title: Identification of a new antinociceptive alkaloid isopropyl N-methylanthranilate from the essential oil of Choisya ternata Kunth.
abstract: BACKGROUND
  Mexican people employed infusion of leaves of Choisya ternata Kunth for their antispasmodic and "simulative properties".
  
  
  OBJECTIVE
  In the present study the detailed GC and GC-MS analyses of the essential oil of Choisya ternata Kunth (Rutaceae) were performed. The presence of a minor constituent isopropyl N-methylanthranilate (1) was revealed among other identified volatiles. A synthesis of 1 was undertaken in order to corroborate this find and obtain gram quantities that would allow the testing of its biological activity (peripheral and central antinociceptive activity).
  
  
  METHODS
  The oils were investigated by GC and GC-MS. Synthesized compounds were spectrally characterized (UV-Vis, IR, 1D and 2D NMR, MS). The obtained synthetic samples of compounds were assayed for peripheral and central antinociceptive activity in two models (effects on acetic acid induced writhing in mice and the hot plate test for nociception).
  
  
  RESULTS
  Detailed GC and GC-MS analyses of the essential oil of Choisya ternata Kunth (Rutaceae) among 157 other identified volatiles revealed the presence of a minor constituent isopropyl N-methylanthranilate (1). Compound 1, named ternanthranin, is therefore detected as a natural product for the first time with a very restricted occurrence (samples of several citrus oils were screened for the presence of 1). The antinociceptive activities were assayed for ternanthranin, the two other synthetic analogs, methyl and propyl N-methylanthranilate, as well as the essential oil and the crude ethanol extract of the leaves. The results clearly demonstrate a very high (even significant at 0.3 mg/kg) dose dependent activity for the anthranilates (and the extracts). Isopropyl N-methylanthranilate showed the highest, while methyl N-methylanthranilate showed the lowest activity (with the methyl ester at 3 mg/kg still better than acetylsalicylic acid, at 200 mg/kg, in the first, or comparable with morphine, at 5mg/kg, in the second test).
  
  
  CONCLUSIONS
  This study once again revealed that detailed investigations of plant species with ethnopharmacologically documented activity may yield new natural compounds-a new alkaloid (ternanthranin), a volatile simple anthranilate that can be considered responsible for the antinociceptive activity of the crude plant extracts.
authors.affiliation: Department of Chemistry, Faculty of Science and Mathematics, University of Niš, Višegradska 33, 18000 Niš, Serbia. vangelis0703@yahoo.com
authors.forename: Niko S
authors.initials: NS
authors.lastname: Radulović
authors.forename: Ana B
authors.initials: AB
authors.lastname: Miltojević
authors.forename: Michael
authors.initials: M
authors.lastname: McDermott
authors.forename: Steve
authors.initials: S
authors.lastname: Waldren
authors.forename: John Adrian
authors.initials: JA
authors.lastname: Parnell
authors.forename: Mariana Martins Gomes
authors.initials: MM
authors.lastname: Pinheiro
authors.forename: Patricia Dias
authors.initials: PD
authors.lastname: Fernandes
authors.forename: Fabio
authors.initials: F
authors.lastname: de Sousa Menezes
mesh_terms: D000700:Analgesics / Q000032:analysis / Q000494:pharmacology / Q000627:therapeutic use*; D000818:Animals; D001241:Aspirin / Q000494:pharmacology; D001522:Behavior, Animal / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D008401:Gas Chromatography-Mass Spectrometry; D008297:Male; D051379:Mice; D009020:Morphine / Q000494:pharmacology; D009822:Oils, Volatile / Q000737:chemistry*; D010146:Pain / Q000188:drug therapy*; D008517:Phytotherapy; D010936:Plant Extracts / Q000737:chemistry / Q000494:pharmacology / Q000627:therapeutic use*; D018515:Plant Leaves; D027821:Rutaceae / Q000737:chemistry*; D062367:ortho-Aminobenzoates / Q000032:analysis / Q000138:chemical synthesis / Q000494:pharmacology / Q000627:therapeutic use*
chemical_list: D000700:Analgesics; D009822:Oils, Volatile; D010936:Plant Extracts; C568549:isopropyl N-methylanthranilate; D062367:ortho-Aminobenzoates; D009020:Morphine; D001241:Aspirin