Bruno Perly

Conformer populations of L-iduronic acid residues in glycosaminoglycan sequences

The 1H-n.m.r. 3J values for the L-iduronic acid (IdoA) residues for solutions in D2O of natural and synthetic oligosaccharides that represent the biologically important sequences of dermatan sulfate, heparan sulfate, and heparin have been rationalized by force-field calculations. The relative proportions of the low-energy conformers 1C4, 2S0, and 4C1 vary widely as a function of sequence and of pattern of sulfation. When IdoA or IdoA-2-sulfate units are present inside saccharide sequences, only 1C4 and 2S0 conformations contribute significantly to the equilibrium. This equilibrium is displaced towards the 2S0 form when IdoA-2-sulfate is preceded by a 3-O-sulfated amino sugar residue, and towards the 1C4 form when it is a non-reducing terminal. For terminal non-sulfated IdoA, the 4C1 form also contributes to the equilibrium. N.O.e. data confirm these conclusions. Possible biological implications of the conformational flexibility and the counter-ion induced changes in conformer populations are discussed.

Conformation of the pentasaccharide corresponding to the binding site of heparin for antithrombin III.

The conformation in solution of the pentasaccharide methyl glycoside (As-G-A*-Is-AM; 1), which represents the binding site of heparin for Antithrombin III, has been investigated using molecular mechanics and 1H-n.m.r. spectroscopy. The pentasaccharide has a rather rigid (As-G-A*) and a more flexible (Is-AM) region. A simplified model of 1, comprising two conformations, corresponding to the 1C4 and the 2S0 forms of the iduronate residue, and modified at the G-A* glycosidic linkage with respect to the energy minimum, reproduces most of the observed 3J values and n.O.e. enhancements. The possible role in the binding to Antithrombin III of a low-energy conformer, not observed in solution, is discussed.

Self-assemblies of amphiphilic cyclodextrins

Cyclodextrins are natural cyclic oligosaccharides widely used as “molecular cages” in the pharmaceutical, agrochemical, food and cosmetical industries. The optimization of their pharmacological properties has led to the synthesis of numerous analogues. Amphiphilic derivatives were designed to improve the cell targeting of the drug-containing cyclodextrin cavities through their transportation in the organism, within self-assembling systems. Amphiphilic cyclodextrins can self-assemble into water-soluble aggregates such as mono or polydisperse micelles, or insert in lipid membranes and liposomes. Polysubstituted amphiphilic cyclodextrins are briefly reviewed, and monosubstituted derivatives of native and methylated β-cyclodextrins are presented in more details, with an emphasis on their self-organization within lipid membranes.

Synthesis of a new molecular carrier: N-(Leu-enkephalin)yl 6-amido-6-deoxy-cyclomaltoheptaose

Abstract The synthesis of N-(Leu-enkephalin)yl 6-amido-6-deoxy-cyclomaltoheptaose has been performed in high yield. The final derivative has been characterized by proton NMR in terms of chemical and inclusion properties and represents a new class of target-directed transporters.

Cholesteryl-cyclodextrins: synthesis and insertion into phospholipid membranes

Abstract 6 I -(Cholest-5-en-3β-yloxycarbonyl)amino-6 I -deoxycyclomaltoheptaose and 6 I -(cholest-5-en-3α-ylamido)succinylamido-6 I -deoxycyclomaltoheptaose were synthesized and fully characterized by NMR spectroscopy experiments and mass spectrometry analysis. Incorporation of these monosubstituted amphiphilic cyclodextrins into phospholipid bilayers was investigated using small-angle X-ray scattering, differential scanning calorimetry and 31 P nuclear magnetic resonance. Different modes of incorporation depending on the spacer length between the cyclodextrin and cholesterol moieties were observed.

NMR investigations of the conformation of new cyclodextrin-based amphiphilic transporters for hydrophobic drugs: molecular lollipops

Abstract Amphiphilic compounds, obtained by grafting aliphatic acids onto a modified cyclodextrin, have been synthesized and studied by solution NMR. The large chain-length dependence of the NMR spectra in aqueous media is explained by the possible formation of auto-inclusion complexes. This process has been evidenced by extensive NMR experiments and by competition with potential guests. This new class of molecules (“lollipops”) provides important information for the optimization of a design for amphiphilic transporters to be included in organized phases such as micelles or liposomes.

Intramolecular host-guest complexes of D- and L-mono-6-phenylalanyl-amino-6-deoxy cyclomalto-heptaoses

Abstract Coupling of L- and D-phenylalanine to mono 6-amino-β-cyclodextrin leads to the formation of diastereoisomeric intramolecular inclusion compounds. The proton NMR spectra of the two products show clear chiral discrimination between the two molecules with regard to the interaction of the aromatic moieties with the cyclodextrin cavity.

Novel Glycolipids Based on Cyclodextrins

Novel amphiphilic cyclodextrins have been prepared by grafting a phospholipid on a modified cyclodextrin through a spacing arm to combine the selectivity in size of cyclodextrins and the transport properties of phospholipids. Synthesis and full characterization by NMR and mass spectrometry have been performed. The aggregation process in water has been characterized by light scattering, DSC and 31P NMR. This compound appears to assemble into large objects and displays a very low CMC. The detergent properties of the phospholipidyl-cyclodextrins have been evaluated.

An approach to vectorisation of pharmacologically active molecules: The covalent binding of leu-enkephalin to a modified β- cyclodextrin.

Abstract The neurotropic peptide Leu-enkephalin has been coupled to a mono-6-amino permethyl βcyclodextrin at the C-terminal residue. The resulting compound has been fully characterized by proton NMR in D 2 O and d6-DMSO evidencing complete reduction of the molecular symmetry of the cyclodextrin.

Inclusion and solubilization properties of 6-S-glycosyl-6-thio derivatives of β-cyclodextrin

The synthesis and physico-chemical properties of branched β-cyclodextrins substituted by one or seven thioglycoside units at the primary hydroxy side are described. The solubilities in water of these compounds are strongly increased compared with the parent β-cyclodextrin although large differences are found between α- and β-anomers, the former exhibiting the larger solubility. The inclusion capacity of these derivatives has been investigated using NMR spectroscopy as the major analytical technique for various host–guest pairs. The apparent discrepancies between the intrinsic solubilities of these host molecules and their ability to solubilize hydrophobic hosts can be explained from geometrical considerations derived from detailed NMR studies. The respective roles of the side of inclusion, of steric effects and of stabilizing interactions are evidenced and allow an a priori selection of the optimal host derivative for a given guest molecule.