Forty alkaloids were detected and characterized from skin extracts of high- and low-elevation populations of the poison frog Dendrobates histrionicus from northwestern Colombia. Combined gc/ms with NH3 or ND3 in a chemical ionization mode detected protonated parent ions and determined the number of exchangeable NH and OH hydrogens. Six previously unknown dendrobatid alkaloids were characterized. Two were 2,5-disubstituted pyrrolidines, which included pyrrolidine 197B, a trans-2-butyl-5-pentylpyrrolidine, while a third was a 2,6-dipentylpiperidine. Indolizidines 239AB and 239CD had the same relative configuration as the parent alkaloid 223AB [(5E,9E)3-butyl-5-propylindolizidine] and contained, respectively, a omega-hydroxy group in the propyl or butyl side chain. The profiles of alkaloids in the new northern populations of D. histrionicus are typical of the species in containing a set of about eight histrionicotoxins, in marked contrast to a related species, Dendrobates lehmanni, which does not contain histrionicotoxins.

No abstract

The structures and absolute configuration of two unique alkaloids isolated from the Colombian frog, Dendrobates histrionicus, have been elucidated by Roent-gen-ray (x-ray) crystallography. Histrionicotoxin is (2pll, 6S, 7pS, 8aS)-7-(cis-l-buteni-3-ynyl)-8-h-ydroxy-2-(cis-2-petiteni-4-ynlyl)-1-azaspiro[5.5] undecane, while in dihydroisohistrionicotoxin the acetylenic 2-pentenynyl side chain is replaced by an allenic 2-(3,4 pentadienyl) substituent. Dendrobates histrionicus exhibits remarkable interpopulational variations in amounts and composition of skin toxins, in behavior, and in phenotypic characters, aspects of which are illustrated in a color plate. The histrionicotoxins are the third class of alkaloids isolated from the defensive skin secretions of Neotropical (Dendrobatidae) frogs.

Structures for 2,5-disubstituted decahydroquinolines (DHQs) are reported for the two diastereomeric pairs cis-275B (14) and cis-275B' (15) and 5-epi-trans-269AB (18) and trans-269AB (19), all isolated from skin extracts of dendrobatid frogs, and for 5-epi-cis-275B' (16) and 5-epi-trans-275B (17) found in the extracts of virgin queens of a myrmicine ant [Solenopsis (Diplorhoptrum) azteca]. Detection of such DHQs in an ant, their first reported occurrence, strengthens a dietary hypothesis for the origin of the approximately 30 DHQs that have been detected in extracts of frog skin. NMR data on the two conformers of cis-decahydroquinoline permit assignment of ring conformations and stereochemistry to cis-DHQs of the "N-endo" type or the "N-exo" type. These conformations are also assigned on whether H-8a is equatorial or axial as determined with E-COSY or 1D-HOHAHA spectra.

The structure and absolute configuration of a new acetylenic alkaloid gephyrotoxin isolated from skin extracts of the Colombian frog Dendrobates histrionicus, has been determined by Röntgen‐ray crystallography. Gephyrotoxin, previously referred to as HTX‐D, is a novel tricyclic alkaloid, [1 S, 3aS, 5aS, 6S(Z), 9a R, 10 R]dodeca‐hydro‐6‐(2‐penten‐4‐yl)pyrrolo[1,2‐a]quinoline‐1‐ethanol. Dihydrogephyrotoxin, a minor skin constituent, contains a 6‐(2,4‐pentadienyl)substituent. Two further spiropiperidine alkaloids related in structure to histrionicotoxin, (6 R[6α[2S*(Z)],[7β(Z), 8α]]7‐(1‐buten‐3‐ynyl)‐2‐(2‐penten‐4‐ynyl)‐1‐azaspiro [5.5]undecan‐8‐ol), have been isolated from Dendrobates histrionicus: allodihydrohistrionicotoxin which differs from histrionicotoxin in having a 2‐(4‐pentynyl)‐substituent, while allotetrahydrohistrio‐nicotoxin, a minor constituent, has 2‐(4‐pentynyl)‐ and 7‐(1,3‐butadienyl)‐substituents. Three alkaloids related in structure to pumiliotoxin C, ([2 S, 4a S, 5R, 8a R]5‐methyl‐2‐n‐propyl‐cis‐decahydroquinoline), have been isolated from Dendrobates histrionicus. These alkaloids, with molecular weights of 195, 223, and 269, have, respectively, a 2‐butylsubstituent, 2‐propyl and 5‐propyl‐substituents, and 2‐(3,4‐pentadienyl) and 5‐(2‐penten‐4‐ynyl)‐substituents. The last compound was hydrogenated to a dodecahydro‐derivative identical in molecular weight, but not in other properties, with authentic dodecahydro‐8‐deoxy‐histrionicotoxin, which was prepared from histrionicotoxin. Gephyrotoxin, in contrast to histrionicotoxin and pumiliotoxin C, is a muscarinic antagonist.

No abstract

No abstract

Let G be a weighted, complete, directed acyclic graph (DAG), whose edge weights obey the Monge condition. We give an efficient algorithm for finding the minimum weight K-link path between a given pair of vertices for any given K. The time complexity of our algorithm is O(n~=) for the concave case and O (ncr (n) log3 n) for the convex case. Our algorithm uses some properties of DAGs with Monge property together with a refined parametric search technique. We apply our algorithm (for the concave case) to get efficient solutions for the following problems, improving on previous results:(1) Finding the largest K-gon contained in a given polygon.(2) Finding the smallest K-gon that is the intersection of K halfplanes out of of given set of halfplanes defining an n-gon. (3) Computing maximum K-cliques of an interval graph. (4) Computing length limited Huffman codes. (5) Computing optimal discrete quantization.