An efficient, inexpensive, and shelf-stable diazotransfer reagent: imidazole-1-sulfonyl azide hydrochloride

Synthesis of an Isotopically-labelled Antarctic Fish Antifreeze Glycoprotein Probe

Antifreeze glycoproteins (AFGPs) are glycosylated polypeptides produced by Antarctic and Arctic fishes, which allow them to survive in seawater at sub-zero temperatures. An investigation into the postulated enteric uptake of AFGP synthesized in the exocrine pancreas of Antarctic fishes required a custom-prepared AFGP probe that incorporated seven isotopically-labelled Ala residues for detection by mass spectrometry. The AFGPs are composed of a repetitive three amino acid unit (Ala-Ala-Thr), in which the threonine residue is glycosylated with the disaccharide β-d-Gal-(1→3)-α-d-GalNAc. The synthesis of isotopically-labelled AFGP8 (1), as well as the optimized synthesis of the protected glycosylated amino acid building block 2, is reported.

Photoaffinity labeling in activity-based protein profiling

Activity-based protein profiling has come to the fore in recent years as a powerful strategy for studying enzyme activities in their natural surroundings. Substrate analogs that bind covalently and irreversibly to an enzyme active site and that are equipped with an identification or affinity tag can be used to unearth new enzyme activities, to establish whether and at what subcellular location the enzymes are active, and to study the inhibitory effects of small compounds. A specific class of activity-based protein probes includes those that employ a photo-activatable group to create the covalent bond. Such probes are targeted to those enzymes that do not employ a catalytic nucleophile that is part of the polypeptide backbone. An overview of the various photo-activatable groups that are available to chemical biology researchers is presented, with a focus on their (photo)chemistry and their application in various research fields. A number of comparative studies are described in which the efficiency of various photo-activatable groups are compared.

Recent advances in transition metal-catalyzed N-atom transfer reactions of azides

Transition metal-catalyzed N-atom transfer reactions of azides provide efficient ways to construct new carbon-nitrogen and sulfur-nitrogen bonds. These reactions are inherently green: no additive besides catalyst is needed to form the nitrenoid reactive intermediate, and the by-product of the reaction is environmentally benign N(2) gas. As such, azides can be useful precursors for transition metal-catalyzed N-atom transfer to sulfides, olefins and C-H bonds. These methods offer competitive selectivities and comparable substrate scope as alternative processes to generate metal nitrenoids.

An improved route to PUGNAc and its galacto-configured congener

An efficient, scalable, and reliable synthesis of PUGNAc and its galacto-configured congener is reported.

Total synthesis of cyclosporine: access to N-methylated peptides via isonitrile coupling reactions

Recent developments in the use of isonitriles to furnish secondary and tertiary amide bond formations have been applied to a novel total synthesis of the important cyclic polypeptide cyclosporine A. Specifically, the disclosed synthetic route demonstrates the utility of microwave-mediated carboxylic acid isonitrile couplings, thioacid isonitrile couplings at ambient temperature, and isonitrile-mediated couplings of carboxylic acids and thioacids with amines to form challenging amide bonds.

Nitrene addition to exfoliated graphene: a one-step route to highly functionalized graphene

We demonstrate a high yield method of functionalizing graphene nanosheets through nitrene addition of azido-phenylalanine [Phe(N(3))] to exfoliated micro-crystalline graphite (microG). This method provides a direct route to highly functionalized graphene sheets. TEM analysis of the product shows few layer (n < 5) graphene sheets. The product was determined to have 1 phenylalanine substituent per 13 carbons.

Asymmetric total synthesis of the caspase-1 inhibitor (-)-berkeleyamide A

The asymmetric total synthesis of (-)-berkeleyamide A (1), a naturally occurring caspase-1 inhibitor, has been achieved by employing Evans' syn-aldol reaction of N-acyl-(4R)-benzyl oxazolidin-2-one 3 as the key step.

