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Monitoring Conformational Dynamics of Single Unmodified Proteins using Plasmonic Nanotweezers

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Rules for Dibenzocyclooctadiene Conformational Dynamics.

Luke P Robertson¹, Wen Xu², Louisa Brieskorn³

¹Pharmacognosy, Department of Pharmaceutical Biosciences, Uppsala University, Uppsala 75123, Sweden.

Journal of Natural Products

|January 31, 2026

Summary

Flexible dibenzocyclooctadiene lignans exhibit conformational dynamics that impact NMR spectra and biological activity. Understanding these dynamics, influenced by substituents, is crucial for accurate interpretation of their behavior.

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Area of Science:

Natural Products Chemistry
Organic Chemistry
Spectroscopy

Background:

Conformational dynamics of flexible molecules significantly affect NMR spectra and biological activity, but are often overlooked.
Dibenzocyclooctadiene lignans are a class of natural products where conformational dynamics are poorly understood, leading to misconceptions in the literature.

Purpose of the Study:

To investigate the cause of ¹³C NMR signal broadening observed in new dibenzocyclooctadienes.
To systematically analyze the influence of substituents on the conformational dynamics of dibenzocyclooctadiene lignans.
To develop predictive rules for substituent effects on dibenzocyclooctadiene ring dynamics.

Main Methods:

¹³C Nuclear Magnetic Resonance (NMR) spectroscopy, including Variable Temperature NMR (VT-NMR).
Computational analysis of molecular conformations and steric interactions.
Review and analysis of ¹³C NMR spectra from 71 published dibenzocyclooctadienes.

Main Results:

¹³C NMR signal broadening, observed in over 70% of analyzed dibenzocyclooctadienes, is linked to specific benzylic substituents at the C-6 position.
These C-6 substituents induce steric interactions, destabilizing the twist-boat chair (TBC) conformation and promoting exchange with the twist-boat (TB) conformation.
Substituents at C-7/C-8 positions were found to stabilize the TBC conformation, indicating that many previously described discrete conformers are actually interconverting mixtures.

Conclusions:

The conformational dynamics of dibenzocyclooctadiene lignans are significantly influenced by substituent positions and types.
Misconceptions regarding the conformational states of dibenzocyclooctadienes can be resolved by considering substituent effects on ring dynamics.
A predictive framework has been established to understand how common substituents modulate the conformational behavior of this important class of natural products.