Selective sulfation of carrageenans and the influence of sulfate regiochemistry on anticoagulant properties

► Carrageenans were selectively sulfated to produce rare diads. ► The new diads synthesized were characterized by 1D and 2D NMR. ► Sulfated derivatives showed higher anticoagulant activities than native carrageenans. ► Sulfation at C2 of anhydro units and C6 of β-d-Galp improved anticoagulant activity.