The major alkaloids of the aerial parts of a Turkish sample of Papaver pseudo-orientale are salutaridine and a new alkaloid, macrantaline, UV, IR, PMR, MS and CD have been used to establish the structure of macrantaline as 1-(2′-hydroxymethylene-3′,4′-dimethoxybenzyl)-2-methyl -6,7-methylenedioxy-8-methoxy-1,2,3,4-tetrahydroisoquinoline. The corresponding 2′-methyl substituted analogue prepared from (-)-α-narcotine and also from macrantaline proved to have identical properties, including CD spectra, thus confirming the structure and establishing the absolute configuration of macrantaline. A new minor alkaloid, macrantoridine, yielded macrantaline on lithium aluminium hydride reduction and differs from the latter in that the 2′-substituent is a carboxyl instead of hydroxymethylene. UV, IR, PMR, MS and CD data are reported for macrantoridine. © 1977.