Toward fluorinated aminoglycosides: Structural studies of phenylhydrazine condensation with carbohydrate derivatives

The reaction of phenylhydrazine with a sugar dialdehyde in water, as a key step for the synthesis of the 3-amino-3-deoxy-d-glucose moiety contained in kanamycin, has been revisited. Structural studies (IR and NMR as well as a simple theoretical model based on energy-minimization calculations and MD calculations) reported herein support the observed stereo- and regioselectivity. Efforts to improve the reproducibility and viability of the process as part of a convenient approach towards fluorinated kanamycin are also now presented.Agencia Española de Cooperación Internacional para el Desarrollo A/023577/09 A/030422/10Junta de Andalucía FQM 142 P09-AGR-459

A novel approach to the synthesis of N-substituted 1-C-aminomethyl glycofuranosides

Reductive amination of formyl C-glycofuranosides, easily available from hexose-derived equatorial-2-OH-glycopyranosides by DAST-promoted ring contraction, afforded N-substituted 1-C-aminomethyl glycofuranosides in most cases in high yield.European Commission, Directorate General for Science and Development FP6-508430Junta de Andalucía FQM14

Easy Access to Configurationally Controlled C-Glycofuranoside-Based Building Blocks by Means of Formyl C-Glycofuranosides

A general approach to enantiopure C-glycofuranoside-based hybridα/β-amino acids and nitrones, among other valuable building blocks, has been established via formyl C-glycofuranosides, easily available from hexose-derived equatorial-2-OH-glycopyranosides by DAST-promoted ring contraction. © Georg Thieme Verlag Stuttgart New York.European Commission. Directorate General for Science and Development FP6-508430Junta de Andalucía FQM14

Chitosan Induces Plant Hormones and Defenses in Tomato Root Exudates

In this work, we use electrophysiological and metabolomic tools to determine the role of chitosan as plant defense elicitor in soil for preventing or manage root pests and diseases sustainably. Root exudates include a wide variety of molecules that plants and root microbiota use to communicate in the rhizosphere. Tomato plants were treated with chitosan. Root exudates from tomato plants were analyzed at 3, 10, 20, and 30 days after planting (dap). We found, using high performance liquid chromatography (HPLC) and excitation emission matrix (EEM) fluorescence, that chitosan induces plant hormones, lipid signaling and defense compounds in tomato root exudates, including phenolics. High doses of chitosan induce membrane depolarization and affect membrane integrity. 1H-NMR showed the dynamic of exudation, detecting the largest number of signals in 20 dap root exudates. Root exudates from plants irrigated with chitosan inhibit ca. twofold growth kinetics of the tomato root parasitic fungus Fusarium oxysporum f. sp. radicis-lycopersici. and reduced ca. 1.5-fold egg hatching of the root-knot nematode Meloidogyne javanica.This work was supported by AGL 2015 66833-R Grant from the Spanish Ministry of Economy and Competitiveness and H2020 MUSA 727624 European Project

Efficient two-step multifunctionalization of substituted 2-Hydro-xyglycopyranosides

A straightforward route to diversely functionalized glycopyranosides is reported. 2,3-Enopyranosides, 2- and/or 3-azido-, 2-halopyranosides, and a hex-3-ulose, among other α- and β-glycopyranosides are easily obtained in good to excellent yields from 2-hydroxyglycopyranosides by means of a two-step process involving trifluoromethanesulfonation and subsequent treatment with the appropriate nucleophilic agent

Synthesis of hyperpolarizable biomaterials at molecular level based on pyridinium-chitosan complexes

Potential NLO-phore materials based on chitosan are described for the first time in this study. A series of fluorescent and quaternized pyridinium– chitosan derivatives have been synthesized by reaction of this polymer with easily available tunable pyrylium tetra fluoroborate salts. Among other spectroscopic techniques, 19 F NMR, 13 C CPMAS NMR and 2D diffusion experiments, were used to con firm the structures of the new pyridinium– chitosan complexes that show high fluorescence intensity. Degrees of N -substitution were achieved lower than 4.3%, allowing the original physicochemical properties of the biopolymer to be preserved. DFT calculations have been performed to investigate the molecular features related to the NLO properties in these compounds. NLO behavior was found to be clearly dependent on the nature and location of the substituent into the pyridinium core. Theoretical data reveal a large permanent dipolar moment, polarizabilities and hyperpolarizabilities making these molecules promising candidates as supramolecular devices exhibiting NLO properties with potentially enhanced solvatochromic properties.Agencia Española de Cooperación Internacional para el Desarrollo A/023577/09, A/030422/10Junta de Andalucía FQM 142, P09-AGR-459

Preparation of chitosan-supported urea materials and their application in some organocatalytic procedures

An efficient and mild procedure was developed for the preparation of three chitosan-supported ureas containing electron-withdrawing groups. These catalysts were characterized and employed as organocatalysts in different transformations, including the enantioselective cyanosilylation of α-ketoesters and aldehydes, the asymmetric addition of formaldehyde tert-butyl hydrazone to prochiral α-ketoesters and a Friedel-Crafts reaction. Several parameters that can affect the activity and selectivity of the reactions were analysed. The supported catalysts can be reused for more than 10 cycles with only a small loss in their properties. Finally, theoretical DFT calculations were carried out to interpret the results of the catalysed reactions.Peer Reviewe

Efficient synthesis of 2,6,7,8-tetrahydroxyindolizidines (castanospermine analogues) via the dipolar cycloadditions of N-benzyl-C-(tetrofuranos-4-yl)nitrones to methyl acrylate

19 páginas, 4 figuras, 2 tablas, 4 esquemas.The dipolar cycloaddition of (Z)-N-benzyl-(3-O-benzyl-1,2-O-isopropylidene-α-d-ribofuranos-5-ylidene)amine N-oxide to methyl acrylate gives a 53:16:26:5 diastereomeric mixture of isoxazolidine derivatives. The dipolar cycloaddition of the xylo analogue to methyl acrylate is more diastereoselective, producing a 44:13:43 mixture of only three diastereomers. The ribo-configured adducts have been converted (4 steps only) into the new (2R,6S,7S,8R,8aR)-, (2S,6S,7S,8R,8aR)-, (2S,6S,7S,8R,8aS)- and (2R,6S,7S,8R,8aS)-2,6,7,8-tetrahydroxyindolizidines. Similarly, the two xylo-configured major isoxazolidine derivatives were converted into the known derivatives (2R,6S,7R,8R,8aS)- and (2S,6S,7R,8R,8aR)-2,6,7,8-tetrahydroxyindolizidines. The six isomeric indolizidine derivatives obtained have been evaluated for their inhibiting activities towards 15 glycosidases. Only the (2R,6S,7S,8R,8aR)-configured isomer is a selective inhibitor of amyloglucosidases from Aspergillus niger (IC50 = 350 μM) and from Rhizopus mold (IC50 = 90 μM, Ki = 195 μM, non-competitive), the other indolizidines show very little inhibitory activity at 1 mM concentration.We thank the ‘Dirección General de Investigación, Ministerio de Ciencia y Tecnología’ of Spain (Grant No. BQU2000-1155), the ‘Dirección General de Universidades e Investigación, Consejería de Educación y Ciencia’ of Andalusia (FQM 142) and the Swiss Federal Science Foundation for financial support. We also thank Miss Catherine Schuetz for her technical assistance.Peer reviewe