A novel dipeptide, N-γ-glutamyl boletine, and a cyclic iminium toxin from the mushroom Tylopilus sp. (Boletaceae)

N-γ-Glutamyl boletine and a toxin, 2-butyl-1-azacyclohexene iminium salt, were isolated from the mushroom Tylopilus sp. (Boltaceae). The absolute stereostructure of N-γ-glutamyl boletine was clarified based on spectroscopic analysis, acidic hydrolysis and total synthesis. N-γ-Glutamyl boletine exhibited moderate antibacterial activity. 2-Butyl-1-azacyclohexene iminium salt exhibited moderate acute toxicity against ddY mice. We proposed feasible biosynthetic pathway of piperidine alkaloids that the cyclic iminium compound might be biosynthesized from boletine, a new amino acid containing an δ-amino ketone moiety.