Tritylation of 14 gave a trityl ether (68, 65% yield), which was subjected to acetylation to give an acetate (69) in 99% yield. Hydrogenolysis of 69 using 20% Pd-C provided the desired 70 in 97% yield. By applying the reported procedure, coupling reaction of phenethyl P-D-glucopyranoside congener (70) and methylthio 2,3,4-tri-O-acetyl-P-D-xylopyranoside in the presence of AgOTf and phenylselenochloride (PhSeCl) gave the coupled product (71) in 44% yield. In this case, an inseparable mixture of the starting material (70) and the migrated product (phenethyl 2, 3, 6, 2', 3', 4'-O-hexaacetyl-P-D-xylopyranosyl-(1 ^ 4)-P-D-glucopyranoside) as a byproduct could be obtained. Finally, treatment of 71
Phenethyl O-p-D-glucopyranoside (14) R1 = H
Phenethyl 6-O-p-o-xylopyranosyl-p-D-glucopyranoside (65) „1 = HO^T -—
Phenethyl 6-O-a-L-arablnopyranosyl-p-D-glucopyranoslde (66) OH
Phenethyl 6-O-a-L-rhamnopyranosyl-p-D-glucopyranoside (67)
Figure 11: Structure of naturally occurring phenethyl P-D-glucopyranosides.
with K2CO3 in MeOH provided the synthetic phenethyl 6-O-P-D-xylopyranosyl-P-D-glucopyranoside (65) in 70% yield.
3.4.2. Synthesis of phenethyl 6-O-a-L-arabinopyranosyl-fi-D-glucopyranoside (66)
By following the reported procedure, coupling reaction of 70 and 2,3,4-tri-O-acetyl-a-L-arabinopyranosyl bromide in the presence of AgOTf and tetramethy-lurea (TMU) gave the coupled product (72) in 73% yield. Finally, treatment of 72 with K2CO3 in MeOH provided the synthetic phenethyl 6-O-a-L-arabinopyranosyl-P-D-glucopyranoside (66) in 86% yield.
3.4.3. Synthesis of phenethyl 6-O-a-L-rhamnopyranosyl-fi-D-glucopyranoside (67)
Methylthio 2,3,4-tri-O-acetyl-a-L-rhamnopyranoside was synthesized in 57% yield by applying the reported method based on the BF3 -Et2O-catalyzed reaction of methylthiotrimethylsilane and tetra-O-acetyl-a-L-rhamnopyranoside obtained by acetylation of a-L-rhamnose. By applying the reported procedure, coupling reaction of phenethyl P-D-glucopyranoside congener (70) and methylthio 2,3,4-tri-O-acetyl-a-L-rhamnopyranoside in the presence of AgOTf and phenylseleno chloride (PhSeCl) gave the coupled product (73) in 81% yield. Finally, treatment of 73 with K2CO3 in MeOH provided the synthetic phenethyl 6-O-a-L-rhamnopyranosyl-P-D-glucopyranoside (67) in 85% yield.
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