The first total synthesis of norlignan glucoside sinenside A has been accomplished. An intramolecular acetalization reaction has been employed as the key skeletal construct to forge the central cyclic disaccharide core. The trans-1,2-diol configuration present in the cyclic disaccharide of this natural product is unique and has been addressed by setting this configuration at the beginning. A 1,2-orthoester group has been selected as a handle for both sp glycosidation and for differentiation of the C2'-OH (that participates in the key acetalization reaction) of the sugar unit.
Synthesis of symmetric difucopyranose dianhydrides
By activation of methyl 3,4-O-isopropylidene-1-methyl thio-β-L-fucopyranoside (1) with copper bromide–tetrabutylammonium bromide, bis(3,4-O-isopropylidene-α-L->fucopyranose)-1,2′∶1′,2->dianhydride (2) with almost> C2-symmetry was obtained. Starting with the monosaccharide precursors 3 and 4 a corresponding activation led to the disaccharide derivative 5 which in turn was converted into the mixed D,L-dianhydride 7 employing an intramolecular imidate glycosylation.