A diverse array of biologically active, lipid-soluble alkaloids have been discovered in amphibian skin. Such alkaloids include the following:  the steroidal samandarines from salamanders, the batrachotoxins, histrionicotoxins, gephyrotoxins, and epibatidine from neotropical poison frogs (Dendrobatidae), the pumiliotoxins, allopumiliotoxins, homopumiliotoxins, and decahydroquinolines from certain genera of anurans from four families (Dendrobatidae, Mantellidae, Bufonidae, and Myobatrachidae), a variety of izidines (pyrrolizidines, indolizidines, quinolizidines, lehmizidines), pyrrolidines, piperidines, various tricyclics (related in structures to the coccinellines), and spiropyrrolizidines from the first three of these four families, the pseudophrynamines from one genus of Australian frogs, and a variety of unclassified alkaloids as yet of undetermined structure. With the exception of the samandarines and the pseudophrynamines, all alkaloids appear to be derived from dietary sources. Although only a few of...

Alkaloids from amphibian skin: a tabulation of over eight-hundred compounds.

Simple indole alkaloids and those with a nonrearranged monoterpenoid unit

Research on natural products containing hexahydropyrrolo[2,3-b]indole (HPI) has dramatically increased during the past few years. Newly discovered natural products with complex structures and important biological activities have recently been isolated and synthesized. This review summarizes the structures, biological activities, and synthetic routes for natural compounds containing HPI, emphasizing the different strategies for assembling this motif. It covers a broad range of molecules, from small alkaloids to complex peptides.

/pdf/structure-bioactivity-and-synthesis-of-natural-products-with-fhmho9imho.pdf

Structure, Bioactivity and Synthesis of Natural Products with Hexahydropyrrolo[2,3‐b]indole

Pyrroloindoline and bispyrroloindoline are a subclass of alkaloid structural motifs that commonly exhibit biological activity. An enantioselective organocatalytic approach to the synthesis of pyrroloindoline architecture is described. The addition–cyclization of tryptamines with α,β-unsaturated aldehydes in the presence of imidazolidinone catalysts 1 and 8 provides pyrroloindoline adducts in high yield and excellent enantioselectivities. This transformation is successful for a wide range of tryptamine and α,β-unsaturated aldehyde substrates. This amine-catalyzed sequence has been extended to the enantioselective construction of furanoindoline frameworks. Application of this pyrroloindoline-forming reaction to natural product synthesis has been accomplished in the context of the enantioselective synthesis of (–)-flustramine B.

https://www.pnas.org/content/pnas/101/15/5482.full.pdf

Enantioselective organocatalytic construction of pyrroloindolines by a cascade addition-cyclization strategy: synthesis of (-)-flustramine B.

Indolizidine and quinolizidine alkaloids

Isolement et etude de la structure chimique de 3 alcalvides presents au niveau de la peau d'un amphibien, Pseudophryne coriacea

Pseudophrynamine A: an unusual prenyl pyrrolo[2,3-b]indole ester from an Australian frog, Pseudophryne coriacea (Myobatrachidae)

Pseudophrynamine A: An Unusual Prenyl Pyrrolo(2,3-b)indole Ester from an Australian Frog, Pseudophryne coriacea (Myobatrachidae).

A Naturally Occurring Erythro Diastereomer (Ic) of Pumiliotoxin B (Ia).

Facile Synthesis of 4-Piperidones by Condensation of an α,β- Unsaturated Ketone, an Aldehyde and Ammonia: Synthesis of the Dendrobatid Frog Alkaloid 241D (XII).

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Pseudophrynamine A: an unusual prenyl pyrrolo[2,3-b]indole ester from an Australian frog, Pseudophryne coriacea (Myobatrachidae)

Pseudophrynamine A: An Unusual Prenyl Pyrrolo(2,3-b)indole Ester from an Australian Frog, Pseudophryne coriacea (Myobatrachidae).

A Naturally Occurring Erythro Diastereomer (Ic) of Pumiliotoxin B (Ia).

Facile Synthesis of 4-Piperidones by Condensation of an α,β- Unsaturated Ketone, an Aldehyde and Ammonia: Synthesis of the Dendrobatid Frog Alkaloid 241D (XII).