Abstract
The Antarctic deep-sea sponge Latrunculia (Latrunculia) biformis Kirkpatrick, 1908 (Class Demospongiae Sollas, Order Poecilosclerida Topsent, Latrunculiidae Topsent) was selected for chemical analyses due to its potent anticancer activity. Metabolomic analysis of its crude extract by HRMS/MS-based molecular networking showed the presence of several clusters of pyrroloiminoquinone alkaloids, i.e., discorhabdin and epinardin-type brominated pyridopyrroloquinolines and tsitsikammamines, the non-brominated bis-pyrroloiminoquinones. Molecular networking approach combined with a bioactivity-guided isolation led to the targeted isolation of the known pyrroloiminoquinone tsitsikammamine A (1) and its new analog 16,17-dehydrotsitsikammamine A (2). The chemical structures of the compounds 1 and 2 were elucidated by spectroscopic analysis (one-dimensional (1D) and two-dimensional (2D) NMR, HR-ESIMS). Due to minute amounts, molecular modeling and docking was used to assess potential affinities to potential targets of the isolated compounds, including DNA intercalation, topoisomerase I-II, and indoleamine 2,3-dioxygenase enzymes. Tsitsikammamines represent a small class of pyrroloiminoquinone alkaloids that have only previously been reported from the South African sponge genus Tsitsikamma Samaai & Kelly and an Australian species of the sponge genus Zyzzya de Laubenfels. This is the first report of tsitsikammamines from the genus Latrunculia du Bocage and the successful application of molecular networking in the identification of comprehensive chemical inventory of L. biformis followed by targeted isolation of new molecules. This study highlights the high productivity of secondary metabolites of Latrunculia sponges and may shed new light on their biosynthetic origin and chemotaxonomy.
Highlights
Marine sponges are the richest and best-studied sources of bioactive marine natural products (MNPs) among all marine organisms [1]
This is the first report of tsitsikammamines from the genus Latrunculia du Bocage and the successful application of molecular networking in the identification of comprehensive chemical inventory of L. biformis followed by targeted isolation of new molecules
The identification and isolation of tsitsikammamines from a species of Latrunculia raises questions regarding the origin of the tsitsikammamines
Summary
Marine sponges are the richest and best-studied sources of bioactive marine natural products (MNPs) among all marine organisms [1]. Sponges are often highly diverse and dominant in the invertebrate communities of Antarctic ecosystems [6,7,8]. They provide structure to the benthos and nursery grounds for juvenile fish and many other organisms [9]. In order to cope with harsh environmental conditions, to deter large predators such as sea stars and nudibranchs, to avoid fouling and to ensure their survival in Antarctica, sponges have developed a range of behavioral, physical and chemical defense mechanisms [6,10] including the production of ‘antifreeze’ peptides [11] and unique, highly complex secondary metabolites [12,13]
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