Alkaloids from dendrobatid poison frogs: trans-decahydroquinolines and indolizidines

Abstract

Skin extracts from one population of the Colombian poison-frog Dendrobates histrionicus contain a variety of histrionicotoxins (2,7-disubstituted 1-azaspiro(5.5)-undecan-8-ols) and other alkaloids. Two of tha major alkaloids are trans-dacahydro-quinolines whose gross structures based on mass and nuclear magnetic resonance spectral analysis are 2,5-diallyl- trans -dacahydroquinoline 219A and 2-allyl-5-pent-2-en-4-ynyl- trans -dacahydroquinoline 243A. A minor isomer, 243A°, is also present. X-ray crystalloraphic analysis of 219A-HC1 raveals the absolute configuration as [2S,4aS,5S,8aS]2,5-diallyl- trans -decahydroauinoline. A dihydroxydihydro-219A was also isolated and shown by nuclear magnetic resonance spectral analyais to be 2-allyl-5-(2,3-dihydroxypropyl)- trans -decahydroquinoline (253D). Four of the alkaloids from Dendrobates histrionicus are indolizidines namely (5E,9E)-3-n-butyl-5-n-propylndolizidine 223AE, its two ω-hydroxy congeners 239AE (hydroxypropyl) and 239CD (hydroxybutyl), and (5E,9E)-3-n-butyl-5-mathylindolizidine 195E. Structures are based on nuclear magnetic resonance spectral analysis.