SYNTHESIS OF MONOTERPENE PIPERIDINES FROM THE IRIDOID GLUCOSIDE ANTIRRHINOSIDE

Synthesis of five novel piperidine monoterpene alkaloids (17-21) using the iridoid glucoside antirrhinoside (4) as a synthon is described. T wo strategies for their preparation were investigated: the first possi ble pathway involved an intermediate diol, 13, from which the piperidi ne ring was expected to be constructed via reaction of its ditosylate with an amine; the second strategy involved a double reductive aminati on as the key step to the piperidine ring, which proved successful. Th e stereochemistry of C-5 and C-9 in the obtained piperidine monoterpen es was the same as that reported for alpha-skytanthine (3), a known is olate from Skytanthus acutus (Apocynaceae).