Salim S. Al-Showiman

Multinuclear NMR studies on new platinum imine complexes

Abstract Platinum(II)-olefin complexes with Schiff bases derived from 2-acetylthiophene, and primary amines were synthesized and characterized on the basis of elemental analysis, I.R., 1 H, 13 C, and 195 Pt-NMR studies. The Schiff bases behave as unidentate bases with N as the only donor ligand and form four coordinate complexes with 1:1 metal-ligand stoichiometry at ambient temperature of composition trans-[PtCl 2 (η 2 -C 2 H 4 )(Imine)]. Long-range coupling constants were observed between different protons of the imine and platinum-195. Addition of excess amine leads to displacement of the imine and rapidly gives the zwitterionic 2-ammonioethanide-platinum(II) complex. The platinum complex of the imine type provide the first example of stable platinum(II)-olefin-monodentate σ-imine bonded complexes. In addition, 1 H, 13 C and 195 Pt-NMR spectra show that only a single rotamer exists. Other more imine complexes were synthesized.

Determination of selenium content in dates of some cultivars grown in Saudi Arabia

The concentrations of selenium in the flesh of ten date cultivars collected from different regions of Saudi Arabia were analysed using an ultraviolet/ visible spectrophotometer. The amount of selenium was found to be in the range between 1.48 and 2.96 μg/g in the ten varieties studied. The cultivar Sillaj from Al-Kharj (south-west region of Saudi Arabia) was found to contain the highest concentration of selenium (2.96 μg/g). The lowest content of selenium (1.48 μg/g) was observed in the cultivar Muneef from Riyadh region. The content of selenium in dates was compared with data for selenium content of other fruits, nuts and vegetables.

Isomerization of imines in platinum-imine complexes

Abstract Multinuclear 1H, 13C and 195Pt spectroscopy provides strong evidence for E-Z isomerization of imine ligands coordinated to platinum(II) of the type trans [PtCl2(η2-C2H4)(imine)].

Antimicrobial Activity of Some Novel Armed Thiophene Derivatives and Petra/Osiris/Molinspiration (POM) Analyses

Tetrasubstituted 2-acetylthiophene derivative 5 was synthesized and then condensed with various nitrogen nucleophiles such as 5-amino-1,2,4-triazole, 2-aminobenzimidazole, aniline or p-chloroaniline to afford the corresponding iminothiophene derivatives 6–8a,b. Condensation of thiophene 5 with malononitrile as carbon nucleophile afforded compound 9, which underwent nucleophilic addition with DMF-DMA to afford compound 10. The newly synthesized products were characterized by elemental analysis, IR, MS, 1H-13C-NMR and CHN analysis and then evaluated for their antimicrobial activity. Results of the in vitro antibacterial activity showed that thiophene derivative 7 was found to be more potent than the standard drug gentamicin against Pseudomonas aeruginosa. Some of these compounds showed potential antimicrobial activities. Molecular docking and Osiris/Molinspiration analyses show the crucial role and impact of substituents on bioactivity and indicate the unfavorable structural parameters in actual drug design: more substitution with electronic donor group doesn’t guarantee more effective bioactivity. This study should greatly help in an intelligent and a controlled pharmacomodulation of antibiotics.

C,N-bipyrazole receptor grafted onto a porous silica surface as a novel adsorbent based polymer hybrid

A simple heterogeneous synthesis of pure adsorbent based polymer hybrid made by condensing a functionalized C,N-bipyrazole with a 3-glycidoxypropyl-trimethoxysilane silylant agent, previously anchored on a silica surface was developed. The formed material (SG2P) was characterized through elemental analysis, FT-IR spectroscopy, (13)C NMR of solid state, scanning electron microscope (SEM), and was studied and evaluated by determination of the surface area using the BET equation, the adsorption and desorption capability using the isotherm of nitrogen and B.J.H. pore sizes. The new material exhibits good thermal stability determined by thermogravimetry curves and good chemical stability was examined in various acidic and buffer solutions (pH 1-7). The binding and adsorption abilities of SG2P were investigated for Hg(2+), Cd(2+), Pb(2+), Zn(2+), K(+), Na(+) and Li(+) cations and compared to the results of classical liquid-liquid extraction with the unbound C,N-bipyrazole compound. The grafting at the surface of silica does not affect complexing properties of the ligand and the SG2P exhibits a high selectivity toward Hg(2+) ion with no complexation being observed towards zinc and alkali metals. The extracted and the complexing cation percentages were determined by atomic absorption measurements.

