The reaction of 5-O-tert-butyldimethylsilyl-1,2-O-isopropylidene-beta-L-ido-hexodialdodifuranose, prepared from D-glucofuranurono-6,3-lactone in four highly efficient steps, with the Grignard reagent generated from 2-(2-bromoethyl)-1,3-dioxolane gave a protected nonodialdose which was transformed into a tetrahydroxyquinolizidine essentially isosteric and homologous with castanospermine.