Francesca Cunsolo

Polycationic calix[8]arenes able to recognize and neutralize heparin

A mutual induced fit mechanism is responsible for the exceptional complexation performances exhibited by calix[8]arene polycations towards heparin. The recognition process was studied in comparison with two other heparin antagonists: protamine and polylysine. The arrangement of multiple functional groups on the flexible macrocyclic scaffold of calix[8]arene, with respect to the conformationally rigid protamine and low ordered polylysine, allowed a mutual adaptability between calixarene polycations and heparin, significantly enhancing the recognition performances. Fluorescence, NMR titration, and activated partial thromboplastin time (aPTT) experiments confirmed that these calixarene derivatives have a very high specificity and affinity towards heparin neutralization as in aqueous solution as in blood. Analogous results were obtained with low molecular weight heparin (LMWH) whose effect protamine is unable to completely reverse.

5,5′‐Bicalix[4]arene: The Bridgeless Prototype of Double Calix[4]arenes of the “Head‐to‐Head” Type

Two molecular bowls can be directly linked to give an open-and-shut capsule simply by heating p-H-calix[4]arene in CH3CN at reflux in the presence of FeCl3⋅6 H2O. Double calixarenes of this type could in principle be present as syn or anti conformers (shown schematically on the right). Whereas the anti form was observed in the solid state, there is presumably an equilibrium of the two forms in solution. The globular architecture of the syn conformation suggests the potential for cooperation between two cone binding sites in the endo-calix complexation of suitable guests.

Resolution of inherently chiral calix[4]arenes with AABB and CDCD substitution patterns on the upper and lower rims, respectively

Abstract Proximal di- tert -butylcalix[4]arene (5,11-di- tert -butylcalix[4]arene-25,26,27,28-tetrol) 1b , obtained by direct partial removal of tert- butyl groups from p-tert- butylcalix[4]arene, gave high yields of inherently chiral derivatives upon ‘symmetry breaking’ by syn -distal di- O -alkylation or di- O -acylation in the presence of K 2 CO 3 . The chirality of these compounds was proven by the splitting of 1 H NMR signals in the presence of Pirkles reagent and in some cases by HPLC enantiomeric resolution using chiral stationary phases and corroborated by mirror-image CD spectra.

Antimicrobial tetraprenyltoluquinol derivatives from Cystoseira spinosa var. Squarrosa

Abstract Six new tetraprenyltoluquinol derivatives have been isolated from the brown alga Cystoseira spinosa var. squarrosa and their structures determined by chemical and spectral methods. Three of these compounds possess antimicrobial activity against both gram-positive and gram-negative bacteria.

Balearone, a metabolite of the brown alga

Abstract The isolation of a new metabolite of mixed biogenesis, balearone 1 from the brown alga Cystoscira balearica is described. The structure was determined by an X-ray diffraction analysis.

Alkali cation ‘conformational templation’ in 1,5-bridged calix[8]arenes: a single crystal X-ray proof

Abstract X-Ray crystallography proves that alkali cations can act as conformational templates for 1,5-bridged calix[8]arenes 1 H 6 – 3 H 6 , folding their skeleton in a ‘tub-shaped’ conformation composed of four 3/4-cone clefts. This templation occurs even for neutral 1 H 6 to give a ( 1 H 6 Cs) + ·Cl − complex, where Cs + was found perfectly fitting inside the eight calix[8]arene oxygens cavity. Conventional ‘electrostatic’ coordination with O atoms occurs whereas cation-π interactions can be excluded.

Tetraprenyltoluquinols from the brown alga Cystoseira jabukae

Abstract The chloroform extract of the brown alga Cystoseira jabukae afforded two new tetraprenyltoluquinols and two tetraprenyltoluquinones. The structures were determined by spectral analysis and chemical correlations. The quinones are possibly artifacts formed by oxidation of the corresponding quinols in the isolation procedure.

Five novel tetraprenylhydroquinols from the brown alga Cystoseira algeriensis

Abstract Five novel metabolises of mixed biogenesis have been isolated from the brown alga Cystoseira algeriensis . They are tetraprenylhydroquinols and their structures have been determined by spectral analysis and chemical correlations.

Three-component supramolecular self-assembly based on a 5,5%-bicalix(4)arene exoditopic receptor

5,5′-Bicalix[4]arene 1 , a ditopic host possessing two divergent cavities, crystallizes from CH 2 Cl 2 and p -xylene to give an iterative assembly of a three-component zigzag array. This array is formed by CH-π inclusion of a linear CH 2 Cl 2 · p -xylene connector within the facing cavities of two molecules of 1 . Each zigzag array is perpendicularly interconnected to the lateral one through hydrophilic interactions of calixarene-OH groups.

On the Occurrence of the 1,3,5-trisubstitution Pattern In the O-alkylation of P-tert-butylcalix[6]arene

Abstract 1,3,5-Trisubstitution at the phenolic hydroxyls of p-tert-butylcalix[6]arene (1), previously obtained in sizeable yield only with MeI (Casnati et al. J. Chem. Soc., Chem. Commun. 1991, 1413), has been now achieved by direct O-alkylation with alkyl iodides (Et, n-Pr, n-Bu) and p-X-benzyl bromides, (X = tert-Bu, Me, Br, NO2) in the presence of a weak base (K2CO3 or CsF). These results suggest that 1,3,5-trisubstitution can also be extended to other alkylating agents provided that an appropriate weak base is used. The 1,3,5-tris(p-X-benzyl) ethers 6–9, whose structure have been established by 1H-NMR spectral analysis and chemical correlation, in CDCl3 solution adopt a conformation with only a 2-fold symmetry element bisecting two aromatic rings.