Funiculosin is a neutral lipophilic 4-hydroxypyridone metabolite first isolated by Ando and colleagues at University of Tokyo in 1969 as an antiviral. Funiculosin exhibits broad spectrum antifungal activity by inhibition of mitochondrial electron transport. More recently, derivatives of funiculosin have been identified as promoting innate immune responses via the Toll-like receptor 4/myeloid differentiation factor 2 complex. NOTE, this metabolite is not the red pigment described by Hisano in 1939 as the anthracycline islandin, also named as funiculosin.