The present invention relates to a saccharide selected from the group consisting of: €ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ{B(E)CD} €ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ{(E)CDAB}n €ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ{AB(E)CD}n Wherein A, B, C, E, D and n are as defined in claim 1. The invention also relates to derivatives thereof, pharmaceutical compositions comprising said derivatives, and kit for the diagnostic of Shigella flexneri type 2a infection comprising said derivatives.