Khalid B. Selim

Chiral N-Heterocyclic Carbene―Copper(I)-Catalyzed Asymmetric Allylic Arylation of Aliphatic Allylic Bromides: Steric and Electronic Effects on γ-Selectivity

Chiral N-heterocyclic carbene ligands were electronically and sterically tuned to improve γ-selectivity in copper(I)-catalyzed asymmetric allylic arylation of aliphatic allylic bromides with several aryl Grignard reagents. High γ-selectivity was realized when either the aryl group of the Grignard reagent or the aryl group on the N-substituent of the carbene ligand was electron-deficient or when either the carbene ligand or allylic bromide was bulky. The results indicated that electron deficiency and steric hindrance of the initially formed σ-allyl copper intermediate enhance the rate of the reductive elimination to give γ-products as major isomers.

Enantioselective Ruthenium-Catalyzed 1,3-Dipolar Cycloadditions between C-Carboalkoxy Ketonitrones and Methacrolein: Solvent Effect on Reaction Selectivity and Its Rational

A catalytic 1,3-dipolar cycloaddition between carboalkoxy ketonitrones and methacrolein under the effect of chiral ruthenium Lewis acid (R,R-1) was developed with high regio-, diastereo-, and enantiocontrol. The diastereochemical outcome of the cycloaddition reaction is marked by a significant solvent effect, and a divergent endo or exo control can be tuned by an appropriate choice of both the solvent and the N- and O-substituents of the ketonitrone. A rationale of the solvent effect, based on the computational study of the interactions between the methacrolein-Ru complex and its counteranion (SbF6(-)), is proposed to explain the selectivities obtained.

Synthesis and anticancer activity of new dihydropyrimidinone derivatives

A series of dihydropyrimidinone derivatives bearing various N-heterocyclic moieties was designed and synthesized. Twelve new compounds were screened for their cytotoxic activity using 60 cancer cell lines according to NCI (USA) protocol. Compound 19 showed a significant activity against NCI-H460, SK-MEL-5, and HL-60 (TB) cell lines with growth inhibition 88%, 86% and 85%, respectively, and was found to be more safe on normal cells when compared to doxorubicin. Enzyme inhibition assay was performed for compound 19 against mTOR (IC50 = 0.64 μM) and VEGFR-2 (IC50 = 1.97 μM) to show high potency in comparison to rapamycin (IC50 = 0.43 μM) and sorafenib (IC50 = 0.3 μM) as references, respectively. Cell cycle analysis of A549 cells treated with 19 showed cell cycle arrest at G2/M phase and pro-apoptotic activity as indicated by annexin V-FITC staining.

Design, synthesis, and molecular modeling of heterocyclic bioisostere as potent PDE4 inhibitors

A new hybrid template was designed by combining the structural features of phosphodiesterase 4 (PDE4) inhibitors with several heterocyclic moieties which present an integral part in the skeleton of many apoptotic agents. Thirteen compounds of the synthesized hybrids displayed higher inhibitory activity against PDE4B than the reference drug, roflumilast. Further investigation indicated that compounds 13b and 20 arrested the cell cycle at the G2/M phase and the pre‐G1 phase, and induced cell death by apoptosis of A549 cells in a caspase‐dependent manner.