Synthesis of the Immunodominant Trisaccharide Related to the Antigen From E. COLI O 126

The trisaccharide derivative methyl 2-O-[4,6-di-O-acetyl-3-O-(2,3,4,6-tetra-O-benzyl-α-D-gal-actopyranosyl)-2-deoxy-2-phthalimido-β-D-gluco-pyranosyl]-4,6-O-benzylidene-β-D-mannopyranoside (12) was obtained when 3-O-(2,3,4,6-tetra-O-benzyl-α-D-galactopyranosyl)-4,6-di-Oacetyl-2-deoxy-2-phtha-limido-β-D-glucopyranosyl trichloroacetimidate (8) was allowed to react with methyl 3-O-benzyl-4,6-O-benzylidene-β-D-mannopyranoside (11) in presence of trimethylsilyl triflate. Removal of protecting groups then gave the desired trisaccharide.     

Conformational Slippage Determines Rotational Frequency in Five‐Component Nanorotors

Several five‐component nanorotors ROT‐3 that rotate at different rates were prepared by adding phenanthrolines of distinct lateral size as brake blocks to the four‐component nanorotor ROT‐2. The brake blocks interfere with the 180° rotor causing the rotational frequency to drop from 97 kHz to 5 kHz. The effect of the rotating brake blocks on the rotational frequency in ROT‐3 is accurately predicted by a nanomechanical model called “conformational slippage”. For quantification, the interaction of the brake blocks with the trajectory of the main rotator is gauged based on the number of interfering vs. non‐interfering conformations as computed by PM6.     

Synthesis of ether-linked oligoribo- and xylonucleosides from 3,5'-ether-linked pseudosaccharides

First examples of di- and trinucleosides with ribose and xylose stereochemistry having internucleoside ether linkage were synthesized from 3,5'-ether-linked pseudosaccharides. The synthetic protocol involved removal of 1,2-isopropylidene protecting groups from the pseudosaccharides followed by acetylation and a subsequent Vorbruggen transglycosylation with uracil and N-benzoylaminopurine. The synthetic strategy is potentially important for the development of RNA analogues with internucleoside ether linkage.     

Iron catalyzed CN bond formation

Diversely functionalized nitrogen-containing heteroaromatic building blocks, fine chemicals and active pharmaceutical or agrochemical ingredients are conveniently prepared via CN bond formation as the key step. Since beginning of the last decade, there has been a flurry of intense research in forging CN bonds using iron catalysts due to their low cost, high natural abundance and non-toxic nature. The present review offers an overview of CN bond forming reactions involving aryl, allyl, propargyl and unactivated alkyl electrophilic substrates with nitrogen nucleophiles via the regular cross coupling reactions catalyzed by iron. In the miscellaneous section, a set of novel transformations facilitated by iron are included as well.     

Synthesis of novel twisted carbazole-quinoxaline derivatives with 1,3,5-benzene core: bipolar molecules as hosts for phosphorescent OLEDs

A series of carbazole/quinoxaline hybrids have been synthesized by classic Ullmann and Pd/Cu-catalyzed Sonogashira coupling reaction. Their photophysical, thermal, and electrochemical properties were investigated. The introduction of electron rich carbazole and electron deficient quinoxaline on to the 1,3,5-benzene center leads to a twisted structure with good glass forming property and imparts a bipolar character. The triplet energies in the range of 2.34-2.53 eV indicate them as potential host materials in phosphorescent OLEDs.     

Synthesis of 2,3,5,6-tetrasubstituted tetrahydropyrans via (3,5)-oxonium-ene reaction

An efficient method for the synthesis of 2,3,5,6-tetrasubstituted tetrahydropyrans has been developed from the reaction of aldehydes and ethyl 2-(1-hydroxyalkyl/hydroxy(phenyl)methyl)-5-methylhex-4-enoate using (3,5)-oxonium-ene reaction promoted by boron trifluoride etherate in good yields under mild conditions.     

Recent advances in transition-metal-free carbon-carbon and carbon-heteroatom bond-forming reactions using arynes

This tutorial review is aimed at highlighting recent developments in transition-metal-free carbon-carbon and carbon-heteroatom bond-forming reactions utilizing a versatile class of reactive intermediates, viz., arynes, which hold the potential for numerous applications in organic synthesis. Key to the success of the resurgence of interest in the rich chemistry of arynes is primarily the mild condition for their generation by the fluoride-induced 1,2-elimination of 2-(trimethylsilyl)aryl triflates. Consequently, arynes have been employed for the construction of multisubstituted arenes with structural diversity and complexity. The versatile transition-metal-free applications of arynes include cycloaddition reactions, insertion reactions and multicomponent reactions. In addition, arynes have found applications in natural product synthesis. Herein, we present a concise account of the major developments that occurred in this field during the past eight years.     

Stereoselective synthesis of sugar-based β-lactam derivatives: docking studies and its biological evaluation

Highly diastereoselective synthesis of cis-β-lactams via [2+2] cycloaddition reactions of sugar-imine derivative possessing free hydroxyl groups at C-2 and C-3 positions and ketenes is described. exo-Approach of sugar-imine with ketene leads to the stereoselective formation of cis product and it is facilitated by hydrogen bonding interaction of C2–OH with carbonyl group of ketene. Docking studies show that these derivatives are having greater affinity towards PBP and it has been validated by in vivo studies. Among the different sugar-based azetidine-2-ones, compounds 6a and 6d were superior in activity to the commercial antibiotic tetracycline.     

Efficient synthesis of γ-keto sulfones by NHC-catalyzed intermolecular Stetter reaction

The N-heterocyclic carbene-catalyzed intermolecular Stetter reaction of aldehydes with α,β-unsaturated sulfones allows the atom-economic and selective formation of γ-keto sulfones in good yields. Key to the success of this unique transition-metal-free carbon-carbon bond-forming reaction is the right choice of the NHC precursor and base. The reaction tolerates a broad range of different aldehydes.