Synthesis of Dual-Responsive Amphiphilic Glycomacromolecules: Controlled Release of Glycan Ligands via pH and UV Stimuli.

This work presents a versatile strategy for the synthesis of dual stimuli-responsive amphiphilic glycomacromolecules with tailored release properties. Amphiphilic precision glycomacromolecules (APGs) derived from tailor-made building blocks using solid phase polymer synthesis form glycofunctionalized micelles, a versatile class of materials with applications in drug delivery, as antiinfection agents as well as simple cell mimetics. In this work, this concept is extended by integrating cleavable building blocks into APGs now allowing stimuli-responsive release of glycan ligands or destruction of the micelles. This study incorporates a newly designed acid-labile building block, 4-(4-(((((9H-fluoren-9-yl)methoxy)carbonyl)amino)methyl)-1,3-dioxolan-2-yl)benzoic acid (DBA), suitable also for other types of solid phase or amide chemistry, and an established UV-cleavable 2-nitrobenzyl linker (PL). The results demonstrate that both linkers can be cleaved independently and thus allow dual stimuli-responsive release from the APG micelles. By choosing the APG design e.g., placing the cleavable linkers between glycomacromolecular blocks presenting different types of carbohydrates, they can tune APG and micellar stability as well as the interaction and cluster formation with a carbohydrate-recognizing lectin. Such dual-responsive glycofunctionalized micelles have wide potential for use in drug delivery applications or for the development as anti-adhesion agents in antiviral and antibacterial treatments.

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.

Divalent Sialylated Precision Glycooligomers Binding to Polyomaviruses and the Effect of Different Linkers.

Divalent precision glycooligomers terminating in N-acetylneuraminic acid (Neu5Ac) or 3'-sialyllactose (3'-SL) with varying linkers between scaffold and the glycan portions are synthesized via solid phase synthesis for co-crystallization studies with the sialic acid-binding major capsid protein VP1 of human Trichodysplasia spinulosa-associated Polyomavirus. High-resolution crystal structures of complexes demonstrate that the compounds bind to VP1 depending on the favorable combination of carbohydrate ligand and linker. It is found that artificial linkers can replace portions of natural carbohydrate linkers as long as they meet certain requirements such as size or flexibility to optimize contact area between ligand and receptor binding sites. The obtained results will influence the design of future high affinity ligands based on the structures presented here, and they can serve as a blueprint to develop multivalent glycooligomers as inhibitors of viral adhesion.