Gouher Rabani

Organocatalysts immobilised onto gold nanoparticles: application in the asymmetric reduction of imines with trichlorosilane

Gold nanoparticles functionalised with a valine-derived formamide have been developed as effective homogenous catalysts for the asymmetric reduction of ketimine 1 with trichlorosilane (< or = 84% ee) in toluene. This methodology both simplifies the recovery of the catalyst and its separation from the product, as the nanoparticles can be readily removed and subsequently recycled by precipitation from the reaction mixture.

Controlled Self‐Assembly of Organic Nanowires and Platelets Using Dipolar and Hydrogen‐Bonding Interactions

Synergistic dipole-dipole and hydrogen-bonding interactions are used to assemble nanostructured materials. Precipitation of a hydrogen-bonding donor-acceptor molecule 8-[[p-[bis(ethyl)amino]phenyl]azo]-isobutylflavin (ABFL) yields nanowires approximately 50-150 nm in diameter and lengths of several millimeters. Precipitation of the non-hydrogen-bonding analog, methylated ABFL (MABFL), generates micrometer-sized hexagonal platelets that are 5-10 microm in length, 1-5 microm in width, and 0.1-0.5 microm thick. The structural similarity of the two molecules allows intermediate morphologies to be formed via co-precipitation. Doping experiments demonstrate efficient control over nanowire length and diameter due to the disruption of the hydrogen bonding within the nanowires.

Soluble Polymer‐Supported Organocatalysts: Asymmetric Reduction of Imines with Trichlorosilane Catalyzed by an Amino Acid Derived Formamide Anchored to a Soluble Polymer

In the development of an efficient catalytic process, facile separation of the product from the catalyst is one of the key technological elements. In organocatalysis, where both the product and the catalyst are small organic molecules, chromatography often represents the only option. Here, immobilization of the catalyst may provide an elegant solution to the problem. Asymmetric reduction of prochiral imines 1 is one of the key reactions in synthetic organic chemistry (Scheme 1). Its organocatalytic version is characterized by two fundamentally different approaches: 1) hydrosilylation with Cl3SiH, catalyzed by chiral Lewis-bases, [4–9] and 2) reduction with Hantzsch dihydropyridine, catalyzed by chiral Brønsted acids. In the past few years, we have developed the amino acidbased formamides 3–5 (Scheme 1) as chiral Lewis-basic organocatalysts for the reduction of imines 1 ( 97 % ee ; 1– 5 mol % loading). The practicality was then improved by tagging the catalyst to a fluorous ponytail (7) and by its anchoring to a polymer support (8). Catalyst 7, working in a homogeneous solution, mirrored the enantioselectivities of 3–5 and the products were separated from the catalyst by filtration through a pad of fluorous silica. The solid-supported catalysts 8 were separated even more easily via mechanical filtration. However, the latter reactions were heterogeneous and that had a negative impact on the enantioselectivities, which reached 82 % ee, that is, about 10–15 % ee below those of the homogeneous system. We reasoned that anchoring the catalyst to a soluble polymeric support might serve as a remedy to the problems associated with the heterogeneous systems. Recovery and recycling of the soluble supported catalysts would then rely on the switch of solubility induced either by changing the solvent polarity (e.g., for PEG support) or the temperature (for thermomorphic support). Traditionally, PEG polymers are precipitated by non-polar solvents, which may also lead to co-precipitation of the polar products, thereby affecting the overall efficiency of the process. Herein, we report [a] Prof. Dr. A. V. Malkov, Dr. M. Figlus, M. R. Prestly, Dr. G. Rabani, Dr. G. Cooke, Prof. Dr. P. Kočovský Department of Chemistry, WestChem University of Glasgow, Glasgow G12 8QQ (UK) Fax: (+44) 141-330-4888 E-mail : graeme@chem.gla.ac.uk pavelk@chem.gla.ac.uk [b] Prof. Dr. A. V. Malkov Present Address: Department of Chemistry Loughborough University, Leicestershire, LE11 3TU (UK) Fax: (+44) 1509-22-3925 E-mail : a.malkov@lboro.ac.uk Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.200901573. Scheme 1. Catalysts for asymmetric reduction of imines; for a–j, see Table 1.

Model systems for flavoenzyme activity: intramolecular self-assembly of a flavin derivative via hydrogen bonding and aromatic interactions

We have synthesised a flavin derivative incorporating functionalities that promote intramolecular self-assembly via hydrogen bonding and aromatic interactions.

Polymeric model systems for flavoenzyme activity: towards synthetic flavoenzymes

We report the synthesis of a water-soluble flavin polymer using ATRP, whereby the oligoethylene glycol backbone provides both a local hydrophobic environment and redox tuning of the flavin moiety typical of flavoenzyme prototypes.

A flavin-based [2]catenane

We report the synthesis, solid-state and preliminary solution properties of a flavin-based [2]catenane.

Dendron-based model systems for flavoenzyme activity: towards a new class of synthetic flavoenzyme

Three generations of water-soluble flavin dendrons have been synthesized and the role dendrimer generation has on the physical and catalytic properties of these assemblies has been investigated.

‘Lock and key’ control of optical properties in a push–pull system

We report the modulation of the absorbance of a flavin push-pull derivative through specific recognition by a complementary diamidopyridine (DAP), shifting the flavin intramolecular charge transfer band by approximately 30 nm.

Tuneable pseudorotaxane formation between a biotin–avidin bioconjugate and CBPQT4+

A biotinylated 1,5-dialkoxynaphthalene derivative has been shown to have the ability to bind strongly to avidin and thus act as an artificial binding site for cyclobis(paraquat-p-phenylene) thereby facilitating the formation of a tuneable pseudorotaxane-based bioconjugate.