Identification of ligand-binding sites that form external mouth of ion pore in calcium and sodium channels

3-Trifluoromethyl-3-aryldiazirine photolabels with enhanced ambient light stability

Ambient light stable 3-trifluoromethyl-3-aryldiazirine photolabels are developed via stabilization of the strained three membered diazirine ring by replacing the phenyl ring with electron withdrawing heterocyclic rings. Photolabeling studies reveal that these ambient light stable photolabels are equally efficient in photolabeling target proteins as the traditional 3-trifluoromethyl-3-phenyldiazirine and found to significantly increase the aqueous solubility of the photoaffinity labels.

Diazirine based photoaffinity labeling

Diazirines are among the smallest photoreactive groups that form a reactive carbene upon light irradiation. This feature has been widely utilized in photoaffinity labeling to study ligand-receptor, ligand-enzyme and protein-protein interactions, and in the isolation and identification of unknown proteins. This review summarizes recent advances in the use of diazirines in photoaffinity labeling.

Stereocontrolled synthesis of 8,11-dideoxytetrodotoxin, unnatural analogue of puffer fish toxin

[structure: see text] 8,11-Dideoxytetrodotoxin, an unnatural tetrodotoxin analogue, was synthesized in a highly stereoselective manner from a common intermediate in our synthetic studies on tetrodotoxin. The synthesis features neighboring group participation of trichloroacetamide for stereoselective hydroxylation, protection of ortho ester, and guanidine installation with Boc-protected isothiourea.

Asymmetric total synthesis of 11-deoxytetrodotoxin, a naturally occurring congener

Tetrodotoxin, a toxic principle of puffer fish poisoning, is a specific blocker of sodium channel. Despite many synthetic efforts since the structure elucidation in 1964, the only total synthesis of the racemic tetrodotoxin has been reported by Kishi and co-workers. In the course of our studies directed toward the total synthesis to analyze biologically interesting issues associated with tetrodotoxin, we accomplished a highly stereocontrolled synthesis of (-)-5,11-dideoxytetrodotoxin in 1999. Based on the synthesis, we describe herein the first total synthesis of 11-deoxytetrodotoxin, a naturally occurring analogue. The synthesis started from an allylic alcohol, the same intermediate for the synthesis of 5,11-dideoxytetrodotoxin. Epoxidation of the allylic alcohol was followed by isomerization with Ti(i-PrO)(4) to give an alpha-hydroxy allylic alcohol, in which the configurations of the two hydroxyl groups were inverted by oxidation and then a 2-step reduction. Further epoxidation of the allylic alcohol and ozonolysis of the remaining vinyl group gave an aldehyde, which reacted with magnesium acetylide to give a propargyl alcohol in a stereoselective manner. Oxidative cleavage of the acetylenic moiety with RuO(4) afforded a fully functionalized lactone for 11-deoxytetrodotoxin. Crucial guanidinylation was achieved from trichloroacetamide according to our own method to give acetyldibenzylguanidine. Finally, deprotection of benzyl groups, acetates, and acetal furnished 11-deoxytetrodotoxin.

TTX resistivity of Na+ channel in newt retinal neuron

We examined voltage-dependent, TTX-resistant Na+ channels of newt retina (nRNaCh) electrophysiologically. IC50-TTX value of nRNaCh is more than 20 microM. We determined partial cDNA sequences of nRNaCh restricted to TTX binding sites (SS2 regions of all four repeats). While the amino acid sequences of SS2 regions of repeats II, III and IV of nRNaCh are identical to those of TTX-sensitive Na+ channels, only one amino acid in SS2 of repeat I of nRNaCh is different. nRNaCh have nonaromatic amino acid (Ala) in this site instead of the aromatic amino acid in a case of TTX-sensitive Na+ channels. Many studies suggested that the differences of TTX sensitivity of Na+ channels are decided by whether amino acid in this site is aromatic or not. Therefore nRNaCh acquire their TTX resistivity with the same mechanism as TTX-resistant cardiac Na+ channels do.

A novel biotinylated heterobifunctional cross-linking reagent bearing an aromatic diazirine

The synthesis of a p-[(3-trifluoromethyl)diazirine-3-yl]benzoic acid derivative is described as a new carbene generating heterobifunctional cross-linking reagent. The cross-linker carries a biotin moiety in order to make use of avidin-biotin technology for specific manipulation of cross-linked components. To evaluate the ability of this reagent, the inter-subunit cross-linking of egg-white avidin tetramer was investigated. As a typical application of avidin-biotin technology for cross-linking experiments, a chemiluminescent detection method was examined to identify photobiotinylated components. A cross-linked dimeric product with an apparent molecular mass of 38 kDa was clearly visualized by the combined use of a horseradish peroxidase-streptavidin conjugate and a luminol-based chemiluminescent system.