An improved synthesis of guanosine TNA phosphoramidite for oligonucleotide synthesis.

The chemical synthesis of guanosine nucleosides generates both the N9 and N7 regioisomers, which require careful separation to obtain the desired N9 isomer. To preferentially obtain the N9 isomer, a bulky diphenylcarbamoyl (DPC) group can be installed at the O6 position of guanine. However, installation of the DPC group presents a challenging task due to low solubility of the N-acetyl protected guanine. Here we report the usage of commercially available 2-amino-6-chloro purine as a new strategy that offers a more efficient route to the synthesis of the guanine phosphoramidite of threose nucleic acid (TNA).

Increasing the functional density of threose nucleic acid.

Chemical strategies that augment genetic polymers with amino acid residues that are overrepresented on the paratope surface of an antibody offer a promising route for enhancing the binding properties of nucleic acid aptamers. Here, we describe the chemical synthesis of α-l-threofuranosyl cytidine nucleoside triphosphate (tCTP) carrying either a benzyl or phenylpropyl side chain at the pyrimidine C-5 position. Polymerase recognition studies indicate that both substrates are readily incorporated into a full-length α-l-threofuranosyl nucleic acid (TNA) product by extension of a DNA primer-template duplex with an engineered TNA polymerase. Similar primer extension reactions performed using nucleoside triphosphate mixtures containing both C-5 modified tCTP and C-5 modified tUTP substrates enable the production of doubly modified TNA strands for a panel of 20 chemotype combinations. Kinetic measurements reveal faster on-rates (kon) and tighter binding affinity constants (Kd) for engineered versions of TNA aptamers carrying chemotypes at both pyrimidine positions as compared to their singly modified counterparts. These findings expand the chemical space of evolvable non-natural genetic polymers by offering a path for improving the quality of biologically stable TNA aptamers for future clinical applications.

Photoinduced Enhanced Decomposition of TBHP: A Convenient and Greener Pathway for Aqueous Domino Synthesis of Quinazolinones and Quinoxalines.

Catalyst-free photoinduced processes in aqueous medium represent significant advancement toward development of green and sustainable pathways in organic synthesis. tert-Butyl hydroperoxide (TBHP) is a widely used oxidant in organic reactions, where the decomposition of TBHP into its radicals by metal catalysts or other reagents is a key factor for efficient catalytic outcome. Herein, we report a simple and environmentally friendly visible light-promoted synthetic pathway for the synthesis of N-heterocyclic moieties, such as quinazolinones and quinoxalines, in the presence of TBHP as an oxidizing agent in aqueous medium that requires no catalysts/photocatalysts. The enhanced rate of decomposition to generate free radicals from TBHP upon visible light irradiation is the driving force for the domino reaction.

One-Pot Magnetic Iron Oxide-Carbon Nanodot Composite-Catalyzed Cyclooxidative Aqueous Tandem Synthesis of Quinazolinones in the Presence of tert-Butyl Hydroperoxide.

The development of synthetic protocols for biologically important molecules using biocompatible catalysts in aqueous medium holds the key in green and sustainable chemistry. Herein, a magnetically recoverable iron oxide-carbon dot nanocomposite has been demonstrated as an effective catalyst for cyclooxidative tandem synthesis of quinazolinones in aqueous medium using alcohols as starting materials. Fluorescent carbon dots, the newest entrant in the nanocarbon family, were used as the stabilizing agent for the iron oxide nanoparticles, and a continuous layer of carbon dots decorates the iron oxide nanoparticle surface as observed by transmission electron microscopy. The fluorescence studies demonstrated the effective electron transfer from carbon dots to the iron oxide nanoparticles resulting in complete quenching of emission owing to carbon dots, once it binds with iron oxide nanoparticles. The nanocatalyst showed high activity with significant reusability for the syntheses of quinazolinones in the presence of tert-butyl hydroperoxide (TBHP) in an aqueous medium. Controlled experiments revealed the synergistic effect of carbon dots in enhancing the catalytic activity of iron oxide, as they might influence the decomposition of TBHP into radicals owing to their peroxidase activity. These radicals stabilized over the nanoparticle surface are known to have increased lifetime compared to solution-based radicals. These surface-stabilized radicals then could catalyze the tandem reaction resulting in the formation of the quinazolinone derivatives in high yields.

Probing Carbocatalytic Activity of Carbon Nanodots for the Synthesis of Biologically Active Dihydro/Spiro/Glyco Quinazolinones and Aza-Michael Adducts.

Herein, we report the fluorescent carbon dots as an effective and recyclable carbocatalyst for the generation of carbon-heteroatom bond leading to quinazolinone derivatives and aza-Michael adducts under mild reaction conditions. The results establish this nanoscale form of carbon as an alternative carbocatalyst for important acid catalyzed organic transformations. The mild surface acidity of carbon dots imparted by -COOH functionality could effectively catalyze the formation of synthetically challenging spiro/glycoquinazolinones under the present reaction conditions.

Carbon dot reduced palladium nanoparticles as active catalysts for carbon-carbon bond formation.

Carbon dots were used as a reducing agent for the synthesis of Pd nanoparticles coated with ultrathin carbon dot shells of ca. 4 nm. The resulting composite nanoparticles showed high catalytic activity for the Heck and Suzuki coupling reactions.