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Purpose <p>This study aimed to investigate the chemical constituents of the trunk bark of <i>Xylopia quintasii</i> and evaluate the antibacterial potential of its isolated terpenoids, with a focus on the structural characterisation and polymorphism of (−)-rhinocerotinoic acid (<b>1</b>).</p> Methods <p>The petroleum ether fraction of the methanol extract was subjected to chromatographic separation, leading to the isolation of eight terpenoids, including six diterpenoids and two lupane-type triterpenoids. Single-crystal X-ray diffraction was employed to determine the molecular framework and relative stereochemistry of (−)-rhinocerotinoic acid (<b>1</b>). Optical rotation, Flack parameter analysis, and complementary spectroscopic techniques (CD, VCD, or chiral HPLC) were considered to assess stereochemistry. Antibacterial activity was evaluated against Gram-negative enterobacteria, and molecular docking was performed on the MurA enzyme to explore potential mechanisms.</p> Results <p>Among the diterpenoids, (−)-rhinocerotinoic acid (<b>1</b>) was identified as a labdane-type compound, crystallising in a triclinic P1 system representing a new polymorph. Optical rotation (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\:{\left[{\upalpha\:}\right]}_{D}^{24}\)</EquationSource> </InlineEquation> −2.04, c = 0.2, MeOH) and Flack parameter (0.20) indicated that the absolute configuration could not be unambiguously assigned. Several diterpenoids exhibited higher antibacterial activity than the crude extract, with 3β-hydroxy-copalic acid (<b>3</b>) showing the most potent effect (MIC = 50&#xa0;µg/mL against <i>E. coli</i>). Docking studies suggested potential interactions with the MurA catalytic site, although predictions for compound <b>1</b> were less reliable (RMSD = 4.48 Å).</p> Conclusion <p><i>Xylopia quintasii</i> trunk bark contains chemically diverse labdane- and kaurane-type diterpenoids. The identification of a new polymorphic form of (−)-rhinocerotinoic acid (<b>1</b>), together with the selective antibacterial activity of certain diterpenoids, highlights their chemotaxonomic significance and potential as scaffolds for further pharmacological studies.</p>

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Terpenoids from Xylopia quintasii Trunk Bark: Structural Characterisation, a New Polymorph of (−)-Rhinocerotinoic Acid, Antibacterial Activity, and Molecular Docking Studies

  • 期刊论文

  • 发表日期：

    2026年6月23日

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  • Aristide Munvera Mfifen,
  • Pamela Kemda Nangmo,
  • Blandine M. W. Ouahouo,
  • Bruno Dupon Ambamda Akamba,
  • Jordan Tonga Lembe,
  • Michael Hermann Kengne Kamdem,
  • Edwin M. Mmutlane,
  • Derek Tantoh Ndinteh,
  • Pierre Mkounga,
  • Augustin Ephrem Nkengfack

摘要

Purpose

This study aimed to investigate the chemical constituents of the trunk bark of Xylopia quintasii and evaluate the antibacterial potential of its isolated terpenoids, with a focus on the structural characterisation and polymorphism of (−)-rhinocerotinoic acid (1).

Methods

The petroleum ether fraction of the methanol extract was subjected to chromatographic separation, leading to the isolation of eight terpenoids, including six diterpenoids and two lupane-type triterpenoids. Single-crystal X-ray diffraction was employed to determine the molecular framework and relative stereochemistry of (−)-rhinocerotinoic acid (1). Optical rotation, Flack parameter analysis, and complementary spectroscopic techniques (CD, VCD, or chiral HPLC) were considered to assess stereochemistry. Antibacterial activity was evaluated against Gram-negative enterobacteria, and molecular docking was performed on the MurA enzyme to explore potential mechanisms.

Results

Among the diterpenoids, (−)-rhinocerotinoic acid (1) was identified as a labdane-type compound, crystallising in a triclinic P1 system representing a new polymorph. Optical rotation ( \(\:{\left[{\upalpha\:}\right]}_{D}^{24}\) −2.04, c = 0.2, MeOH) and Flack parameter (0.20) indicated that the absolute configuration could not be unambiguously assigned. Several diterpenoids exhibited higher antibacterial activity than the crude extract, with 3β-hydroxy-copalic acid (3) showing the most potent effect (MIC = 50 µg/mL against E. coli). Docking studies suggested potential interactions with the MurA catalytic site, although predictions for compound 1 were less reliable (RMSD = 4.48 Å).

Conclusion

Xylopia quintasii trunk bark contains chemically diverse labdane- and kaurane-type diterpenoids. The identification of a new polymorphic form of (−)-rhinocerotinoic acid (1), together with the selective antibacterial activity of certain diterpenoids, highlights their chemotaxonomic significance and potential as scaffolds for further pharmacological studies.