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

Horner–Emmons olefination of 4-hydroxy-2-oxoalkylphosphonates, readily available by hydrogenation of 5-substituted 3-phosphinylmethyl-2-isoxazolines, gives mainly E-isomers of 1-hydroxy-4-alken-3-ones bearing a variety of substituents at the 1-position. Use of the combination of triethylamine (or DBU)+lithium bromide as a weak base on the O-unprotected phosphonates is favored. Similar olefinations on the isoxazolines, 2-oxo-3-alkenylphosphonates, and 4-alkoxy-2-oxoalkylphosphonates have been also examined. Their synthetic applications to (±)-Gingerol, (±)-Yashabushiketol, and (±)-Dihydroyashabushiketol are described.

Horner–Emmons Olefination of 4-Hydroxy-2-oxoalkylphosphonates and Related Compounds: Applications to the Syntheses of (±)-Gingerol, (±)-Yashabushiketol, and (±)-Dihydroyashabushiketol

Michael addition of methyl 2-(trimethylsilyl)propenoate with organomagnesiums or organolithiums leads to 1:1 and/or 1:2 adduct anions which can be utilized in the subsequent step of Peterson olefination with carbonyl compounds. The 1:1/1:2 ratio depends upon the nature of donor molecules, the reaction conditions such as reaction temperature, polarity of solvent, and rate of addition of the acceptor molecule. Use of acceptors in excess results in the selective formation of 1:2 and/or 1:3 adducts.

Michael addition of methyl 2-(trimethylsilyl)propenoate with organomagnesiums or organolithiums leading to 1:1 and/or 2:1 adducts and subsequent Peterson olefination by condensation with carbonyl compounds.

The investigations of cycloaddition reactions of benzoyl and thiobenzoyl isocyanates with carbodiimides have shown that the adducts formed from benzoyl isocyanates and N,N′-dicyclohexylcarbodiimide are the corresponding (4+2) cycloadducts, and not the (2+2) cycloadducts proposed by Neidlein. The reaction of isocyanates with N,N′-diphenylcarbodiimide at 0°C gave (2+2) cycloadducts, which were thermally isomerized into the corresponding (4+2) cycloadducts. Benzoyl isocyanates reacted with N-cyclohexyl-N′-phenylcarbodiimide to give (4+2) cycloadducts of isocyanates to the cyclohexyl-N=C bond in the carbodiimide. On treatment with neutral alumina, (4+2) cycloadducts were easily isomerized into 1,3,5-triazines. Thiobenzoyl isocyanate reacted with both the N=C bonds of the carbodiimide to afford two isomeric (4+2) cycloadducts. It has been found that benzoyl isocyanates reacted with N-phenyl-N′-o-tolylcarbodiimide to yield the corresponding (4+2) cycloadducts of isocyanates to the o-tolyl-N=C bond and/or the is...

Otohiko Tsuge

Papers

Horner–Emmons Olefination of 4-Hydroxy-2-oxoalkylphosphonates and Related Compounds: Applications to the Syntheses of (±)-Gingerol, (±)-Yashabushiketol, and (±)-Dihydroyashabushiketol

Michael addition of methyl 2-(trimethylsilyl)propenoate with organomagnesiums or organolithiums leading to 1:1 and/or 2:1 adducts and subsequent Peterson olefination by condensation with carbonyl compounds.

Studies of Acyl and Thioacyl Isocyanates. VIII. Cycloaddition Reactions of Benzoyl and Thiobenzoyl Isocyanates with Carbodiimides

Dipolar Cycloaddition Reaction of Benzoyl and Thiobenzoyl Isocyanates

Diene-transmissive hetero Diels-Alder reaction of 1,5-diphenyl-1,4-pentadien-3-one