Kazunari Sakai

A new insecticidal meroterpenoid, named sesquicillin F (1), has been isolated from a culture broth of Mariannaea macrochlamydospora FKI-4735, together with 4-hydroxy-5,6-dimethylpyran-2-one (2). Compounds 1 and 2 were insecticidally active against Halyomorpha halys at 1 ppm.

An anti-mannheimiosis agent, aldsulfin, was isolated from a culture broth of the fungus Lasiodiplodia pseudotheobromae FKI-4499, together with a known compound, lasiodipline C, using bioassay-guided fractionation. Spectroscopic analysis of aldsulfin, using NMR, mass spectrometry, and CD analyses revealed it to be an epithiodiketopiperazine with an unstable and unusual hemithioaminal moiety. Aldsulfin showed antibacterial activity against Mannheimia haemolytica and Pasteurella multocida.

Saprolegnia parasitica, belonging to oomycetes, is one of virulent pathogen of fishes such as salmon and trout, and causes tremendous damage and losses in commercial aquacultures by saprolegniasis. Previously, malachite green, an effective medicine, had been used to control saprolegniasis. However, this drug has been banned around the world due to its mutagenicity. Therefore, novel anti-saprolegniasis compounds are urgently needed. As a new frontier to discover bioactive compounds, we focused on the deep-sea fungi for the isolation of anti-saprolegniasis compounds. In this paper, on the course of anti-saprolegniasis agents from 546 cultured broths of 91 deep-sea fungal strains, we report a new compound, named quellenin (1) together with three known compounds, diorcinol (2), violaceol-I (3) and violaceol-II (4), from deep-sea fungus Aspergillus sp. YK-76. This strain was isolated from an Osedax sp. annelid, commonly called bone-eating worm, collected at the São Paulo Ridge in off Brazil. Compounds 2, 3 and 4 showed anti-S. parasitica activity. Our results suggest that diorcinol and violaceol analogs and could be good lead candidates for the development of novel agents to prevent saprolegniasis.