N-gamma-Glutamyl boletine and a toxin, 2-buty1-1-azacyclohexene iminium salt, were isolated from the mushroom Tylopilus sp. (Boltaceae). The absolute stereostructure of N-gamma-glutamyl boletine was clarified based on spectroscopic analysis, acidic hydrolysis and total synthesis. N-gamma-Glutamyl boletine exhibited moderate antibacterial activity. 2-Buty1-1-azacyclohexene iminium salt exhibited moderate acute toxicity against ddY mice. We proposed feasible biosynthetic pathway of piperidine alkaloids that the cyclic imimum compound might be biosynthesized from boletine, a new amino acid containing an delta-amino ketone moiety. (C) 2002 Elsevier Science Ltd. All rights reserved.