A new route to 2-substituted perimidines based on nitrile oxide chemistry

A new route to perimidines has been developed which involves reaction of a nitrile oxide with 1,8-diaminonaphthalene. Benzonitrile oxide, generated by dehydrochlorination of benzohydroximoyl chloride, and 1,8-diaminonaphthalene afforded 2-phenylperimidine. 2-Pyranosylperimidines were prepared by the same approach from pyranosyl hydroximoyl chlorides.     

"Click chemistry"en route to pseudo-starch

Rapid assembly of starch fragment analogues was achieved using "click chemistry". Specifically, two hexadecasaccharide mimics containing two parallel maltoheptaosyl chains linked via [1,2,3]-triazoles to a maltose core were synthesized using Cu(i)-catalyzed [3 + 2] dipolar cycloaddition of azido saccharides and 6,6'- and 4',6'-dipropargylated p-methoxyphenyl maltoside.     

Convenient route to water-sensitive sol-gel precursors using click chemistry

The CuAAC-'click' reaction under anhydrous conditions is reported as a new tool for the preparation of moisture-sensitive triethoxysilyl compounds that are obtained in 5 minutes in excellent yield with simple purification.     

Selective functionalization of a genetically encoded alkene-containing protein via "photoclick chemistry" in bacterial cells

We report a tetrazole-based, photoclick chemistry that can be employed to selectively functionalize an alkene genetically encoded in a protein inside E. coli cells. The reaction involved the treatment of E. coli cells with cell-permeable tetrazoles followed by a brief photo irradiation at 302 nm (4 min) and an overnight incubation at 4 degrees C. This in vivo alkene functionalization procedure was simple, straightforward, and nontoxic to E. coli cells. Additionally, fluorescent adducts were formed, facilitating the monitoring of the reaction in vivo. This reaction should offer a new tool for the study of alkene-containing proteins in living systems.     

A fast and parallel route to cyclic isothioureas and guanidines with use of microwave-assisted chemistry

A fast and simple approach to novel cyclic isothioureas and related guanidine derivatives is presented in this study. The construction of the central basic scaffolds is achieved solely by the application of microwave-assisted chemistry, without any need of activating agents or protecting group manipulations. The product formation of various substituted guanidines from the corresponding isothiouronium salts was controlled by the nucleophilicity of the counterion and influenced by the reaction temperature. Further, a new fast-track access to tetrahydropyrimidin-2-ylamines was developed.     

En route to erucalexin: a unique rearrangement in the crucifer phytoalexin biosynthetic pathway

The first biosynthetic studies revealing that both 1-methoxybrassinin and sinalbin B are close precursors of the phytoalexins erucalexin and 1-methoxyspirobrassinin.     

Structure and noncanonical chemistry of nonribosomal peptide biosynthetic machinery

Covering up to January 2012Structural biology has provided significant insights into the complex chemistry and macromolecular organization of nonribosomal peptide synthetases. In addition, novel pathways are continually described, expanding the knowledge of known biosynthetic chemistry.     

A synthetic approach to kingianin A based on biosynthetic speculation

A synthetic approach towards the structurally complex dimer, kingianin A is reported. The strategy involved a cascade of complexity generating reactions, inspired through biosynthetic speculation. A concise protecting group free synthesis of the proposed monomeric precursor pre-kingianin A has been achieved using a tandem Stille cross-coupling reaction and electrocyclisation process. However, preliminary studies of the key dimerisation reaction have been conducted, which indicate that the process is not spontaneous, raising questions as to the origin of this complex natural product.     

Modification of polysaccharides via thiol‐ene chemistry: A versatile route to functional biomaterials

We present herein a mild and rapid method for the modular functionalization of polysaccharides. Several ene‐functional charged and neutral polysaccharides, that is, hyaluronic acid and dextran, were prepared by esterification of the hydroxyl groups with pentenoic anhydride. The modified polysaccharides were then reacted with six model mercaptans under UV light, leading to linear polymers modified with hydrophobic groups, peptides, or oligosaccharides as well as chemical hydrogels. The thiol‐ene coupling reactions were found to proceed with high efficiency in short reaction times and with nearly no degradation of the polysaccharide backbone. Moreover, they were carried out in aqueous media, without the use of any metal catalysts, enhancing the attractive nature of this process. Notably, we investigated whether it is feasible to prepare cell‐responsive hydrogels by sequential bioconjugation and cross‐linking of the polysaccharide backbone with a bioactive peptide and poly(ethylene glycol)‐dithiol, respectively. All together, these results highlight the potential of this coupling strategy for the modular functionalization of polysaccharides under click chemistry‐like conditions. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Surface organometallic chemistry on metals: a novel and effective route to custom-designed bimetallic catalysts

The synthesis, characterization and catalytic properties of new materials obtained by reaction of organometallic complexes of groups IIb, IVa, and VIa with the surface of metallic particles are reviewed. Two types of materials may be obtained by surface organometallic chemistry on metals: metal particles covered with organometallic fragments, and bimetallic particles of predetermined composition. Characterization of the organometallic fragments on the metal particles has demonstrated their thermal stability. These particles covered with surface organometallic fragments are new catalytic materials, highly selective in several reactions such as the hydrogenation of α,β-unsaturated aldehydes, ethyl pyruvate, nitrobenzene, acrylonitrile, and olefins. The bimetallic particles without organometallic fragments are also highly active and selective for a variety of reactions such as hydrogenolysis of various alkanes and hydrogenolysis of esters. For these systems, the concept of “site isolation” has been advanced to account for the high selectivity of the reactions.     

An entry route into non-aqueous plutonyl coordination chemistry

The Pu(VI) molecular complex, [PuO(2)Cl(2)(thf)(2)]2, is prepared by addition of a HCl/Et(2)O solution to a suspension of PuO(2)CO(3) in thf, yielding the first example of a precursor suitable for investigation of the non-aqueous chemistry of the plutonyl dioxo cation under inert atmospheric conditions.     

Colorful Friedel-Crafts chemistry of meso-tetraarylporphyrins. An unexpected route to porphyrinic spiro dimers

Under Friedel-Crafts conditions, meso-tetraarylporphyrins give porphyrin spiro dimers in good yield. This reaction involves acylation, acid-catalyzed cyclization, and dimerization. A stable dimer possessing three additional six-membered rings could be isolated and its structure determined. By modifying the substrate and reagents, intermediates could be isolated and characterized. The reactivity of the substrates, the side-reactions, and the concentration requirements to form the dimers, all explain why this reaction remained apparently unexplored in the widely used meso-tetraarylporphyrin series. [reaction: see text]     

A cyclotrimerization route to cannabinoids

Three members of the cannabinoid class, cannabinol, cannabinol methyl ether, and cannabinodiol, were synthesized using a microwave-mediated [2 + 2 + 2] cyclotrimerization reaction as the key step. This approach provides a high level of synthetic flexibility allowing for the facile synthesis of cannabinoid analogues.