Our initial studies on the contents of Turkish Papaver pseudo-orientale (Medw.) Fedde (Papaveraceae) have yielded a variety of modified phthalideisoquinoline alkaloids, including (-)-papaveroxinoline [1] and (-)-papaveroxine [2]. A new alkaloid, (-)-papaveroxidine [3], the carboxylic acid acetate completing the alcohol-aldehyde-carboxylic acid triad, was isolated from the same plant collected at a different site. (-)-Papaveroxidine (C₂₄H₂₅NO₉) was characterized by UV (λmax (MeOH) 237 sh, 283 nm, log ε 4.09, 3.44), IR (CHCl₃ carbonyl bands at 1615 and 1735 cm⁻¹), MS (EIMS base peak at m/z 220, CIMS [M+1]⁺ at m/z 474), and ¹H NMR (in CD₃CN) data including N-methyl, three O-methyl, acetate methyl, H-1 and H-α doublets, methylenedioxy, and aromatic protons. Its structure was confirmed by esterification to (-)-papaveroxidine methyl ester [4] and LiAlH₄ reduction of 4 to known (-)-narcotinediol. The plant extracts contained major alkaloids (+)-salutaridine and (-)-papaveroxine [2], and minor alkaloids such as (-)-narcotinehemiacetal, (-)-papaveroxinoline [1], (-)-narcotinediol, (+)-norsalutaridine, (-)-thebaine, and (-)-papaveroxidine [3].