From Klebsiella pneumoniae (t)(11S, 11aS) - 1,2,3,10,11,11a - hexahydro - 9 - hydroxy - 11 - (3' indolyl) - 5H - pyrrolo[2,1-c][1,4]benzodiazepin - 5 - one (1) has been isolated for which the name tilivalline is suggested. Structure elucidation and synthesis are reported.