Synthesis of "sugar-rods" with phytohemagglutinin cross-linking properties by using the palladium-catalyzed Sonogashira reaction

A palladium-catalyzed Sonogashira reaction has been applied for the syntheses of divalent "sugar-rods" which exhibited excellent lectin cross-linking properties. The procedure, which involves a tetrakis(triphenylphosphine)palladium-catalyzed cross-coupling reaction between an alkyne and a halogen-bearing sp2-carbon in DMF at 60 degrees C, is very efficient and the dimeric or heterobifunctional "sugar-rods" (8-13, 15-17) were isolated in 65-100% yields. Dimers 8a and 15a were both shown to form insoluble cross-linked lattices when mixed with the tetrameric plant lectin from Canavalia ensiformis (Concavalin A, Con A). Moreover, the relative inhibitory properties of the synthetic dimannosides were determined by means of the hemagglutination of rabbit erythrocytes, whereby dimer 15a was shown to be 20-fold more potent than monomeric methyl alpha-D-mannopyranoside.