Synthesis of Multibranched Australine Derivatives from Reducing Castanospermine Analogues through the Amadori Rearrangement of <i>gem</i>-Diamine Intermediates: Selective Inhibitors of β‑Glucosidase

A practical one-pot synthesis of bi- and triantennated australine analogues from a pivotal sp2-iminosugar-type reducing castanospermine precursor is reported. The transformation involves a gem-diamine intermediate that undergoes the indolizidine → pyrrolizidine Amadori-type rearrangement and proceeds under strict control of the generalized anomeric effect to afford a single diastereomer. The final compounds behave as selective competitive inhibitors of β-glucosidase and are promising candidates as pharmacological chaperones for Gaucher disease.