A Click Ligation Based on SuFEx for the Metal-Free Synthesis of Sugar and Iminosugar Clusters
Résumé
Although the preparation of anomeric glycosyl-sulfonyl fluoride was unsuccessful, a tetra-O-acetylatedC-gluc-osylpropanesulfonyl fluoride was synthesized starting from thecorresponding thioacetate via sulfonate formation as the keyintermediate. This sulfonyl fluoride was a bench-stable productthat reacted promptly with primary and secondary alkylaminesat 80 °C to give the corresponding sulfonamides in good yield.On the other hand, the same fluoridewas inert toward aryl-amines whereas its precursor, the sulfonyl chloride, showedgood reactivity. Another limitation of the acetylated sugar sulf-onyl fluoride was its lack of reactivity with a multivalentaminated calixarene, this being due to acetyl transfer from thecarbohydrate moiety to the aminogroups of the scaffold. Fortu-nately, the tetra-O-benzylatedC-glucosylpropanesulfonyl fluor-ide, prepared by the same reaction sequence employed for the synthesis of the acetylated analogue, reacted with the tetra-aminopropyl-calix[4]arene to afford the corresponding sulfon-amide-linked sugar cluster in high isolated yield. A similar ap-proach to the synthesis of calixarene-based iminosugar clusterswas unsuccessful because 1-deoxynojirimycin sulfonyl fluoridederivatives could not be generated. However, a tetra-propyl-sulfonyl fluoride calixarene, obtained from the free-OH calix-[4]arene through a three-step reaction sequence, underwentclean coupling with bothC-glucosylpropylamine andN-amino-pentyl-1-deoxy-deoxynojirimycin derivatives to give the corre-sponding tetravalent sugarand iminosugar clusters. This metal-free click reaction may constitute a valuable tool in the arsenalof ligation tools for the synthesis of multivalent carbohydratearchitectures