent (X) have essential impact on the thermal parameters and optical properties of possible geometries.