Synthesis of Differentially Protected Glucosamine Building Blocks and Their Evaluation as Glycosylating Agents

The modular assembly of heparin oligosaccharides requires glucosamine building blocks with amine protecting groups for a-selective glycosylations that can be readily removed. The synthesis of N-4-nitrobenzensulphonamide (nosyl)- and N-2,4-dinitrophenyl (DNP)-protected glucosamine building blocks and their evaluation as glycosylating agents is described. The N-nosyl-protected glucosamine building blocks were challenging to prepare and their glycosylations resulted in inseparable mixtures of products. The N-DNP-protected glucosamines, however, were readily synthesized and resulted in a-selective couplings to protected L-iduronic acid derivatives.