Allobetulone rearrangement to l8αH,19βH-ursane triterpenoids with antiviral activity.

Allobetulone E-ring rearrangement under treating with HClO4 in Ac2O under reflux afforded new triterpenoids: 3,28-diacetoxy-21-acetyl-2(3),20(21)-18α,19βH-ursandiene 3 and 3,28-diacetoxy-2(3),18(19...