p-Isothiocyanatophenyl 6-phospho-.alpha.-D-mannopyranoside coupled to albumin. A model compound recognized by the fibroblast lysosomal enzyme uptake system. 1. Chemical synthesis and characterization

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Abstract
A simple synthesis was developed for a conjugate of albumin and p-aminophenyl 6-phospho-.alpha.-D-mannopyranoside to study the requirements of the fibroblast lysosomal enzyme recognition system. p-Aminophenyl 6-phospho-.alpha.-D-mannopyranoside was prepared in 2 ways: phosphorylation of p-nitrophenyl .alpha.-D-mannopyranoside and subsequent reduction of the nitro group by catalytic hydrogenation and direct phosphorylation of p-aminophenyl .alpha.-D-mannopyranoside. Mannosides were phosphorylated in a reaction with phosphoryl chloride, pyridine and water at O.degree. C for 1 h, by a procedure selective for primary hydroxyl groups. Purified p-aminophenyl 6-phospho-.alpha.-D-mannopyranoside was characterized by chromatographic, enzymatic and 13C NMR spectroscopic methods. p-Isothiocyanatophenyl glycosides of .alpha.-mannose, .alpha.-glucose, .alpha.- and .beta.-galactose and .alpha.-L-fucose were formed by reaction of the respective p-aminophenyl glycosides with thiophosgene. Incubation of the p-isothiocyanatophenyl glycosides with bovine serum albumin at pH 8.5, 25.degree. C for 18 h generally resulted in the coupling, primarily through lysine residues, of up to 20-30 mol of glycoside/mol of protein. Biological properties of the conjugates in the fibroblast lysosomal enzyme recognition system are described in the accompanying paper.