Reversing resistance: Rose myrtle extracts analysed by NMR

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  • Published: Mar 1, 2017
  • Author: David Bradley
  • Channels: NMR Knowledge Base
thumbnail image: Reversing resistance: Rose myrtle extracts analysed by NMR

Rose myrtle extract

Novel natural products found in rose myrtle could hold promise of a new way to make breast cancer cells that have become resistant to the conventional anticancer drug doxorubicin susceptible once more. Franz Xaver https://commons.wikimedia.org/wiki/Rhodomyrtus_tomentosa?uselang=en-gb#/media/File:Rhodomyrtus_tomentosa_1.jpg

Novel natural products found in rose myrtle could hold promise of a new way to make breast cancer cells that have become resistant to the conventional anticancer drug doxorubicin susceptible once more. Nuclear magnetic resonance (NMR) spectroscopy, electronic circular dichroism (ECD) and X-ray crystallography were used to determine the structures and absolute configurations of the compounds.

Rose myrtle, Rhodomyrtus tomentosa, is an evergreen flowering shrub native to southern and southeastern Asia. It is used as an ornamental plant and also grown as a firebreak in some regions because of its flame-retardant properties. Its sweet, edible fruit is made into jams, preserves, wines and even baked in pies. But, it is the biochemistry of the Myrtaceae that has attracted the attention of chemists. This family of plants contain syncarpic acid-conjugated terpenoids (SACTs). The skeletons of this class of meroterpenoids generally comprises an alkylated syncarpic acid moiety and a terpenoid unit, they are a structurally diverse group of materials.

Absolutely

Ya-Long Zhang, Xu-Wei Zhou, Lin Wu, Xiao-Bing Wang, Ming-Hua Yang, Jun Luo, Jian-Guang Luo, and Ling-Yi Kong of the China Pharmaceutical University, in Nanjing, China, have investigated extracts of the leaves of the only member of the Myrtaceae family that grows in China, the rose myrtle. They have now isolated and identified three new syncarpic acid-conjugated sesquiterpenoids, tomentodiones E to G together with six new syncarpic acid-conjugated monoterpenoids, tomentodiones H to M. Three of the new natural products represent the first examples of beta-calacorene-based meroterpenoids, the team reports in the Journal of Natural Products.

Of course, for any medicinal study involving structure-activity relationships (SARs) absolute configurations are essential. Rather than using long-winded biomimetic syntheses and analytical studies, the team turned to their ECD data, which is highly sensitive to geometrical changes and electronic structure. This gave them an empirical rule for the determination of the absolute configuration around the C7' carbon atom in the compounds and thus together with the NMR and XRD data they could obtain complete absolute structures of their discoveries.

Reversing resistance

With those structures in hand, the team then looked at activity against doxorubicin-resistant human breast cancer cells. One of the compounds, the non-cytotoxic tomentodione H proved itself to be most effective in reversing resistance in the cancer cell line. It had the strongest potentiation effect on doxorubicin susceptibility, enhancing the drug's effects some 16.5 times at a concentration of just 30 micromolar.

Related Links

J Nat Prod 2017, online: "Isolation, Structure Elucidation, and Absolute Configuration of Syncarpic Acid-Conjugated Terpenoids from Rhodomyrtus tomentosa"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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