37 Axinellamine A,Bの全合成(口頭発表の部)

抄録

Dimeric pyrrole alkaloids, such as the axinellamines A and B (1), palau'amine (2) and the massadines (3) are marine derived natural products that represent a great opportunity to advance fundamental chemical synthesis. They bear as structural features a highly functionalized cyclopentane that is spiroannulated upon a guanidine unit, a second incorporation of a guanidine group within another ring framework, as well as one or two pyrrole moieties. To confirm the structures of this rare and peculiar group of natural products, many well-known synthetic organic chemists worldwide have embarked on their total synthesis. By considering a biosynthetic hypothesis, we reasoned that the syntheses of 1-3 should be feasible through an intermediate such as pre-axinellamines (4 and 5). As a result, we achieved the synthesis of an oxidative precursor to 4, namely 1,9-dideoxy-pre-axinellamine (9), via a tandem dehydration-chlorination event and direct incorporations of the two guanidine units as key steps in the 19-step synthetic accomplishment. Moreover, starting from an intermediate produced en route to 9, an oxidative ring-closing event of an intramolecular guanidine followed by a silver picolinate-catalyzed, novel C-H oxidation reaction that activated one of the guanidine units at the α position, allowed the achievement of the first total synthesis of axinellamines A and B.