A synthetic tetrasaccharide with the GlcAβ1-4GlcNAcα1-4GlcAβ1-4GlcNAc sequence, an unsulfated extension of the heparan sulfate (HS) / heparin backbone (N-acetylheparosan-like), supplied as the disodium salt for improved handling and solubility. Used as a model substrate and reference standard for HS biosynthesis, sulfotransferase activity, and HS-binding protein research. 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.