Triterpenoids and
related abeo-steroids are of
interest to the scientific community for their potent and varied biological
activities as well as their unique structures. Within this large and
diverse family of natural products, the fir metabolites (−)-spirochensilide
A and B are particularly noteworthy for their controversial biogenesis.
We herein report the chemical synthesis of the spirochensilides, which
involves a concerted sequence of bioinspired rearrangements contributing
to its resolution. Points of divergence after each rearrangement step
also allow for an approach to the abifarine family of natural products
with abifarine B as a synthetic target. Key to this strategy is a
radical-polar crossover event to initiate the first rearrangement
without the need for a sacrificial functionality to be introduced
beforehand.
The anthrasteroid rearrangement has been discussed for the formation of the eponymous substance class since its discovery. We here report its chemical emulation from a plausible biogenetic precursor and show how it accounts for the formation of asperfloketals A and B through a mechanistic bifurcation event. As a result, these natural products arise from double Wagner− Meerwein rearrangements and, thus, are 1(10→5),1(5→6)-and 1(10→5),4(5→6)diabeo-14,15-secosteroids, respectively. To establish an efficient route to a bioinspired precursor, we devised a sequence of orchestrated oxidative activation and rearrangement from ergosterol.
Biogenetic space-guided synthesis is a tool to design efficient chemical syntheses of complex terpenoids by evaluating their surrounding biogenetic space.
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