Mantella frogs

A similar procedure was applied to the synthesis of quinazolidine 189 from precursor 188 in the total synthesis of the natural product known as ( )-quinolizidine 2071 190, an alkaloid isolated from the skin of the Madagascar mantelline frog Mantella baroni, that shows an exceptional axial stereochemistry for the ethyl group at C-l. Quinolizidine 189 was transformed into 190 by oxidation and two consecutive Wittig methylenations (Scheme 34) <1999CC2281>. 

The decahydrocyclazine skeleton is also found in the alkaloid 395, currently known only by the designation 261C. This compound bears a passing resemblance to some of the myrmicarins (Section 16.6.5.2), but occurs in the skin of a totally different animal species, namely poisonous frogs of the genus Mantella <2003H(59)745>. 

Fig. 6. Structures of pumiliotoxins. Absolute configurations are known for 251D, 307A, and 323A and are assumed to be the same for the others. All occur in dendrobatid frogs except for 3QSB, which has been delected only in ranid frogs (Mantella) (73), and eryihro-323A, which has been detected only in ranid (Mantella) and myobatrachid frogs (Pseu-dophryne) (73,85,86).

Fig. 13. Structures of other S,8-disubstituted indolizidines from amphibians. Most have been characterized from ranid frogs of the genus Mantella (73). Absolute configurations are unknown. All have the S,9Z configuration. The configuration at the 8 position could not be determined from FTIR spectra.

Provisional struct. Minor alkaloid from skin extracts of 2 populations of the Madagascan frog Mantella madagascariensis. 

Consists of two diastereomers, poss. allylic rearr. prods, of Pumiliotoxin A, P-02169. Trace alkaloid from skin extracts of the Madagascan frogs Mantella aurantiaca and M. crocea. Minor constit. of M. viridis. 

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