A synthetic heparan sulfate (HS) / heparin disaccharide bearing 2-O-sulfated iduronic acid (IdoA2S) linked to 2-N,6-O-disulfated glucosamine (GlcNS6S), the trisulfated I2S6 sulfation pattern, supplied as the tetrasodium salt. This is the most abundant disaccharide repeat unit of heparin and a key structural element of the antithrombin-binding pentasaccharide motif. Heparan sulfate (HS) and heparin are sulfated glycosaminoglycans found as components of proteoglycans. HS, in close proximity to cell surfaces and extracellular matrix proteins, plays essential physiological roles binding hundreds of proteins, and may play a role in SARS-CoV-2 infection through virus binding to ACE2; heparin is mainly found in mast cell secretory granules. Synthetic, structurally defined HS/heparin fragments are valuable probes for sulfation-pattern-dependent protein binding, anticoagulant and growth-factor signaling research, and as standards for analytical and structure-activity studies.