Asymmetric electrophilic amination of various carbon nucleophiles with enantiomerically pure chiral N-h oxaziridines derived from camphor and fenchone

The first two stable enantiomerically pure chiral N-H oxaziridines, derived from camphor and fenchone, are shown to act as electrophilic sources of nitrogen upon reaction with various carbon nucleophiles. Nitrogen is transferred, together with the camphor/fenchone unit, when deprotonated esters, malonates, and nitriles are used as nucleophiles. One of the ester or nitrile units in the substrate usually undergoes hydrolysis; a cyclic mechanism is proposed to account for this observation.     

New and efficient procedure for the preparation of unsymmetrical silaketals

[reaction: see text] A new and efficient procedure for the preparation of unsymmetrical silaketals via a three-step protocol without isolation of the intermediates is presented. The unsymmetrical silyl ethers and silanes can also be readily obtained via this sequence of reactions.     

Efficient synthesis of extended guanine analogues designed for recognition of an A·T inverted base pair in triple helix based-strategy

We report herein an efficient synthesis of new nucleosides N1, N2, and N3 as extended guanine analogues, derived from aminobenzimidazole and thymine or 5-substituted uracil. These nucleosides were devised for the recognition of an A·T inverted base pair by three hydrogen bonds, in triple helix-based technology.     

Site-isolated porphyrin catalysts in imprinted polymers

A meso-tetraaryl ruthenium porphyrin complex having four polymerizable vinylbenzoxy groups (2) has been synthesized by reaction of pyrrole with 4-(vinylbenzoxy)benzaldehyde and subsequent metalation with [Ru3(CO)12]. The porphyrin complex was immobilized by copolymerization with ethylene glycol dimethacrylate. The resulting polymer P2 was found to catalyze the oxidation of alcohols and alkanes with 2,6-dichloropyridine N-oxide without activation by mineral acids. Under similar conditions, the homogeneous catalyst 2 was completely inefficient. By using diphenylaminomethane and 1-aminoadamantane as coordinatively bound templates during the polymerization procedure, the molecularly imprinted polymers P3 and P4 have been synthesized. Compared with the polymer P2, the imprinted catalysts displayed a significantly increased activity with rate enhancements of up to a factor of 16.     

New chemical cross-coupling between aryl halides and allylic acetates using a cobalt catalyst

[reaction: see text] The cobalt-catalyzed coupling reaction of aromatic halides and allylic acetates proceeds readily under mild conditions in the presence of the appropriate reducing agent to produce allylaromatic derivatives either in pure acetonitrile (aryl bromides) or in an acetonitrile/pyridine mixture (aryl chlorides).     

A convenient synthesis of 2-amino-6-methoxy-1-methyl (and 1,4-dimethyl)carbazole derivatives and their 6-aza analogues

2,6-Diaminotoluene ( 3a ) and 2,6-diamino-p-xylene ( 3c ) led to 2-methyl (and 2,5-dimethyl)-3-acetylamino-phenylhydrazines 5a,b. Fischer indolization of their hydrazones 6a,b and 7a,b derived from 4-methoxycy-clohexanone and 4-piperidone, and subsequent aromatization of intermediate tetrahydrocarbazole derivatives 8a,b and 9a,b allowed us to work out a convenient route to the title compounds.     

Electron transfer of horse spleen ferritin at gold electrodes modified by self-assembled monolayers

Electron transfer is known to be an important step in the sequestering of iron by cellular ferritin. In this work, direct electron transfer between ferritin and a gold electrode was performed in order to probe its electron transfer kinetics. Gold electrodes were modified by the formation of self-assembled monolayers of 3-mercapto-propionic acid on the gold surface. Cyclic voltammetry using these electrodes shows that ferritin exhibits slow electron transfer kinetics at low potentials, yet fairly well-defined current—potential curves. In addition, the voltammetry indicates that adsorption of ferritin precedes the electron transfer step. Controlled potential electrolysis measurements yielded an n-value of 1910 electrons transferred per mole of ferritin. Cyclic voltammetry of a solution containing ferritin as well as nitrilotriacetate yields no electrolytic currents at potentials where the iron—nitrilotriacetate complex undergoes redox reactions, indicating that the currents observed in the voltammetry of ferritin were not due to free iron in the ferritin sample. In addition, the voltammetry of iron-free ferritin (apoferritin) did not yield appreciable currents, providing additional support to the suggestion that the observed voltammetric currents were due to the redox reactions of ferritin iron. Self-assembled monolayers containing carboxylate end groups effectively promoted the direct electron transfer of ferritin at a gold electrode, thus demonstrating that the electron transfer mechanisms of ferritin can now be probed electrochemically.     

Enantioselective Entry to the Homalium Alkaloid Hoprominol: Synthesis of an (R,R,R)‐Hoprominol Derivative

The diastereoselective synthesis of the N‐ and O‐protected hoprominol derivative (R,R,R)‐ 6 is described. The building up of the bicyclic O‐silylated and di(N‐tosylated) asymmetric scaffold 6 succeeded by convergent preparation of the two basic chiral azalactam units 7a and 7b and their subsequent iterative linking by a known method (Scheme 5). Both 4‐alkyl‐hexahydro‐1,5‐diazocin‐2(1H)‐ones 7a and 7b were prepared from the chiral β‐amino acid portions 10a and 10b , respectively, by application of a set of reactions (e.g., N‐alkylation of 10a , b and Sb(OEt)₃‐assisted cyclization of the resulting open‐chain intermediates) already known. In comparison with the total syntheses of homaline ( 1 ) and homoprine ( 2 ), the newness of the described synthesis lies in the asymmetric approach to the difunctionalized fatty acid derivative 10b starting from (?)‐(S)‐malic acid ( 9 ) (Schemes 3 and 4). Key step in the preparation of 10b was the diastereoselective amination of the optically pure α,β‐unsaturated δ‐hydroxy homoallylic ester 14 via conjugate intramolecular aza‐Michael cyclization of the acylic δ‐(carbamoyloxy) intermediate 11 .