Synthesis of plantamajoside, a bioactive dihydroxyphenylethyl glycoside from Plantago major L.

The first total synthesis of plantamajoside (1), 2-(3′,4′-dihydroxylphenyl)ethyl-4-O-caffeoyl-3-O-(β-D-glucopyranosyl)-β-D-glucopyranoside, which is one of the dihydroxyphenylethyl glycosides (caffeic acid sugar esters), is described. Key intermediate 2, 2-[3′,4′-bis(O-benzyl)phenyl]ethyl 2,6-di-O-acetyl-4-O-[3′,4′-bis(O-benzyl)caffeoyl]-β-D-glucopyranoside was glycosylated with trichloroacetoimidoyl 2,3,4,6-tetra-O-acetyl-α-D-glycopyranoside (3) to afford plantamajoside derivative 4a, 2-[3′,4′-bis(O-benzyl)phenyl]ethyl 2,6-di-O-acetyl-4-O-[3′,4′-bis(O-benzyl)caffeoyl]-3-O-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl)-β-D-glucopyranoside, in 39% yield. Plantamajoside derivative 4a was successfully converted into the target compound, plantamajoside (1), through a series of de-protective procedures. 1H- and 13C nuclear magnetic resonance (NMR) spectral data of the synthesized plantamajoside (1) were identical to those of the natural compound.