Henok H. Kinfe

NaHSO4 supported on silica gel: an alternative catalyst for Ferrier rearrangement of glycals

NaHSO(4) supported on silica gel catalyses the Ferrier rearrangement reaction of 3,4,6-tri-O-acetyl-D-glucal with alcohols and thiols to give the corresponding 2,3-unsaturated glycosides in high anomeric selectivity and good to excellent yield in short reaction time.

Aluminium triflate catalysed O-glycosidation: temperature-switched selective Ferrier rearrangement or direct addition with alcohols

A temperature-controlled mechanism switch between the Al(OTf)(3)-catalysed direct addition of alcohols or the Ferrier rearrangement reactions in some glycals is presented. The scope and limitations are investigated as are the influence of the stereochemistry and nature of the protecting groups on the glycal substrate.

Stereoselective Synthesis of Thiochromenes via Intramolecular Tandem Thio-Michael Addition of in Situ Generated α,β-Unsaturated Aldehydes

An efficient and highly stereoselective strategy for the synthesis of 2,3-substituted thiochromenes having a complex and easily transformable group at the stereogenic center has been developed via a tandem thio-Michael addition reaction of an in situ generated α,β-unsaturated aldehyde sugar derivative. The protocol is superior to reported protocols in that the carbohydrate-derived substituent at the stereogenic center of the thiochromene is versatile and is amenable for further transformation.

Preparation and antimalarial activity of a novel class of carbohydrate-derived, fused thiochromans.

A novel class of fused thiochroman derivatives has been prepared by an efficient and versatile synthetic procedure involving nucleophilic displacement of the side-chain iodo substituent in 2-deoxy-2-C-iodomethyl glucosides by thiophenolate ions, and subsequent intramolecular C-glycoside formation. A range of aromatic substituents is tolerated, and the subsequent facile selective oxidation of the sulfur to the sulfoxide or sulfone level expands the range and molecular diversity of the series of compounds. A selection of the sulfoxide and sulfone derivatives bearing lipophilic substituents on the aromatic portion were found to have antimalarial activities in the low micromolar range.

Facile Diastereoselective Synthesis of Carbohydrate-Based Thiochromans

An efficient and novel diastereoselective thiochroman synthesis using the carbohydrate chiral pool via intramolecular Friedel-Crafts alkylation is presented. The scope and limitations of the method are investigated.

Aluminum Triflate Catalyzed Tandem Reactions of d-Galactal: Toward Chiral Benzopyrans, Chromenes, and Chromans

3,4,6-Tri-O-acetyl-D-galactal is selectively converted into 1-O-aryl-2-deoxy derivatives or chiral bridged benzopyrans under Al(OTf)3 catalysis, depending on reaction conditions. The benzopyrans react with Al(OTf)3/acetic anhydride in ring-opening reactions in the absence or presence of acetic acid to selectively produce chiral chromenes or chromans, respectively, in high yields.

Evaluation of the Influence of thiosemicarbazone–triazole hybrids on genes implicated in lipid oxidation and accumulation as potential anti-obesity agents

A series of thiosemicarbazone-triazole hybrids 1a-h are efficiently synthesised and evaluated for their influence on the expression of genes, cpt-1, acc-1 and pgc-1, which are essential in lipid metabolism. The test results show that hybrids 1c and 1g exhibited relatively high influence on the expression of cpt-1 and pgc-1 and suppression of acc-1 as desired.

Regiospecific synthesis of 2-halo-3-(2'-glucalyl)benzo[b]thiophenes.

A regiospecific synthetic strategy for the synthesis of 2-chloro-3-substituted benzo[b]thiophenes is developed via a dichlorocarbene insertion and sigmatropic rearrangement of an in situ generated ylide. The current protocol provides a reversed regiochemistry to the commonly employed electrophilic cyclization reaction for the synthesis of benzo[b]thiophenes and access to their hitherto under-represented chlorinated derivatives.

New Carbohydrate-Derived S,S-Dioxothiochroman Derivatives and Their Unexpected Easy Epimerization at the Anomeric Position

An efficient and stereoselective procedure is developed for high-yield preparation of novel S,S-dioxothiochroman carbohydrate derivatives 5a–e from their corresponding sulfone epimers 3a–e via anomeric epimerization in the presence of sodium hydride.

Novel bio-friendly and non-toxic thiocarbohydrate stabilizers of gold nanoparticles

Several bio-friendly carbohydrate disulfides and thiocarbohydrates have been synthesized via the reaction of D-(+)-gluconic acid δ-lactone with aminoalkylthiols, leading to n-gluconamidoalkyldisulfides {di-(2-gluconamidoethyl)disulfide (L1), di(3-gluconamidopropyl)-disulfide (L2), di(4-gluconamidobutyl) disulfide (L3) and (2-gluconamidoethyl)thiol (L4)}. Acetylation of hydroxy groups in L1–L3 and subsequent reduction produced the following disulfides and thiols: acetylated di(2-gluconamidoethyl)disulfide (L5), acetylated di(3-gluconamidopropyl)disulfide (L6), acetylated di(4-gluconamidobutyl)disulfide (L7), acetylated di(2-gluconamidoethyl)thiol (L8), acetylated di(3-gluconamidopropyl)thiol (L9) and acetylated di(4-gluconamidobutyl)thiol (L10). Compounds L1–L10 were characterized by combination of NMR and infrared spectroscopy, microanalysis, mass spectrometry and in a selected case X-ray crystallographic data. These thiocarbohydrate compounds were used to stabilize gold nanoparticles to gold glyconanoparticles (AuNPs) of sizes in the range of ca. 2–9 nm. The thiocrabohydrates are non-toxic toward both cancer and normal cell lines and have IC50 values generally ≥200 μM.