By reaction of 4,6-O-ethylidene-2,3-di-O-acetyl-beta-D-glucopyranose (I) and 4'-benzyloxycarbonyl-4'-demethyl-epipodophyllotoxin (II) in the presence of boron trifluoride etherate to give the compound (III), which is treated with Zn(OAc)2 and NaOAc followed by reduction with Pd-C.
The condensation of dibenzyl-sugar (II) with 4'-demethyl-epipodophyllotoxin (I) by means of BF3稥t2O in acetonitrile gives a mixture of the alpha and beta coupled products (IV) + (III), which by crystallization in dichloromethane/methanol afforded pure diastereomer beta (III). Finally this compound is debenzylated by hydrogenolysis with H2 over Pd/C in THF.