Discrimination between the 2,3- and the 2′,3′-hydroxyl groups of maltose and cellobiose through their specific protection

Abstract

1,6-Anhydro-4′,6′- O-benzylidene-maltose and -cellobiose were subjected to temporary O-protection with a tetraisopropyldisiloxane-1,3-diyl group at the 2′,3′- and the 2,3-positions, giving 1,6-anhydro-4′,6′- O-benzylidene-2′,3′- O-(tetraisopropyldisiloxane- 1,3-diyl)maltose ( 15) and 1,6-anhydro-4′,6′- O-benzylidene-2,3- O-(tetraisopropyldisiloxane-1,3-diyl)cellobiose ( 19), respectively, in 60–64% yield. These were then subjected to various types of O-protection fo the hydroxyl groups remaining. Treatment of 15 and 19 with acetic anhydride or phenyl isocyanate gave the corresponding diacetyl and dicarbamoyl derivatives in high yield. Benzylation of the maltose derivative 15 was rather difficult, but was finally achieved through a phase-transfer reaction, to give the 2,3-di- O-benzyl derivative ( 18) in moderate yield. In the cellobiose series, benzylation of 19 was conducted similarly, giving 22, and also by employing a modification of the conventional procedure. The silyl groups of 18 and 22 were removed by treatment with tetrabutylammonium fluoride, to afford the corresponding diols in high yield.