Menominin A and B: Cytotoxic Cyclodepsipeptides from the Freshwater Sponge-Associated Cyanobacterium <i>Nostoc</i> sp. UIC 10607

Menominin A (<b>1</b>) and B (<b>2</b>), two cyclodepsipeptides containing a 3,8-dihydroxy-2-methyltetradecanoic acid residue, were isolated from the freshwater sponge-associated cyanobacterium, <i>Nostoc</i> sp. UIC 10607, using bioactivity-guided and spectroscopic approaches. The planar structures of <b>1</b> and <b>2</b> were established using HRESIMS and one- and two-dimensional NMR experiments. Comparative genomic analysis revealed unique differences in the putative menominin biosynthetic gene cluster compared to that of the closely related cyanobacterial cyclic lipodepsipeptide, hapalosin, assisting in structure elucidation and highlighting the structural diversity of this class of compounds. Configuration assignments were determined using a combination of <i>J</i>-based configuration analysis, chiral HPLC, modified Mosher's ester analysis, and DFT calculations. Menominin A and B demonstrate antiproliferative bioactivity against the high-grade serous ovarian cancer cell line OVCAR3 (IC₅₀ = 3.1 (<b>1</b>) and 2.4 μM (<b>2</b>)). Menominin A and B are the first reported secondary metabolites from a freshwater sponge-associated cyanobacterium, underscoring the potential of freshwater sponges as a microbial culture source in natural product discovery.