Unexpected Noremestrin with a Sulfur-Bearing 15-Membered Macrocyclic Lactone from sp. 1454.

Two previous unreported epipolythiodioxopiperazines of the emestrin family, namely, noremestrin A () and secoemestrin E (), were successfully isolated from the fungal source sp. 1454. Employing comprehensive spectroscopic techniques, such as high-resolution electrospray ionization mass spectrometry, infrared, and nuclear magnetic resonance (NMR), along with NMR and electronic circular dichroism calculations, the chemical structures of compounds and were elucidated. Particularly noteworthy is the distinctive nature of noremestrin A, representing the inaugural instance of a noremestrin variant incorporating a sulfur-bearing 15-membered macrocyclic lactone moiety. Compounds and exhibited weak cytotoxic activities against the human chronic myelocytic leukemia cell lines MEG-01 and K562.