Divalent triazole‐linked carbohydrate mimetics: Synthesis by click chemistry and evaluation as selectin ligands

Starting from an enantiopure 3‐amino‐substituted pyran derivative, the synthesis of a series of divalent 1,2,3‐triazole‐linked carbohydrate mimetics is described. The preparation of the required 3‐azido‐substituted pyran proceeds smoothly by copper‐catalyzed diazo transfer. Using different conditions for the Huisgen‐Meldal‐Sharpless cycloaddition, this azide reacts with several diynes to furnish the desired divalent carbohydrate mimetics bearing rigid or flexible linker units. The in situ generation of the 3‐azidopyran in the presence of Cu/C as catalyst followed by the reaction with the alkyne allows a direct one‐pot transformation from the 3‐aminopyran to the desired click products. We also examined the Sakai‐Westermann method that transfers primary amines with the aid of α,α‐dichlorotosylhydrazones into 1,2,3‐triazoles. These copper‐free click conditions were applied for the first time to the preparation of a divalent compound. The O‐sulfation of the carbohydrate mimetics was achieved using the SO3‐DMF complex under careful 1H‐NMR control. Five polysulfated compounds could be obtained in pure form and these were tested by surface plasmon resonance spectroscopy as inhibitors of L‐selectin giving IC50 values between 45 nm and 50 µm

Ammonium Pertechnetate in Mixtures of Trifluoromethanesulfonic Acid and Trifluoromethanesulfonic Anhydride

Ammonium pertechnetate reacts in mixtures of trifluoromethanesulfonic anhydride and trifluoromethanesulfonic acid under final formation of ammonium pentakis(trifluoromethanesulfonato)oxidotechnetate(V), (NH$_{4}$)$_{2}$ [TcO(OTf) $_{5}$]. The reaction proceeds only at exact concentrations and under the exclusion of air and moisture via pertechnetyl trifluoromethanesulfonate, [TcO$_{3}$(OTf)], and intermediate Tc$^{VI}$ species. $^{99}$Tc nuclear magnetic resonance (NMR) has been used to study the Tc$^{VII}$ compound and electron paramagnetic resonance (EPR), $^{99}$Tc NMR and X-ray absorption near-edge structure (XANES) experiments indicate the presence of the reduced technetium species. In moist air, (NH$_{4}$)2[TcO(OTf)5] slowly hydrolyses under formation of the tetrameric oxidotechnetate(V) (NH$_{4}$)$_{4}$ [{TcO(TcO$_{4}$)$_{4}$}$_{4}$] ⋅10 H$_{2}$O. Single-crystal X-ray crystallography was used to determine the solid-state structures. Additionally, UV/Vis absorption and IR spectra as well as quantum chemical calculations confirm the identity of the species

Breslow intermediates (aminoenols) and their keto tautomers: first gas‐phase characterization by IR ion spectroscopy

Breslow intermediates (BIs) are the crucial nucleophilic amino enol intermediates formed from electrophilic aldehydes in the course of N‐heterocyclic carbene (NHC) catalyzed Umpolung reactions. Both in organocatalytic and enzymatic Umpolung, the question whether the Breslow intermediate exists as the nucleophilic enol, or in the form of its electrophilic keto‐tautomer, is of utmost importance for its reactivity and function. We herein report the preparation of charge‐tagged Breslow intermediates/keto tautomers derived from three different types of NHCs (imidazolidin‐2‐ylidenes, 1,2,4‐triazolin‐5‐ylidenes, thiazolin‐2‐ylidenes) and aldehydes. An ammonium charge‐tag is introduced by either the aldehyde unit or the NHC. ESI‐MS IR‐Ion spectroscopy allowed for the unambiguous conclusion that in the gas‐phase, the imidazolidin‐2‐ylidene derived BI indeed exists as a diamino enol, while both 1,2,4‐triazolin‐5‐ylidenes and thiazolin‐2‐ylidenes give the keto‐tautomer. This result coincides with the tautomeric states observed for the BIs in solution (NMR) and in the crystalline state (XRD), and is in line with our earlier calculations on the energetics of BI keto‐enol equilibria

Grasshopper - A Universal Agent Platform Based On Omg Masif And Fipa Standards

This paper provides an overview of the Grasshopper Agent platform

Redetermination of the solvent-free crystal structure of L-proline

The title compound, (S)-pyrrolidine-2-carboxylic acid (C5H9NO2), commonly known as l-proline, crystallized without the inclusion of any solvent or water molecules through the slow diffusion of diethyl ether into a saturated solution of l-proline in ethanol. l-Proline crystallized in its zwitterionic form and the molecules are linked via N-H center dot center dot center dot O hydrogen bonds, resulting in a two-dimensional network. In comparison to the only other publication of a single-crystal structure of l-proline without inclusions [Kayushina & Vainshtein (1965). Kristallografiya, 10, 833-844], the R-1 value is significantly improved (0.039 versus 0.169) and thus, our data provides higher precision structural information