title: Insecticidal pyrido[1,2-a]azepine alkaloids and related derivatives from Stemona species.
abstract: Eight new alkaloids, the pyrido[1,2-a]azepines stemokerrin, methoxystemokerrin-N-oxide, oxystemokerrin, oxystemokerrin-N-oxide, and pyridostemin, along with the pyrrolo[1,2-a]azepines dehydroprotostemonine, oxyprotostemonine, and stemocochinin were isolated from four Stemona species together with the known compounds protostemonine, stemofoline, 2'-hydroxystemofoline, and parvistemonine. Their structures were elucidated by 1H and 13C NMR including 2D methods and two key compounds additionally by X-ray diffraction. Besides the formation of a six membered piperidine ring, additional oxygen bridges and N-oxides contributed to structural diversity. The co-occurrence of pyrrolo- and pyridoazepines suggested biosynthetic connections starting from more widespread protostemonine type precursors. Bioassays with lipophilic crude extracts against Spodoptera littoralis displayed very strong insecticidal activity for the roots of S. curtisii and S. cochinchinensis, moderate activity for S. kerrii, but only weak effects for the unidentified species HG 915. The insect toxicity was mainly caused by the accumulation of stemofoline, oxystemokerrin, and dehydroprotostemonine displaying two different modes of action. Based on the various insecticidal activities of 13 derivatives structure-activity relationships became apparent.
authors.affiliation: Comparative & Ecological Phytochemistry Department, Institute of Botany, University of Vienna, Rennweg 14, A-1030 Vienna, Austria.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Kaltenegger
authors.forename: Brigitte
authors.initials: B
authors.lastname: Brem
authors.forename: Kurt
authors.initials: K
authors.lastname: Mereiter
authors.forename: Hermann
authors.initials: H
authors.lastname: Kalchhauser
authors.forename: Hanspeter
authors.initials: H
authors.lastname: Kählig
authors.forename: Otmar
authors.initials: O
authors.lastname: Hofer
authors.forename: Srumya
authors.initials: S
authors.lastname: Vajrodaya
authors.forename: Harald
authors.initials: H
authors.lastname: Greger
mesh_terms: D000470:Alkaloids / Q000737:chemistry* / Q000494:pharmacology*; D000818:Animals; D007306:Insecticides / Q000302:isolation & purification*; D007928:Lethal Dose 50; D009682:Magnetic Resonance Spectroscopy; D019684:Magnoliopsida / Q000737:chemistry* / Q000145:classification; D015394:Molecular Structure; D018515:Plant Leaves / Q000737:chemistry; D018517:Plant Roots / Q000737:chemistry; D018411:Spodoptera / Q000187:drug effects; D013329:Structure-Activity Relationship
chemical_list: D000470:Alkaloids; D007306:Insecticides