Alzheimer's disease (AD) is a neurodegenerative disorder pathologically characterized by extensive extracellular deposition of amyloid-beta (Abeta) peptides as senile plaques, and inhibition of "amyloidogenic" amyloid precursor protein (APP) processing by gamma-secretase is an important strategy for prevention and treatment of AD. Here we show that beta-peptide foldamers designed to adopt a 12-helical conformation in solution are potent and specific inhibitors of gamma-secretase. Subtle modifications that disrupt helicity substantially reduce inhibitory potency, suggesting that helical conformation is critical for effective inhibition. These beta-peptides competed with helical peptide-type inhibitor, suggesting that they interact with the substrate binding site of gamma-secretase. The beta-peptide with inhibitory activity at nanomolar concentration should be a useful lead compound for development of gamma-secretase-specific inhibitors and molecular tools to explore substrate recognition by intramembrane proteases.

A new gold catalyst, [Au(CO) n ]+ (n = 1, 2), was synthesized by using a facile method from commercial gold(III) oxide, Au2O3, in concentrated H2SO4, which exhibits high catalytic activity for carbonylation of olefins. The gold monocarbonyl [Au(CO)]+ (1) and dicarbonyl [Au(CO)2]+ (2) cations coexist in H2SO4 solution, the former of which is much more stable than the latter. Both of the carbonyls show IR spectra of νCO (2194, 2208 cm-1) higher than that of free CO (2143 cm-1), indicating nonclassical (σ-only) gold−CO bonding. The gold carbonyl complexes coexisting in the concd H2SO4 solution exhibit a single resonance in the 13C NMR spectrum at 171 ppm at ambient temperature and pressure, reflecting rapid CO exchange between 1 (164 ppm) and 2 (175 ppm). The nonclassical gold(I) carbonyl solution worked as an excellent catalyst, with which olefins reacted with CO to give tert-carboxylic acids in good yields at room temperature and atmospheric pressure. The gold(I) dicarbonyl cation 2 was found to function as an active species for the carbonylation. An olefin−gold(I)−carbonyl complex was proposed as a possible intermediate in the metal carbonyl-catalyzed carbonylation in the strongly acidic medium.

A cobalt complex, [CoCl2(dpph)] (DPPH = [1,6-bis(diphenylphosphino)hexane]), catalyzes an intermolecular styrylation reaction of alkyl halides in the presence of Me3SiCH2MgCl in ether to yield beta-alkylstyrenes. A variety of alkyl halides including alkyl chlorides can participate in the styrylation. A radical mechanism is strongly suggested for the styrylation reaction. The sequential isomerization/styrylation reactions of cyclopropylmethyl bromide and 6-bromo-1-hexene provide evidence of the radical mechanism. Crystallographic and spectroscopic investigations on cobalt complexes reveal that the reaction would begin with single electron transfer from an electron-rich (diphosphine)bis(trimethylsilylmethyl)cobalt(II) complex followed by reductive elimination to yield 1,2-bis(trimethylsilyl)ethane and a (diphosphine)cobalt(I) complex. The combination of [CoCl2(dppb)] (DPPB = [1,4-bis(diphenylphosphino)butane]) catalyst and Me3SiCH2MgCl induces intramolecular Heck-type cyclization reactions of 6-halo-1-hexenes via a radical process. On the other hand, the intramolecular cyclization of the prenyl ether of 2-iodophenol would proceed in a fashion similar to the conventional palladium-catalyzed transformation. The nonradical oxidative addition of carbon(sp2)-halogen bonds to cobalt is separately verified by a cobalt-catalyzed cross-coupling reaction of alkenyl halides with Me3SiCH2MgCl with retention of configuration of the starting vinyl halides. The cobalt-catalyzed intermolecular radical styrylation reaction of alkyl halides is applied to stereoselective variants. Styrylations of 1-alkoxy-2-bromocyclopentane derivatives provide trans-1-alkoxy-2-styrylcyclopentane skeletons, one of which is optically pure.