Synthesis of Aryl, Glycosyl, and Azido Septanosides through Ring Expansion of 1,2-Cyclopropanated Sugars

Abstract

A ring-expansion methodology for the preparation of aryl septanosides, arabinofuranosyl and glucopyranosyl septanoside disaccharides, and azido septanosides is reported. A cyclopropanated adduct of the oxyglycal upon reaction with phenols, sugars, and azide led to the formation of ring-expanded septanoside derivatives. The ring expansion was found to be stereoselective with sugars, whereas phenols and the azide afforded an anomeric mixture of the ring expanded product. It was observed further that the conversion of the intermediate diketones to the diols, using NaBH(4), occurred with high diastereoselectivities for the alpha-anomers of the septanosides. This report consolidates further the generality of the oxyglycal ring-expansion method to prepare septanosides, possessing different substituents at their reducing ends.

Synthesis of new enantiopure poly(hydroxy)aminooxepanes as building blocks for multivalent carbohydrate mimetics

“…One interesting option is the pathway via oxepines [15–18] and the subsequent dihydroxylation or direct reduction of their C=C double bond to give the corresponding oxepane derivatives [19–20]. Alternatively, oxepanes were also synthesized by the ring enlargement of their six-membered homologues [21–22]. Disappointingly, these methods often involve long reaction sequences and display sometimes restricted flexibility.…”

Display of Rich Reactivities of Endo‐ and Exocyclic Unsaturated Sugars that Parallel the Native Sugars

“…The disaccharides 23 and 24 possessed either a furanoside or a pyranoside as the reducing end moiety (Figure 1). [29] …”

“…Interestingly, phenyl septanosides 26 were secured as an α/β‐mixture. Further, whereas the α‐anomer of phenyl septanosides underwent diastereoselective reduction of the diketone intermediate, that in the β‐anomer afforded the alcohol functionality at C ‐3 as an epimeric mixture [29] …”

“…Steps of conversions on p ‐methoxybenzyl (PMB)‐protected lactose derivative 27 (Scheme 5), afforded the corresponding dihalocyclopropanated derivative 28 . Ring‐expansion with 6‐ O ‐unprotected methyl glucopyranoside 29 to halo‐oxepene 30 and further synthetic manipulations led to secure the trisaccharide 31 , in moderate to good yields at the individual steps of the reactions [29] …”

Analysis of the conformations of septanoside sugars

“…Subsequent oxidation and reduction reactions on the resulting oxepine afforded fully functionalized septanosides derivatives. Synthesis of methyl, alkyl, aryl, azidoseptanosides were thus prepared [37][38][39]. The methodology was extended to the synthesis of septanoside containing disaccharides and trisaccharides [40,41].…”