Indolizidine 239Q and quinolizidine 275I. Major alkaloids in two Argentinian bufonid toads (Melanophryniscus)

Abstract

Alkaloid profiles in skin of poison frogs/toads (Dendrobatidae, Mantellidae, Bufonidae, and Myobatrachidae) are highly dependent on diet and hence on the nature of habitat. Extracts of the two species of toads (Melanophryniscus klappenbachi and M. cupreuscapularis) from similar habitats in the Corrientes/Chaco Provinces of Argentina have similar profiles of alkaloids, which differ considerably from profiles from other Melanophryniscus species from Brazil, Uruguay and Argentina. Structures of two major alkaloids 239Q (1) and 275I (2) were determined by mass, FTIR, and NMR spectral analysis as 5Z,9Z-3-(1-hydroxybutyl)-5-propylindolizidine and 6Z,10E-4,6-di (pent-4-enyl) quinolizidine, respectively. A third alkaloid, 249F (3), is postulated to be a homopumiliotoxin with an unprecedented conjugated exocyclic diene moiety.

A review of chemical ecology in poison frogs

“…Most alkaloids present in poison frogs appear to be of oribatid mite and myrmicine ant origin, which is consistent with the natural diet of poison frogs, which are known to be composed largely of mites and ants (e.g., Bonansea and Vaira 2007;Daly et al 2008a;Valderrama-Vernaza et al 2009 and references therein). Some dendrobatid frogs have been called ''ant-mite specialists'' (Caldwell 1996;Donnelly 1991;Simon and Toft 1991).…”

“…Although the literature suggests that arthropod sources for alkaloids are well known, fewer than 10% of the more than 850 alkaloids known from poison frogs have been identified in arthropods. Furthermore, the majority of frog dietary studies (i.e., analysis of stomach contents) do not identify arthropods below the family level (however, see Clark et al 2005;Daly et al 2008a), making determination of dietary sources difficult or impossible. Future studies devoted to the identification of arthropod sources of alkaloids will need to include detailed chemical analyses coupled with studies of frog diet and the availability of arthropods, which will help to solve the interesting questions posed by the poison-frog sequestration system.…”

“…Variation in alkaloid composition (a measure of the number, type, and amount) within and among species of poison frogs has been documented for dendrobatids (Daly et al 1987Saporito et al 2007c), bufonids (Daly et al , 2008aMebs et al 2005), mantellids (Daly et al 1996(Daly et al , 2008bClark et al 2006), and myobatrachids (Daly et al 1990;Smith et al 2002). The majority of studies described variation at a population level, in which samples of frogs collected from a population were pooled together for chemical analysis (e.g., Daly et al 1987Daly et al , 1996Daly et al , 2008aMortari et al 2004). Recently, studies have focused on alkaloid variation among individuals within populations of dendrobatids (Myers et al 1995;Saporito et al 2006), bufonids Mebs et al 2005) and mantellids (Clark et al 2006;Daly et al 2008b).…”

Diel pattern of migration in a poisonous toad from Brazil and the evolution of chemical defenses in diurnal amphibians

“…Although several of the diurnal groups within Agastorophynia are also poisonous, including the true toads (Bufonidae) and Neotropical poison frogs (Dendrobatidae), others are not. The occurrence of bufadienolides is a synapomorphy of Bufonidae (Daly et al 2008), the occurrence of lipophilic alkaloids is independently derived in Melanophryniscus, Ameerega, Epipedobates, and Dendrobatinae, and the occurrence of tetrodotoxin and related compounds is independently derived in Atelopus and Colostethus (Grant et al 2006;Grant 2007), whereas Aromobatidae, Hylodidae, and the dendrobatid clades Hyloxalinae and Silverstoneia are not poisonous. As such, the shift to diurnal activity occurred prior to the evolution of chemical defenses in Bufonidae and Dendrobatidae (Fig.…”

“…Specifically, they secrete lipophilic alkaloids and bufadienolides (Daly et al 2008) and employ the unken reflex to display bright red or orange ventral surfaces when disturbed ( Fig. 1).…”