Modular synthesis of heparin-related tetra-, hexa- and octasaccharides with differential o-6 protections: programming for regiodefined 6-o-modifications.

Heparin and heparan sulphate (H/HS) are important members of the glycosaminoglycan family of sugars that regulate a substantial number of biological processes. Such biological promiscuity is underpinned by hetereogeneity in their molecular structure. The degree of O-sulfation, particularly at the 6-position of constituent D-GlcN units, is believed to play a role in modulating the effects of such sequences. Synthetic chemistry is essential to be able to extend the diversity of HS-like fragments with defined molecular structure, and particularly to deconvolute the biological significance of modifications at O6. Here we report a synthetic approach to a small matrix of protected heparin-type oligosaccharides, containing orthogonal D-GlcN O-6 protecting groups at programmed positions along the chain, facilitating access towards programmed modifications at specific sites, relevant to sulfation or future mimetics.