Enantioselective formal synthesis of (−)-aurantioclavine using Pd-catalyzed cascade cyclization and organocatalytic asymmetric aziridination

The enantioselective formal synthesis of (?)-aurantioclavine is described. The core tricyclic skeleton was synthesized using a Pd-catalyzed Heck insertion–allylic amination cascade. The stereocenter was constructed by a highly enantioselective organocatalytic asymmetric aziridination reaction.     

New methods and reagents in organic synthesis. 58. : A synthesis of patellamide a, a cytotoxic cyclic peptide from a tunicate. Revision of its proposed structure

The real structure of patellamide A, a cytotoxic lipophilic cyclic peptide from a marine tunicate, has been unambiguously determined by the synthesis of both its proposed and revised structures.     

Preparation of highly deuterated zeaxanthin, lycopene, and β-carotene from fully deuterated mevalonate using engineered Escherichia coli

Carotenoids are important natural pigments produced by various microorganisms and plants. Specific deuterium-labeling of these compounds is invaluable in biochemical and physiochemical research. In this paper, preparation of highly deuterated zeaxanthin, lycopene, and β-carotene using engineered Escherichia coli with fully deuterated mevalonate is described. Also described are physico-chemical properties of the obtained deuterated carotenoids.     

Determination of 0.1 to 1000 μ g/ml cadmium in a hydrometallurgical zinc refining process stream by a flow injection technique with computer controlled injection method

A computer-controlled flow injection system was developed for the determination of cadmium in a hydrometallurgical zinc refining process stream. An anion-exchange method in acidic potassium iodide medium was used for the on-line separation of cadmium from the matrix zinc. 1-(4-Nitrophenyl)-3-(4-phenylazophenyl)triazene (Cadion) was used as the chromogenic reagent for the spectrophotometric detection of cadmium. In order to expand the dynamic range of the flow injection - spectrophotometry, a computer-aided time-based variable-volume injection method has been employed for the introduction of the sample into the flow injection system. Samples ranging from 0.56 to 350 microl can be delivered by controlling the time period of the sample introduction valve and the flow rate of the carrier solution. The system permits a throughput of 5 samples per hour. The reproducibility has been proven to be satisfactory with a relative standard deviation of less than 6.2% (sample injected: 0.56 microl of 850 microg Cd/ml; n=100) and 5.0% (350 microl of 0.14 microg Cd/ml; n=5). The determination limit was 20 microg Cd/ml with 0.56 microl sample injection and 0.05 microg Cd/ml with 350 microl sample injection (the absolute amount of cadmium injected into the system was 11 ng and 17.5 ng, respectively).     

Monoclonal-based enzyme-linked immunosorbent assay and immunochromatographic assay for enrofloxacin in biological matrices

Enrofloxacin has been increasingly used in veterinary medicine to treat microbial infections. A simple and reliable analytical method for this drug is required. The current determination by high performance liquid chromatography (HPLC) is sensitive but labor-intensive. This paper reports an enzyme-linked immunosorbent assay (ELISA) using a monoclonal antibody (MAb) and the development of a rapid test kit based on immunochromatography. The detection limits using the ELISA were 10 ppb for chicken liver and muscle, and 1 ppb for cattle milk, respectively. The mean recovery values were 77.3-96.0% for chicken liver, 72.4-92.0% for chicken muscle and 84.0-99.0% for cattle milk. The detection limits using the kit were ca. 100 ppb for chicken muscle and ca. 10 ppb for cattle milk, respectively. All ELISA results for assay of chicken liver, chicken muscle and cattle milk were confirmed using HPLC which is used as the routine assay. The HPLC (x) and ELISA (y) results showed close correlation for chicken liver (y = 8.7 + 0.85x, r2 = 0.99, n = 25), chicken muscle (y = -3.9 + 0.94x, r2 = 0.98, n = 25) and cattle milk (y = 18.4 + 0.92x, r2 = 0.99, n = 25).     

