An Orthogonally Protected alpha,alpha-bis(aminomethyl)-beta-alanine building block for the construction of glycoconjugates on a solid support

Synthetic glycoclusters are extensively used as mimetics of naturally occurring, multivalent carbohydrate ligands in various glycobiological applications. Their preparation, however, is far from trivial, and it still is a limiting factor in the study of carbohydrate binding. We herein report the synthesis of an orthogonally protected building block, N-Alloc-N'-Boc-N' '-Fmoc-alpha,alpha-bis(aminomethyl)-beta-alanine (1), and its use in the preparation of triantennary peptide glycoclusters (21-24) on a solid support. The assembly of the clusters involves removal of the amino protections of the solid-supported branching unit 1 in the order Fmoc, Boc, and Alloc, and subsequent coupling of peracetylated O-(glycopyranosyl)-N-Fmoc-L-serine pentafluorophenyl esters (galactose, glucose, mannose, and ribose) to each amino group exposed.