Photoinduced Skeletal Rearrangements Reveal Radical-Mediated Synthesis of Terpenoids
Xiaoguang Lei and Houhua Li use photoinduced skeletal rearrangements to synthesize terpenoids.
Isodon diterpenoids are a large family of bioactive polycyclic natural products isolated from plants of Isodon species. Biosynthetically, these diterpenoids are derived from geranyl-geranyl-diphosphate (GGPP) by carbocationic cyclization rearrangements, which are catalyzed by a series of terpenoid cyclases. Several known bicyclo[3.2.1]octene-containing isodon diterpenoid skeletons are generated via carbocationic rearrangements from a common intermediate ent-pimarenyl cation. An initial biosynthetic hypothesis speculated that jungermannenone-type diterpenoids could be generated from ent-kaurane diterpenoids via two intermediates through carbocationic rearrangements. During a research program aimed at developing the synthesis of complex isodon diterpenoids, the research group led by Professors Xiaoguang Lei and Houhua Li at Peking University (P. R. of China) discovered a late-stage photoinduced radical skeletal rearrangement of the bicylco[3.2.1]octene ring system, which suggested that these photoinduced radical rearrangements are possibly involved in the biosynthetic pathway of ent-kauranes and jungermannenones.
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