Simultaneous separation of common mono- and divalent cations on a calcinated silica gel column by ion chromatography with indirect photometric detection and aromatic monoamines-oxalic acid,containing crown ethers,used as eluent

The application of unmodified silica gel (Super Micro Bead Silica Gel B-5, SMBSG B-5) as a cation-exchange stationary phase in ion chromatography with indirect photometric detection (IC-IPD) for the separation of common mono- and divalent cations (Li+, Na+, NH4+, K+, Mg2+ and Ca2+) was carried out using various aromatic monoamines [tyramine [4-(2-aminoethyl)phenol], benzylamine, phenylethylamine, 2-methylpyridine and 2,6-dimethylpyridine] as eluents. When using these amines as eluents, the peak resolution between these mono- and divalent cations was not quite satisfactory and the peak shapes of NH4+ and K+ were largely destroyed on the SMBSG B-5 silica gel column. Hence, the application of SMBSG B-5 silica gel calcinated at 200, 400, 600, 800 and 1000 degrees C for 5 h in the IC-IPD was carried out. The peak shapes of the monovalent cations were greatly improved with increasing calcination temperature and, as a result, symmetrical peaks of these mono- and divalent cations were obtained on the SMBSG B-5 silica gel calcinated at 1000 degrees C as the stationary phase. In contrast, the peak resolution between these mono- and divalent cations was not improved. Therefore, crown ethers [18-crown-6 (1,4,7,10,13,15-hexaoxacyclooctadecane), 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane)] were added to the eluent for the complete separation of these mono- and divalent cations. Excellent simultaneous separation and highly sensitive detection at 275 nm were achieved in 25 min on a column (150x4.6 mm I.D.) packed with SMBSG B-5 silica gel calcinated at 1000 degrees C by elution with 0.75 mM tyramine-0.25 mM oxalic acid at pH 5.0 containing either 1.0 mM 18-crown-6 or 10 mM 15-crown-5.     

Pairings of function spaces

Pairings and copairings of topological spaces induce pairings of function spaces. These induced pairings of function spaces are studied. For this purpose, the C-open topology of function spaces is studied for subcategories C of Top. It is shown that the C-open topology enjoys good properties for homotopy theory. Making use of the C-open topology, theory of induced pairings is established and fundamental results on pairings which deduce various commutativity properties of elements in homotopy set are extended to function spaces.     

Development of new methods in organic synthesis and their applications to the synthesis of biologically interesting natural products

2,6-Dimethyl-9-Aryl-9-phosphabicyclo[3.3.1]nonanes (9-PBN and 9-NapBN) and the chiral diaminophosphine oxides (DIAPHOXs) derived from aspartic acid have been introduced as useful ligands and preligands, respectively, for transition metal-catalyzed asymmetric synthesis. anti-Selective asymmetric hydrogenation of α-amino-β-ketoesters using Ru-, Rh-, Ir-, and Ni-catalysts through dynamic kinetic resolution have been developed for the first time, producing efficiently important anti β-hydroxy-α-amino acids. The total synthesis of several biologically active natural products was achieved by use of the transition metal-catalyzed reaction using DIAPHOX, anti-selective asymmetric hydrogenation, and reactions developed by us. Synthesis of tangutorine, an antitumor indole alkaloid, has been enantioselectively achieved for the first time. Enantioselective synthesis of a martinelline chiral core was accomplished using the asymmetric tandem Michael-Aldol reaction as a key step developed by us. This synthesis represents the formal total synthesis of martinelline and martinellic acid. Papuamide B was synthesized through the elucidation of unknown stereostructures by using the anti-selective asymmetric hydrogenation and reactions developed by us.     

Steric tuning of C2-symmetric chiral N-heterocyclic carbene in gold-catalyzed asymmetric cyclization of 1,6-enynes

Steric tuning of C₂-symmetric chiral N-heterocyclic carbene (NHC) was performed in Au(I)-catalyzed asymmetric cyclization of 1,6-enyne. Higher enantioselectivity was realized when chiral NHC–AuCl/AgSbF₆ catalysts whose N-substituent on the NHC overlays the Au–Cl bond was utilized.     

Asymmetric synthesis of chiral 9,10-dihydrophenanthrenes using Pd-catalyzed asymmetric intramolecular Friedel-Crafts allylic alkylation of phenols

We developed a novel asymmetric synthetic method for multisubstituted 9,10-dihydrophenanthrenes based on the Pd-catalyzed asymmetric intramolecular Friedel-Crafts allylic alkylation of phenols, which produces 10-vinyl or 10-isopropenyl chiral 9,10-dihydrophenanthrene derivatives in high yield with up to 94% ee.