Mini-Reviews in Organic Chemistry - Volume 10, Issue 3, 2013

In this review, we classified discussion about recent advances in asymmetric organocatalytic Michael reactions carried out under various aqueous media. Many organocatalysts were discussed based on their chemical structures and properties. The role of water and proposed mechanisms were summarized.

Coordination compounds based on bis-quinolizidine derivatives as ligands are described from the viewpoint of their spectroscopic and structural properties. The metal ligand ability of C2 substituted sparteines and bis-quinolizidine Noxides is discussed in order to establish how far the presence of a substituent at α position to the nitrogen atom, involved in the formation of metal complexes or N-oxide function, influences the course of the complexation reaction and geometry of the complexes. The results are confronted with theoretical calculations. Potential pharmacological properties of selected complexes are also determined.

Ag(I) complexes formed by polydentate phenolic derivatives of thioglycolic and thiopropionic acids with Ag(I) ions could be a promising field of search for potential chemotherapeutic agents. Convenient synthetic methods to prepare these ligands have been developed on the basis of addition reactions occurring between S-nucleophiles and obenzoquinones. The results are presented of physicochemical investigation of Ag(I) ions complexation with phenolic ligands, which made it possible to determine ionic and redox ligand forms with high nucleophilicity of metal-ion binding sites, the peculiarities of the structural organization of the coordination cores of the newly synthesized complexes. The investigation of the molecular and electronic structure of Ag(I) complexes has been performed within the density functional theory framework. On the basis of the pharmacological screening results the selection is justified of a lead compound possessing antibacterial, antifungal and antiherpetic activity comparable to those of some standard drugs to develop effective pharmaceuticals for combination therapy of mixed infections. Data have been obtained on the ability of some phenolic derivatives of thioglycolic and thiopropionic acids as well as their Ag(I) complexes to reduce bovine cytochrome c.

Hepatitis B is a serious liver infectious disease, which remains a major public health problem worldwide. Though some effective treatments have been taken clinically, the therapeutic effects are moderate and suffer from the significant side effects and inevitable drug resistance. Therefore, the safer and more effective anti-HBV drugs are urgently required. Many natural products are well documented as their novel structures and potent bioactivity. Researchers worldwide, especially in China, have been exploring natural drugs against HBV. Some natural products with anti-HBV activities were found. Extracting and isolating pure compounds with anti-HBV bioactivity from natural resources are therefore a promising approach to discover and develop new drugs. Herein, we systematically elucidated the anti-HBV activity, chemical structure of some herb medicine extracts reported in literature recently. Furthermore, we compared the anti-HBV activities of these natural products, which would provide useful information for the pharmaceutical synthesis and evaluation.

Since the discovery of the aggregation-induced emission (AIE) phenomenon of siloles in 2001, extensive research has been devoted to the synthesis of AIE-active group 14 metalloles and their applications. A large number of new systems have been designed, synthesized, and studied. It has been determined that the restriction of intramolecular rotation is the main cause for AIE, and the effect that the nature of the substituents has on the electronic structures allows one to control the properties of these materials. Siloles hold a number of favourable attributes for application in organic electronics; therefore many applications can be conceived for the siloles and other metalloles. In this mini-review we illustrate recent progress in the development of group 14 metallole-based OLEDs, bio/chemosensors and soft materials.

There has been an increasing interest in discovering and developing small molecules that are of pharmaceutical importance. Heterocyclic compounds are known to be the most versatile class of these types of molecules, either prepared synthetically or occurring in nature. However, in some cases, it has been reported that the activity is enhanced to a larger extent when these heterocycles are repeated in the molecule separated by a suitable spacer, i.e., a bis-heterocycle. Thus, the synthesis of new bis-heterocyclic compounds has become an eye-catchy field to explore in the recent past owing to their pharmacological, biological and industrial importance. The synthesis of bis-heterocycles is mainly achieved by joining heterocyclic nuclei together using a variety of linkers and points of linkages. These structural permutations and combinations have given an unlimited number of available bis-heterocycles. Use of S-S linkage is one such facile method of getting bis-heterocycles as they are easily obtained from the oxidation of thiols and protected thiols by using broad range of reagents and reaction conditions. Disulphide linkage being an integral part of the biological system, as disulphide bonds are found in peptides and proteins, also adds to the efficacy of these bis-heterocycles.

Different cross-coupling reactions for the formation of biologically important motifs and intermediates in organic synthesis using various suitable copper catalysts are reviewed. These include C-C, C-N, C-O, C-S heteroatom bond forming, cyclization and other miscellaneous reactions catalyzed by elemental copper, copper salts, CuI, Cu (OTf)2, CuBr, Cu2O etc. The use of copper reagents instead of palladium catalysts and ligands seems to be advantageous from the commercial point of view. The methods described herein afford the products in excellent yield without using expensive and moisture/air sensitive palladium catalysts, ligands and reagents.

5,8-Dihydroxy-[1,4]-naphthoquinone (DHNQ) is one of the key chromophores found in aged cellulosics. Cellulose aging and yellowing as well as bleaching of cellulosic materials are key processes in the pulp and paper industries and have considerable economic importance: the knowledge of the general reactivity and chemistry of this compound is thus helpful for a better understanding of these phenomena and the related technologies. This paper reviews the reactions reported for 5,8-dihydroxy-[1,4]-naphthoquinone, from the viewpoints of both synthesis and general reactivity. The compound exhibits a rich chemistry due to the presence of interconvertible hydroquinone and quinone moieties, reflected in strong resonance stabilization in alkaline medium. One of the most prominent reaction pathways is cycloaddition to the 2,3-double bond with various dienes to form polycyclic quinones, mainly anthraquinones. DHNQ also undergoes nucleophilic addition of amines, alcohols, olefins, water, and sulfides mainly at the 2-position followed by re-oxidation of the quinoid moiety, eventually resulting in 2-substituted DHNQ. Derivatization of the hydroxyl groups into O-acyl, O-alkyl, O-tosyl, and O-silyl derivatives is also widely reported, as are reductive conversions.

2,5-Dihydroxy-[1,4]-benzoquinone is one of the three key chromophores found in aged cellulosics. Knowledge of the general reactivity and chemistry of this compound is helpful for a better understanding of cellulose aging and yellowing as well as bleaching of cellulosic materials - processes which also have considerable economic importance. This paper reviews the reactions reported for 2,5-dihydroxy-[1,4]-benzoquinone, from the viewpoints of both synthesis and general reactivity. The exhibits a rich chemistry because of the presence of both carbonyl and enol motifs, and is able to undergo both nucleophilic and electrophilic substitutions. Other major pathways are the condensation with amines, derivatization of the hydroxyl groups, reductions, and oxidative degradation.