The recent advances in nanotechnology and the corresponding increase in the use of nanomaterials in products in every sector of society have resulted in uncertainties regarding environmental impacts. The objectives of this review are to introduce the key aspects pertaining to nanomaterials in the environment and to discuss what is known concerning their fate, behavior, disposition, and toxicity, with a particular focus on those that make up manufactured nanomaterials. This review critiques existing nanomaterial research in freshwater, marine, and soil environments. It illustrates the paucity of existing research and demonstrates the need for additional research. Environmental scientists are encouraged to base this research on existing studies on colloidal behavior and toxicology. The need for standard reference and testing materials as well as methodology for suspension preparation and testing is also discussed.

Nanomaterials in the environment: Behavior, fate, bioavailability, and effects

Since the discovery of organic azides by Peter Griess more than 140 years ago, numerous syntheses of these energy-rich molecules have been developed. In more recent times in particular, completely new perspectives have been developed for their use in peptide chemistry, combinatorial chemistry, and heterocyclic synthesis. Organic azides have assumed an important position at the interface between chemistry, biology, medicine, and materials science. In this Review, the fundamental characteristics of azide chemistry and current developments are presented. The focus will be placed on cycloadditions (Huisgen reaction), aza ylide chemistry, and the synthesis of heterocycles. Further reactions such as the aza-Wittig reaction, the Sundberg rearrangement, the Staudinger ligation, the Boyer and Boyer-Aube rearrangements, the Curtius rearrangement, the Schmidt rearrangement, and the Hemetsberger rearrangement bear witness to the versatility of modern azide chemistry.

Organic Azides: An Exploding Diversity of a Unique Class of Compounds

Asymmetric 1,3-Dipolar Cycloaddition Reactions

One of the initial steps in the development of therapeutic agents is the identification of lead compounds that bind to the receptor or enzyme target of interest. Many analogs of these lead compounds are then synthesized to define the key recognition elements for maximal activity. In general, many compounds must be evaluated in both the lead identification and optimization steps. Increasing burdens have been placed on these efforts due to the large number of new therapeutic targets that continue to be identified thorough modern molecular biology methods.1 To address this demand, very powerful chemical and biological methods have been developed for the generation of large combinatorial libraries of peptides2 and oligonucleotides3 that are then screened against a receptor or enzyme to identify high-affinity ligands or potent inhibitors, respectively. While these studies have clearly demonstrated the power of library synthesis and screening strategies, peptides and oligonucleotides generally have poor oral activities and rapid in vivo clearance;4 therefore their utility as bioavailable therapeutic agents is often limited. Due to the favorable pharmacokinetic properties of many small organic molecules (<600-700 molecular weight),5 the design, synthesis, and evaluation of libraries of these compounds6 has rapidly become a major frontier in organic chemistry. Lorin A. Thompson was born in Lexington, KY, in 1970. He received the Bachelor of Science degree from the University of North Carolina, Chapel Hill, in 1992 where he worked under the guidance of Joseph Desimone. He is currently pursuing his doctorate in the laboratory of Jonathan Ellman at UC Berkeley where he is the 1994 Glaxo-Wellcome fellow. His research interests include the development of synthetic methodology for organic library construction.

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Synthesis and Applications of Small Molecule Libraries.

1,2-Amino Alcohols and Their Heterocyclic Derivatives as Chiral Auxiliaries in Asymmetric Synthesis

Publisher Summary Azomethine ylides are planar molecules composed of one nitrogen and two terminal sp2 carbons At most, four geometrical isomers are possible for these transient molecules Their cycloadditions to olefin or acetylene dipolarophiles give rise to the formation of two sets of carbon-carbon bonds in a single step Because of the structural complexity of azomethine ylide itself compared to other dipoles and the stereochemical selectivity in the cycloadditions, a number of stereoisomers are possible for the cycloadducts These two points make azomethine ylides one of the most attractive 1,3-dipoles, both in the fields of ylide chemistry and synthetic organic chemistry Azomethine ylides can be classified in groups according to their structure This chapter concentrates on the most basic ylides, acyclic azomethine ylides, in order to catch the generalized concepts involved in the azomethine ylide chemistry Accordingly, it also deals with the recent advances of the chemistry of acyclic azomethine ylides covering its preparation, cycloadditions, intramolecular cycloadditions, and synthetic applications

Recent Advances in Azomethine Ylide Chemistry

The synthetic applications of nitrile oxide cycloadditions, developed in the 1980s, are briefly reviewed. Topics discussed in the present review are the modern developments on the generation methods of nitrile oxides, on the cycloadditions with multiple bonds other than carbon-carbon double and triple bonds, on reductive cleavage of the nitrogen-oxygen bonds of 2-isoxazolines, on the unmasking of functionalities, and on the asymmetric cycloadditions of nitrile oxides

Recent advances in synthetic applications of nitrile oxide cycloaddition (1981-1989)

Lithium bromide-triethylamine induced cycloaddition of N-alkylidene 2-amino esters and amides to electron-deficient olefins with high regio- and stereoselectivity

Stereochemistry of the cycloadditions of twenty-four heteroaromatic N-ylides with several symmetrically substituted cis and trans olefins has been investigated. Cyclic and acyclic cis olefins cycloadd to the and form of the ylides in a highly endo-selective manner giving almost quantitative yields of stereospecific endo 3+2 cycloadducts. N-Ylides stabilized with a substituent of carbonyl type react with trans olefins to form mostly two stereoisomeric 3+2 cycloadducts to the anti form of the ylides. In most cases, they undergo the stereospecific interconversion through a retro cycloaddition process, the isomer ratios and the easiness of transformation depending upon the nature and size of substituents on the five-membered ring which has been built up in the cycloaddition step. On the other hand, N-ylides stabilized with a substituent of noncarbonyl type react with trans olefins to give stereospecific and stereoselective 3+2 cycloadducts as single isomers which are assigned as the cycloadducts to the syn fo...

Stereochemical study on 1,3-dipolar cycloaddition reactions of heteroaromatic N-ylides with symmetrically substituted cis and trans olefins.

Heating α-amino acids with a variety of carbonyl compounds generates N-unsubstituted or N-substituted azomethine ylides of nonstabilized types through the elimination of water and carbon dioxide. The ylides are captured by olefinic, acetylenic, and carbonyl dipolarophiles producing pyrrolidines, pyrrolines, and oxazolidines. The reaction involves intermediary 5-oxazolidinones which can be sometimes isolated. Some synthetic equivalents of parent azomethine ylide, methaniminium methylide, are accessible by this route.

Simple generation of nonstabilized azomethine ylides through decarboxylative condensation of α-amino acids with carbonyl compounds via 5-oxazolidinone intermediates

Otohiko Tsuge

Papers

Recent Advances in Azomethine Ylide Chemistry

Recent advances in synthetic applications of nitrile oxide cycloaddition (1981-1989)

Lithium bromide-triethylamine induced cycloaddition of N-alkylidene 2-amino esters and amides to electron-deficient olefins with high regio- and stereoselectivity

Stereochemical study on 1,3-dipolar cycloaddition reactions of heteroaromatic N-ylides with symmetrically substituted cis and trans olefins.

Simple generation of nonstabilized azomethine ylides through decarboxylative condensation of α-amino acids with carbonyl compounds via 5-oxazolidinone intermediates