Synthesis and structural studies of oligomers of 6-amino-2,5-anhydro-6-deoxy-d-mannonic acid

A novel cycloetherification process involving a facile 5-exo SN2-type ring closure by intramolecular opening of a terminal aziridine ring by a γ-hydroxyl group, led to the stereoselective synthesis of 6-amino-2,5-anhydro-6-deoxy-d-mannonic acid (1). Oligomerization of 1 by solution phase peptide coupling methods gave oligomers 2–5. While most of the oligomers, in either protected or deprotected form, did not show any significant secondary structure, octamer 5 (P=H) exhibited a very strong positive band at 216 nm in its CD spectrum in MeOH and TFE, indicating the possibility of the presence of an ordered structure in solution. Its 1H NMR spectra in various polar solvents, however, failed to produce any distinct dispersion of the amide proton chemical shifts. Compounds 1–5 were found to be inactive in hypoglyceamic tests in rats.