Polyamidoamine (PAMAM) dendrimer conjugates of "clickable" agonists of the A3 adenosine receptor and coactivation of the P2Y14 receptor by a tethered nucleotide

We previously synthesized a series of potent and selective A(3) adenosine receptor (AR) agonists (North-methanocarba nucleoside 5'-uronamides) containing dialkyne groups on extended adenine C2 substituents. We coupled the distal alkyne of a 2-octadiynyl nucleoside by Cu(I)-catalyzed "click" chemistry to azide-derivatized G4 (fourth-generation) PAMAM dendrimers to form triazoles. A(3)AR activation was preserved in these multivalent conjugates, which bound with apparent K(i) of 0.1-0.3 nM. They were substituted with nucleoside moieties, solely or in combination with water-solubilizing carboxylic acid groups derived from hexynoic acid. A comparison with various amide-linked dendrimers showed that triazole-linked conjugates displayed selectivity and enhanced A(3)AR affinity. We prepared a PAMAM dendrimer containing equiproportioned peripheral azido and amino groups for conjugation of multiple ligands. A bifunctional conjugate activated both A(3) and P2Y(14) receptors (via amide-linked uridine-5'-diphosphoglucuronic acid), with selectivity in comparison to other ARs and P2Y receptors. This is the first example of targeting two different GPCRs with the same dendrimer conjugate, which is intended for activation of heteromeric GPCR aggregates. Synergistic effects of activating multiple GPCRs with a single dendrimer conjugate might be useful in disease treatment.

A modular synthesis of alkynyl-phosphocholine headgroups for labeling sphingomyelin and phosphatidylcholine

A general route to phospho- and sphingolipids that incorporate an alkyne in the phosphocholine headgroup is described. The strategy preserves the ammonium functionality of the phosphocholine and can be easily modified to introduce desired functional groups at the N-acyl chain. The targets accessible with this strategy provide a bioorthogonal handle for postsynthetic introduction of fluorophores or other labeling agents with aqueous phase chemistry. We report the synthesis of sphingomyelin derivatives that incorporate a fluorophore and an alkyne. The modified sphingolipids retain activity as substrates for sphingomyelinase, making these compounds viable probes of enzymatic activity. Importantly, the strategy allows modification of the lipid across the phosphodiester, making the alkyne a potential probe of sphingomyelinase activity.

Synthesis of Self-assembling Cyclic Peptide-polymer Conjugates using Click Chemistry

Self-assembling cyclic peptide-polymer conjugates were prepared by ‘clicking’ polymers (prepared by RAFT polymerization) to an azide functionalized d-alt-l cyclic octapeptide via the Huisgen 1,3-dipolar cycloaddition reaction. Due to the high graft density, the efficiency of the click chemistry conjugation reaction was found to be highly dependent on the size of the polymer. At relatively low molecular weights, as many as four polymer chains could be grafted to each 8 residue cyclic peptide ring. Evidence for the self assembly of the conjugates into peptide-polymer nanotubes was observed by TEM and IR.

Synthetic mRNA splicing modulator compounds with in vivo antitumor activity

We report our progress on the development of new synthetic anticancer lead compounds that modulate the splicing of mRNA. We also report the synthesis and evaluation of new biologically active ester and carbamate analogues. Further, we describe initial animal studies demonstrating the antitumor efficacy of compound 5 in vivo. Additionally, we report the enantioselective and diastereospecific synthesis of a new 1,3-dioxane series of active analogues. We confirm that compound 5 inhibits the splicing of mRNA in cell-free nuclear extracts and in a cell-based dual-reporter mRNA splicing assay. In summary, we have developed totally synthetic novel spliceosome modulators as therapeutic lead compounds for a number of highly aggressive cancers. Future efforts will be directed toward the more complete optimization of these compounds as potential human therapeutics.

