A concise bioinspired
synthesis of Schisandra nortriterpenoid
propindilactone G has been accomplished from a readily accessible
steroidal lactone. Key transformations include a Breslow remote functionalization,
a Suárez remote radical functionalization, a ring expansion
enabled by a Wagner–Meerwein rearrangement, a stereoinversion
of a tertiary alcohol, and a biomimetic transesterification/oxa-Michael
addition cascade. This work also provides experimental evidence of
the putative propindilactone G biosynthesis pathway.
of main observation and conclusion The natural product propindilactone G is a complex Schisandra nortriterpenoid with a unique 5/5/7/6/5 pentacyclic framework. This full paper describes the development of concise biomimetic synthesis of propindilactone G from a known steroid lactone. The key C19-OH intermediate was synthesized via Breslow and Suárez radical remote C-H functionalizations. Wagner-Meerwein rearrangement was subsequently utilized for the expansion of the B ring. To invert the configuration of the C10 tertiary alcohol, an intramolecular peroxide cyclization catalyzed by BF3•Et2O was devised. The 5/5 fused lactone system was then assembled in a biomimetic transesterification/oxa-Michael addition sequence. Our work should provide experimental support for the proposed biosynthetic pathway and facilitate investigation of the biological activities of propindilactone G.
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