Synthesis of bis(alk-3-en-1-ynyl)benzene with either E- or Z-configuration via a one-pot three-component coupling reaction and its optical properties

A convenient, efficient and stereoselective synthesis of a range of bis(alk-3-en-1-ynyl)benzenes with E- and Z-configuration is described. The protocol involves Cu-mediated cross-coupling reaction of (E)- and (Z)-alk-1-enyldisiamylboranes with (trimethylsilyl)ethynyl bromide and Pd/Cu-catalyzed cross-coupling reaction with diiodobenzene. The sequential cross-coupling reaction proceeds readily under extremely mild conditions in a one-pot manner to afford bis(alk-3-en-1-ynyl)benzenes in good to excellent yields. The optical properties of the products are also described.     

Extraction—spectrophotometric determination of trace amounts of iron in waters with pyrogallol red and zephiramine

The simple removal of excess of co-extracted reagent in the solvent extraction of metal complex anions with a quaternary ammonium salt greatly improves the determination of iron(II) with pyrogallol red and zephiramine. The method with pyrogallol red is suitable for the determination of trace amounts of iron in natural waters. The apparent molar absorptivities of the iron(II) complex in chloroform are 7.5×10⁴ and 10.3×10⁴ 1 mol^-1 cm^-1 at 560 and 298 nm, respectively. A large excess of reagent can be added, and the ternary complex can be completely extracted over the pH range 8.5–10. Masking agents allow most interferences to be suppressed. The method is suitable for the analysis of potable, river and sea waters.     

Strong ferromagnetic exchange couplings in copper(II) and nickel(II) complexes with a paramagnetic tridentate chelate ligand, 2,2'-bipyridin-6-yl tert-butyl nitroxide

A paramagnetic ligand 6bpyNO (2,2'-bipyridin-6-yl tert-butyl nitroxide) is a newcomer in the field of metal-radical hybrid magnetic materials. Complexes [CuII(6bpyNO)Cl2] and [NiII(6bpyNO)2](PF6)2 having highly planar chelate rings showed considerably strong ferromagnetic exchange couplings J/kB = 202 and 192 K, respectively, across the direct radical oxygen coordination bonds (the spin Hamiltonian is defined as -2JSi.Sj).     

Tuning the chiral cavity of macrocyclic receptor for chiral recognition and discrimination

The size and shape of the chiral cavity of a macrocyclic receptor were tuned by the alteration of the binaphthyl moiety to improve the chiral recognition/discrimination ability. For example, host 3 with the 3,5-bis(trifluoromethyl)phenyl group at the 3,3'-positions showed improved enantioselectivity for small molecules such as 2-chloropropionic acid and methyl lactate as evaluated by the binding constants. This host 3 also had an excellent ability as an NMR chiral solvating agent.     

Total synthesis of pteridic acids A and B

Pteridic acid A (1) is a spirocyclic octaketide produced by the phytoepiphytic actinomycete Streptomyces hygroscopicus TP-A0451 and possesses potent plant-growth-promoting activity comparable to that of indole-3-acetic acid. The enantioselective total synthesis of this natural product was achieved by employing the Sn(OTf)(2)-mediated Evans aldol reaction and the Fukuyama acetylenic coupling reaction as the key C--C bond-forming steps producing 1 through a 14-step sequence in 22 % overall yield from a known oxazolidinone derivative. MgBr(2)-mediated equilibration of an anomerically favored spirocyclic intermediate used for the synthesis of 1 brought about partial epimerization of the spirocenter to give the corresponding anomerically disfavored epimer, which was converted into pteridic acid B (11-epi-1), another plant-growth promoter of the same microbial origin.     

Peroxidase activity enhancement of horse cytochrome c by dimerization

The peroxidase activity of horse cytochrome c was enhanced by its dimerization, where its Compound III (oxy-form) and Compound I (oxoferryl porphyrin π-cation radical) species were detected in the reactions with hydrogen peroxide and meta-chloroperbenzoic acid, respectively. These results show that oligomeric cytochrome c can contribute as a proapoptotic conformer by the increased peroxidase activity.     

Microbiological synthesis of 16-ketopregnanes from steroidal sapogenins

Incubation of diosgenone (1, 25D-spirost-4-en-3-one) with Verticillium theobromae (Turconi) Mason et Hughes (CBS) afforded 20α-hydroxypregn-4<ne-3,16-dione (3) and 3α,11β,20α-trihydroxy-5α-pregnan-16-one (4). The same transformation products were also obtained by the use of Stachylidium bicolor Link (IFO 6647). Isolation and identification processes of the products are discussed.     

Formation of supramolecular polymers and discrete dimers of perylene bisimide dyes based on melamine-cyanurates hydrogen-bonding interactions

Melamine-linked perylene bisimide dyes (MPBIs) bearing an ethylene or trimethylene group as linker moieties were synthesized, and their self-aggregation and coaggregation with cyanurates through complementary triple hydrogen bonds have been investigated. UV/vis studies revealed that both the MPBIs self-assemble in nonpolar organic solvent through pi-pi stacking interaction between perylene cores, giving self-aggregates with nearly identical thermal stabilities. Upon addition of 1 equiv of cyanurate components, however, the stabilities of the resulting aggregates were dramatically changed between the two systems, suggesting the formation of different types of hydrogen-bonded supramolecular species. Dynamic light scattering and atomic force microscopic studies revealed that the system featuring ethylene linker moieties generates a discrete dimer of MPBI supported by two cyanurate molecules, whereas the system featuring trimethylene linker moieties affords extended supramolecular polymers hierarchically organizing into nanoscopic fibers. These results demonstrate that it is possible to obtain distinct supramolecular species by just changing the number of carbon atoms at the linker moieties of MPBI components. The present strategy for the fabrication of discrete or polymeric supramolecular assemblies should be applicable to other functional pi-conjugated molecules.     

m × n] metal ion arrays templated by coordination cages

Three-dimensional m × n arrays of metal ion clusters can be assembled as aromatic stacks of planar polynuclear metal complexes within columnar coordination cages. The polynuclear complexes and cage height program the final array structures of the metal ion clusters. Cyclic trinuclear Au(I) complexes (m = 3) assembled into trigonal prismatic arrays (n = 1-3) within the cages and the array structures were clearly shown by X-ray crystallographic analysis. A silver-sandwiched hetero-Au(3)-Ag-Au(3) cluster was also prepared by treating a hexanuclear Au(3)-Au(3) cluster with Ag(I) ion.     

Total synthesis of valeriananoids A, B, and C via autocatalytic diastereoselective domino Michael reaction

Natural enantiomers of unique tricyclic sesquiterpenoids, valeriananoids A-C 1-3, have been synthesized starting from bicyclo[2.2.2]octane-2,5-dione derivative 11, which was obtained by diastereoselective catalytic domino Michael reaction of oxophorone 5 with 8-phenylmenthyl acrylate 10 by LDA or silica-gel-base (NMAP-Li). The tricyclic ring was closed selectively by intramolecular 6-endo-trig mode cyclization of the ketyl radical, which was generated from keto-allylether 25 by either lithium or sodium naphthalenide.