Abstract
This thesis is concerned with the syntheses of bleomycin-disaccharide and alginate oligosaccharides that both contain the rare L-gulopyranosyl sugars as basic components. 1,6-Anhydro-□-L-idopyranose 60, obtained from diacetone □-D-glucose 54 in three steps in 51% overall yield, was converted to the 1,6-anhydro-□-L-gulopyranosyl sugar 75 (72%) via one-pot O2-triflation and O3,O4-dibenzoylation followed by nucleophilic substitution with NaNO2 at C2. Consecutive O2,O4-dibenzoylation and O3-carbonylation of commercially available 1,6-anhydro-□-D-mannopyranose 73 provided the ester 77 (48%), which underwent acetolysis, anomeric deacetylation, and imidation to yield the corresponding imidate 80 (61%) in three steps. Coupling of 80 with 75 in the presence of TMSOTf led to the disaccharide 81 (82%), which was subjected to acetolysis followed by nucleophilic displacement with ammonia to afford the bleomycin-disaccharide moiety 83 in 57% yield. For the synthesis of alginate oligosaccharides, a four-stepped conversion of vitamin C via hydrogenation, isopropylidenation, DIBAL reduction, and acidic hydrolysis gave 1,6-anhydro-□-L-gulopyranose 88 in 56% overall yield, which was transformed into the donor 108 (81%) and the acceptor 104 (61%) in four and five steps, respectively. TMSOTf-activated coupling of 108 and 104 furnished the □-linked disaccharide 109 (70%), which was opened under acetolysis conditions followed by anomeric deacetylation to yield the 1-alcohol 112 (79%). The elongation cycle was then repeated twice to assemble the tri- and tetrasaccharides 116 and 120 through a four-stepped protocol [imidation-glycosylation- acetolysis-anomeric deacetylation], respectively. Anomeric allylation of 112, 116, and 120, individually, led to the □-linked ethers 121-123, which underwent sequential deacetylation, TEMPO oxidation, and reduction to afford alginate oligosaccharides 130-132, respectively.