Synthesis of Sphere-Type Monodispersed Oligosaccharide−Polypeptide Dendrimers

A sphere-type fully substituted oligosaccharide−β-alanine−poly(lysine) dendrimer having a sharp molecular weight distribution was synthesized. Sphere-type poly(lysine) dendrimers were prepared using 1,4-diaminobutane as an initiator core and N,N ‘-bis( tert -butyloxycarbonyl)- l -lysine as a branching unit. β-Alanine was bound to the poly(lysine) dendrimer generation 3 to form β-alanine−poly(lysine) dendrimer generation 3, which has 16 terminal amino groups on its surface. A series of sphere-type oligosaccharide−β-alanine−poly(lysine) dendrimers were obtained by binding such an oligosaccharide as maltose, lactose, cellobiose, maltotriose, or a mixture of lactose and maltose to the surface of the β-alanine−poly(lysine) dendrimer scaffolding by reductive amination using the borane−pyridine complex. Oligosaccharide−β-alanine−poly(lysine) dendrimers having 32 oligosaccharide residues were obtained in high yields. NMR and MALDI−TOF mass measurements revealed that the oligosaccharide−polypeptide dendrimers have a monodispersed molecular weight distribution, the molecular weight of which was 13 418.36, 13 472.50, and 13 507.28 g/mol for cellobiose, maltose, and lactose, respectively, indicating that a complete substitution of the amino group by the oligosaccharide occurred.