Enantioselective chemoenzymatic synthesis of trans-aziridines

A straightforward, five-step procedure for the synthesis of enantiomerically pure 2,3-disubstituted trans-aziridines has been developed starting from commercially available aldehydes. Hydroxynitrile lyase-mediated cyanohydrin formation provided cyanohydrins in excellent enantioselectivities and good yields. Subsequent formation of diastereomerically pure anti-amino alcohols via a one-pot Grignard addition-reduction sequence, Cu(II)-catalyzed diazotransfer, and triphenylphosphine-mediated reductive cyclization provided the corresponding trans-aziridines in good yields and excellent diastereoselectivities.

A novel click chitooligosaccharide for hydrophilic interaction liquid chromatography

A novel chitooligosaccharide stationary phase for hydrophilic interaction liquid chromatography (HILIC) was developed via click chemistry and showed great HILIC characteristics on separation of polar compounds and enrichment of glycopeptides.

Click azide-nitrile cycloaddition as a new ligation tool for the synthesis of tetrazole-tethered C-glycosyl alpha-amino acids

Glycoproteins play a key role in a multitude of biological events in living organisms. Hence, neoglycopeptides obtained from unnatural C-glycosyl alpha-amino acids can be used as synthetic probes in studies aiming at clarifying the role of the carbohydrate domain in glycoprotein biological activity. A new class of C-glycosyl alpha-amino acids featuring a nitrogenated heterocycle ring holding the carbohydrate and glycinyl moiety was designed in our laboratory. Having previously prepared isoxazole-, 1,2,3-triazole-, and pyridine-tethered compounds, the family has now been enlarged by a group of newcomers represented by tetrazole derivatives. Two sets of compounds have been prepared, one being constituted of C-galactosyl and C-ribosyl O-tetrazolyl serines while the other contains S-tetrazolyl cysteine derivatives. In both cases, the synthetic scheme involved a two-step route, the first one being the thermal cycloaddition of a sugar azide with p-toluensulfonyl cyanide (TsCN) to give a 1-substituted 5-sulfonyl tetrazole and the second the replacement of the tosyl group with a serine or cysteine residue. For the high efficiency and operational simplicity, the azide-TsCN cycloaddition appears to be a true click process. Finally, one of the amino acids prepared was incorporated into a tripeptide.

Design of triazole-tethered glycoclusters exhibiting three different spatial arrangements and comparative study of their affinities towards PA-IL and RCA 120 by using a dna-based glycoarray

Sugar-coated chips: Glycoside clusters are valuable tools for carbohydrate-lectin recognition studies. However, the spatial arrangement of the sugar residues is a key issue in the design of high-affinity glycoclusters. Here the affinities of linear and antenna- and calixarene-based galactoside clusters towards two lectins derived from Pseudomonas aeruginosa and Ricinus communis were compared by means of glycoarrays.Interactions between proteins and carbohydrates are involved in a large number of crucial biological events. Many efforts have been devoted to the design and synthesis of unnatural saccharides displaying high affinities towards targeted lectins. Among others, glycoside clusters have proven to be valuable tools for these recognition studies. However, the spatial arrangements of the sugar residues are a key issue in the design of high-affinity glycoclusters. Here, the affinities of linear and antenna- and calixarene-based galactoside clusters against two lectins, derived from Pseudomonas aeruginosa and Ricinus communis, have been compared by means of glycoarrays.

Imidazolylsulfonates: electrophilic partners in cross-coupling reactions

Aryl imidazolylsulfonates participate as electrophilic coupling partners in palladium-mediated cross-coupling reactions. The aryl imidazolylsulfonates display good stability while maintaining good reactivity in a variety of palladium-catalyzed coupling reactions. Imidazolylsulfonates are a practical and economic alternative to triflates.

Rh(2)(II)-catalyzed synthesis of carbazoles from biaryl azides

An array of carbazoles (23 examples) can be synthesized from substituted biaryl azides at 60 degrees C using substoichiometric quantities of Rh(2)(O(2)CC(3)F(7))(4) or Rh(2)(O(2)CC(7)H(15))(4).