Solid-phase Synthesis of Oligosaccharides Using Novel Alkyne-type Linkers: Selection of Reactive Sites on the Support by Sonogashira Reaction

Abstract

Two new alkyne-type linkers having alkynylmethyloxy moieties were elaborated for solid-phase synthesis of oligosaccharides. A propargyl glycoside-type linker between a sugar residue and a solid support was formed by the Sonogashira reaction of a propargyl glycoside with polymer-supported iodobenzene. A propargyl ester-type linker was also constructed by the same reaction of a 4-(proparygyloxycarbonyl)benzyl glycoside with the latter. Both linkers are stable against acids such as TFA but can be readily cleaved with this acid after conversion to the corresponding alkyne-cobalt complex by treatment with Co 2 (CO) 8 . The latter ester linker is generally advantageous in that mild cleavage liberates a product as its carboxybenzyl glycoside which is readily purified. The Sonogashira reaction was found to proceed only at spatially reactive sites on the solid support where the reagent accesses readily, so that the subsequent reactions including glycosylation on solid phase proceeded smoothly to result in high total yields of the desired oligosaccharides.