Pd-Catalyzed Picolinamide-Directed Late-Stage Chalcogenation of Tryptophan-Containing Peptides.

This report describes the Pd-catalyzed late-stage chalcogenation of tryptophan-containing peptides with disulfides/diselenides in moderate to good yields. It comprises broad substrate scope, functional group diversity, late-stage modification of drug molecules, and various valuable synthetic transformations, including room temperature easy removal of the picolinamide auxiliary, which could be applicable to tune the structure and function of peptides.

Rh-Catalyzed tandem C-C/C-N bond formation of quinoxalines with alkynes leading to heterocyclic ammonium salts.

An efficient Rh-catalyzed oxidative C-H activation/annulation of 2-arylquinoxalines with internal alkynes is described using Cu(OAc)2·H2O and AgBF4 to afford a diverse variety of substituted quarternary ammonium salts at room temperature. The mechanism of the protocol is established on the basis of isolation of the 5-membered rhodacycle intermediate and kinetic isotope studies. The mild reaction conditions, substrate scope and functional group diversity are the salient practical features.

Aerobic Metal-Free Dioxygenation of Alkenes with tert-Butyl Nitrite and N-Hydroxylamines.

Metal-free dioxygenation of alkenes with tert-butyl nitrite and N-hydroxylamines (N-hydroxyphthalimide, N-hydroxybenzotriazole, and N-hydroxysuccinimide) is described to produce ß-aminoxy nitrate esters using air as the oxidant. These organic nitrates can be readily converted into 1,2-diols and 1,2-diketone with broad substrate scope and functional group diversity.

Iron(III)-catalyzed aerobic dioxygenation of styrenes using N-hydroxyphthalimide and N-hydroxybenzotriazole.

Iron-catalyzed dioxygenation of alkenes in air using N-hydroxyphthalimide (NHPI) and N-hydroxybenzotriazole (HOBt) is described at room temperature. The products can be readily converted into 1,2-vicinal diols using PPh3 and Mo(CO)6. The use of Fe(NO3)3·9H2O as the catalyst, mild reaction conditions and the selectivity are the significant practical features. The radical scavenger experiment suggests that the reaction proceeds via a radical intermediate. The synthetic and mechanistic aspects have been presented.

Synthesis of Functionalized Pyrazoles via Vanadium-Catalyzed C-N Dehydrogenative Cross-Coupling and Fluorescence Switch-On Sensing of BSA Protein.

Vanadium-catalyzed C-N dehydrogenative cross-coupling of alkenyl hydrazones leading to functionalized pyrazoles is described in a 1:1 mixture of toluene/H2O using air as the terminal oxidant. Significant practical features include use of the commercial nontoxic VOSO4 as a recyclable catalyst, mild reaction conditions, scalability, and the broad substrate scope. Some of the product pyrazoles exhibit interesting photophysical properties. Fluorescence light-up sensing of BSA protein by one of the pyrazoles is also highlighted.

Iron(III)-Mediated Radical Nitration of Bisarylsulfonyl Hydrazones: Synthesis of Bisarylnitromethyl Sulfones.

Iron(III)-mediated radical nitration of bisarylsulfonyl hydrazones is described. In this protocol, the nontoxic and inexpensive Fe(NO3)3·9H2O plays a dual role as catalyst as well as nitro source. The mild conditions, broad substrate scope, and the functional group compatibility are the significant features. The reaction pathway has been demonstrated using DFT calculations, and the products can be subsequently converted into oximes using SnCl2·2H2O in high yields.

Copper(II)-catalyzed direct dioxygenation of alkenes with air and N-hydroxyphthalimide: synthesis of ß-keto-N-alkoxyphthalimides.

Copper(II)-catalyzed direct dioxygenation of alkenes using air and a simple N-hydroxyphthalimide leading to ß-keto-N-alkoxyphthalimides has been developed. The reaction system is mild, efficient, and effective at room temperature with broad substrate scope and substantial steric hindrance. The radical-trapping and (18)O-labeling experiments have been demonstrated.

Wavelength shifting oligonucleotide probe for the detection of adenosine of a target DNA with enhanced fluorescence signal.

The modulated photophysical property of strong electronically coupled naphthyl uridine linked via a single C-C bond was explored in DNA detection via wavelength shifting and enhanced fluorescence emission by a simple 'Just-Mix & Read' strategy of homogeneous DNA detection.

Triazolyl-donor-acceptor chromophore-decorated unnatural amino acids and peptides: FRET events in a ß-turn conformation.

The ß-turn conformation and FRET process were established in the designed tripeptide containing fluorescent triazolyl donor and acceptor-decorated unnatural amino acids separated by a natural alanine.