A new antibacterial neo-clerodane diterpenoid and other constituents from Chasmanthera dependens Hochst. (Menispermaceae) and their chemotaxonomic significance

The leaves, stems and fruits methanol extracts of Chasmanthera dependens were chemically investigated to afford one new neo-clerodane diterpenoid (1) along with seventeen known compounds including three diterpenoids (2–4), six triterpenoids (5–10), four steroids (11–14), one sesquiterpenoid (15), one lignan (16) and two phenolic acids (17 and 18). Structures were established by analysis of their spectroscopic and spectrometric data and in comparison with those reported from the literature. Except columbin (2), compounds are reported for the first time from the genus Chasmanthera. The extracts, fractions, and isolated compounds were subjected to in vitro antibacterial assays against three Gram-positive and three Gram-negative bacteria, using the broth microdilution method. The MeOH extract of the leaves and its fractions F1–F4 had significant (MIC = 93.8 μg/mL for F4) or moderate (187.5 ≤ MIC ≤ 375 μg/mL) activities against Pseudomonas aeruginosa. Chasmantherenolide (1) was moderately active (MIC = 75 μg/mL, 202.6 μM) against Gram-positive bacterial strains. Significant antibacterial activity (MIC = 9.4 μg/mL, 20.6 μM) was recorded for oleanolic acid (7) against Mycobacterium smegmatis. The chemotaxonomic significance of the isolated compounds was discussed.