Iron(III)Picolinate-Induced Oxygenation and Subsequent Rearrangement of Triterpenoid Derivatives with Hydrogen Peroxide

Abstract

The reaction of oleanane triterpenoid 1b with a Fe^III(PA; picolinate)₃/H₂O₂/MeCN system (reagent system A), a simple model system for mono-oxygenase, gave the 11α-hydroxyl derivative 3 as major product, along with 11-oxo derivative 4 and 12-oxo derivative 6. The reaction of lupane triterpenoid 2b with reagent system A gave only oxidative rearrangement compounds, (20R)-aldehyde 8 and (20S)-aldehyde 9 were epimeric isomers. Then, we have found that iron(III) picolinate complex, Fe^III(PA)₃ is efficient in effecting the rearrangement of triterpenoid epoxides 5 and 7 into the corresponding cargonyl compounds, 6, 8 and 9 with 1, 2-shift of the hydride.