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Total Synthesis of Racemic Benzosceptrins via an Electrocyclization Cascade.

Yudai Fujino1, Taisei Matoba1, Ayami Amano1

  • 1Biotechnology Research Center and Department of Biotechnology, Toyama Prefectural University, 5180 Kurokawa, Imizu, Toyama 939-0398, Japan.

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|November 26, 2025
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Summary

Researchers synthesized benzosceptrins A, B, and C, which are marine alkaloids from Agelas sponges. The synthesis utilized sequential electrocyclizations, guided by a Gibbs energy evaluation of the biosynthetic pathway.

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Area of Science:

  • Marine natural products chemistry
  • Organic synthesis
  • Biomimetic synthesis

Background:

  • Benzosceptrins are dimeric pyrrole-2-aminoimidazole alkaloids.
  • These compounds are isolated from marine sponges of the genus Agelas.
  • They possess a characteristic C2 symmetric benzocyclobutane structure.

Purpose of the Study:

  • To achieve the total synthesis of (±)-benzosceptrins A, B, and C.
  • To explore biomimetic synthetic strategies based on proposed biosynthetic pathways.
  • To investigate the utility of sequential electrocyclizations in constructing complex alkaloid frameworks.

Main Methods:

  • The synthesis employed sequential 8π and 6π electrocyclizations.
  • Key precursors included nagelamide I and its structural analogues.
  • Gibbs energy evaluation was used to guide the synthetic strategy based on the proposed biosynthetic pathway.

Main Results:

  • Successful total synthesis of (±)-benzosceptrins A, B, and C was achieved.
  • The synthetic route demonstrated the feasibility of using sequential electrocyclizations.
  • The study provided insights into the potential biosynthetic routes to these marine alkaloids.

Conclusions:

  • The total synthesis of benzosceptrins A, B, and C was accomplished.
  • The employed synthetic strategy, inspired by biosynthesis, is effective for constructing these complex molecules.
  • This work expands the synthetic accessibility of benzosceptrin alkaloids and related natural products.