A new synthetic route to 1,2‐pyran‐annulated O‐glycosides (pyranopyrans) with β‐manno configuration is presented. Starting from a benzyl‐protected allyl β‐2‐uloside obtained by C2‐oxidation from the corresponding allyl glucoside, vinylation and ring‐closing metathesis provided a bicyclic alkene as a key substrate. Optimized reaction conditions involving the 2‐uloside were required to circumvent the formation of the unwanted 3,2‐enolone. Subsequent stereoselective alkene dihydroxylations were investigated and are presented. Diastereoselective catalytic osmoylation afforded the bicyclic β‐mannoside with syn‐diol configuration. In contrast, a sequence featuring a directed vanadium‐catalyzed alkene epoxidation and epoxide opening provided the corresponding 2,10‐dioxadecalin target compound with trans‐diol configuration. X‐ray crystallography was employed to study the molecular structure of the target compound with syn‐diol configuration. In addition, the molecular packing and hydrogen‐bonding interactions of the hydroxy‐rich molecule were examined.

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Abstract:Benzyl 3,4,6-tri-O-benzyl-β-D-arabino-hexos-2-ulo-1,5-pyranoside was subjected to mannoselective ketone alkynylation with propiolaldehyde dibenzyl acetal, resulting in the formation of a 2-C-alkynyl β-mannoside bearing a γ-dibenzyl acetal functionality. Subsequent transacetalization of the acetal moiety with methanol and 1,3-dihydroxypropane and acetylation of position 2, respectively, gave 4 different 2-C-alkynyl branched mannosides. Lindlar hydrogenation of the latter under optimized conditions in dimethylformamide afforded a series of 2-C-cis-alkenyl mannosides. X-ray molecular structures of benzyl 3,4,6-tri-O-benzyl-β-D-arabino-hexos-2-ulo-1,5-pyranoside and of the branched glycoside benzyl 3,4,6-tri-O-benzyl-2-C-((Z)-3,3-dibenzyloxyprop-1-en-1-yl)-β-Dmannopyranoside are reported.

Incidence rates in this southern Poland city are comparable to those reported previously for Poland. Early case fatality decreased, compared to previous data, probably as a result of improved management of acute stroke and hospitalizing all stroke patients.

The synthesis of three 4‐C‐formyl branched octoses with variable stereoconfiguration at the C‐2 and C‐3 stereogenic centers is described. This class of compounds is of interest due to potential structural analogies to the naturally occurring bradyrhizose monosaccharide. Branched key sugar intermediates of the synthesis are 2‐C‐(1,2,3‐trihydroxyprop‐1‐yl)‐β‐d‐mannosides. A new mild oxidation protocol using known TEMPO/trichloroisocyanuric acid in ethyl acetate/toluene, buffered with 3‐(N‐morpholino)propanesulfonic acid, is described as a valuable reaction for selective primary alcohol oxidation and, hence, the formation of 2‐(spirofuranose)pyranoses. Upon global deprotection these spirofuranoses give complex mixtures of diverse hemiacetal forms of the liberated 4‐C‐formyl octoses. As revealed by detailed NMR studies, the bradyrhizose‐type annulated forms do not represent the major isomers. For each of the target octoses, these potential neighboured acetal‐hemiacetal‐forms (9,7‐pyranose‐1,9‐pyranoses) seem to be unfavorable, and instead remote bis(hemiacetals) are formed (1,5‐pyranose‐9,7‐pyranoses or 1,4‐furanose‐9,7‐pyranoses) as the major species.