Three Diketopiperazine Alkaloids with Spirocyclic Skeletons and One Bisthiodiketopiperazine Derivative from the Mangrove-Derived Endophytic Fungus Penicillium brocae MA-231

Four new diketopiperazines including spirobrocazines A–C (1–3) and brocazine G (4) were characterized from the mangrove-derived Penicillium brocae MA-231. Compounds 1 and 2 had a 6/5/6/5/6 cyclic system with a rare spirocyclic center at C-2. Their structures and absolute configurations were determined by spectroscopic analysis, TDDFT-ECD calculations, and X-ray diffraction. Compound 4 exhibited potent cytotoxicity against both sensitive and cisplatin-resistant human ovarian cancer cells and strong antimicrobial activity against pathogenic Staphylococcus aureus.