Batrachotoxinins structures

Unique structural features of this steroidal alkaloid are the cis junctions between rings A/B and C/D, the ether linkage between C-3 and C-9, the OH group on C-11, and the alkaloid function in a seven-membered ring formed by a methylethylamine moiety bridging the methyl on C-13 and OH on C-14 of a steroid nucleus. A reanalysis of the spectral data showed that batrachotoxin is the 20-a-dimethylpyrrole carboxylate and homobatrachotoxin the 20-a-ethylmethylpyrrolc carboxylate of batrachotoxinin A (31). 

The structure of batrachotoxinin A (26), a component of an arrow poison from the skin of the frog Phyllobates aurotaenia, has been elucidated by X-ray crystallography52. 

A knowledge of the structure of batrachotoxinin A led to a re-evaluation of the spectral properties of the much more toxic batrachotoxin and homobatrachotoxin. It soon became apparent that the ultraviolet absorption peaks (A.max 234, 264 nm), the infrared red absorption band at 1690 cm " S and additional nuclear magnetic resonance absorption peaks in... 

Fig. 3. Structures for batrachotoxin class alkaloids. A Batrachotoxinin A. B Batrachotoxin.

The structure of batrachotoxin was confirmed by a partial synthesis from batrachotoxinin A. This proved feasible using a mixed anhydride prepared from 2,4-dimethylpyrrole-3-carboxylic acid and ethyl chlorofor-mate (Scheme I). A variety of analogs of batrachotoxin were prepared in a similar manner. These compounds are documented in Table 4. A dihydro-batrachotoxin was prepared by sodium borohydride reduction (Scheme II) and apparently is subject to allylic rearrangement to other dihydroproducts 251). 

Karle, I. L., and J. Karle The structural formula and crystal structure of the 0-p-bromobenzoate derivative of batrachotoxinin A, CaiHssNOeBr, a frog venom and steroidal alkaloid. Acta Crystallogr. B25, 428—434 (1969). 

Tokuyama, T., J. Daly, B. Witkop, I. L. Karle, and J. Karle The structure of batrachotoxinin A, a novel steroidal alkaloid from the Colombian arrow poison frog. J. Amer. Chem. Soc. 90, 1917—1918 (1968). 

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