**Ekaterina A. Yurchenko 1,\*, Ekaterina S. Menchinskaya 1, Evgeny A. Pislyagin 1, Phan Thi Hoai Trinh 2,3, Elena V. Ivanets 4, Olga F. Smetanina <sup>4</sup> and Anton N. Yurchenko <sup>4</sup>**


Received: 26 October 2018; Accepted: 19 November 2018; Published: 21 November 2018

**Abstract:** A new melatonin analogue 6-hydroxy-*N*-acetyl-β-oxotryptamine (**1**) was isolated from the marine-derived fungus *Penicillium* 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 (**2)** and 8-methoxy-3,5-dimethylisochroman-6-ol (**3**) from *Penicillium* sp. KMM 4672, candidusin A (**4**) and 4"-dehydroxycandidusin A (**5**) from *Aspergillus* sp. KMM 4676, and diketopiperazine mactanamide (**6**) from *Aspergillus flocculosus*, 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 *p*-terphenyl polyketides in both the 6-OHDA- and PQ-induced PD models.

**Keywords:** neuroprotective activity; Parkinson's disease; ROS; DPPH-scavenging activity; 6-OHDA; paraquat; marine fungal metabolites
