Acetylstachyflin

Two novel compounds, stachyflin and acetylstachyflin, have been isolated by solid-state fermentation of Stachybotrys sp. RF-7260. The structures of both metabolites, determined by detailed NMR analyses and X-ray crystallographic analysis, are novel with a pentacyclic moiety including cis-fused decalin. The absolute stereochemistry of stachyflins was determined by circular dichroism analysis. Stachyflin showed antiviral activity against influenza A virus (H1N1) in vitro with an IC50 value of 0.003 microM. Acetylstachyflin was about 77-fold less active than stachyflin.

Stachyflin and acetylstachyflin, produced by Stachybotrys sp. RF-7260, were found to have potent anti-influenza A virus activity. Stachyflin is a new class of hemagglutinin fusion inhibitors of influenza A virus. Several derivatives were synthesized from acetylstachyflin and subjected to preliminary examination of their structure-activity relationships. Among them, the 3-oxo and 3,8'-dioxo derivatives showed potent antiviral activity similar to stachyflin. The 3-epi derivative was four times less active than stachyflin. Modification of the 6'-hydroxy group and the C-5' position markedly diminished the antiviral activity.

Stachybotrys sp. RF-7260 was found to produce stachyflins, novel anti-influenza virus agents, under solid-state fermentation conditions. Feeding DL-lysine to a culture of Stachybotrys sp. RF-7260 induced the formation of the novel compounds, SQ-02-S-L2 and -L1, and feeding DL-valine the formation of SQ-02-S-VI and -V2. The structures of these metabolites were determined by detailed 2D NMR analyses in comparison with acetylstachyflin. SQ-02-S-L2 and -L1 have the lysine moiety and SQ-02-S-V1 has the valine moiety. SQ-02-S-V2 has an amidine moiety instead of the lactam moiety in acetylstachyflin. SQ-02-S-L2, -L1 and -V1, substituted on the lactam amide hydrogen, displayed only a low level of the antiviral activity. However, deacetyl SQ-02-S-V2 showed potent antiviral activity similar to stachyflin.