Enzymatic glycosylation of reducing oligosaccharides linked to a solid phase or a lipid via a cleavable squarate linker

Reducing oligosaccharides were converted into their corresponding glycosyla mines, and these were reacted with 3,4-diethoxy-3-cycIobuten-1,2-dione (squ aric acid diethyl ester). The resulting derivatives could be linked to amin o-functionalized lipids, solids, or proteins. Treatment of the obtained lip id or solid conjugates with aqueous bromine or, alternatively, with ammonia -ammonium berate cleaved the linkage and regenerated the oligosaccharide gl ycosylamines, which were in turn rapidly hydrolyzed to the reducing oligosa ccharides. To demonstrate the usefulness of this linkage in enzymatic oligo saccharide synthesis, lactose was linked to a lipid or a solid phase, the o btained conjugates were then subjected to two enzymatic glycosylations (eit her consecutively or 'one-pot'). The resulting materials were then cleaved to give, in both cases, the expected reducing tetrasaccharide (lacto-N-neot etraose) in good yield. (C) 1999 Elsevier Science Ltd. All rights reserved.