Synthesis of clustered xenotransplantation antagonists using palladium-catalyzed cross-coupling of prop-2-ynyl α-D-galactopyranoside

Abstract

Hyperacute rejection of pig liver transplantation can be antagonized using high affinity anti α-galactoside epitopes (Galα1-3Galβ, Galili antigen). To this end, clusters containing the Galili antigen were synthesized using palladium cross-coupling reactions. Thus, benzyl 3-(O-α-D-galactopyranosyl)-β-D-galactopyranoside derivative 6 was prepared using perbenzylated thiophenyl β-D-galactopyranosyl donor 5 and benzyl 2,6-di-O-benzoyl-α-D-galactopyranosyl acceptor 3. Aglycone interchange from benzyl to prop-2-ynyl disaccharide 8 was successively achieved by hydrogenolysis, peracetylation, regioselective anomeric de-O-acetylation, trichloroacetimidate activation, and finally coupling to propargyl alcohol with triflic acid. The resulting prop-2-ynyl disaccharide 8 was transformed in high yields (>85%) into dimer 10, trimer 12, and tetramer 17 using oxidative homocoupling (10) and palladium-catalyzed aryl iodide cross-coupling (12, 17), respectively. Ester protecting group removal under transesterification conditions afforded fully deprotected α-Gal clusters.