Synthesis of per-glycosylated β-cyclodextrins having enhanced lectin binding affinity

A cyclomaltooligosaccharide containing seven alpha-(1-->4)-D-glucopyranosyl units (beta-cyclodextrins) was transformed into heptakis 6-deoxy-6-iodo (13) and heptakis 6-amino-6-deoxy (25) derivatives using known procedures. Compound 13 was peracetylated and condensed in one pot with the known peracetylated pseudothiouronium salts of beta-D-glucopyranose (4), B-D-galactopyranose (5), or beta-D-N-acetylglucopyranosylsamine (6) or with alpha-D-1-deoxy-1-thiomannopyranose (8) using cesium carbonate in dimethylformamide, Alternatively, peracetylated 4-aminophenyl-alpha-D-mannopyranoside (9) was transformed into either extended pseudothiouronium 11 following N-chloroacetylation and nucleophilic substitution by thiourea or into 4-isothiocyanatophenyl alpha-D-mannopyranoside 12 using thiophosgene. Each of the four thiolated sugar derivatives 4-6 or 8 were also coupled to heptakis chloroacetamido beta-CD 26 obtained from heptakis amine 25 after N-chloroacetylation. Further incorporation of a hexamethylenediamine spacer arm onto heptakis iodo beta-CD 13 using thiol derived from mono-Boc derivative 36 and coupling to isothiocyanate 12 after suitable deprotection afforded permannosylated derivative 38. Zemplen de-O-acetylation of all beta-CD derivatives provided water-soluble persubstituted compounds containing D-glucopyranosides (18, 30), D-galactopyranosides (19, 31), D-N-acetylglucosaminides (20, 32), and D-mannopyranosides (22, 24, 34, 39), respectively The compounds were then evaluated for their relative binding properties toward natural carbohydrate binding plant lectins using both microtiter plate competitive inhibition experiments, double sandwich assays using horseradish peroxidase labeled lectins and by turbidimetric assays. The plant lectins from Pisum sativum (pea), Arachis hypogea (peanut), Canavalia ensiformis (Concanavalin A), and Triticum vulgaris (WGA, wheat germ agglutinin) were used for beta-D-glucose, beta-D-galactose, alpha-D-mannose, and beta-D-N-acetylglucosamine, respectively. All persubstituted beta-CDs showed good to excellent inhibitory properties together with abilities to cross-link their analogous plant lectins. The capacity of perglycosylated beta-CDs to anchor both microtiter plate-coated lectins and their corresponding peroxidase-labeled derivatives further confirmed the usefulness of these multivalent neoglycoconjugates in bioanalytical assays.