Eight Rings, Five Flavors

Eight Rings, Five Flavors

Author: Theresa Kueckmann

Schindilactone A is a naturally occuring nortriterpenoid from the family of climbing plants Schisandraceae. The Chinese name means “five-flavor berry”, and the salty, sweet, sour, spicy, and bitter berries of these plants have been used in traditional Chinese medicine for thousands of years. More recently, biological assays have indicated the activity of the nortriterpenoids in inhibiting hepatitis, tumor growth, and HIV-1, but more detailed investigation has been hampered by their limited availability.

Zhen Yang and colleauges at Peking University, Tsinghua University, and Xiamen University, all China, have completed a 29-step total synthesis of highly oxygenated, octacyclic schindilactone A. They developed their methodology by dividing schindilactone A into three principal components, that is, the ABC, FGH, and CDEF ring moieties.

Construction of the ABC moiety was based on Diels–Alder and enyne ring-closing metathesis (RCM) reactions, while the FGH moiety was prepared using cobalt/thiourea-catalyzed stereoselective Pauson–Khand reaction and palladium/thiourea-catalyzed stereoselective annulation. Construction of the highly ring-strained 7–8-fused ring system in the CDEF moiety proved to be the most challenging part of the synthesis. Key steps included palladium/thiourea-catalyzed carbonylative annulation, methylation, and sequential RCM/oxa-Michael-addition reactions.

Image: © Wiley-VCH

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