Innate immunity is the front line of self-defense against microbial infection. After searching for natural substances that regulate innate immunity using an ex vivo Drosophila culture system, we identified a novel dimeric chromanone, gonytolide A, as an innate immune promoter from the fungus Gonytrichum sp. along with gonytolides B and C. Gonytolide A also increased TNF-α-stimulated production of IL-8 in human umbilical vein endothelial cells.

Innate immunity is the front line of self-defense against microbial infection. After searching for natural compounds that regulate innate immunity using an ex vivo Drosophila culture system, we identified a new cyclic depsipeptide, aspergillicin F, from the fungus Aspergillus sp., as an innate immune suppressor. The total synthesis and biological evaluation of the aspergillicin family, including aspergillicin F, were performed, revealing that slight structural differences in the side chains of amino acid residues alter innate immunity-regulating activity.

Gonytolide A (1), a dimeric chromanone substituted with the γ-lactone, shows promoting activity of innate immune responses. However, biological studies on this compound have been limited by the low amounts of 1 available from natural resources and the difficulty of its synthesis. In this study, we designed and synthesized structure-simplified gonytolide derivatives. Bischromone 10 and biflavone 13 both promoted the mammalian TNF-α signaling pathway and Drosophila innate immunity. They did not contain a chiral center and were easy to synthesize. Hence, they can be used as lead compounds for a new type of immunostimulating drugs and as research reagents.