Synthesis and Raman spectra of 3-deoxy-α-l-rhamnosides as model sugars of the Ascaris egg shell

The synthesis of two 3-deoxy-α-l-rhamnosides (i.e., 3,6-dideoxy-l-arabino-hexopyranosides) as models of ascaroside natural products is reported. The present approach is based on a Ferrier rearrangement from l-rhamnal, epoxidation of the resulting glycal and reductive opening of the isolated β-epoxide. The 3-deoxy-α-rhamnoside linked to a long aglycone chain was used to ascertain by Raman vibrational spectroscopy the presence of this peculiar sugar in the inner shell of Ascaris eggs.