Marine sponges, regarded as valuable resources of bioactive natural products, are the most ancient polycellular animals that adorn tropical reefs and the ocean bottom.

However, many lines of evidence support that marine sponge-associated microorganisms are the actual producers for structurally diverse and pharmaceutically important secondary metabolites.

Recently, a research group led by Prof. ZHANG Changsheng in South China Sea Institute of Oceanology (SCSIO) of the Chinese Academy of Sciences and their collaborators discovered two sulfur-containing alkaloids dassonmycins A (1) and B (2) from marine sponge-derived microbe.

Fig. 1 Chemical structures of novel sulfur-containing alkaloids (Image by SCSIO)

Both compounds were isolated from the marine sponge-derived actinomycete SCSIO 40065, featuring an unprecedented naphthoquinone[2,3-e]piperazine[1,2-c]thiomorpholine scaffold.

This work was published as a front cover paper in Organic Letters.

Fig. 2 The issued cover art of two novel sulfur-containing alkaloids (Image by Organic Letters)

Sulfur is an indispensable element for all kinds of lives. Sulfur-containing natural products, such as penicillin, ecteinascidin-743 and calicheamicin γ1, have been used as antibiotics and anti-tumor drugs.

Several kinds of natural products except for the sulfur-containing compounds have been reported from the actinomycetal species of Nocardiopsis dassonvillei. Interestingly, analysis of the extracts from N. dassonvillei SCSIO 40065 indicated the presence of sulfur-containing natural products.

The researchers elucidated the structures of these two sulfur-containing alkaloids by comprehensive spectroscopic analysis.

They investigated these unique metabolites from N. dassonvillei SCSIO 40065 and obtained two sulfur-containing alkaloids, dassonmycins A (1) and B (2). Natural alkaloids are generally composed of four elements: carbon, hydrogen, oxygen and nitrogen. Sulfur is seldom introduced into the chemical structures of natural alkaloids.

Bioactivity evaluations indicated that both dassonmycins A (1) and B (2) displayed moderate antibacterial and cytotoxic activities.

These results not only expanded the chemical diversity of alkaloid natural products, but also provided an example to highlight the value of marine sponge-derived microbes for discovering bioactive natural products with novel structures.