Selective synthesis of curdlan ω-carboxyamides by Staudinger ylide nucleophilic ring-opening

Regioselective and controlled-density branching in amylose esters

Herein, we report creation of methodology for one-pot synthesis of 2,3-O-acetyl-6-bromo-6-deoxy (2,3Ac-6Br) amylose with controlled degree of substitution of bromide (DS(Br)) followed by quantitative azide substitution as a route to branched polysaccharide derivatives. This methodology affords complete control of "tine" location, and strong control of degree of branching of comb-structured polymers. In this way, we achieved bromination strictly at C6 and esterification at the other hydroxy groups, where the DS(Br) at C6 was well-controlled by bromination/acylation conditions in the one-pot process. Azide displacement of all C6 bromides followed by copper-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction with the small molecule tert-butyl propargyl ether (TBPE) demonstrated the potential to create such branched structures. This synthetic method has broad potential to generate well-defined polysaccharide-based comb-like structures, with a degree of structural control that is very unusual in polysaccharide chemistry.

S-protected thiolated cyclodextrins as mucoadhesive oligomers for drug delivery

AIM

The purpose of this study was to develop a novel mucoadhesive thiolated and S-protected gamma cyclodextrin (γ-CD) with an intact ring backbone to assure a prolonged residence time at specific target sites.

METHOD

Thiolated γ-CD was generated through bromine substitution of its hydroxyl groups followed by replacement to thiol groups using thiourea. In the second step, thiol groups were protected by disulfide bond formation with 2-mercaptonicotinic acid (2-MNA).

RESULT

Thiolated γ-CD displayed 1385 ± 84 µmol thiol groups per gram of oligomer and the amount of MNA determined in the S-protected oligomer was 1153 ± 41 µmol per gram of oligomer. In-vitro screening of mucoadhesive properties of thiolated and S-protected γ-CD was done by two methods. Rheological investigation revealed the conjugates non-mucolytic with only a slight increase in viscosity of thiolated and S-protected γ-CD as compared to unmodified γ-CD, whereas mucoadhesive properties of the new thiolated and S-protected γ-CD performed on freshly excised porcine intestinal mucosa showed 44.4- and 50.9-fold improvement in mucoadhesion, respectively. The new conjugates did not show any cytotoxicity to Caco-2 cells even at a concentration of 1% (m/v) for 24 h. In addition, in-vitro studies of α-amylase degradation of γ-CD, γ-CD-SH and γ-CD-SS-MNA confirmed that all conjugates are biodegradable.

CONCLUSION

These outcomes predict that these new conjugates of γ-CD might provide a new favorable tool for drug delivery providing a prolonged residence time on mucosal surfaces.