H. M. Garraffo

Arthropod–Frog Connection: Decahydroquinoline and Pyrrolizidine Alkaloids Common to Microsympatric Myrmicine Ants and Dendrobatid Frogs

Neotropical poison frogs (Dendrobatidae) contain a wide variety of lipophilic alkaloids, apparently accumulated unchanged into skin glands from dietary sources. Panamanian poison frogs (Dendrobates auratus) raised in a large, screened, outdoor cage and provided for six months with leaf-litter from the frogs natural habitat, accumulated a variety of alkaloids into the skin. These included two isomers of the ant pyrrolizidine 251K; two isomers of the 3,5-disubstituted indolizidine 195B; an alkaloid known to occur in myrmicine ants; another such indolizidine, 211E; two pyrrolidines, 197B and 223N, the former known to occur in myrmicine ants; two tricyclics, 193C and 219I, the former known to occur as precoccinelline in coccinellid beetles; and three spiropyrrolizidines, 222, 236, and 252A, representatives of an alkaloid class known to occur in millipedes. The alkaloids 211E, 197B, and 223N appear likely to derive in part from ants that entered the screened cage. In addition, the frog skin extracts contained trace amounts of four alkaloids, 205D, 207H, 219H, and 231H, of unknown structures and source. Wild-caught frogs from the leaf-litter site contained nearly 40 alkaloids, including most of the above alkaloids. Pumiliotoxins and histrionicotoxins were major alkaloids in wild-caught frogs, but were absent in captive-raised frogs. Ants microsympatric with the poison frog at the leaf-litter site and at an island site nearby in the Bay of Panamá were examined for alkaloids. The decahydroquinoline (−)-cis-195A and two isomers of the pyrrolizidine 251K were found to be shared by microsympatric myrmicine ants and poison frogs. The proportions of the two isomers of 251K were the same in ant and frog.

A Siphonotid Millipede (Rhinotus) as the Source of Spiropyrrolizidine Oximes of Dendrobatid Frogs

Poison frogs of the neotropical family Dendrobatidae contain a wide variety of lipophilic alkaloids, which are accumulated from alkaloid-containing arthropods. A small millipede, Rhinotus purpureus (Siphonotidae), occurs microsympatrically with the dendrobatid frog Dendrobates pumilio on Isla Bastimentos, Bocas del Toro Province, Panamá. Methanol extracts of this millipede contain the spiropyrrolizidine O-methyloxime 236, an alkaloid previously known only from skin extracts of poison frogs, including populations of D. pumilio. Thus, R. purpureus represents a likely dietary source of such alkaloids in dendrobatid frogs.

Chemistry of venom alkaloids in someSolenopsis (Diplorhoptrum) species from Puerto Rico

A number of 15-carbon alkaloids have been identified in venom extracts of four Puerto Rican species of ants in the genusSolenopsis (Diplorhoptrum). Workers of a species from El Verde produced thecis andtrans isomers of 2-methyl-6-nonylpiperidine with the latter isomer predominating. The same compounds were identified in queens of a species from Río Grande, but in this species no alkaloids were detected in worker extracts. Workers of aDiplorhoptrum species collected on Mona Island produced primarily atrans-2-methyl-6-(Z-4-nonenyl)piperidine,3, with smaller amounts of thecis isomer, whereas the major compound found in the queens of the same species on Mona Island was (5Z,9Z)-3-hexyl-5-methylindolizidine, identical with the alkaloid produced by queens of a species collected on Cabo Rojo. Surprisingly, workers of the Cabo Rojo species produced (5Z,9Z)- and (5E,9E)-3-butyl-5-propylindolizidine (4 and5, respectively) reported earlier as the 223AB indolizidines from skins of dendrobatid frogs. The possible significance of the qualitative and quantitative differences in the venom alkaloids synthesized by queens and workers is discussed as is the possibility that ants containing such alkaloids may serve as a dietary source for the skin alkaloids used by certain frogs in chemical defense.

Alkaloids in the mite Scheloribates laevigatus: further alkaloids common to oribatid mites and poison frogs.

Poison frogs are chemically defended from predators by diverse alkaloids, almost all of which are sequestered unchanged from alkaloid-containing arthropods in the frog diet. Oribatid mites recently have been proposed as a major dietary source of poison frog alkaloids. Here, we report on alkaloids common to an oribatid mite and poison frogs. Gas chromatographic-mass spectrometric analysis of methanol extracts of adult Scheloribates laevigatus (Oribatida: Scheloribatidae) revealed nine alkaloids. Five of these have been detected previously in the skin glands of poison frogs: two isomers of the pumiliotoxin 291G, two isomers of the 5,6,8-trisubstituted indolizidine 209C, and the 5,6,8-trisubstituted indolizidine 195G. The other four alkaloids, a pumiliotoxin, a tricyclic (coccinelline-like), and two isomers of an izidine, were not previously known, but are similar in structure to alkaloids found in poison frogs. Alkaloids were not detected in immature S. laevigatus, suggesting that they are adult-specific and possibly the result of mite biosynthesis. Although most of the alkaloids detected in S. laevigatus are common to poison frogs, the geographic distributions of these organisms are not sympatric. The findings of this study indicate that oribatid mites, and in particular, members of the genus Scheloribates, represent a relatively unexplored arthropod repository for alkaloids and a significant dietary source of alkaloids in poison frogs.

