Phenylhydrazone Alkaloids from the Deep-Sea Cold Seep Derived Fungus <i>Talaromyces amestolkiae</i> HDN21-0307

Abstract

Alkaloids with a phenylhydrazone architecture are rarely found in nature. Four unusual phenylhydrazone alkaloids named talarohydrazones A-D (<b>1</b>-<b>4</b>) were isolated from the deep-sea cold seep derived fungus <i>Talaromyces amestolkiae</i> HDN21-0307 using the one strain-many compounds (OSMAC) approach and MS/MS-based molecular networking (MN) combined with network annotation propagation (NAP) and the unsupervised substructure annotation method MS2LDA. Their structures were elucidated by spectroscopic data analysis, single-crystal X-ray diffraction, and quantum chemical calculations. Talarohydrazone A (<b>1</b>) possessed an unusual skeleton combining 2,4-pyridinedione and phenylhydrazone. Talarohydrazone B (<b>2</b>) represents the first natural phenylhydrazone-bearing azadophilone. Bioactivity evaluation revealed that compound <b>1</b> exhibited cytotoxic activity against NCI-H446 cells with an IC₅₀ value of 4.1 μM. In addition, compound <b>1</b> displayed weak antibacterial activity toward <i>Staphylococcus aureus</i> with an MIC value of 32 μg/mL.