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Compounds bearing two hydroxyl groups are known as diols. When the hydroxyl groups are located on adjacent carbon atoms, the diols are called vicinal diols or glycols. Under acidic conditions, vicinal diols undergo a specific reaction called pinacol rearrangement.
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In this lesson, we delve into the role of ring conformation and its stability, which determines the spatial arrangement and, consequently, the molecular symmetry and stereoisomerism of cyclic compounds. 1,2-Dimethylcyclohexane is used as a case study to evaluate the possible number of stereoisomers. Here, given the multiple (n = 2) chiral centers, there are 2n = 4 possible configurations that lack a plane of symmetry, as the ring skeleton exists in a non-planar chair conformation. In addition,...
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Diels–Alder reactions between cyclic dienes locked in an s-cis configuration and dienophiles yield bridged bicyclic products.
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The Diels–Alder reaction is an example of a thermal pericyclic reaction between a conjugated diene and an alkene or alkyne, commonly referred to as a dienophile. The reaction involves a concerted movement of six π electrons, four from the diene and two from the dienophile, forming an unsaturated six-membered ring. As a result, these reactions are classified as [4+2] cycloadditions.
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Seven-Membered Ring Formation in Triterpene Biosynthesis: A Key Cyclopropane Rearrangement in Ilelic Acid

Moe Nakano1, Kazuma Hiasa1, Satoko Sato-Shimizu1

  • 1Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, 4-4-37 Takeda, Kofu, Yamanashi 400-8510, Japan.

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|February 17, 2025
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Summary

This study reveals how natural compounds called triterpenes form complex seven-membered rings through a carbocation mechanism, not a radical one. This finding deepens our understanding of natural product biosynthesis and aids in designing new synthetic methods.

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Area of Science:

  • Natural Product Biosynthesis
  • Computational Chemistry
  • Organic Chemistry

Background:

  • Triterpenes are complex natural compounds with diverse biological activities.
  • Seven-membered ring formation is key to triterpene structural diversity.
  • Understanding these biosynthetic pathways is crucial for natural product synthesis.

Purpose of the Study:

  • To elucidate the reaction mechanism of seven-membered ring formation in ilelic acid biosynthesis.
  • To investigate the role of cyclopropane rearrangement in this process.
  • To utilize computational methods for mechanistic elucidation.

Main Methods:

  • Density Functional Theory (DFT) calculations were employed.
  • The biosynthetic pathway of ilelic acid was thoroughly investigated.
  • Focus was placed on the critical ring expansion step.

Main Results:

  • The seven-membered ring formation proceeds via a cationic mechanism.
  • A radical-mediated process was ruled out.
  • A concerted reaction pathway was identified, driven by carbocation intermediate instability, avoiding high-energy intermediates.

Conclusions:

  • The study provides a detailed mechanistic understanding of ilelic acid biosynthesis.
  • Findings have broader implications for other triterpene pathways involving similar transformations.
  • This work highlights the utility of computational methods in deciphering complex biosynthetic mechanisms and suggests potential biomimetic synthesis approaches.