Current Organic Chemistry - Volume 16, Issue 11, 2012

Cyclic oligonucleotides and analogues (cONs) are highly specific ligands for DNA, RNA and proteins. cONs are described in several diagnostic and therapeutic applications, as well as in elucidating enzyme mechanisms and as lead structures for development of new drugs because of their unusual chemical and biological properties in comparison with linear counterparts. In numerous structural studies it has been shown that conformational constraints imposed by circularity cause unique topologies, which in some cases can result into peculiar ON nanostructures. The wide field of applications of cONs has called for the definition of easy and efficient strategies to produce such compounds. In this review, we will describe the enzymatic and chemical approaches reported for the synthesis of cONs with a particular focus on the chemical ones. We proceed following a chronological order from the earliest to the latest methods and improvements, describing at first the natural cyclic ONs and then modified linkages and cyclic analogues.

Non-steroidal anti-inflammatory drugs (NSAIDs) are an important class of therapeutics, incorporate a heterocyclic core in their molecular structure and are used for the alleviation of pain and inflammation associated with several pathological conditions. NSAIDs exert anti-inflammatory effects by inhibiting cyclooxygenase enzymes (COXs) which, are useful in the synthesis of prostanoids generated from arachidonic acid. Selective COX-II inhibitors, compared to nonselective inhibitors exhibit reduced gastrointestinal, ulceration and renal side effects. In general, COX-II inhibitors incorporate a five or six-membered heterocyclic motif with built-in sulfonamide or methylsulfonate moiety. Celecoxib, a selective COX-II inhibitor drug, commercialized by Pfizer is applied in the treatment of rheumatoid arthritis, osteoarthritis, and painful menstruation related symptoms. The current review provides a discussion on the methodologies used to construct celecoxib/celebrex® and structural analogs.

This article discusses advantages and limitations of the biotransformations with enzymes and whole-cell catalysts. It reviews biocatalytic synthesis of the chiral, organophosphorus compounds of different structures and characterizes their biological importance.

Recent investigations on silole derivatives have shown that materials based on siloles possess a number of intriguing properties, such as high charge carrier mobilities, high photoluminescence quantum yields, and good thermal stabilities, which are favorable for the applications in organic optoelectronic devices. Great achievements have been made in the silole-based conjugated materials for high performance optoelectronic devices. The recent development of silole-based materials for organic light-emitting diodes (OLEDs) and organic photovoltaic devices (OPVs) is described in this review. We will mainly focus upon the optoelectronic properties of substituted siloles, dibenzosiloles, and dithienosiloles.

The reaction of 5-aminouracil with peroxyl radicals generated by the thermal decomposition of 2,2'-azo-bis(2- methylpropionitrile) (AIBN) and 2,2'-azo-bis(2-amidinopropane) dihydrochloride was studied at 50°C in ethanol and water (pH 7.0) solution respectively. The oxidation product of 5-aminouracil formed by peroxyl radicals was dihydro-5,5,6-trihydroxypyrimidine-2,4-dione. The relative rate constant of 5-aminouracil vs. quercetin and 2,6-di-tert-butyl-4-methylphenol by peroxyl radicals generated from AIBN was measured in ethanol and found to be 0.19 (50°C) and 3.6 (70°C) respectively. Theoretical data of the redox potential and the bound dissociation energy oppose against single electron/proton transfer mechanism and provide support for a hydrogen atom abstraction mechanism. Transition structures and activation barriers of the hydrogen abstraction from 5-aminouracil, 5-hydroxy-6-methyluracil and 2,6-di-tert-butyl-4-methylphenol by methyl peroxyl radical were determined with the BB1K/6-31+G(d,p) level of theory. The relative theoretical reactivity was found to be in a good agreement with the experimental results and also supported the hydrogen abstraction mechanism.

The electrophilic amination of functionalized organocopper and organozinc reagents by N,N-dialkyl-O-benzoyl hydroxylamine derivatives to provide functionalized tertiary aryl amines has been accomplished efficiently at ambient temperature using in situ generated Fe(0) nanoparticles from Fe(acac)3. The formation and role of Fe(0)-nanoparticles were investigated. The mechanism involving Feassisted nucleophilic displacement at the nitrogen centre of the hydroxylamine derivative by the Cu/Zn-reagents is described. The organo- copper/zinc reagents are readily prepared by the treatment of the corresponding Grignard reagents with CuI and ZnCl2 respectively.