A new purine nucleoside coupled with an amino acid derivative,N~2-(1-methoxycarbonylethyl)guanosine 1,along withβ-carboline and russulaceramide was isolated from the fruiting bodies of Amanita exitialis,a newly described poisonous mushroom. Its structure was elucidated by spectroscopic methods.This is the first report of naturally occurring nucleosides in which anα-amino acid derivative is bonded through itsα-amino nitrogen to a nucleobase aglycone by a C-N bond.The new compound was found to be toxic in brine shrimp lethality test(BST). A new purine nucleoside coupled with an amino acid derivative, N ~ 2- (1-methoxycarbonylethyl) guanosine 1, along with β-carboline and russulaceramide was isolated from the fruiting bodies of Amanita exitialis, a newly described poisonous mushroom. Its structure was elucidated by spectroscopic methods. This is the first report of naturally occurring nucleosides in which an α-amino acid derivative is bonded through its α-amino nitrogen to a nucleobase aglycone by a CN bond. The new compound was found to be toxic in brine shrimp lethality test (BST ).