Mini-Reviews in Organic Chemistry - Volume 5, Issue 4, 2008

Nature's use of a simple genetic code to enable life's complex functions is an inspiration for supramolecular chemistry. DNA nucleobases carry the key information utilizing a variety of cooperative and non-covalent interactions. This mini-review describes some recent advances in the form and function provided by self-assembly of guanine (G) based systems. Although the large variety of supramolecular networks originated by guanosine derivatives has been investigated for a couple of decades, only in recent years several research groups focused on their applications in supramolecular chemistry, material science and nanotechnology. Our attempt here is to make connections between the structures of the assemblies and their properties. The review begins with a brief historical context of G self-assembly in water and then describes studies on lipophilic guanosine analogs in organic solvents. The article finally focuses on examples of how G analogs have been used as building blocks for functional applications.

Many important biological processes including fertilization, tissue formation, cell adhesion, antigen/antibody interactions, cancer metastasis or pathogen infection involve polyvalent interactions between oligomeric proteins and carbohydrate-based ligands. The synthesis of multitopic, molecularly-defined structures that display both clustered sugars and immobilization or bioactive agents represents an attractive approach for the discovery of new diagnostics and therapeutics. This mini-review updates the current developments in this field by focusing on the recent interests on cyclopeptide-based glycoclusters.

In this review, the organic cycloaddition and complexation of transition metal oxides with alkene, diamond (100), fullerene and carbon nanotube have been summarized. A clear scenario that analogous chemistry reaction is able to occur in materials featuring an analogous bonding motif has been obtained. In particular, it is demonstrated that theoretical predictions can be employed as a very useful tool to provide experiments with potentially guided information. RuO4 is proposed to be a better candidate than OsO4 for investigating the cycloaddition of transition metal oxides with fullerene and carbon nanotube. In perspective, the typical organic cycloaddition and complexation of transition metal oxides with alkenes in organic chemistry could be extended to functionalize other structure-like substances including Si (100), Ge (100), disilene, digermene, silene and germene.

Angular N-tricyclic systems as triazolo[4,5-f]quinolines, triazolo[4,5-h]quinolines, imidazo[4,5-f]quinolines, imidazo[4,5- h]quinolines were in the past obtained by connection of either f or h sides of the quinoline ring and both the adjacent carbon atoms of five-membered rings containing nitrogen atoms. Several attempts at obtaining the corresponding linear N-tricycles were made in the last century, but only the angular derivatives were obtained. Since 2000 a new simple pathway, involving suitable quinoline derivatives, which afforded the linear azolo and pyrido quinolines (imidazo[4,5-g]quinolines, triazolo[4,5-g]quinolines and pyrido[2,3- g]quinoxalines) has been developed. Several linear N-tricyclic derivatives have shown some interesting pharmaceutical activity.

Recent examples on the functionalization of the ferrocene core by means of cross-coupling reactions are reported in this review. Several methods are discussed including Negishi, Suzuki and Stille couplings for ferrocene-aryl bond formation and Sonogashira reaction for ferrocene-alkyne coupling. The properties in material science and asymmetric catalysis of the prepared ferrocenyl compounds are briefly discussed.

Chiral secondary alcohols are useful synthetic building blocks. One direct approach to chiral secondary alcohols is by catalytic reduction of ketones using molecular hydrogen or by asymmetric transfer hydrogenation. This review focuses on recent developments using immobilized chiral metal catalysts, and their role in developing greener chemistry. Immobilization of chiral ligands on silica, polymer, dendrimer and magnetite nanoparticles and their application as catalyst with metals in the hydrogenation of ketones under environmentally friendly solvent conditions is discussed.

N-arylated azoles have broad applications either alone or as intermediates in the synthesis of natural products, drugs, polymers, agrochemicals, among other items. Recently, instead of the less universal “classic” methods of arylation, a series of approaches based on the use of a complex of transition metals - derivatives of palladium and copper - was suggested. This mini-review looks into one of the most promising trends in this group of methods, arylation with the use copper(I)-based catalysts. The emphasis is made on a detailed consideration of each arylation method, in order to give the reader a possibility to compare the effectiveness and the limitations of one method or another, evaluate the conditions of conducting a reaction and the availability of reactants. In each subsection, results are presented in chronological order to demonstrate sequential progress in this area.

The selective incorporation of halogen into organic molecules provides a challenge to academic and industrial research. This microreview presents an overview of the available methodologies for the synthesis of 4-iodopyrazoles, valuable precursors for the selective construction of highly functionalized organic molecules of synthetic and biological importance.

1,3-Thiazolidin-4-ones are an important group of heterocyclic compounds that are used in the field of medicinal chemistry. The utility of 1,3-thiazolidin-4-ones as synthons for various biological compounds has given impetus to these studies. In recent years, 1,3-thiazoldin-4-ones have been among the most extensively studied compounds. This review aims to review the work reported on the chemistry and biological activities of 1,3-thiazolidin-4-ones during the past few years.

The review considers the intra- and intermolecular transformations of terpenes and their oxygen-containing derivatives in the presence of acidic clays. Using clays as catalysts of terpenoid transformations leads to improved characteristics of known processes and often to reaction routes other than those that occur in the presence of the traditional acid catalysts. This opens up new prospects for the application of renewable plant raw materials in fine organic chemistry.

Mangosteen (Garcinia mangostana L.; Clusiaceae) is a popular botanical dietary supplement in the United States, where it is used principally as an antioxidant. It is referred to as the “queen of fruits” in Thailand, a country of origin. The major secondary metabolites of mangosteen, the xanthones, exhibit a variety of biological activities including antibacterial, antifungal, antiinflammatory, antioxidant, antiplasmodial, cytotoxic, and potential cancer chemopreventive activities. Moreover, some of the xanthones from mangosteen have been found to influence specific enzyme activities, such as aromatase, HIV-1 protease, inhibitor κB kinase, quinone reductase, sphingomyelinase, topoisomerase and several protein kinases, and they also modulate histamine H1 and 5-hydroxytryptamine2A receptor binding. Several synthetic procedures for active xanthones and their analogs have been conducted to obtain a better insight into structure-activity relationships for this compound class. This short review deals with progress made in the structural characterization of the chemical constituents of mangosteen, as well as the biological activity of pure constituents of this species and synthetic methods for the mangosteen xanthones.