Purification of residualizing glycoconjugate labels for protein by reversed-phase high-pressure liquid chromatography

Residualizing labels are radioactive or fluorescent tracers used for identifying the tissue and cellular sites in which circulating proteins are catabolized in the body. When attached to protein the labels do not affect normal mechanisms of protein catabolism, but remain at the cellular site of protein uptake, after the carrier protein itself is degraded to diffusible catabolites. Until recently these labels consisted of biologically indigestible carbohydrates attached to a radioactive reporter molecule. In this report we describe the synthesis and purification of a new fluorescent residualizing label, N,N-dilactitol-N'-fluoresceinyl-ethylenediamine. The label is prepared by first derivatizing ethylenediamine 1:1 with fluorescein isothiocyanate and then coupling lactose to the remaining primary amino group by reductive amination. A rapid one step purification of this and other glycoconjugate labels by reversed-phase high-pressure liquid chromatography is described.