Abstract
Two methods are described for the regioselective displacement
of the primary hydroxy group in methyl glycosides with iodide. The
first method is a modification of a literature procedure employing
triphenylphosphine and iodine, where purification has been carried
out on a reverse phase column in order to efficiently separate the
desired iodoglycosides from triphenylphosphine oxide. The second
method employs a new procedure using sulfonylation in pyridine with
sterically hindered 2,4,6-trichloro- and 2,4,6-tribromobenzenesulfonyl
chloride. The sulfonates thus formed are effective leaving groups
and substitution with iodide can be carried out in a one-pot process.
Protection of the iodoglycosides is also described either by benzylation
with benzyl trichloroacetimidate or silylation with triethylsilyl
chloride.
Key words
carbohydrates - halogenation - regioselectivity - substitution - sulfonates
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