Chondroitin sulfate (CS) is a glycosaminoglycan composed of D-glucuronic acid (D-GlcA) and N-Acetyl-D-galactosamine (D-GalNAc), with repeating sequences of D-GlcA(1,3b)-D-GalNAc- (1,4-b) disaccharides, typically in excess of 100 units. During biosynthetic assembly, enzymatic modification of the repeating nascent disaccharide backbone gives rise to a number of different sulfation patterns, creating a multitude of CS subtypes and heterogenous structures. Naturally occurring CS therefore contains an assortment of subtypes, and proportions that also vary depending on the polysaccharide source. CS-A (D-GalNAc 4-Osulfation) and CS-C (D-GalNAc 6-O-sulfation) are abundant compared to other subtypes such as CS-D (2'-O-D-GlcA-6-O-D-GalNAc sulfation) and CS-E (4,6-O-D-GalNAc sulfation). CS interacts with growth factors, cytokines, chemokines and adhesion molecules, regulating physiological processes including embryonic and brain development, anti-inflammatory effects, wound healing and signalling. Whilst it is established that CS sulfation patterns correlate to related biological function, the specificities of such molecular interactions is an underdeveloped field. Access to homogenous, structurally defined CS oligosaccharides is therefore of utmost importance for the study of related CS-protein interactions, but is hampered by difficulties in obtaining significant amounts of structurally defined sequences from natural sources, particularly for rarer subtypes such as CS-D. Relatedly, synthetic approaches to heparan sulfate (HS) fragments have advanced more rapidly and proven extremely successful. Despite recent advances in the synthesis of CS oligosaccharides and related building blocks, approaches are required that allow diversification to CS subtypes with varying sulfation patterns, chain lengths and conjugation capabilities. Herein, and as part of a wider program targeting approaches to other glycosaminoglycans, we develop a reliable and versatile synthesis of CS D-GlcA-b-1,3-D-GalN building block disaccharides from a small library of D-Glc and D-GalN monosaccharides (Figure ). Careful consideration of protecting groups was made, to enable: b-stereoselectivity using a participating C2-OBz protecting group, variation of sulfation site programming using regiospecific ring opening of D-GalN 4,6-Obenzylidene acetals, orthogonal D-GlcA-C4'-O-substituents for elongation potential and a reducing end anomeric allyl group as a conjugable handle or orthogonal group for alternative donor formation. approach to install capability for regiodefined CS sulfation, conjugation and non-reducing end iterative extension into appropriate disaccharides from monosaccharide precursors.