Pyrazinopyrimidine alkaloids from a mangrove-derived fungus Aspergillus versicolor HDN11-84

Pyrazinopyrimidine-type alkaloids bearing a pyrazino[1,2-a] pyrimidine moiety, often have different functional groups substituted at C-8' or C-2'/C-8', generally further forming unique spiro-/conjugated ring systems. Four undescribed pyrazinopyrimidine-type alkaloids, including three natural products pyrasplorines A-C and an artifact deg-pyrasplorine B, as well as a biogenetically related versicoloid A were discovered from the extract of a mangrove-derived fungus Apergillus verisicolor HDN11-84. Pyrasplorine A contains unique spiral-type skeleton (composed of cyclopentenone ring with the pyrazino[1,2-a] pyrimidine core) which is unprecedented in pyrazinopyrimidine-type alkaloids. The deg-pyrasplorine B could be spontaneously converted from pyrasplorine B in mild conditions. Their structures including absolute configurations were elucidated based on NMR spectroscopic analysis, computational calculations and Marfey's method. The absolute configuration of versicoloid A was re-assigned in this study. All the isolated compounds are non-cytotoxic and deg-pyrasplorine B showed anti-influenza A virus H1N1 activity with the IC₅₀ of 50 μM.