Novel synthesis of zerumbone-pendant derivatives and their biological activity

Zerumbone 1, having powerful latent reactivity and containing two conjugated double bonds and a double conjugated carbonyl group is the major component of the essential oil of wild ginger, Zingiber zerumbet Smith. The conjugation system plays an important role in the expression of biological activity. N-Bromosuccinimide (NBS) reaction of 1 gave high reactive intermediate 2 with an exo-methylene group, which was obtained from 1 quantitatively. Treatment of 2 with nucleophiles gave various zerumbone-pendant derivatives, including C–H, C–O, C–N, and C–C bond formation, maintaining the conjugation system through S_N2′-type reaction. Almost all zerumbone-pendant derivatives showed a good value of IC₅₀ against the suppressive effect of NO generation. Among them, amine derivative 5, binding with 2 mol of zerumbone, showed the strongest activity (IC₅₀: 0.24 μM).     

Effects of Inorganic Salts on Micellization and Solubilization in an Aqueous Solution of Poly(ethylene oxide)/Poly(propylene oxide)/Poly(ethylene oxide) Triblock Copolymer

The effects of inorganic salts on micellization and solubilization of prednisolone in aqueous solution of poly(ethylene oxide)/poly(propylene oxide)/poly(ethylene oxide) triblock copolymer (Pluronic P85) were studied. The effect of inorganic salts on decrease in the cloud point and the critical micelle concentration (cmc) of Pluronic P85 was the order of Na₂HPO₄ > NaH₂PO₄ > NaCl > NaBr. Moreover, it was found that Pluronic P85 forms two kinds of micelles: monomolecular micelles and polymolecular micelles. The polymolecular micelle increased with increasing amount of added inorganic salts. Moreover, solubilization behavior is explained from the standpoint of salting out for prednisolone and association characteristics of Pluronic P85.     

Ni‐Catalyzed [4+3+2] Cycloaddition of Ethyl Cyclopropylideneacetate and Dienynes: Scope and Mechanistic Insights

A detailed study of the Ni‐catalyzed [4+3+2] cycloaddition reaction between ethyl cyclopropylideneacetate and dienynes has been conducted, resulting in the development of a new method for the synthesis of compounds containing nine‐membered rings. We studied the reactivity of various dienynes, together with their substituent and conformational effects. The mechanism of the reaction was probed by examining the stoichiometric reactions of the Ni complexes and dienynes.     

Palladium‐Catalyzed Coupling Reaction of Perfluoroarenes with Diarylzinc Compounds

This report describes the first Pd⁰‐catalyzed cross‐coupling of hexafluorobenzene (C₆F₆) with diarylzinc compounds to give a variety of pentafluorophenyl arenes. This reaction could be applied to other perfluoroarenes, such as octafluorotoluene, pentafluoropyridine, and perfluoronaphthalene, to give the corresponding polyfluorinated coupling products. The optimal ligand in this catalytic reaction was PCy₃, and lithium iodide was indispensable as an additive for the coupling reaction. One of the roles of lithium iodide in this catalytic reaction was to promote the oxidative addition of one C?F bond of C₆F₆ to palladium. Stoichiometric reactions revealed that an expected oxidative‐addition product, trans‐[Pd(C₆F₅)I(PCy₃)₂], generated from the reaction of [Pd(PCy₃)₂] with C₆F₆ in the presence of lithium iodide, was not involved in the catalytic cycle. Instead, a transient three‐coordinate, monophosphine‐ligated species, [Pd(C₆F₅)I(PCy₃)], emerged as a potential intermediate in the catalytic cycle. Therefore, we isolated a novel Pd^II complex, [Pd(C₆F₅)I(PCy₃)(py)], in which pyridine (py) acted as a labile ligand to generate the transient species. In fact, in the presence of lithium iodide, this Pd^II complex was found to react smoothly with diphenylzinc to give the desired pentafluorophenyl benzene, whereas the same reaction conducted in the absence of lithium iodide resulted in a decreased yield of pentafluorophenyl benzene, which indicated that the other role of lithium iodide was to enhance the reactivity of the organozinc species during the transmetalation step.     

