Antichlamydial sterol from the Red Sea sponge Callyspongia aff. implexa

Marine sponges are rich sources of natural products exhibiting diverse biological activities. Bioactivity-guided fractionation of the Red Sea sponge Callyspongia aff. implexa led to the isolation of two new compounds, 26,27-bisnorcholest-5,16-dien-23-yn-3β,7α-diol, gelliusterol E (1) and C27-polyacetylene, callimplexen A (2), in addition to the known compound β-sitosterol (3). The structures of the isolated compounds were determined by 1D- and 2D-NMR techniques as well as high-resolution tandem mass spectrometry and by comparison to the literature. The three compounds (1-3) were tested against Chlamydia trachomatis, an obligate intracellular gram-negative bacterium, which is the leading cause of ocular and genital infections worldwide. Only gelliusterol E (1) inhibited the formation and growth of chlamydial inclusions in a dose-dependent manner with an IC50 value of 2.3 µM.