Synthesis of L-iduronic acid derivatives via [3.2.1] and [2.2.2] L-iduronic lactones from bulk glucose-derived cyanohydrin hydrolysis: a reversible conformationally switched superdisarmed/rearmed lactone route to heparin disaccharides.

Abstract

L-Idofuranoside cyanohydrin 1 is converted on large scale into a mixture of L-IdoA methyl pyranosides and furanosides, which is converged to provide short 2-step routes to bicyclic [3.2.1] or [2.2.2] L-iduronate lactones. The former is obtained via a 100 g scale synthesis of 3-OBn L-IdoA. A two-step conversion of this mixture provides either pure anomer of the novel [2.2.2] l-iduronate thioglycoside lactones. Both [3.2.1] and [2.2.2] lactones are converted into GlcN-IdoA heparin precursor disaccharides. The [2.2.2] lactone enables a scalable 3-step route from 1 to a new type of highly disarmed O-4 iduronate thioglycoside, which is an effective acceptor with glucoazide thioglycoside donors. The resulting new iduronic [2.2.2] lactone disaccharides are readily rearmed by mild methanolysis to provide GlcN-IdoA thiophenyl disaccharide donors, intercepting their established utility for the assembly of both heparin- and heparan sulfate-like oligosaccharides. The [2.2.2] lactonization acts as a conformational switch to superdisarm iduronate components, reversible by lactone ring opening. In addition, the separated 2,4-diacetates also provide short access to all four anomeric and ring size isomers of l-iduronic acid methyl glycosides, including the first syntheses of the parent idofuranosides. X-ray structures are reported for a [2.2.2] iduronate lactone and examples of both methyl L-idopyranoside and novel methyl-L-idofuranoside systems.