Enzymatic Sialylation of Synthetic Multivalent Scaffolds: From 3'-Sialyllactose Glycomacromolecules to Novel Neoglycosides.

Sialoglycans play a key role in many biological recognition processes and sialylated conjugates of various types have successfully been applied, e.g., as antivirals or in antitumor therapy. A key feature for high affinity binding of such conjugates is the multivalent presentation of sialoglycans which often possess synthetic challenges. Here, the combination is described of solid phase polymer synthesis and enzymatic sialylation yielding 3'-sialyllactose-presenting precision glycomacromolecules. CMP-Neu5Ac synthetase from Neisseria meningitidis (NmCSS) and sialyltransferase from Pasteurella multocida (PmST1) are combined in a one-pot reaction giving access to sequence-defined sialylated macromolecules. Surprisingly, when employing Tris(hydroxymethyl)aminomethane (Tris) as a buffer, formation of significant amounts of α-linked Tris-sialoside is observed as a side reaction. Further exploring and exploiting this unusual sialylation reaction, different neoglycosidic structures are synthesized showing that PmST1 can be used to derive both, sialylation on natural carbohydrates as well as on synthetic hydroxylated scaffolds.

Highly Fluorescent Merocyanine and Cyanine PMMA Copolymers.

Polymerizable merocyanine and cyanine dye monomers are synthesized and applied in a statistical copolymerization with methylmethacrylate, giving a series of highly fluorescent poly(methyl methacrylate) (PMMA) copolymers. Photophysical properties of yellow to red merocyanine- and of pink to dark purple cyanine-containing copolymers are studied by fluorescence spectroscopy in solid state as well as in different solvents. The highest quantum yield measured in the solid state is observed for copolymers with the lowest dye content: 16% for merocyanine-based and 13% for cyanine-based copolymers, respectively. Fluorescence properties in solution show positive solvatochromism for both merocyanine monomer and copolymer. Copolymer, in comparison to monomer, is hypsochromically shifted to lower wavelengths which point toward H-aggregation of the chromophores in the copolymer matrix.