Dynamic stereochemistry of imines and derivatives. Part IX. The mechanism of E–Z isomerization in N-alkylimines

Rates of E–Z isomerization in N-alkylimines have been determined by direct thermal stereomutation and by dynamic n.m.r. spectroscopy. Thermal racemization rates of optically active para-disubstituted 2-t-butyl-3.3-diphenyloxaziridines have also been measured, and show a small but consistent correlation with Hammett σp. Comparison of the activation parameters for imine isomerization with data for nitrogen inversion in oxaziridines indicates that N-alkylimines isomerize by a planar inversion (lateral shift) mechanism. Barriers determined for an aldimine under optimal conditions are higher than previously reported for imines (ca. 30 kcal mol–1).

Synthesis, Bioactivity, Molecular Docking and POM Analyses of Novel Substituted Thieno[2,3-b]thiophenes and Related Congeners

Several series of novel substituted thienothiophene derivatives were synthesized by reacting the synthone 1 with different reagents. The newly synthesized compounds were characterized by means of different spectroscopic methods such as IR, NMR, mass spectrometry and by elemental analyses. The new compounds displayed significant activity against both Gram-positive and Gram negative bacteria, in addition to fungi. Molecular docking and POM analyses show the crucial role and impact of substituents on bioactivity and indicate the unfavorable structural parameters in actual drug design: more substitution doesn’t guaranty more efficiency in bioactivity.

Synthesis and Structure-Activity Relationship of Some New Thiophene-Based Heterocycles as Potential Antimicrobial Agents

Several new pyrazole, pyridine, [1,2,4]triazolo[1,5-α]pyrimidine, benzimidazo[1,2-a]pyrimidine and 1,2,4-triazolo[3,4-c][1,2,4]triazine derivatives incorporating a thiophene moiety were synthesized from (E)-ethyl 5-(3-(dimethylamino)acryloyl)-4-phenyl-2-(phenylamino)thiophene-3-carboxylate (1). The structures of the newly synthesized compounds were confirmed by IR, 1H-, 13C-NMR, mass spectral data and elemental analysis. The antibacterial and antifungal activities of all the synthesized compounds were evaluated. The results indicated that compounds 9, 12, and 19 were found to be more potent than the standard drug Amphotericin B against Aspergillus fumigates. Additionally, compound 12 exhibited higher activity than the standard drug Amphotericin B against Syncephalastrum racemosum.

Synthesis and Biological Evaluation of 2-Aminobenzamide Derivatives as Antimicrobial Agents: Opening/Closing Pharmacophore Site

A series of new 2-aminobenzamide derivatives (1–10) has been synthesized in good to excellent yields by adopting both conventional and/or a time-efficient microwave assisted methodologies starting from isatoic anhydride (ISA) and characterized on the basis of their physical, spectral and microanalytical data. Selected compounds of this series were then tested against various bacterial (Bacillus subtilis (RCMB 000107) and Staphylococcus aureus (RCMB 000106). Pseudomonas aeruginosa (RCMB 000102) and Escherichia coli (RCMB 000103) and fungal strains (Saccharomyces cerevisiae (RCMB 006002), Aspergillus fumigatus (RCMB 002003) and Candida albicans (RCMB 005002) to explore their potential as antimicrobial agents. Compound 5 was found to be the most active compound among those tested, which showed excellent antifungal activity against Aspergillus fumigatus (RCMB 002003) more potent than standard Clotrimazole, and moderate to good antibacterial and antifungal activity against most of the other strains of bacteria and fungi. Furthermore, potential pharmacophore sites were identified and their activity was related with the structures in the solution.

Dynamic stereochemistry of imines and derivatives. Part V. Acid catalysis of E–Z imine interconversion

The rate of E–Z isomerization in N-(α-phenyl-4-nitrobenzylidene)methylamine at 35° is shown to be markedly increased by trace amounts of benzoic acid. Dynamic n.m.r. experiments at higher temperature show that the isomerization rate is proportional to the acid concentration and enable activation parameters to be determined. CNDO/2 Calculations performed on the benzylideneammonium ion suggest that the C[graphic omitted] rotational barrier is ca.46 kcal mol–1, and high temperature n.m.r. studies on a related immonium perchlorate also indicate a high rotational barrier. It is suggested that benzoic acid promotes imine isomerization by nucleophilic addition to the C[graphic omitted] bond in the conjugate acid. The relevance of the rate of imine isomerization to the mechanism of the imine–peroxyacid reaction is discussed.