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Iriomoteolide-1a and -1b: Structure Elucidation by Integrating NMR Spectroscopic Analysis, Theoretical Calculation,

Tomohiro Obana1, Miyu Nakajima1, Kazuki Nakazato1

  • 1Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan.

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|October 17, 2024
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Summary

The correct structure of iriomoteolide-1a, a marine macrolide with anticancer properties, has been determined. This study corrects the previously proposed structure and clarifies the stereochemistry of related compounds.

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Area of Science:

  • Marine natural products chemistry
  • Organic synthesis
  • Chemical structure elucidation

Background:

  • Iriomoteolide-1a is a marine macrolide with potent cytotoxic activity against human cancer cells.
  • The proposed structure has been synthesized, but its correctness remained uncertain for over a decade.
  • Elucidating the precise stereochemistry of complex natural products is crucial for understanding their biological activity.

Purpose of the Study:

  • To determine the correct structure of iriomoteolide-1a.
  • To resolve the configurational ambiguity of the macrolactone and side chain stereoisomers.
  • To confirm the structure through total synthesis and determine the structure of the congener iriomoteolide-1b.

Main Methods:

  • Integrated strategy involving NMR spectroscopic analysis and molecular mechanics-based conformational analysis for configurational reassignment.
  • Model synthesis to validate the reassigned configuration of the macrolactone domain.
  • GIAO NMR calculation and DP4+ analysis for stereoisomer differentiation of the side chain.
  • Total synthesis of the elucidated structure and its congener iriomoteolide-1b.

Main Results:

  • The correct structure of iriomoteolide-1a has been definitively established, correcting the previously proposed structure.
  • The stereochemistry of the macrolactone and side chain was accurately assigned.
  • The structure of the natural congener iriomoteolide-1b was also determined.
  • Successful total synthesis validated the proposed structures.

Conclusions:

  • The study provides the correct structural assignment for iriomoteolide-1a and iriomoteolide-1b.
  • The integrated approach combining spectroscopic, computational, and synthetic methods proved effective for complex natural product structure elucidation.
  • This work clarifies the structural basis for the cytotoxic activity of iriomoteolides, aiding future drug development efforts.