Although pinning of domain walls in ferromagnets is ubiquitous, the absence of an appropriate characterization tool has limited the ability to correlate the physical and magnetic microstructures of ferromagnetic films with specific pinning mechanisms. Here, we show that the pinning of a magnetic vortex, the simplest possible domain structure in soft ferromagnets, is strongly correlated with surface roughness, and we make a quantitative comparison of the pinning energy and spatial range in films of various thickness. The results demonstrate that thickness fluctuations on the lateral length scale of the vortex core diameter, i.e., an effective roughness at a specific length scale, provides the dominant pinning mechanism. We argue that this mechanism will be important in virtually any soft ferromagnetic film.
The direct conversion of secondary to tertiary alcohols via ruthenium(0) catalyzed C-C coupling of substituted 3-hydroxy-2-oxindoles with various dienes is described. Coupling occurs in a completely regioselective manner in the absence of stoichiometric byproducts.In the course of exploring hydrogen-mediated C-C couplings outside of hydroformylation, 1 our laboratory has developed metal catalysts that promote the transfer of hydrogen from primary alcohols to various π-unsaturated compounds resulting in pairwise generation of aldehydeorganometallic nucleophile-electrophile pairs that combine to form products of aldehyde addition. These processes merge redox and C-C bond construction events, 2 bypassing both discrete alcohol-to-aldehyde oxidation and the stoichiometric use of premetallated reagents. Although conditions for the C-C coupling of primary alcohols to dienes 3, 4, 5 and other π-unsaturated reactants (allenes, enynes, alkynes and allylic acetates) 1 have been developed, corresponding couplings of secondary alcohols have proven more challenging.Recently, it was found that ruthenium(0) complexes derived from Ru 3 (CO) 12 and phosphine ligands catalyze C-C coupling of mandelic esters with 2-substituted dienes at the C4-position to form prenylated and geranylated compounds from isoprene and myrcene, respectively. 4e As corroborated by mechanistic studies, this regioselectivity is a consequence of a catalytic mechanism wherein alcohol dehydrogenation drives oxidative coupling between the diene and a transient α-oxoester. 6 To our knowledge, such C4 regioselectivity is unique for intermolecular reductive couplings of 2-substituted dienes to carbonyl partners. 7,8,9 Given the structural homology of substituted mandelic esters and 3-hydroxy-2-oxindoles, which represent important natural product substructures, the latter compounds were explored as partners for redox triggered C-C coupling with dienes. 10 Here, we report that exposure of 3-hydroxy-2-oxindoles to isoprene or myrcene and the ruthenium(0) catalyst derived from Ru 3 (CO) 12 and tricyclohexylphosphine, PCy 3 , results in direct,
The ruthenium catalyst generated in situ from Ru3(CO)12 and tricyclohexylphosphine, PCy3, promotes the redox-neutral C-C coupling of aryl substituted α-hydroxy esters to isoprene and myrcene at the diene C4-position, resulting in direct carbinol C-H prenylation and geranylation, respectively. This process enables direct conversion of secondary to tertiary alcohols in the absence of stoichiometric byproducts or premetallated reagents, and is the first example of C4-regioselectivity in catalytic C-C couplings of 2-substituted dienes to carbonyl partners. Mechanistic studies corroborate a catalytic cycle involving diene-carbonyl oxidative coupling.
The synthesis and biological evaluation of chromane-containing bryostatin analogues WN-2 to WN-7 and the previously reported salicylate-based analogue WN-8 are described. Analogues WN-2 to WN-7 are prepared through convergent assembly of the chromane-containing Fragment B-I with the “binding domain” Fragment A-I or its C26-des-methyl congener, Fragment A-II. The synthesis of Fragment B-I features enantioselective double C-H allylation of 1,3-propane diol to form the C2-symmetric diol 3 and Heck cyclization of bromodiene 5 to form the chromane core. The synthesis of salicylate WN-8 is accomplished through the union of Fragments A-III and B-II. The highest binding affinities for PKCα are observed for the C26-des-methyl analogues WN-3 (Ki = 63.9 nM) and WN-7 (Ki = 63.1 nM). All analogues, WN-2 to WN-8, inhibited growth of Toledo cells, with the most potent analogue being WN-7. This response, however, does not distinguish between phorbol ester-like and bryostatin-like behavior. In contrast, while many of the analogues contain a conserved C-ring in the binding domain and other features common to analogues with bryostatin-like properties, all analogues evaluated in the U937 proliferation and cell attachment assays displayed phorbol ester-like and/or toxic behavior, including WN-8, for which “bryostatin-like PKC modulatory activities” previously was suggested solely based on PKC binding. These results underscore the importance of considering downstream biological effects, as tumor suppression cannot be inferred from potent PKC binding.
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