Johannes Brussee

On the mechanism of the formation of s(−)-(1, 1'-binaphthalene)-2,2'-diol via copper(II)amine complexes

Abstract The oxidative dimerization of 2-naphthol is studied by means with several copper(II)amine complexes as oxidants. Using primary amines a chemical yield of 95%–98% is obtained. Using (+)amphetamine as complexing amine a 94%–96% optically pure product is obtained It is established that this stereoselectivity is a result of selective precipitation of the copper(II)-(+)amphetamine-(−)binaphthol complex with a simultaneous racemization of the (+)binaphthol

Chiral Induction Effects in Ruthenium(II) Amino Alcohol Catalysed Asymmetric Transfer Hydrogenation of Ketones: An Experimental and Theoretical Approach

The enantioselective outcome of transfer hydrogenation reactions that are catalysed by ruthenium(II) amino alcohol complexes was studied by means of a systematically varied series of ligands. It was found that both the substituent at the 1-position in the 2-amino-1-alcohol ligand and the substituent at the amine functionality influence the enantioselectivity of the reaction to a large extent: enantioselectivities (ee values) of up to 95% were obtained for the reduction of acetophenone. The catalytic cycle of ruthenium(II) amino alcohol catalysed transfer hydrogenation was examined at the density functional theory level. The formation of a hydrogen bond between the carbonyl functionality of the substrate and the amine proton of the ligand, as well as the formation of an intramolecular H...H bond and a planar H-Ru-N-H moiety are crucially important for the reaction mechanism. The enantioselective outcome of the reaction can be illustrated with the aid of molecular modelling by the visualisation of the steric interactions between the ketone and the ligand backbone in the ruthenium(II) catalysts.

Bio-organic synthesis of optically active cyanohydrins and acyloins

Abstract Chiral acyloins of high optical purity have been obtained in good yields by enzyme catalyzed formation of optically active cyanohydrins, followed by hydroxyl protection and reaction with a Grignard reagent.

Synthesis of Optically Active Cyanohydrins Using Almond Meal

Abstract Asymmetric hydrocyanation of aldehydes was accomplished using almond meal, containing the enzyme oxynitrilase. Optically active cyanohydrins with high levels of enantiomeric purity were obtained following a simple procedure.

Synthesis of optically active silyl protected cyanohydrins

Abstract Mandelonitrile lyase as present in a crude extract of almond flour has been tested for the synthesis of several chiral cyanohydrins. Silylated cyanohydrins of benzaldehyde, 4-methoxybenzaldehyde, piperonal, 5-methylfurfural, butyraldehyde and crotonaldehyde were obtained in good yield and high enantiomeric excess (93%) after treatment with silyl chlorides and imidazole in DMF.

2-Amino-6-furan-2-yl-4-substituted nicotinonitriles as A2A adenosine receptor antagonists.

A 2A adenosine receptor antagonists usually have bi- or tricyclic N aromatic systems with varying substitution patterns to achieve desired receptor affinity and selectivity. Using a pharmacophore model designed by overlap of nonxanthine type of previously known A 2A antagonists, we synthesized a new class of compounds having a 2-amino nicotinonitrile core moiety. From our data, we conclude that the presence of at least one furan group rather than phenyl is beneficial for high affinity on the A 2A adenosine receptor. Compounds 39 (LUF6050) and 44 (LUF6080) of the series had K i values of 1.4 and 1.0 nM, respectively, with reasonable selectivity toward the other adenosine receptor subtypes, A 1, A 2B, and A 3. The high affinity of 44 was corroborated in a cAMP second messenger assay, yielding subnanomolar potency for this compound.

Hybrid ortho/allosteric ligands for the adenosine A1 receptor

Many G protein-coupled receptors (GPCRs), including the adenosine A(1) receptor (A(1)AR), have been shown to be allosterically modulated by small molecule ligands. So far, in the absence of structural information, the exact location of the allosteric site on the A(1)AR is not known. We synthesized a series of bivalent ligands (4) with an increasing linker length between the orthosteric and allosteric pharmacophores and used these as tools to search for the allosteric site on the A(1)AR. The compounds were tested in both equilibrium radioligand displacement and functional assays in the absence and presence of a reference allosteric enhancer, (2-amino-4,5-dimethyl-3-thienyl)-[3-(trifluoromethyl)phenyl]methanone, PD81,723 (1). Bivalent ligand N(6)-[2-amino-3-(3,4-dichlorobenzoyl)-4,5,6,7-tetrahydrothieno[2,3-c]pyridin-6-yl-9-nonyloxy-4-phenyl]-adenosine 4h (LUF6258) with a 9 carbon atom spacer did not show significant changes in affinity or potency in the presence of 1, indicating that this ligand bridged both sites on the receptor. Furthermore, 4h displayed an increase in efficacy, but not potency, compared to the parent, monovalent agonist 2. From molecular modeling studies, we speculate that the allosteric site of the A(1)AR is located in the proximity of the orthosteric site, possibly within the boundaries of the second extracellular loop of the receptor.

Synthesis of optically active ethanolamines.

Abstract (1 R ,2 S )-2-amino-1-arylethanols of high optical purity have been obtained from optically active tert -butyldimethylsilyl protected cyanohydrins by a Grignard reaction, directly followed by reduction of the intermediate imine. Chiral induction gave a large preponderance of the erythro isomers.

(β-Amino alcohol)(arene)ruthenium(II)-Catalyzed Asymmetric Transfer Hydrogenation of Functionalized Ketones − Scope, Isolation of the Catalytic Intermediates, and Deactivation Processes

The asymmetric transfer hydrogenation of functionalized ketones with (β-amino alcohol)(arene)RuII catalysts using 2-propanol as the hydrogen source has been studied. The structure of the catalyst has been systematically screened using a wide variety of [(η6-arene)RuCl2]2 complexes and β-amino alcohols R1CH(OH)CHR2NHR3, some of which were specifically designed for optimized performance, e.g. (1S,2R)-N-(4-biphenylmethyl)norephedrine (9o). The efficiencies of the catalytic combinations have been evaluated in the reduction of β-oxo esters and ketones bearing heteroatoms at the α-position. The catalyst precursor [{η6-p-cymene}{η2-N,O-(9o)}RuCl] (35), the 16-electron true catalyst [{η6-p-cymene}{η2-N,O-(9o1−)}Ru] (36), and the hydride [{η6-p-cymene}{η2-N,O-(9o)}RuH] (37) involved in the reduction process have been isolated, characterized by NMR and ESI-MS, as well as by X-ray crystallography in the case of 35, and their reactivities have been investigated. The results reveal two general trends regarding this catalytic process: (1) the apparent reaction rate and the enantioselectivity are largely controlled by the nature of the amine functionality of the chiral ligand and the arene ring of the RuII precursor; (2) side reactions occur between the ketone substrate and the active catalytic species that affect the concentration of the latter and consequently the apparent rate; the formation of inactive (β-diketonato)RuII complexes is demonstrated in the case of β-oxo esters.

Stereoselective synthesis of β-hydroxy-α-amino acids from chiral cyanohydrins

Abstract An efficient one-pot reduction-transimination-hydrocyanation synthesis of β-hydroxy-α-cyanoamines 3 from optically active O-protected mandelonitrile (1) is described. These β-hydroxy-α-cyanoamines were easily converted into optically active (2S,3R) β-hydroxy-α-amino acids 6.