Total synthesis of (+)-macquarimicin A

The first total synthesis of (+)-macquarimicin A (1), a novel inhibitor of neutral sphingomyelinase (N-SMase) with antiinflammatory activity, has been accomplished. The present work determined the absolute configuration of (+)-1 and revised the C(2)-C(3) geometry to be Z. The synthesis features a transannular Diels-Alder reaction, which constructed the tetracyclic framework stereoselectively, and a convergent and efficient synthetic pathway, which afforded (+)-macquarimicin A (1) in 27 steps (longest linear sequence) with 9.9% overall yield.     

Preparation and characterization of carbonated barium-calcium hydroxyapatite solid solutions

Particles of carbonated barium-calcium hydroxyapatite solid solutions (BaCaHap) with different Ba/(Ba+Ca) (X(Ba)) atomic ratios were prepared by a wet method at 100 degrees C and characterized by various means. The crystal phases and structures of the products strongly depended on the composition of the starting solution, that is, the Ba/(Ba+Ca) atomic ratio ([X(Ba)]) and H3PO4 concentration ([H3PO4]) in the solution. BaCaHap with X(Ba)0.43 could be prepared at [X(Ba)]0.7 by changing [H3PO4], but could never be obtained at [X(Ba)]=0.8-0.95 regardless of [H3PO4]. The carbonated calcium hydroxyapatite particles prepared at [X(Ba)]=0 were fine and short rod-shaped particles (ca. 14x84 nm). With increasing [X(Ba)] from 0 to 0.8, the particles obtained became large spherical agglomerates. The carbonated barium hydroxyapatite particles formed at [X(Ba)]=1 were long rod-shaped agglomerates (ca. 0.2x2 microm) of fine primary particles. The amount of CO2 adsorbed irreversibly on a series of BaCaHaps showed a minimum at (Ba+Ca)/(P+C) atomic ratio of around 1.56, which agreed well with the minimum cation/P ratio obtained for the other hydroxyapatites, as already reported.     

Perfluoroalkylated eight- and nine-membered benzoheterocycles from F-2-methyl-2-pentene

The reactions of $\text{F}$-2-methyl-2-pentene (1) with several $\text{ortho}$- difunctional benzenes afforded eight- and nine-membered benzoheterocyclic compounds carrying perfluoroalkyl groups. Salicylic acid, salicylaldehyde, and their methyl or chloro derivatives reacted in triethylamine-acetonitrile system giving perfluoroalkylated 2H,6H-1,5-benzodioxocin-2,6-dione (8) and 4H,6H-1,5-benzodioxocin (9) compounds respectively, while phthalyl alcohol and o-hydroxyphenethyl alcohol in triethylamine-diethyl ether system gave perfluoroalkylated 1H,3H,7H-2,6- and 4H,6H,7H-1,5-benzodioxonin compounds, (10) and (11). o-Aminobenzyl alcohol and (1) in diethyl ether afforded a perfluoroalkylated benzoxazocinobenzoxazocinone compound (15).     

Continuous electrophoretic separation of106Ru species in sea water and uptake of the separated fractions by sea algae

¹⁰⁶Ru chloro and nitrosyl-nitrato complexes in sea water were separated into several species by continuous electrophoresis on a filter paper curtain. Biological uptake experiments were carried out on sea algae Fucus virsoides with fractionated¹⁰⁶Ru chloro and nitrosyl-nitrato complex species in sea water. The biological uptake of¹⁰⁶Ru chloro complex species was about 8 times higher than the uptake of¹⁰⁶Ru nitrosyl-nitrato species. Electrophoretically most mobile electrically positively charged cationic species in both systems also showed about 8 times higher biological uptake than the most mobile negatively charged anionic species. A close relation of the biological uptake to the sign of the electrical charge and the electrophoretic mobility of the species is demonstrated. The results are discussed with respect to possible danger to the biological environment as a consequence of the aging of ruthenium species in sea water resulting from¹⁰⁶Ru waste disposal to the sea from a nuclear reprocessing plant. On leave of absence from the National Institute of Radiological Sciences, 9-1, 4-chome, Anagawa, Chiba-shi, Japan, on a fellowship from The Science and Technology Agency of the Japanese Govemment.     

Asymmetric crystallization of bisguanidinobenzene derivatives

We show that the mono-N-methylated and -ethylated derivatives of the achiral compound bisguanidinobenzene undergo spontaneous asymmetric crystallization into a chiral form with chiral space group P2₁2₁2₁. The absolute configurations of the chiral crystals were determined by X-ray crystallography and correlated with circular dichroism (CD) spectra recorded in the solid state. The corresponding protonated and isopropylated derivatives, by contrast, afforded achiral crystals.     

(+)-Phorboxazole A synthetic studies. A highly convergent, second generation total synthesis of (+)-phorboxazole A

[structure: see text] A second generation total synthesis of the potent antitumor agent (+)-phorboxazole A (1) has been achieved. The cornerstone of this approach comprises a more convergent strategy, involving late-stage Stille union of a fully elaborated C(1-28) macrocycle with a C(29-46) side chain. The second generation synthesis entails the longest linear sequence of 24 steps, with an overall yield of 4.2%.     

Solid-phase extraction system for Pb (II) ions enrichment based on multiwall carbon nanotubes coupled on-line to flame atomic absorption spectrometry

The present paper proposes the application of multiwall carbon nanotubes (MWCNTs) as a solid sorbent for lead preconcentration using a flow system coupled to flame atomic absorption spectrometry. The method comprises the preconcentration of Pb (II) ions at a buffered solution (pH 4.7) onto 30 mg of MWCNTs previously oxidized with concentrated HNO₃. The elution step is carried out with 1.0 mol L⁻¹ HNO₃. The effect of the experimental parameters, including sample pH, sampling flow rate, buffer and eluent concentrations were investigated by means of a 2⁴ full factorial design, while for the final optimization a Doehlert design was employed. Under the best experimental conditions the preconcentration system provided detection and quantification limits of 2.6 and 8.6 μg L⁻¹, respectively. A wide linear range varying from 8.6 up to 775 μg L⁻¹ (r > 0.999) and the respective precision (relative standard deviation) of 7.7 and 1.4% for the 15 and 200 μg L⁻¹ levels were obtained. The characteristics obtained for the performance of the flow preconcentration system were a preconcentration factor of 44.2, preconcentration efficiency of 11 min⁻¹, consumptive index of 0.45 mL and sampling frequency estimated as 14 h⁻¹. Preconcentration studies of Pb (II) ions in the presence of the majority foreign ions tested did not show interference, attesting the good performance of MWCNTs. The accuracy of the method was assessed from analysis of water samples (tap, mineral, physiological serum and synthetic seawater) and common medicinal herbs submitted to the acid decomposition (garlic and Ginkgo Biloba). The satisfactory recovery values obtained without using analyte addition method confirms the feasibility of this method for Pb (II) ions determination in different type of samples.     

Intramolecular catalytic Friedel-Crafts reactions with allenyl cations for the synthesis of quinolines and their analogues

[reaction: see text] This paper describes a novel method to synthesize a quinoline backbone by incorporating allenyl cations into a catalytic intramolecular Friedel-Crafts reaction. The initial products were isomerized and aromatized upon treatment with acid and base, respectively, to give quinolines. The basic concept also proved to be promising for 1-benzazepine, 1-benzazocine, or isoquinoline synthesis.