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Drug resistance due to the extensive abuse and over-use of antibiotics has become an increasingly serious problem and researchers started to use plants as an alternative source of new antibiotics. The aim of the present study was to assess the antimicrobial properties of secondary metabolites isolated from A. liebrechtsiana. A new secoiridoid derivative, anthocleistenolide B (1), along with three known compounds, the monoterpene diol, djalonenol (2), the xanthone O-glycoside, decussatin 1-O-β-D-glucopyranoside and the fatty acid, dotriacontanoic acid (4) was isolated from the leaves and bark of this plant. Their structures were elucidated by extensive analysis of spectroscopic (1D and 2D NMR) and mass spectrometric data. The isolated compounds were screened for their antimicrobial properties against five strains of bacteria (two gram positive: Staphylococcus aureus 29213, Enterococcus faecalis ATCC 25922 and three gram negative: Escherichia coli ATCC51299, Proteus mirabilis (isolate), and Pseudomonas aeruginosa QC76110), but all were inactive.

This paper describes eight new triterpenoid saponins, including afzeliioside A (1), four acetylated afzeliiosides as pairs of inseparable regioisomers, called afzeliiosides B/C (2/3) and D/E (4/5), afzeliiosides F-H (6−8), and a known impatiprin C (9), which were isolated from the n-BuOH fraction of the liana of Microglossa afzelii. Their structures were established mainly by extensive spectroscopic analysis, including 1D and 2D NMR, HRFAB-MS, tandem ESI-MS/MS, and chemical methods, as well as a comparison of their spectral data with those of related compounds. All the isolates were screened for their cytotoxic activity against the CAL-27 oral squamous carcinoma cell line. Only compounds 4/5 (EC50 = 36.0 µg/mL (32.7 µM)) exhibited moderate cytotoxic activity. This work presents the first chemical and biological investigation of Microglossa afzelii and reports, for the first time, on the isolation of saponins in the genus Microglossa.