Amphibian alkaloids from ants

The number of natural products containing these tricyclic systems is relatively small, viz. a few alkaloids from marine (compound 293), fungal (compound 282), amphibian (compound 395), insect (compound 387), and plant sources (compound 288) and also some iridoid molecules (compounds 98-100). Some of those Myrmkaria alkaloids (from ants Section 12.16.6.5.2) which contain the 5 5 6 fused-ring system are perhaps the most extensively studied of these natural products, with several successful syntheses now recorded. 

The following post-1986 reviews in this treatise provide the antecedents for several sections of this chapter. The important contribution of Takahata and Momose in Volume 44, entitled "Simple Indolizidine Alkaloids", covered the period 1986 to 1992, but dealt only with Elaeocarpus alkaloids, slaframine, polyhydroxylated indoUzidines such as swainsonine and castanospermine, and alkdoids fiiom ants and amphibians (2). This partial update is especially valuable as a guide to published totd syntheses of these alkaloids. Materi of relevance is also to be found in a number of reviews on more specialized topics. Numata and Ibuka reviewed the chemistry of alkaloids from ants and other insects in Volume 31... 

Several other general reviews dealing with aspects of indoHzidine and quinolizidine alkaloid chemistry were pubHshed during the period under consideration. The series of annual reports in the Royal Society of Chemistry s journal Natural Product Reports, which provided regular coverage of both simple and various more complex indolizidine and quinolizidine alkaloids, ended in 2008.Another important review that dealt principally with pertinent alkaloids from ants and amphibians, slaframine, polyhydroxy-lated indolizidine alkaloids, and the lupin quinolizidine alkaloids was published in the series Studies in Natural Product Chemistry in 2002, and covered the period 1994 to 1999. ... 

The neotropical dart poison frogs contain a remarkable diversity of alkaloids, and the 2,5-disubstituted decahydroquinolines represent, a major class of these amphibian alkaloids[21]. Isolation of these alkaloids from some ants strengthens a dietary hypothesis for the origin of the above alkaloids that have been detected in extracts of frog skin[22]. In addition, these alkaloids containing both cis and trans ring fusion have been identified as well as diastereomers at the C-2 and C-5 position. 

The biological activity of 3,5-disubstituted pyrrolizidines from amphibians has not been studied. It is presumed that the pyrrolizidine alkaloids isolated from ants serve as venoms (123). 

Disubstituted indolizidines, unlike many classes of amphibian alkaloids, are not unique to amphibians. 3,5-Disubstituted indolizidines such as monomorine I [(5Z,9Z)-195B] occur in ants of the genera Monomorium and Solenopsis (125,129,134). Some of the ant indolizidines are as follows (5Z,9Z)-3-n-butyl-5-methylindolizidine (monomorine I), (5Z,9Z)-3- -ethyl-5-methylindolizidine, (5Z,9Z)-3-hexyl-5-methylindolizidine, and (5 ,9Z)-3-butyl-5-(4-pentenyl)indolizidine. A series of 5-substituted indolizidines, the piclavines, were reported recently from a marine tunicate (Clavelina picta) (135). 

INDOLIZIDINE AND QUINOLIZIDINE ALKALOIDS FROM AMPHIBIANS AND ANTS... 

Table 1. Mass Spectra of Newly Identified Indolizidine and Quinolizidine Alkaloids from Amphibians And Ants.

The most common indolizidine and quinolizidine alkaloids from amphibians and ants are usually identified by their GC-MS and GC-FTIR spectral characteristics. These spectral features were collected by Garraffo and co-workers [18,19], and can be summarized as follows ... 

Frogs have alkaloid-containing defensive chemicals in their skin. More than 800 alkaloids are found from the amphibian skin, and 500 alkaloids from neotropical poison frogs. Experimental data found that bufonid poison frogs sequester alkaloid-based defenses from dietary sources, especially from consumption of mites and ants. In the case of Cuban endemic miniaturized frogs (Eleutherodactylus limbatus), the capacity to sequester alkaloids is evolutionary determined and followed by evolution of miniaturization. Moreover, it is in direct relation to the increase of brightness of color and possible aposematic function in this species. ... 

Indolizidine and quinolizidine alkaloids have been found in different natural sources and have been isolated from amphibians, ants, fungi, marine organisms and plants. Most of them have noxious or toxic properties and... 

Indolizidine and quinolizidine alkaloids found in amphibians and ants were studied by Daly and co-workers who classified them in two different classes, A and B, Fig. (1) [2,15-17]. The former include 3,5- and 5,8-disubstituted indolizidines, 5,6,8-trisubstituted indolizidines and 1,4- and 4,6-disubstituted quinolizidines that can be derived from straight-chain carbon precursors. The latter contain one or more isoprene units, and include pumiliotoxins (PTX-A), allopumiliotoxins (a//o-PTX-A or... 

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