Centro Risonanze Magnetiche CERM

Sesto Fiorentino, Italy

Centro Risonanze Magnetiche CERM

Sesto Fiorentino, Italy

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Arda A.,CSIC - Biological Research Center | Vnturi C.,CSIC - Biological Research Center | Nativi C.,University of Florence | Nativi C.,Centro Risonanze Magnetiche CERM | And 5 more authors.
Chemistry - A European Journal | Year: 2010

The prototype of a new family of chiral receptors based on a tripodal scaffold and featuring pyrrolic binding arms containing the trans-1,2- diaminocyclohexane motif, was reported. A cage endowed with a somewhat enlarged cavity was designed, in the belief that fine-tuning of the cage size would lead to a significantly improved affinity even in more polar media. Reaction of the trialdehyde 4 with the mono-BOC-protected diamine 2, followed by reduction of the resulting Schiff base and subsequent deprotection of the amino groups, yielded the tripodal hexaamine 5, which was condensed with pyrrole-2,5- dicarbaldehyde under the conditions used for preparing the bicyclic receptor 1. A preliminary screening indicated that, while Glc, Gal, and GlcNAc were moderately bound, strong recognition occurred with mannosides. βMannose was also extracted in benzene, though to a lesser extent (10%), and αMannose could not be detected.


Arda A.,CSIC - Biological Research Center | Canada F.J.,CSIC - Biological Research Center | Nativi C.,University of Florence | Nativi C.,Centro Risonanze Magnetiche CERM | And 5 more authors.
Chemistry - A European Journal | Year: 2011

The structural features of a representative set of five complexes of octyl α- and β-mannosides with some members of a new generation of chiral tripodal diaminopyrrolic receptors, namely, (R)-5 and (S)- and (R)-7, have been investigated in solution and in the solid state by a combined X-ray, NMR spectroscopy, and molecular modeling approach. In the solid state, the binding arms of the free receptors 7 delimit a cleft in which two solvent molecules are hydrogen bonded to the pyrrolic groups and to the benzenic scaffold. In a polar solvent (CD3CN), chemical shift and intermolecular NOE data, assisted by molecular modeling calculations, ascertained the binding modes of the interaction between the receptor and the glycoside for these complexes. Although a single binding mode was found to adequately describe the complex of the acyclic receptor 5 with the α-mannoside, for the complexes of the cyclic receptors 7 two different binding modes were required to simultaneously fit all the experimental data. In all cases, extensive binding through hydrogen bonding and CH-π interactions is responsible for the affinities measured in the same solvent. Furthermore, the binding modes closely account for the recognition preferences observed toward the anomeric glycosides and for the peculiar enantiodiscrimination properties exhibited by the chiral receptors. Binding modes: The binding modes of the interaction between α- and β-mannosides and chiral diaminopyrrolic tripodal receptors, elucidated by combined X-ray, NMR spectroscopy, and molecular modeling calculations, account for the affinities and the enantioselectivity features measured in a polar solvent. Extensive hydrogen bonding and CH-π interactions are the driving force for recognition, in which docking of the mannosyl into the cleft of the receptor occurs with the β face anchored on the benzenic scaffold through the H-4 proton (see graphic). Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Nativi C.,University of Florence | Nativi C.,Centro Risonanze Magnetiche CERM | Francesconi O.,University of Florence | Gabrielli G.,University of Florence | And 2 more authors.
Chemistry - A European Journal | Year: 2011

A new generation of chiral tripodal receptors for recognition of carbohydrates, featuring trans-1,2-diaminocyclohexane as a key structural element, and their recognition properties toward a set of glycosides of biologically relevant monosaccharides is described. The introduction of a chelating diamino unit into the pyrrolic tripodal architecture markedly enhanced their binding abilities compared with the parent aminopyrrolic receptors previously reported by our group. In addition, the chirality of the structure had a clear impact on affinities, as well as on selectivities, displaying high enantiodiscrimination levels. These second-generation diaminopyrrolic tripodal receptors are highly selective for mannose among other monosaccharides, with two members of the family being selective for the α and the β anomers respectively. The measured affinities in acetonitrile, 83μM of (S)-7 for the β mannoside and 127μM of (R)-5 for the α mannoside, make them the most effective synthetic receptors for mannosides reported to date. The affinity assessment required a further evolution of the ${BC{{0\hfill \atop 50\hfill}}}$ parameter, a previously developed binding descriptor, which in its ultimate formulation has now been extended to include, with no restrictions, complexes of any stoichiometry, and can thus be generally employed to rank affinity data from heterogeneous systems on a common scale. Highly receptive: A family of second-generation aminopyrrolic tripodal receptors, featuring a chiral diamine as a key structural element, represents a substantial step forward in the design of biomimetic receptors for carbohydrates (see scheme). The new family is selective for mannose, displays high enantiodiscrimination, and features two members showing the best recognition properties reported to date for α- and β-mannosides, respectively. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Francesconi O.,University of Florence | Gentili M.,University of Florence | Nativi C.,University of Florence | Nativi C.,Centro Risonanze Magnetiche CERM | And 4 more authors.
Chemistry - A European Journal | Year: 2014

A set of structures designed for the recognition of glucosides has been obtained by systematically destructuring a tripodal aminopyrrolic cage receptor that selectively recognizes octyl-β-D-glucopyranoside (OctβGlc). NMR spectroscopy and isothermal titration calorimetry binding measurements showed that cleavage of one pillar of the cage was beneficial to the binding properties of the receptor, as long as two residual amino groups of the cleaved pillar were present. Removal of these two residual amino groups produced a dramatic loss of affinity for OctβGlc of the resulting monocyclic analogue of the parent cage receptor. A significant improvement in the binding ability was achieved by replacing one pillar with two aminopyrrolic hydrogen-bonding arms, despite the loss of a preorganized structure. In contrast to the cage receptor, recognition of OctβGlc was observed, even in a competitive medium (30% DMF in chloroform). Structural studies in solution, carried out through NMR spectroscopy and molecular modeling calculations, led to the elucidation of the 3D binding modes of the side-armed monocyclic receptors; this highlighted the key role of the amino groups and demonstrated the occurrence of a rotaxane-like complex, which featured the octyl chain of the glucoside threaded through the macrocyclic ring. Comfort is paramount! A set of structures designed for the recognition of glucosides has been obtained by systematically destructuring a tripodal aminopyrrolic cage receptor. A β-glucoside is more effectively recognized by an adaptive cleft than by a preorganized cage, if a more comfortable fit can be achieved (see picture). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Cacciarini M.,CNR Methodological Chemistry Institute | Nativi C.,CNR Methodological Chemistry Institute | Nativi C.,Centro Risonanze Magnetiche CERM | Norcini M.,CNR Methodological Chemistry Institute | And 3 more authors.
Organic and Biomolecular Chemistry | Year: 2011

The contribution from several H-bonding groups and the impact of geometric requirements on the binding ability of benzene-based tripodal receptors toward carbohydrates have been investigated by measuring the affinity of a set of structures toward octyl β-d-glucopyranoside, selected as a representative monosaccharide. The results reported in the present study demonstrate that a judicious choice of correct geometry and appropriate functional groups is critical to achieve the complementary hydrogen bonding interactions required for an effective carbohydrate recognition. © 2011 The Royal Society of Chemistry.

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