Abstract
The Persian Gulf is a unique and biologically diverse marine environment dominated by invertebrates. In continuation of our research interest in the chemistry and biological activity of marine sponges from the Persian Gulf, we selected the excavating sponge Cliona celata for detailed metabolome analyses, in vitro bioactivity screening, and chemical isolation studies. A UPLC-MS/MS (MS2) molecular-networking-based dereplication strategy allowed annotation and structural prediction of various diketopiperazines (DKPs) and etzionin-type diketopiperazine hydroxamates (DKPHs) in the crude sponge extract. The molecular-networking-guided isolation approach applied to the crude extract afforded the DKPH etzionin (1) and its two new derivatives, clioetzionin A (2) and clioetzionin B (3). Another new modified DKP (4) was identified by MS/MS analyses but could not be isolated in sufficient quantities to confirm its structure. The chemical characterization of the purified DKPHs 1–3 was performed by a combination of 1D and 2D NMR spectroscopy, HRMS, HRMS/MS, and [α]D analyses. Compounds 1 and 2 exhibited broad antibacterial, antifungal, and anticancer activities, with IC50 values ranging from 19.6 to 159.1 µM. This is the first study investigating the chemical constituents of a C. celata specimen from the Persian Gulf. It is also the first report of full spectroscopic data of etzionin based on extensive spectroscopic analyses.
Highlights
Iran covers the entire northern coastline of the Persian Gulf, a marginal sea of the Indian Ocean
The molecular-networking-guided isolation approach applied to the crude extract afforded the diketopiperazine hydroxamates (DKPHs) etzionin (1) and its two new derivatives, clioetzionin A (2) and clioetzionin B (3)
The chemical characterization of the purified DKPHs 1–3 was performed by a combination of 1D and 2D NMR spectroscopy, HRMS, HRMS/MS, and [α]D analyses
Summary
Iran covers the entire northern coastline of the Persian Gulf, a marginal sea of the Indian Ocean. The Persian Gulf is a shallow sea with high temperature fluctuations, ranging from 12 to 35 ◦C, representing a significant stress factor for marine flora and fauna [1,2]. Despite all these harsh environmental conditions, plus additional anthropogenic pressures, such as busy shipping lines, the Persian Gulf has a highly diverse fauna dominated by coral and sponge communities [3]. Two Cliona species, namely C. celata and C. vastifica, have been reported from the fauna of the Persian Gulf [15], but they have not been subjected to any chemical or bioactivity study so far
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