Alkaloid dendrobatid

Two classes of dendrobatid alkaloids have potential dietary sources. The first are the pyrrolizidine oximes (32), whose carbon skeleton is identical to that of nitropolyzonamine, an alkaloid from a small millipede (33). Indeed, raising the dendrobatid frog D. auratus in Panama on leaf-litter arthropods, gathered weekly, resulted in skin levels of the... 

Frogs of the genus Dendrobates are ant specialists. Of the more than 20 structural classes of lipophilic alkaloids found in the frogs, six occur in myrmicine ants. However, many dendrobatid alkaloids such as the batrachotoxins, histri-onicotoxins, and pumiliotoxins, have not yet been found in insects and other leaf-litter prey such as beetles and millipedes (Daly et al., 2000). The snake Lio-phis epinephelus feeds on Dendrobates and may further bioaccumulate alkaloids. 

First Enantioselective Synthesis of Dendrobatid Alkaloids Indolizidine 2091 and 223J 53... 

Sundarababu Baskaran of -Madras offers (Organic Lett. 5 583,2003) an alternative route to indolizidines. Exposure of the epoxide 7 to Lewis acid followed by reduction leads to 11 as a single diastereomer. The authors hypothesize that this rearrangement is proceeding via intermediates 8 -10. Tosylation of 11 followed by homologation leads to the Dendrobatid alkaloid 12. 

Deacetoxyalcyonin acetate synthesis 76 Dendrobatid alkaloid 25 IF synthesis 112, 168... 

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. 

Extracts from skins of the neotropical frog Dendrobates tricolor from Ecuador have given the alkaloid 8-hydroxy-6-(2-methylhexylidene)azabicyclo[4.3.0]non-ane (4), the structure and absolute configuration of which have been determined by X-ray crystallography of the hydrochloride salt. This alkaloid is the first structurally defined member of the pumiliotoxin A class of dendrobatid alkaloids. Spectroscopic studies (m.s. and n.m.r.) have allowed the formulation of the... 

The indispensable contribution of crystallography has been to establish the molecular formulas, the stereoconfigurations, and the absolute configurations of five quite different toxins representative of the five major classes of dendrobatid alkaloids. Each of the five substances had unexpected and novel chemical bonding. Knowledge of the structures from crystal structure analyses led to reevaluations of the spectral properties of analogs and congeners and to the definitions of the structures of more than 200 dendrobatid alkaloids. 

A simple route to the Dendrobatid alkaloid 251F (19) nicely illustrates the synthetic utility of Rh-mediated C-H insertion [8. The excellent diastereoselectivity observed in the cyclization of 16 to 17 was in fact predicted computationally [9]. 

Physical and spectral properties of batrachotoxins are presented in Table I. Mass spectra have been presented and interpreted (3,13,14). The parent ion of batrachotoxin is virtually nondetectable by direct probe methods, and instead an apparent molecular ion of miz 399 is seen, probably because of pyrolytic elimination of the pyrrole carboxylate moiety. Batrachotoxin alkaloids do not chromatograph on capillary gas chromatographic columns, but a pyrolysis product has been detected at 280°C on the temperature-programmed, packed OV-1 columns used for analysis of other dendrobatid alkaloids (see Appendix). The pyrrole carboxylate moiety is responsible for major ions of C7H9N02 (m/z 139), C6H9N ... 

In contrast to dendrobatid alkaloids, which are not present in captive-raised dendrobatid frogs, lire salamanders produce samandarine alkaloids when reared in captivity (G. Habermehl, personal communication, 1989). No apparent differences in alkaloid content occurred for at least three generations. Incubation of secretions from salamander parotoid glands with radiolabeled cholesterol in buffer for 3 days at room temperature led to some apparent incorporation of radioactivity into samandarine alkaloids (53). 

Most amphibian alkaloids are not as complex in structure as the steroidal batrachotoxins and samandarines. Of the 300 known amphibian alkaloids, most have been characterized from the skin extracts of frogs of the family Dendrobatidae and, hence, have been referred to as dendrobatid alkaloids. The major bicyclic classes of dendrobatid alkaloids are the histrionicotox-ins, decahydroquinolines, and pumiliotoxin-A class. Because of the presence of a piperidine ring in most dendrobatid alkaloids, they also have been referred to as piperidine-based alkaloids. 

The properties of the natural histrionicotoxins are presented below in a format introduced in 1978 60) for the dendrobatid alkaloids. The entries are as follows (1) the code designation based on molecular weight and identifying letter(s) in boldface (2) the trivial name, if any (3) an empirical formula based on high-resolution mass spectrometry (tentative formulas... 

A number of other dendrobatid alkaloids appear to be decahydroquinolines based on spectral and chemical properties. All of these alkaloids are secondary amines no simple N-alkyl derivatives have been found. FTIR spectra are not yet available for many of these alkaloids. Many decahydro-... 

Simple 2,5-disubstituted decahydroquinolines do not appear to have been reported to occur in Nature except in certain amphibians. Decahydroquinolines, like histrionicotoxins, occur in a range of dendrobatid frogs. These two classes of dendrobatid alkaloids often occur together in the same species or population. Indeed, the 19-carbon decahydroquinoline 269AB (or 269A and 269B) always appears to accompany the 19-carbon... 

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