Antibacterial stigmastane-type steroids and other constituents from the leaves of Vernonia glabra (Steetz) Vatke (Asteraceae)

Abstract

Two new stigmastane steroids (1 and 2) were isolated from the methanol extract of the leaves of Vernonia glabra, together with seventeen known compounds (3–19) including one fatty acid, four triterpenoids, four steroids, one trinitropropanoyl glucoside, and seven flavonoids. The structures of compounds 1 and 2 were assigned based on their IR, NMR and MS data, and by comparison with literature values. The MeOH extract, its fractions and isolated compounds were subjected to in vitro antibacterial assay against two Gram-positive (Staphylococcus aureus ATCC25923 and Streptococcus pneumoniae ATCC49619) and two Gram-negative (Escherichia coli ATCC8739 and Klebsiella pneumoniae ATCC10031) bacteria, using broth microdilution method. The extract and fractions exhibited (16 ≤ MIC ≤ 512 μg/mL) antibacterial activities. The isolated and tested compounds were also active (16 ≤ MIC ≤ 128 μg/mL) against the four pathogenic bacteria, with compound 2 being the most active and E. coli, the most sensitive microorganism.

Graphical Abstract

Keywords:

• Vernonia glabra
• Asteraceae
• Stigmastane steroids
• Vernoglabrosterol
• Vernoglabroside
• Antibacterial activity

Acknowledgements

We are grateful to the University of Dschang and the Cameroonian Ministry of higher education for financing some consumable items used in this work.

Authors’ contributions

AASM and JDDT carried out the study; ATT, ARND and DKW contributed to structural determination; GMT helped in analysis of biological data; AASM, ATT, JDDT, AT and MT wrote the manuscript; MT and AT provided access to instrumentation; JDDT provided the bacterial strains and facilities for the antibacterial testing; JDDT and MT designed and supervised the work; all authors read and approved the final manuscript.

Disclosure statement

The authors declare no competing interest.

Additional information

Funding

The author(s) reported there is no funding associated with the work featured in this article.