OLEANANE TRITERPENOIDS FUNCTIONALIZED AT C-25 AND C-26

Reaction of 25-oximino-19 beta,28-epoxy-18 alpha-oleanan-2 beta-ol (4) with nitrous acid afforded hemiacetal 22 ((25S)-2 beta,25;19 beta,28- diepoxy-18 alpha-oleanan-25-ol). Functionalization of 19 beta,28-epoxy -18 alpha-oleanan-2 beta-ol (1) with lead(IV) acetate gave 2 beta,25;1 9 beta,28-diepoxy-18 alpha-oleanane (31). A series of derivatives with an oxygen functionality at position 25 has been prepared by modificat ion of the functional groups in compounds 22 and 31. 26-Oximino-19 bet a,28-epoxy-18 alpha-oleanan-2 beta-ol (7) on reaction with nitrous aci d afforded the corresponding nitrimine 10 which could not be converted into derivatives with an oxygen group at C-26: all the attempted prep arations led invariably to compounds containing a nitrile group in pos ition 8 beta. The nitrile groups in positions 10 beta and 8 beta appea red to be extremely unreactive.