The synthesis of photoaffinity neoglycolipid probes as tools for studying membrane lectins

A method for the synthesis of photoaffinity neoglycolipid probes with a highly efficient carbene-generating diazocyclopentadien-2-ylcarbonyl (Dcp) label, which can be radioiodinated under standard oxidation conditions, was developed. The probes are intended for incorporation into the lipid bilayer. They are lipophilic glycoconjugates on the basis of an amphiphilic aglycone built up from a diacylglycerol and a polyethylene glycol spacer (with a polymerization degree of 9-16) bearing the Dcp label at the terminal unit. The location of the label in the aglycone provides the possibility of one-step preparation of a wide range of probes using various carbohydrate synthons. We have synthesized photoaffinity neoglycoconjugates containing the oligosaccharides Sialyl LewisX and A trisaccharide, which are specific to some tumor cells. A probe containing an inactive pentaol (aminodeoxyglucitol) was also synthesized to detect nonspecific binding. The Dcp label is bound to the probe molecule by ester bond; its lability under alkaline conditions facilitates the analysis of crosslinked products after photoaffinity labeling.