SOLID-PHASE SYNTHESIS AND SECONDARY STRUCTURAL STUDIES OF (1-]5) AMIDE-LINKED SIALOOLIGOMERS

A series of dimeric through octameric (1-->5) amid-linked sialooligome rs were prepared using solid-phase peptide methods on Rink resin with Fmoc protecting group chemistry. The oligomers were conjugated to epsi lon-amino caproic acid in order to model membrane-bound conformations. The secondary structure of the oliogomers was probed with NH/ND excha nge rates determined by NMR, and with circular dichroism. The combined structural studies show that a tetramer is required for ordered secon dary structure, and that secondary structure is stabilized upon elonga tion to pentameric and hexameric species. Interestingly, the heptamer shows rapid NH/ND exchange rates; however, ordered secondary structure is restored in the octamer. These studies provide the first evidence that oligomers composed of constrained carbohydrate-derived amino acid s form stable secondary structures in water.