Abstract
Some analogs of stevoiside (I), a sweet diterpene glycoside, were synthesized. Coupling of hepta-O-acetylsteviolbioside with hexa-O-acetyl-2-O-a-L-rhamnopyranosyl-a-D-glucopyranosyl bromide, bexa-O-acetyl-2-O-a-L-rhamnopyranosyl-a-D-galactopyranosyl bromide and hexa-O-acetyl-2-O-a-L-quinovopyranosyl-a-D-galactopyranosyl bromide, in the presence of silver carbonate-celite in dichloroethane followed by deacetylation yielded steviol-13-O-β-sophoroside-19-O-(2-O-a-L-rhamnopyranosyl-β-D-glucopyranosylester) (VIII), steviol-13-O-β-sophoroside-19-O-(2-O-a-L-rhamnopyranosyl-β-D-galactopyranosylester) (IX) and steviol-13-O-β-sophoro-side-19-O-(2-O-a-L-quinovopyranosyl-β-D-glueopyranosylester) (X), respectively. Methylation of steviolbioside heptaacetate followed by deacetylation yielded steviolbioside-19-O-methylester (XII). Reduction of stevioside and XII with hydrogen gave dihydrostevioside (XIV) and dihydrosteviolbioside-19-O-methylester. The relative sweetness of I, VIII, IX, X, steviolbioside, XII, dihydrosteviolbioside, XIV and XV as expected by the percentage of that of sucrose were 210, 300, 230, 90, 6, 30 and 3, respectively.
