Divergent Nine-Step Syntheses of Perhydrohistrionicotoxin Analogs and Their Inhibition Activity Toward Chicken α4ß2-Neuronal Nicotinic Acetylcholine Receptors.

Histrionicotoxin (HTX) alkaloids, which are isolated from Colombian poison dart frogs, are analgesic neurotoxins that modulate nicotinic acetylcholine receptors (nAChRs) as antagonists. Perhydrohistrionicotoxin (pHTX) is the potent synthetic analogue of HTX and possesses a 1-azaspiro[5.5]undecane skeleton common to the HTX family. Here, we show for the first time the divergent nine-step synthesis of pHTX and its three stereoisomers from the known aldehyde through a one-step construction of the 1-azaspiro[5.5]undecane framework from a linear amino ynone substrate. Surprisingly, some pHTX diastereomers exhibited antagonistic activities on the chicken α4ß2-neuronal nAChRs that were more potent than pHTX.

Crystal Structure of the Native Chromoprotein from Pleurotus salmoneostramineus Provides Insights into the Pigmentation Mechanism.

The pink-colored protein from the fungus Pleurotus salmoneostramineus (PsPCP) possesses unusual primary sequences with little resemblance to those of known proteins and exhibits a red color in aqueous solution. To understand the pigmentation mechanism of PsPCP, we elucidated the X-ray crystal structure of the native PsPCP. We identified a highly conjugated polyene ligand 2-dehydro-3-deoxylaetiporic acid A as a chromophore ligand, whose solution exhibits yellow. The crystal structure of PsPCP indicated that the ligand is secured in the central cavity and anchored at both termini by hydrophilic interactions and that surrounding residues show CH-pi and C-H···O hydrogen bondings. Geometrical analyses of the bound ligand demonstrated that the conjugated C-C and C═C bonds exhibit similar bond distances. The result indicated enhanced electron delocalization within the conjugated CC bond system, resulting in a redshift of the chromophore ligand. The computational estimates of the UV-vis spectra support the view that the electron delocalization within the conjugated CC bonds system of the bound ligand, induced by the specific ligand geometry within a limited space of PsPCP cavity, is responsible for the red pigmentation of PsPCP. Thus, we propose that the coloring mechanism of PsPCP, which constrains the geometry of a highly conjugated polyene ligand, is a novel type of pigment chemistry.

Unravelling nicotinic receptor and ligand features underlying neonicotinoid knockdown actions on the malaria vector mosquito Anopheles gambiae.

With the spread of resistance to long-established insecticides targeting Anopheles malaria vectors, understanding the actions of compounds newly identified for vector control is essential. With new commercial vector-control products containing neonicotinoids under development, we investigate the actions of 6 neonicotinoids (imidacloprid, thiacloprid, clothianidin, dinotefuran, nitenpyram and acetamiprid) on 13 Anopheles gambiae nicotinic acetylcholine receptor (nAChR) subtypes produced by expression of combinations of the Agα1, Agα2, Agα3, Agα8 and Agß1 subunits in Xenopus laevis oocytes, the Drosophila melanogaster orthologues of which we have previously shown to be important in neonicotinoid actions. The presence of the Agα2 subunit reduces neonicotinoid affinity for the mosquito nAChRs, whereas the Agα3 subunit increases it. Crystal structures of the acetylcholine binding protein (AChBP), an established surrogate for the ligand-binding domain, with dinotefuran bound, shows a unique target site interaction through hydrogen bond formation and CH-N interaction at the tetrahydrofuran ring. This is of interest as dinotefuran is also under trial as the toxic element in baited traps. Multiple regression analyses show a correlation between the efficacy of neonicotinoids for the Agα1/Agα2/Agα8/Agß1 nAChR, their hydrophobicity and their rate of knockdown of adult female An. gambiae, providing new insights into neonicotinoid features important for malaria vector control.