Convergent total synthesis of gymnocin-A and evaluation of synthetic analogues

The first total synthesis of gymnocin-A (1), a cytotoxic polycyclic ether isolated from a notorious red tide dinoflagellate, Karenia mikimotoi, has been accomplished. The synthesis relies heavily on the Suzuki-Miyaura cross-coupling-based methodology to assemble the tetradecacyclic polyether skeleton. Convergent union of the GHI (5) and KLMN (6) rings, both of which were prepared from a common intermediate 7, and the subsequent ring closure of the J ring delivered the GHIJKLMN ring. The crucial coupling between the ABCD and FGHIJKLMN ring fragments (3 and 4, respectively) and stereoselective installation of the C17 hydroxyl group, followed by cyclization of the E ring gave rise to the tetradecacyclic polyether skeleton 2. Finally, incorporation of the 2-methyl-2-butenal side chain completed the total synthesis of gymnocin-A. The convergent nature of the synthesis, which employs three fragments of comparable complexity, is well-suited for preparation of various structural analogues of gymnocin-A to explore the structure-activity relationship. The results of preliminary structure-activity relationship studies of several synthetic analogues are also provided.     

Preparation and Properties of Nb-Coated Barium Titanate Composite Particles by Surface Modification with Nb Alkoxide in Hydrophobic Solvent

Chemical processing for the preparation of Nb-coated barium titanate composite particles was investigated using surface modification technology, hydrolyzing Nb ethoxide on the surface of barium titanate particles dispersed in hydrophobic solvent.It was confirmed from the measurements of specific surface area and zeta potential as well as SEM, TEM and EDX observations of the resulting composite particles that the original barium titanate particles were coated uniformly with hydrolysis product of Nb ethoxide.Barium titanates coated with 1 wt% of Nb as oxide were well sintered at 1200–1300°C. The dielectric constants of the sintered barium titanates showed flattened temperature dependence, but it depended upon the average particle size of original barium titanate. The sintered bodies of Nb-coated barium titanate powders with average particle size of 0.2 m gave dielectric constants of 2000–3000 and those of barium titanate with average particle size of 0.5 m showed dielectric constants of 3000–4000 at room temperature.The microstructure of the sintered barium titanate coated with Nb oxide consisted of grains of about 1 m, smaller than those of sintered original barium titanate.     

Interactions of Tetrakis(4-sulfonatophenyl)porphyrin with γ-Cyclodextrin and Alkyltrimethylammonium Bromides in Aqueous Solutions

Tetrakis(4-sulfonatophenyl)porphyrin (TSPP) forms complexes with octyltrimethylammonium bromide (OTMA) and hexyltrimethylammonium bromide (HTMA) in pH 7.3 buffers. At low concentrations of OTMA (HTMA), a 1:1 TSPP–OTMA complex is formed. As the OTMA (HTMA) concentration is increased, a 1:2 TSPP–OTMA (HTMA) complex is also formed. The equilibrium constants for the formation of the TSPP–OTMA (HTMA) complexes have been evaluated from a simulation of the observed fluorescence intensity data. In the induced circular dichroism spectrum, the signal intensity of TSPP in aqueous solutions containing both γ-CD and OTMA has been similar to that containing only γ-CD, suggesting the formation of the 1:1:1 γ-CD–TSPP–OTMA (HTMA) inclusion complex. Capillary electrophoretic study has exhibited the formation of the 1:1 TSPP–OTMA (HTMA) complex, although the 1:2 TSPP–OTMA (HTMA) complex could not be observed, probably because the OTMA (HTMA) concentration used was low. The equilibrium constants for these 1:1 complexes have been evaluated from the variation in the electrophoretic mobility. The equilibrium constant for the formation of the 1:1:1 γ-CD–TSPP–OTMA or γ-CD–TSPP–HTMA complex has been evaluated from a simulation of the electrophoretic mobility change in TSPP solution containing γ-CD and OTMA or HTMA, although the equilibrium constants for the ternary inclusion complexes could not be evaluated using the fluorescence method due to the small fluorescence intensity change.     

