| Summary: | A new melatonin analogue 6-hydroxy-<i>N</i>-acetyl-β-oxotryptamine (<b>1</b>) was isolated from the marine-derived fungus <i>Penicillium</i> sp. KMM 4672. It is the second case of melatonin-related compounds isolation from microfilamentous fungi. The neuroprotective activities of this metabolite, as well as 3-methylorsellinic acid (<b>2)</b> and 8-methoxy-3,5-dimethylisochroman-6-ol (<b>3</b>) from <i>Penicillium</i> sp. KMM 4672, candidusin A (<b>4</b>) and 4″-dehydroxycandidusin A (<b>5</b>) from <i>Aspergillus</i> sp. KMM 4676, and diketopiperazine mactanamide (<b>6</b>) from <i>Aspergillus flocculosus</i>, were investigated in the 6-hydroxydopamine (6-OHDA)- and paraquat (PQ)-induced Parkinson’s disease (PD) cell models. All of them protected Neuro2a cells against the damaging influence of 6-OHDA to varying degrees. This effect may be realized via a reactive oxygen species (ROS) scavenging pathway. The new melatonin analogue more effectively protected Neuro2A cells against the 6-OHDA-induced neuronal death, in comparison with melatonin, as well as against the PQ-induced neurotoxicity. Dehydroxylation at C-3″ and C-4″ significantly increased free radical scavenging and neuroprotective activity of candidusin-related <i>p</i>-terphenyl polyketides in both the 6-OHDA- and PQ-induced PD models.
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