Rukhsana I. Kureshy

Enantioselective epoxidation of non-functionalised alkenes using a urea–hydrogen peroxide oxidant and a dimeric homochiral Mn(III)-Schiff base complex catalyst

Abstract The catalytic enantioselective epoxidation of chromenes, indene and styrene using a urea–hydrogen peroxide adduct as an oxidising agent and the novel dimeric homochiral Mn(III)-Schiff base catalyst 1 has been investigated in the presence of carboxylate salts and nitrogen and oxygen coordinating co-catalysts. Conversions of more than 99% were obtained with all alkenes except styrene. Absolute chiral induction, as determined by 1 H NMR using the chiral shift reagent (+)-Eu(hfc) 3 , was obtained in the case of nitro- and cyanochromene. The catalyst could be re-used for up to five cycles with some loss of activity due to degradation of the catalyst under epoxidation condition with retention of e.e.s.

Heterogeneous Chiral Copper Complexes of Amino Alcohol for Asymmetric Nitroaldol Reaction

Chiral amino alcohols supported on mesoporous silicas were synthesized and evaluated as a new class of chiral ligands in copper-catalyzed nitroaldol reaction under heterogeneous and mild reaction conditions. The activity and enantioselectivity of the present catalytic system is immensely influenced by the presence of achiral and chiral bases as an additive. The heterogenized chiral copper(II) complex of amino alcohol was found to be an effective recyclable catalyst for the nitroaldol reaction of different aldehydes such as aromatic, aliphatic, alicyclic, and α-β unsaturated aldehydes to produce nitroaldol products with remarkably high enantioselectivity (≥99%) and yields.

Chiral Mn(III) salen complex-catalyzed enantioselective epoxidation of nonfunctionalized alkenes using urea–H2O2 adduct as oxidant

AbstractEnantioselective epoxidation of chromenes, indene, and styrene mediated by manganese salen complexes 1a–b, 2a–b (1 mol%) as catalystswith urea–H 2 O 2 adduct as an oxidant is observed to give excellent epoxide yield ( > 99%) in 0.5–4 h with enantiomeric excess (ee) in therange 56–99% except for styrene in which case 23–39% ee was obtained in 20 h. Even with a catalyst loading of 0.4 mol%, the system worksefficiently with retention of enantioselectivity, albeit with an increase in reaction time. Kinetic investigations of a representative substrate,indene, with these catalysts indicated a kinetic profile having first-order dependence with respect to the concentrations of the catalyst andoxidant and independent of-initial concentration of the substrate. Based on kinetic, catalytic and experimental evidence, the mechanism ofthe epoxidation reaction is suggested.  2003 Elsevier Inc. All rights reserved. Keywords: Enantioselective; Chiral; Manganese; Nonfunctionalized alkenes; Catalysis; Urea–H

Influence of chirality of V(V) Schiff base complexes on DNA, BSA binding and cleavage activity.

New chiral V(V) Schiff base complexes (S)-[VO(OMe)L] and (R)-[VO(OMe)L] were synthesized and characterized by microanalysis, infrared (IR), UV-Visible, Circular dichroism (CD) spectroscopy and single crystal X-ray studies. The interaction of these complexes with calf thymus (CT) DNA and bovine serum albumin (BSA) protein showed chiral expression DNA/protein binding strength. The influence of chirality was also observed in cytotoxicity assay of Hep 2 cells. (R)-[VO(OMe)L] enantiomer exhibited higher binding constant (5 ± 1 × 10(5) M(-1)) as compared to (S)-[VO(OMe)L] (8 ± 1 × 10(4) M(-1)). The fluorescence quenching, thermal melting and viscosity data suggest DNA surface and/or groove binding nature of the complexes and electrophoresis studies also showed greater activity for (R)-[VO(OMe)L] in cleaving DNA and protein as against (S)-[VO(OMe)L].

Dimeric chiral Mn(III) Schiff base complex-catalysed enantioselective epoxidation of non-functionalised alkenes

Abstract Dimeric chiral Mn(III) Schiff base complex 1 has been investigated as a catalyst for enantioselective epoxidation of chromenes, indene and styrene with an objective to explore its efficiency and recycling capability. Excellent conversions were obtained with all alkenes. More than 99% chiral induction, as determined by 1 H NMR using the chiral shift reagent Eu(hfc) 3 , was obtained in the case of electron deficient chromenes, viz. nitro and cyano chromene.

