piperidines and perhydrohistrionicotoxin

The anodic cyanation of methanolic solutions of the 2-alkyl-N-phenylpiperidines 6b-d was performed in a flow cell equipped with a graphite felt anode. The reaction led to the formation of the 2-cyano-6-alkyl-N-phenylpiperidines 2b-d and proceeded with a high degree of regioselectivity. The 1H NMR spectra of the aminonitriles 2b-d showed an epimeric mixture at C-6. The major isomer has a trans configuration in which the cyano group is axial and the alkyl substituent is equatorial. Conversely, electrochemical oxidation of the 4-methyl-6-pentyl-N-phenylpiperidine 6e afforded the trisubstituted aminonitrile 2e as a single diastereomer (> 98% de). The 4-cyanobutyl side chain was incorporated in a two-step procedure to yield dinitrile 4e. This latter compound was directly converted into spiropiperidine 5e by using the Thorpe-Ziegler annulation procedure. The overall sequence (4 steps, 43%) allows the construction of the basic carbon framework of perhydrohistrionicotoxin.

Topics: Amphibian Venoms; Cyanides; Models, Molecular; Neurotoxins; Piperidines; Spiro Compounds; Stereoisomerism

The interactions of eight piperidine derivatives with nicotinic receptor complexes from Torpedo californica electric organ were studied using [125I] alpha-bungarotoxin [( 125I]BGT) as a probe for the acetylcholine binding site and [3H]perhydrohistrionicotoxin [( 3H]H12-HTX) as a probe for a site associated with the receptor-gated ion channel. Cis- and trans-2-methyl-6-n-undecanyl piperidines (MUP), major constituents of fire ant venom, had a high-affinity for [3H]H12-HTX binding sites (Ki = 0.08-0.24 microM), but had no affect on receptor binding. MUP affinity for [3H]H12-HTX binding sites was approximately doubled in the presence of 1 microM carbamylcholine. Introduction of a 2'-hydroxyl group to the undecanyl side channel had little effect on activity of the alkaloid. The analog 2,6- (but not 3,5-) dimethylpiperidine was a moderately active inhibitor of [3H]H12-HTX binding (Ki = 8.8 microM). 2-Methylpiperidine was considerably less active (Ki = 600 microM), although it was more potent than either 3- or 4-methylpiperidine. The affinities of 2,6-dimethylpiperidine and 2-methylpiperidine for [3H]H12-HTX binding sites were decreased in the presence of 1 microM carbamylcholine. Carbamylcholine affinity for the receptor was increased by up to 7 fold in the presence of 10 and 32 microM MUP, but was decreased in the presence of 2,6-dimethylpiperidine and 2-methylpiperidine. The cis- and trans-isomers of MUP were equipotent in producing each of its effects. In these actions, MUP resembles a variety of other compounds derived from 2,6-disubstituted piperidines, including histrionicotoxins, gephyrotoxins and pumiliotoxins.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Amphibian Venoms; Animals; Bungarotoxins; Electric Organ; Ion Channels; Piperidines; Receptors, Nicotinic; Structure-Activity Relationship; Torpedo

Histrionicotoxin from the Colombian frog Dendrobates histrionicus and its perhydro derivative reversibly block the acetylcholine-sensitive ion conductance system in frog neuromuscular preparations. The perhydro derivative and [3H]perhydrohistrionicotoxin, like histrionicotoxin, caused a significant decrease in the peak amplitude of the end-plate current and shortened its rise time and half-decay time. In membrane preparations from Torpedo electroplax, [3H]perhydrohistrionicotoxin bound reversibly to a limited number of high-affinity sites [dissociation constant, (KD) = 0.4 micronM]. The ratio of perhydrohistrionicotoxin to acetylcholine binding sites in these membrane preparations approached 2. Histrionicotoxins, local anesthetics, and certain cholinergic agonists inhibited binding of perhydrohistrionicotoxin. Binding of perhydrohistrionicotoxin to membranes was decreased by heat or treatment with proteases. Treatment of membranes with Triton X-100 solubilized acetylcholine binding proteins and apparently also perhydrohistrionicotoxin-binding proteins. However, the detergent Triton X-100 also bound [3H]perhydrohistrionicotoxin. This nonspecific binding was not saturable and complicated studies on the antagonism by drugs of binding of [3H]perhydrohistrionicotoxin. In solubilized preparations the binding protein for acetylcholine could be removed by affinity chromatography or immunoprecipitation without affecting binding of perhydrohistrionicotoxin. Sephadex chromatography also separated acetylcholine- from perhydrohistrionicotoxin-binding proteins. Perhydrohistrionicotoxin did not bind significantly to purified acetylcholine-receptor protein but presumably bound to an ion conductance modulator protein that was associated with the acetylcholine-receptor in intact membrane and readily separable from the receptor protein after solubilization.

Topics: Amphibian Venoms; Animals; Anura; Electric Conductivity; Electric Organ; Fishes; Kinetics; Ligands; Membrane Potentials; Membrane Proteins; Motor Endplate; Neuromuscular Junction; Piperidines; Rana pipiens; Receptors, Cholinergic; Structure-Activity Relationship; Toxins, Biological