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

Abstract

A novel cycloetherification process involving a facile 5-exo S_N2-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.