Anti-Parkinsonian 4-hydroxy-2-pyridones from an endolichenic fungus, Tolypocladium sp. (strain CNC14).

Abstract

4-Hydroxy-2-pyridone alkaloids have attracted considerable attention because of their intriguing structures and diverse bioactivities. In our previous study, 4-hydroxy-2-pyridone alkaloids were shown to exhibit potent activity against neuron-associated targets. To discover this class of neuroactive compounds, an array of endolichenic fungal extracts was screened by analyzing liquid chromatography-ultraviolet-mass spectrometry (LC-UV-MS) profiles. The screening yielded strain Tolypocladium sp. (strain CNC14), which produced compounds with characteristic Ultraviolet patterns for 4-hydroxy-2-pyridone alkaloids using our in-house library. Based on these findings, we conducted a chemical investigation, which led to the isolation of four new (1-4) and ten known (5-14) compounds. Their structures were elucidated via spectroscopic methods such as nuclear magnetic resonance and mass spectrometry. The stereochemistry of the new compounds (1-4) was established using rotating frame overhauser effect spectroscopy (ROESY), and the electronic circular dichrosim (ECD) was compared with the calculated data. Interestingly, the side chains of 4-hydroxy-2-pyridone in 1 and 2 were cyclized in different directions to form benzopyrano[3,4-b]pyridinol from previously reported compounds, and all the new compounds were predicted to be biosynthesized from reduced tolypyridone C (7) via the hetero-Diels-Alder reaction. Among the isolated compounds, 4 significantly protected neuronal cells against treatment with 1-methyl-4-phenylpyridinium (MPP+), a Parkinsonian neurotoxin, in an in vitro Parkinson's disease model. One-Sentence Summary: Four new neuroprotective 4-hydroxy-2-pyridone alkaloids were discovered from an endolichenic fungus Tolypocladium sp.