Asymmetric epoxidation of styrene by novel chiral ruthenium(II) Schiff base complexes, synthesis and characterization.

Abstract Synthesis of some novel Chiral Ru(II) Schiff base complexes of the type [RuL(PPh3)(H2O)2] 1–6 where L = Chiral Schiff bases derived from salicylaldehyde and L-amino acids namely, L-alanine, L-valine, L-Serine, L-Arginine, L-Cystein and L-aspartic acid are reported. The characterisation of the complexes has been accomplished by microanalysis. IR-,UV/visible,[1H], 13C[1H] and 31P[1H] NMR spectroscopy, conductance measurements, electrochemical studies, optical rotation and circular dichroism soectroscopy. The conformational aspects regarding the asymmetric arrangement of substituents R at aminoacid moiety of the Schiff bases around Ru(II) metal ion has been discussed. The complexes show quasireversible behaviour and the redox potential of Ru(II)/Ru(I) couple lie in the range −0.34 to −0.18 volts. In the asymmetric epoxidation of styrene by the complexes 1 – 6 and idosylbenzene, we observed that on employment of the R form of the catalyst resulted in the formation of (S) styrene oxide as dominant enantiomer by GLC and NMR. Enantiomeric excess for the resulting epoxides were determined by [1H] NMR spectroscopy using Chiral shift reagent, tris[3-(heptafluoropropyl hydroxymethylene − (+) camphoratoleuropium(III), Eu(hfc)3.

Chiral discrimination asserted by enantiomers of Ni (II), Cu (II) and Zn (II) Schiff base complexes in DNA binding, antioxidant and antibacterial activities.

Chiral Schiff base ligands (S)-H(2)L and (R)-H(2)L and their complexes (S-Ni-L, R-Ni-L, S-Cu-L, R-Cu-L, S-Zn-L and R-Zn-L) were synthesized, characterized and examined for their DNA binding, antioxidant and antibacterial activities. The complexes showed higher binding affinity to calf thymus DNA with binding constant ranging from 2.0×10(5) to 4.5×10(6) M(-1). All the complexes also exhibited remarkable superoxide (56-99%) and hydroxyl scavenging (45-89%) activities as well as antibacterial activities against gram (+) and gram (-) bacteria. However, none of the complexes showed antifungal activity. Conclusively, S enantiomers of the complexes were found to be relatively more efficient for DNA interaction, antioxidant and antibacterial activities than their R enantiomers. This study reveals the possible utilization of chiral Schiff base complexes for pharmaceutical applications.

C2-Symmetric Recyclable Organocatalyst for Enantioselective Strecker Reaction for the Synthesis of α-Amino Acid and Chiral Diamine- an Intermediate for APN Inhibitor

Recyclable chiral amide-based organocatalyst 5 efficiently catalyzed asymmetric Strecker reaction of various aromatic and aliphatic N-benzhydrylimines with ethyl cyanoformate as cyanide source at -10 °C to give a high yield (95%) of α-aminonitriles with excellent chiral induction (ee, up to 99%) with the added advantage of recyclability. Based on experimental observations a probable mechanism was proposed for this reaction. This protocol with catalyst 5 was extended for the synthesis of (R)-phenylalanine and pharmaceutically important drug intermediate (R)-3-phenylpropane-1,2-diamine in high yield with high enantioselectivity.

Enantioselective epoxidation of chromenes using chiral Mn(III) salen catalysts with built-in phase-transfer capability

New chiral Mn(III) salen epoxidation catalysts 1 and 2 (a catalyst loading in the range of 2.0–0.4 mol%) have been investigated for enantioselective epoxidation of chromene derivatives to chromene epoxides using pyridine N-oxide as a proximal ligand with excellent conversions and chiral induction.

Unravelling a New Class of Chiral Organocatalyst for Asymmetric Ring-Opening Reaction of Meso Epoxides with Anilines

Chiral sulfinamide based organocatalyst 11 was synthesized from readily available starting materials and used for the asymmetric ring-opening (ARO) reaction of meso epoxides with anilines. A high yield (up to 95%) of chiral β-amino alcohols with excellent enantioselectivity (ee up to 99%) was achieved in 24-30 h at rt under optimized reaction conditions. A probable mechanism for the catalytic ARO reaction is envisaged by (1)H and (13)C NMR experiments.