Removal of benzyl moiety
Catalytic hydrogenolysis (10%Pd/C) of ethers BnGB
(6) and BnGC (7) under 4 atm of H2 effected quantitative
deprotection in 24 h to obtain native GB (3) andGC
(4) (Scheme 2). Interestingly, BnGA (8), which was
formed in small amounts when the benzylation was conducted
for more than 3 h, did not undergo hydrogenolysis;
therefore GB (3) was not contaminated with GA (2)
and the purification was facile. It appears that 1-OH in
BnGB (6) and BnGC (7) coordinates to Pd during
hydrogenolysis. As this activation is not possible in the
case of BnGA (8), which lacks 1-OH, Pd cannot reach
the sterically hindered benzyl group.