Minyobates frogs

The Dendrobatid poison arrow frogs of Central and South America exude a potent mixture of alkaloids from their skins. It was originally thought that the frogs biosynthesized these alkaloids, but it has since been shown that they are of dietary origin. The skin exudate of the Colombian frog Minyobates bombetes causes severe locomotor difficulties, muscle spasms and convulsions upon injection in mice. The major component of the alkaloid mixture is 251F3. Jeff Aube of the University of Kansas recently described (J. Am. Chem. Soc. 2004,126,5475) the enantioselective total synthesis of 3. The key step in the synthesis was the cyclization of the keto azide 2. 

The dendrobatid alkaloid 251F 213 (Figure 12.4) was isolated from the skin exudates of a Columbian dendrobatid poison frog, Minyobates bombetes [105]. The asymmetric total synthesis of this molecule has been reported by Aube and co-workers [106], The synthesis featured a Noyori-type three-component reaction to access an advanced bicyclopentenone intermediate, and also included a tandem ROM/RCM reaction sequence and a Schmidt rearrangement as key steps. 

Fig. 18. Alkaloids of the cyclopentaf/ilquinolizidine class from the dendrobatid frog, Minyobates bombetes. The structure of 251F was determined by nuclear magnetic resonance spectroscopy (/52), but the absolute configuration of 2S1F is unknown. The other structures are tentative and are based primarily on analogy and mass spectra.

C. CpHzsN,—, 153°C, mIz 195(65), 152(100). OD. Infrared data(7i). Hq derivative. Alkaloid 195C may prove to represent different compounds in different extracts. Major alkaloid in one population of Dendrobates speciosus minor alkaloid in certain populations of D. leucomelus, D. pumilio, and D. speciosus and in D, reticulatus and Minyobates steyer-marki. Detected in a ranid frog (73),... 

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