1H and 13C NMR spectra of cyclic trimers,tetramers and pentamers derived from p-substituted phenylacetylenes

The ¹H and ¹³C spectra of p-substituted 1,3,5-triarylbenzenes, 7- and p-substituted 1,3,9-triaryl-9-methyl-fluorenes and 2-, 10- and p-substituted 6,12,13a-triaryl-12-methylbenzo(6,7)cycloheptadieno[1,2,3-jk]fluorenes have been examined. p-Substituents were methoxy, methyl and fluorine groups. The ¹H spectra were recorded at 300 MHz and permitted assignments for the aromatic protons by selective proton decouplings. Partial assignment of the carbon atoms in the ¹³C spectra was also possible.     

Lipase-catalysed one-pot synthesis of thiazole-based Betti bases and their evaluation as potential cholinesterase inhibitors

Research on Chemical Intermediates - A series of 1-[aryl-(thiazol-2-ylamino)-methyl]-naphthalen-2-ol derivatives were synthesized using porcine pancreatic lipase as a catalyst. The major assets of...     

Magnesium ferrichromate nanoparticles: an efficient and recyclable catalyst in the synthesis of pyrano[2,3-c]pyrazole derivatives

Research on Chemical Intermediates - Magnetically separable magnesium ferrichromate nanoparticles (MgFeCrO4 NPs) were synthesized by aqueous combustion synthesis (ACS) using glycine as the fuel....     

Solid-state NMR evidence for a protonation switch in the binding pocket of the H1 receptor upon binding of the agonist histamine

G protein coupled receptors (GPCRs) represent a major superfamily of transmembrane receptor proteins that are crucial in cellular signaling and are major pharmacological targets. While the activity of GPCRs can be modulated by agonist binding, the mechanisms that link agonist binding to G protein coupling are poorly understood. Here we present a method to accurately examine the activity of ligands in their bound state, even at low affinity, by solid-state NMR dipolar correlation spectroscopy and confront this method with the human H1 receptor. The analysis reveals two different charge states of the bound agonist, dicationic with a charged imidazole ring and monocationic with a neutral imidazole ring, with the same overall conformation. The combination of charge difference and pronounced heterogeneity agrees with converging evidence that the active and inactive states of the GPCR represent a dynamic equilibrium of substates and that proton transfer between agonist and protein side chains can shift this equilibrium by stabilizing the active receptor population relative to the inactive one. In fact, the data suggest a global functional analogy between H1 receptor activation and the meta I/meta II charge/discharge equilibrium in rhodopsin (GPCR). This corroborates current ideas on unifying principles in GPCR structure and function.     

Thin-layer chromatography of aluminium: quantitative densitometric determination of Fe2+, Ni2+, Cu2+, and Si4+

Thin-layer chromatography in combination with scanning densitometry is used as a tool for the quantitative determination of some impurity and additive elements in aluminium. Microgram levels of iron, silicon, copper, nickel, titanium, magnesium, manganese, and zinc present in a high concentration aluminium matrix is detected, and selective separations of some of these elements are achieved on silica gel H layers developed with a mobile phase containing aqueous sodium chloride solution. The quantitative determination of iron, silicon, nickel, and copper are obtained from the densitometric evaluation of chromatograms and are compared with the respective optical emission spectral analytical data.     

Multiutility sophorolipids as nanoparticle capping agents: synthesis of stable and water dispersible Co nanoparticles

Sophorolipids are a class of glycolipids that can be obtained from fatty acids by simply treating them with yeast cells (Candida bombicola, ATCC 22214) and glucose. In this letter, we demonstrate the application of sophorolipids obtained from oleic acid as a capping agent for Co nanoparticles. Upon capping the nanoparticle surface, the sugar moiety of these sophorolipids is exposed to the solvent environment, making the nanoparticles stable and water-redispersible.     

Additional minor diterpene glycosides from Stevia rebaudiana

From the commercial extract of the leaves of Stevia rebaudiana, two additional new diterpenoid glycosides were isolated and their structures were characterized as 13-[(2-O-beta-glucopyranosyl-3-O-beta-D-xylopyranosyl-beta-D-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid beta-D-glucopyranosyl ester (1) and 13-[(2-O-beta-D-xylopyranosyl-beta-D-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid beta-D-glucopyranosyl ester (2) on the basis of extensive spectral data (NMR and MS) and chemical studies.     

A [Pd]-mediated ω-alkynone cycloisomerization approach for the central tetrahydropyran unit and the synthesis of C(31)-C(48) fragment of aflastatin A

A concise assembly of the central tetrahydropyran unit of aflastatin A featuring a Pd-mediated alkynone cycloisomerization to provide a glycal and its subsequent stereoselective hydroboration to deliver the requisite stereochemistry at C(33) and C(34) centers is documented.     

Synthesis of sugar-derived spiroaminals via lactamization and metathesis reactions

A series of sugar-derived spiroaminals has been synthesized by utilizing cross metathesis, ring closing metathesis and lactamization reactions as key steps from 1-C-alkylated glycosyl azides and important correlations in the spectral data between spiroaminals and their respective anomers are reported.