Total Synthesis of a Macrocyclic Pyrrolizidine Alkaloid, (+/-)-Integerrimine, Utilizing an Activable Protecting Group

Article abstract of DOI:10.1021/ja00322a036

A new esterification reaction has been developed utilizing a (methylthio)methyl (MTM) group as an activable protecting group of carbocyclic acid.A total synthesis of a 12-membered pyrrolizidine alkaloid, (+/-)-integerrimine (1), has been achieved by applying the above method to formation of the macrocyclic bislactone skeleton.The acid anhydride (16b) of the integerrinecic acid derivative was coupled with lithium alkoxide of retronecine silyl ether (5b) in the presence of DMAP to afford the α,β-unsaturated ester.Oxidation of the MTM group afforded an active (methylsulfonyl)methyl ester (28b), which cyclized to give the macrocyclic bislactone 29.