Mini-Reviews in Organic Chemistry - Volume 8, Issue 1, 2011

Supramolecular chemistry---the branch of chemistry involved with the control of intermolecular interactions to produce valuable new devices and molecular assemblies--- has been a major research theme for the past four decades. Especially, anionic species based supramolecular chemistry, including recognition and sensing of anions, has emerged rapid growth recently. Arising from the important roles the anionic species play in biological and environmental fields, there is great current interest in developing molecular receptors to selectively recognize and sense them. In this special issue, the recent progress referring to anion recognition and sensing has been summarized by different experts in the field. It is well-known that development of novel and efficient artificial receptors is the central task for anion recognition and sensing. Compared with other hydrogen-bond donor groups, indole NH was relatively less studied as recognition unit of anion receptors. Thus, the first review by Dr. Bao summarizes the progress on synthetic anion receptors containing indole group from 2008 to date. Furthermore, the second review by Prof. Lin introduces their recent results about colorimetric sensing of biologically important acetate ion based on indole derivation. On the other hand, the development of fluororeceptors capable of selective sensing of anionic species has aroused great interest in supramolecular chemistry. Fluororeceptors are attractive due to the simplicity and high detection limit of fluorescence. In this case, the third review by Prof. Ghosh presents their excellent recent work on selective sensing of fumarate over maleate by benzimidazolium - based fluororeceptors. Prof. Goswami reports in the fourth review article that metal coordinated urea based fluorescent receptors for anion recognition. In the final review article, also Prof. Lin presents their recent work on selective sensing of F- based on 2,4-dinitrophenylhydrazine and 1,10-phenanthroline conjugated colorometric receptor. In summary, I hope this special issue will provide a good impact on readers with an overview of supramolecular chemistry based on anionic species, especially of anion recognition and sensing. Finally, as a guest editor for this special issue, I am very grateful for the valuable and excellent contributions from my colleagues and I am also highly appreciative of all the referees for their expert comments on the papers, despite their tight schedules and for their precious time. My sincere thanks are attributed to the editors of MROC for giving me the chance to organize this special issue on this exciting topic. I hope that the readers will enjoy reading the complete issue.

A new chromogenic sensor, 1,10-phenanthroline affixed to the 2,4-dinitrophenylhydrazine moiety, was synthesized and characterized. Among anions added into it, F-, AcO- and H2PO4- ions resulted in the color changes from light brown to dark brown, while other tested anions did not induce color changes. Meanwhile, the anion-binding ability has been investigated by UV-vis and 1H NMR titrations in DMSO-d6. The sensor displays an even stronger binding to F- over AcO- and H2PO4- ions with 1:1 stoichiometry through hydrogen bonding.

Two bis urea based acyclic receptors (1 and 2) containing two pyridyl moieties with different spacers are synthesized. These receptors are further transformed to metallo-macrocyclic receptors (3 and 4) by coordinating with metal center through pyridine ring ‘N’. The binding-behavior as well as selectivity of the receptors towards anions upon metal coordinated cyclization is studied and the results are compared with parent acyclic receptors. Receptors 2 and 4 containing a naphthalene moiety as a spacer as well as a fluorophore behave as ‘on-off’ sensors towards anions.

Indole-based anion receptors are developing rapidly nowadays due to a nearly limitless derivatizing capability of indole functionality. This mini-review summarizes the progress on synthetic anion receptors containing indole functionality from 2008 to date, including the recognition behaviors and sensing properties of these receptors for different anions.

A simple and novel receptor 1 based on indole-3-aldehyde and 2, 4-diphenylhydrazine is synthesized by a simple way, which displays good selectively and sensitivity for detection of acetate, fluoride and dihydregen phosphate anion in dry DMSO and in DMSO/H2O (95/5) solutions. Combining with the anions induces the visible color changes that the naked-eye detection maybe realized. Meanwhile, the binding properties are tested and determined by UV-vis, fluorescent changes and 1H NMR experiments in DMSO-d6.

A new benzimidazolium - based chiral fluororeceptor 1 has been designed and synthesized. The open cleft of 1 is found to recognize fumarate selectively over maleate in CH3CN by exhibiting greater change in emission. In comparison, the achiral receptor 2, under similar condition, shows poor selectivity in the recognition of fumarate over maleate. Interaction studies were performed by 1H NMR, fluorescence and UV-vis spectroscopic methods.

Among the synthetic vectors exploitable in Human Gene Therapy (HGT), complexes of DNA with cationic liposomes (lipoplexes) are considered the best candidates. Some degree of cytotoxicity and a limited stability on serum are still limiting factors for applications in vivo. On the contrary the corresponding complexes of neutral liposomes are enough stable and non toxic. This review has the aim to offer a survey of existing data, namely structural properties, on neutral liposomes from the point of view of HGT; and to compare, whenever possible, the different features of the two classes of compounds. The outlook is that in near future neutral liposomes could behave as efficient and safe vectors of genetic material.

A review on the tandem [4+2]/[3+2] cycloaddition reactions of 1,3,4-oxadiazoles with alkenes is presented. This reaction presents a powerful synthetic tool in the construction of complex polycyclic molecules in a one-pot reaction. Special attention is paid to synthesis of [n]polynorbornane and oxanorbornyl systems. In continuation, a review on the 1,3,4-oxadiazole reactions used in stereoselective total synthesis of alkaloids is given. Both intermolecular and intramolecular tandem [4+2]/[3+2] reactions are discussed. Stereospecificities and mechanistic rationale of various reactions are supported by quantum-chemical calculations (RHF/6-31G*).

This review will focus on the recent applications of chiral Schiff base in asymmetric catalysis. The developments in the preparation and use of chiral Schiff base in a variety of asymmetric transformations will be covered. Some remarkable characteristics and catalytic mechanisms of these reactions will be mentioned and the limitations of some asymmetric reactions will be also discussed.

Silica sulfuric acid (SSA) has been used as an efficient solid acidic catalyst for many organic reactions. In this review, we wish to report some applications of this catalyst in organic synthesis.

Benzoxathiolones and its derivatives are important pharmacophores with diversified pharmacological activities like antibacterial, antimycotic, antioxidant and anti-inflammatory. These different biological applications for benzoxathiolone compounds have motivated new studies in searching novel derivatives with better activity results and also other applications in pharmaceutical industry. Owing to the importance of this system, the aim of this review is to present the main aspects of the chemistry and biological properties of 1,3- benzoxathiol-2-ones.