Dendrobates Alkaloids

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 alio series of the pumiliotoxin A class have an additional hydroxyl group that has been placed at C-7 on the indolizidine ring, without assignment of configuration. Three members of the alio series have been assigned the tentative structures (7), (8), and (9).3 Pumiliotoxins A and B are relatively toxic, and comparable in potency to strychnine. Pumiliotoxin B has a potent cardiotonic and myotonic activity.3 An enantioselective total synthesis of pumiliotoxin A alkaloids from L-proline has already been announced.4 

The dendrobatid toxin 25 ID (18) has been synthesized by a new approach which utilizes an iminium-vinylsilane cyclization to produce the (Z)-6-alkylidene-indolizidine ring-system in a stereospecific manner. The key intermediate (19) was prepared from L-proline and converted into toxin 25 ID (18) by reaction with paraformaldehyde and (+)-camphor-10-sulphonic acid in refluxing ethanol. The method is potentially a general one for forming unsaturated azacyclic rings, and it provides a convenient route to the pumiliotoxin A alkaloids.7 

A highly stereoselective synthesis of ( )-gephyrotoxin (20) has been carried out. An interesting feature is the reversal of the stereochemical course of the hydrogenation of the vinylogous amide (21) by the use of an alumina support. Hydrogenation of (21) over palladium on charcoal gives the amino-alcohol (22) as 

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Tetrahydropyridines 103 undergo a Michael reaction to afford [ran.s-(2,3)-cis-(2,6)-trisubstituted piperidines 104 (97T9553). The reaction is stereoselective (a single stereoisomer was obtained) and provides a convenient route to the 5,8-disubstituted indolizidine 105 and 1,4-disubstituted quinolizidine system 106 (found in Dendrobates alkaloids) by introduction of various alkyl, alkenyl, or... 

Stereodivergent process for synthesis of the decahydroquinoline type of Dendrobates alkaloids... 

Indollzidine alkaloids. A group of alkaloids from various classes based on the bicyclic ring system of in-dolizidine. They differ in structure, biogenesis, and occurrence thus, the indolizidine ring system has very little value as a characterizing structural. The I. a. include the pumiliotoxins (Dendrobates alkaloids), poly hydroxy alkaloids such as swainsonineand cas-tanospermine, Elaeocarpus alkaloids, Securinega alkaloids, Tylophora alkaloids, and the Ipom(o)ea alkaloids. 

Alisol E 23-acelate, in T-20092 Alisol F, A-20076 Alisol G, in T-20223 Dendrobates Alkaloid 253. A-20079 Dendrobates Alkaloid 255, in H-30189 Dendrobates Alkaloid 269, A-20080... 

Dendrobates Alkaloid 25IB, A-30053 Deoxypumiliotoxin 25IH, D-30042 Herculin, in D-10301... 

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