5- N,4- O -carbonyl-7,8,9-tri- O -chloroacetyl-protected sialyl donor for the stereoselective synthesis of α-(2→9)-tetrasialic acid

Abstract

(Figure presented) An efficient stereoselective synthesis of α-(2→9)-tetrasialic acid was achieved using tri-O-chloroacetyl- derivatized sialyl donor and a triol sialyl acceptor. Both the acceptor and the donor were also protected with a cyclic 5-N-4-O-carbonyl protecting group. The donor is highly reactive and enabled α-selective sialylation with various primary, secondary, and tertiary acceptors under in situ activation conditions (NIS/TfOH, -78 °C, acetonitrile/dichloromethane). The trans-fused oxazolidinone ring and O-chloroacetyl protecting groups were easily removed under mild reaction conditions to provide the fully deprotected α(2→9)-tetrasialic acid. © 2010 American Chemical Society.