The synthesis and analytical capabilities of chromogenic aza-12-crown-4 as a selective reagent for lithium ion

The synthesis and analytical capabilities of a new chromogenic crown ether, 1-(2-hydroxy-5-nitrobenzyl)-1-aza-4,7,10-trioxacyclododecane, chromogenic aza-12-crown-4. Constants found for this aza-12-crown-4 were pK_a1 = 5.77, pK_a2 = 10.31, pK_ex (Li) = 10.18, and pK_ex (Na) = 12.50. The calibration curve obtained for the extraction-spectrophotometric procedure was linear from 0.3 to 2 μg ml^?1. The imprecision of the measurement was calculated from the mean value of the standard deviations of triplicate samples over the linear range and was less than 5%. Results for the determination of lithium in blood serum and urine exhibited good agreement with atomic absorption data.     

Small-angle electron scattering by formaldehyde and ketene: Effects of electron correlation and chemical binding

The total (elastic plus inelastic) intensities of 51 keV electrons scattered by H₂CO and H₂CCO have been measured over a range of K = (4π/λ) sin(θ/2) = 1–9.5 Å^?1 and compared with the theoretical intensities calculated with SCF and CI wave functions. Significant discrepancies are found between the experimental intensities and the theoretical ones based on the SCF wave functions. Most of the chemical binding and electron correlation effects observed in the total scattered intensities are reproduced by the theoretical intensities based on the CI wave functions calculated with the basis set including polarization functions on all atoms. © 1992 John Wiley & Sons, Inc.     

Elimination of HX (X = Cl,Br) from haloalkenes on the Ru2Q2 (Q = S,Se) core complex

Treatment of [[Ru(P(OCH3)3)2(CH3CN)3]2(mu-Q2)](CF3SO3)4 (1, Q = S; 2, Q = Se) with haloalkenes resulted in the formation of complexes carrying unsaturated C3Q2 five-membered or C4Q2 six-membered rings via elimination of HX (X = Cl, Br). The reactions of 1 and 2 with allyl bromide gave the corresponding addition products, [[Ru(P(OCH3)3)2(CH3CN)3]2(mu-QCH=CHCH2Q)](CF3SO3)4 (3, Q = S; 4, Q = Se), via elimination of HBr. The elimination process seems to be thermodynamically controlled and takes place at the final stage of the reaction. The steric effect of the halogen atoms seems more operative than the electronic one.     

Construction of porphyrin-cyclodextrin self-assembly with molecular wedge

A new host porphyrin bearing four permethyl-beta-cyclodextrin moieties for multi-porphyrin assembly forms a unique 2 : 2 assembly with the tetra-anion of tetrakis(p-sulfonylphenyl)porphyrin (TPPS) in aqueous solution.     

Field theoretical construction of an infinite set of quantum commuting operators related with soliton equations

The quantum version of an infinite set of polynomial conserved quantities of a class of soliton equations is discussed from the point of view of naive continuum field theory. By using techniques of two dimensional field theories, we show that an infinite set of quantum commuting operators can be constructed explicitly from the knowledge of its classical counterparts. The quantum operators are so constructed as to coincide with the classical ones in the 0 limit (; Planck's constant divided by 2). It is expected that the explicit forms of these operators would shed some light on the structure of the infinite dimensional Lie algebras which underlie a certain class of quantum integrable systems.     

Doubly-bridged binuclear complexes of oxomolybdenum(V) and oxotungsten(V) containing sexadentate ligands

Binuclear oxomolybdenum(V) and oxotungsten(V) complexes of the type, [M ₂(O)₂(-X)(-X ¹)], where M=Mo, W;X.X ¹=O, S; L=edta, pdta (n=2-), tpen, tppn (n=2+) (edta^4– =ethylenediaminetetraacetate(4–), pdta=R- orR,S-propylenediaminetetraacetate(4–), tpen=N,N,N ¹,N¹-tetrakis(2-pyridyhnethyl)-ethylenediamine, and tppn=R- orR,S-N,N,N ¹,N¹-tetrakis(2-pyridylmethyl)-propylenediami ne) are reviewed with respect to their preparation, structure, spectroscopic properties, reactivities, and in particular asymmetric distortion around the bicyclo [4.1.1 ] type core and stereoselectivity related to this distortion,Dedicated to Professor Jiaxi Lu on the occasion of his 80th birthday and in recognition of his pioneering contributions.