Identification of histrionicotoxins by GC-MS and GC-FTIR: Photo- and chemical-artefacts and revised 13C NMR assignments

Abstract GC-mass and CG-FTIR spectral data together permit the rapid identification of the histrionicotoxin (HTX) alkaloids. 13C-NMR chemical shifts (δc) are reported for HTX 235A and revised δc are tabulated for nine HTXs and a perhydro-derivative. A butylboronic acid HTX derivative offers GC-MS and GC-FTIR advantages. Artefactural trans diene photoisomers of the HTX class are described as are formaldehyde condensation products. Two new HTX alkaloids 261 and 265E, are characterized by mass and FTIR spectra.

3-Hexyl-5-Methylindolizidine Isomers from Thief Ants, Solenopsis (Diplorhoptrum) Species

The venom alkaloids from the workers of nine collections of Solenopsis (Diplorhoptrum) from California contain either (5E,9E)-3-hexyl-5-methylindolizidine (1c) or (5Z,9E)-3-hexyl-5-methylindolizidine (1d) along with cis-2-methyl-6-nonylpiperidine. The structures of these compounds were determined from their mass spectra and by comparison of their GC-FTIR spectra with those of a synthetic mixture. In view of the facts that a third diastereomer of 3-hexyl-5-methylindolizidine had been reported in previous collections of Solenopsis (Diplorhoptrum) queens from Puerto Rico, and that indolizidines along with other ant venom alkaloids are sequestered by amphibians, the determination of species in this difficult group of ants is significant. In particular, the chemotaxonomic value of the stereochemistry of these venom alkaloids is discussed.

Pyrrolizidine oximes : a novel new class of dendrobatid alkaloids

Abstract Analysis of GC-FTIR spectra and reexamination of 1 H- and 13 C-NMR data led to revised structures for three closely related tricyclic alkaloids from a dendrobatid poison-frog Dendrobates pumilio . The simplest member, 222 , is a spiropentano-pyrrolizidine oxime, while 236 is the corresponding O-methyl oxime and 252 , a hydroxy-O-methyl oxime.

Alkaloids from dendrobatid poison frogs: Further pumiliotoxins and allopumiliotoxins and a reassignment of the keto function in pumiliotoxin 307F

Abstract Skin extracts from the Panamanian poison-frog Dendrobates pumilio have afforded further trace alkaloids of the pumiliotoxin-A class (6-alkylidene-8-hydroxy-8-methylindolizidines) and an allopumiliotoxin subclass (7-hydroxy-PTX-As). Structures for pumiliotoxins 209F and 225F and allopumiliotoxin 225E, all with four carbon 6-alkylidene side chains, for allopumiliotoxins 309D, 325A′ and 325A″, all with ten carbon 6-alkylidene side chains, and a reassignment of the position of the keto function in the ten carbon 6-alkylidene side chain of pumiliotoxin 307F are presented. Carbon-13 magnetic resonance assignments for these and the 15-0-methyl ether artefacts of pumiliotoxin 307A and allopumiliotoxin 323B, are tabulated.

Caste-Specific Tyramides from Myrmicine Ants

Analysis of the extracts of male ants of Monomorium minimum and Monomorium ebeninum by GC-MS and GC-FTIR revealed the presence of tyramides 2 and 4c, for which the structures were established by comparison with synthetic samples. These compounds and their analogues 1 and 3 were also found in males of other Monomorium species, males of Myrmicaria opaciventris, and males of several Solenopsis (Diplorhoptrum) species. Vapor-phase FTIR spectra revealed critically important structural clues to two of the tyramides, which had methyl branching in the tyramide acyl moiety. Tyramide 4c exhibited a strong intramolecular amide NH hydrogen bond where an alpha-keto group was deduced to be present in the acyl moiety and also showed the overlap of this ketone group frequency with that of the amide nu(C horizontal lineO). The biological function of these compounds is uncertain; however, their role in ant-mating behavior may be suggested by a large body of evidence.

Elucidation of dimethylalkylpyrazines from the ant Streblognathus aethiopicus by GC-FTIR

The presumed mandibular gland secretions from the workers and gamergates of two colonies of Streblognathus aethiopicus have been found to contain a homologous series of 3,5-dimethyl-2-alkylpyrazines (3,5-dimethyl-2-butylpyrazine, 1; 3,5-dimethyl-2-pentylpyrazine, 2; and 3,5-dimethyl-2-hexylpyrazine, 3). The structures of these compounds were determined from their mass spectra along with a comparison of their GC-FTIR spectra with those of all the isomers of a lower homolog. This is the first time that this combination of techniques has been applied to the study of insect pyrazines. The relative amounts and proportions of these compounds were different for gamergates and workers, with the latter containing 2–10 times more total pyrazines and having a higher proportion of 2 and 3. The possible significance of this finding is discussed.