Regulated Single‐Axis Rotations of a Carbonaceous Guest in a van der Waals Complex with an Entropy Cost

In a tight host–guest complex assembled solely by nondirectional van der Waals forces, unique motions of the guest, such as solid‐state inertial rotations, emerge. The regulation of dynamic motions is an important element to be explored for novel functions of such complexes, which may be seemingly difficult to achieve because of the nondirectionality of the assembling forces. A regulated, single‐axis rotation was made possible by choosing an appropriate shape of the guest in the tubular host. Specifically, an ellipsoidal guest was made to stand along a cylinder axis of the host, which consequently resulted in single‐axis rotations of the guest in the solid. The rotational frequency was considerably high for solid‐state rotations but was suppressed to 10 GHz, which was 1/20 of the isotropic rotation of a spherical guest. In‐depth kinetic analyses quantitatively revealed that the entropy cost was a determining factor that regulated the dynamics.     

Quasi-particle structure around a single vortex in high-Tc superconductors

For analyzing the checker-board like modulation of the local density of states (LDOS) around a vortex observed in the slightly overdoped Bi₂Sr₂CaCu₂O_x, we examined the effect of pseudogap state of high-T_c superconductors to the LDOS around the vortex. We first derived the Bogoliubov-de Gennes equation for d-wave superconductivity (d-SC) in the presence of d-spin density wave (d-SDW). Using the Fourier–Bessel expansion, we solved this equation for a single vortex state, numerically. We found that the peak of the bound states around E = 0 becomes small and modulation of the LDOS is observed for larger d-SDW order parameter.     

Novel photodegradation of the antifungal antibiotic pyrrolnitrin in anhydrous and aqueous aprotic solvents

The UV irradiation of pyrrolnitrin (1a), which is an antibiotic clinically useful against dermatophytosis and possesses a unique 2-(pyrrol-3-yl)nitrobenzene moiety in the molecule, in an anhydrous aprotic solvent resulted in the exclusive formation of transient 7,4'-dichlorospiro[1,3-dihydrobenzo(c)isoxazole-3,3'-pyrrolin-2'-one] (2a) via the intramolecular oxidation of the juxtaposed pyrrole ring by the triplet-excited nitro group. The irradiation in an aqueous aprotic solvent, however, allowed the concurrent occurrence of intramolecular cyclization by the singlet-excited nitro group in 1a and the hydroxylation at the 2-position of the pyrrole ring by water to afford 3,7-dichloro-8-hydroxy-8,8a-dihydropyrrolo[2,3-b]indol-2-one (3a), accompanied by the formation of 2a. Elongation of the irradiation time in these photoreactions caused a rapid consumption of the products, 2a and 3a, to give undetermined polar polymeric products. The present results indicate that the photodegradation of 1a is significantly influenced by the presence of water in the reaction media and by the nature of its excited state. Thus, the loss of the antifungal activities by the photosensitive antibiotic 1a was chemically proved.     

Chemoselective transfer hydrodechlorination of aryl chlorides catalyzed by Cp*Rh complexes

An effective Cp*Rh catalyzed transfer hydrodechlorination of aryl chlorides was achieved with high tolerance towards a variety of functional groups using 2-butanol as a hydrogen source.     

Selective sterol-phospholipid associations in fluid bilayers

The nearest-neighbor preferences of three exchangeable lipid monomers (two phospholipids that differ in length, A and B, and a derivative of cholesterol, C) have been quantified in the fluid bilayer state by use of the nearest-neighbor recognition method (Davidson, S. K. M.; Regen, S. L. Chem. Rev. 1997, 97, 1269). Thus, an analysis of the equilibrium dimer distributions has shown that (i) the sterol favors both phospholipids as nearest neighbors relative to other sterol molecules, (ii) that this recognition is selective (i.e., the sterol favors the longer phospholipid as a nearest neighbor over the shorter one, especially when the sterol concentrations in the bilayer is high (e.g., 40 mol %), and (iii) the phospholipids, themselves, are unable to recognize each other. Taken together, these findings indicate that the probable mechanism by which cholesterol induces homoassociation of A and B in analogous bilayers is one in which the sterol "pulls" two or more of the longer phospholipid monomers (B) out of a "sea" of randomly mixed A and B. These findings also lend support for the notion of cholesterol-phospholipid complexation in fluid bilayers. The biological implications of these findings are briefly discussed.