Streamlined Synthesis of Per-O-acetylated Sugars, Glycosyl Iodides, or Thioglycosides from Unprotected Reducing Sugars¹

Abstract

Solvent-free per-O-acetylation of sugars with stoichiometric acetic anhydride and catalytic iodine proceeds in high yield (90-99%) to give exclusively pyranose products as anomeric mixtures. Without workup, subsequent anomeric substitution employing iodine in the presence of hexamethyldisilane (i.e., TMS-I generated in situ) gives the corresponding glycosyl iodides in 75-95% isolated yield. Alternatively, and without workup, further treatment with dimethyl disulfide or thiol (ethanethiol or thiocresol) gives anomerically pure thioglycosides in more than 75% overall yield.

Sisal cellulose acetates obtained from heterogeneous reactions

“…Figure 1 illustrates the mechanism proposed for cellulose acetylation, using iodine as catalyst. The reaction is supported by the fact that iodine shows great efficiency in catalyzing the esterification of primary and secondary alcohols, as recently demonstrated [13,14]. This catalyst is resistant to humidity, with no adverse environmental impact and can be recycled.…”

Synthesis of Oligosaccharides Related to a Biodynamic Saponin from Calamus Insignis as Their Propargyl Glycosides

“…The trisaccharide acceptor 12 required no modifications. For the disaccharide part, the known p-methoxyphenyl 2,3-O-isopropylidene-α--rhamnopyranoside (15) [25] was glycosylated with the known thioglucoside 16 [26] to afford the disaccharide 17 in 86 % yield. In order to convert disaccharide 17 into a donor for the pentasaccharide formation, the oxidative removal of the p-methoxyphenyl group was necessary.…”

Synthesis of a tetra- and a trisaccharide related to an anti-tumor saponin “Julibroside J28” from Albizia julibrissin

“…Orthoesterification of the diol 6 with trimethyl orthoacetate and 10-camphorsulfonic acid in dry acetonitrile followed by rearrangement of the orthoester by aqueous work-up with 1N HCl afforded the disaccharide acceptor 7 in 86% yield. N-iodosuccinimide and H 2 SO 4 -silica promoted glycosylation of the disaccharide acceptor 7 with known p-tolyl 2,3,4,6-tetra-O-acetyl-1-thio-β-D-glucopyranoside (8) [16] furnished the trisaccharide (9) in 91% yield. The next challenge was to convert the p-methoxyphenyl trisaccharide to an activated donor for the final coupling.…”