Targeted Isolation of a Cytotoxic Cyclic Hexadepsipeptide from the Mesophotic Zone Sponge-Associated Fungus Cymostachys sp. NBUF082.

LC-MS/MS-based molecular networking facilitated the targeted isolation of a new cyclic hexadepsipeptide, cymodepsipeptide (1), and two known analogues, RF-2691A (2) and RF-2691B (3), from the fungus Cymostachys sp. NBUF082 that was derived from a mesophotic zone Aaptos sponge collected near Apo Island. The constitution and configuration of 1 was elucidated through 1D and 2D NMR-spectroscopy, high resolution mass-spectrometry, and chemical degradations including Marfey's analysis and chiral HPLC. It was observed that 1 was moderately cytotoxic against CCRF-CEM human acute lymphocytic leukemia cells in vitro with the IC50 value of 9.2 ± 1.1 μM.