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181.
Teruaki Suzuki Minoru Suzuki Akio Furusaki Takaheshi Matsumoto Arata Kato Yoshihiko Imanaka Etsuro Kurosawa 《Tetrahedron letters》1985,26(10):1329-1332
Two new cyclic ethers consisting of squalene carbon skeleton have been isolated from the red alga L. obtusa. The absolute stereostructure of teurilene () was elucidated by x-ray crystallographic method, and the structure of thyrsiferyl 23-acetate () was established from the spectral and chemical evidence. 相似文献
182.
Tsubaki K Tanima D Nuruzzaman M Kusumoto T Fuji K Kawabata T 《The Journal of organic chemistry》2005,70(12):4609-4616
Various types of chiral host molecules 2-7 based on a phenolphthalein skeleton and two crown ethers were prepared for use in visual enantiomeric recognition, and we examined their enantioselective coloration in complexation with chiral amino acid derivatives 9-22 in methanol solution. Methyl-substituted host (S,S,S,S)-3 showed particularly prominent enantiomer selectivity for the alanine amide derivatives 11 and 12. A combination of methyl-substituted host (S,S,S,S)-3 with guest (R)-11 or (R)-12 developed a purple color, whereas no color development was observed with (S)-11 or (S)-12. On the other hand, phenyl-substituted host (S,S,S,S)-6 showed deeper coloration with a wide range of (S)-beta-amino alcohols compared to that seen with host (S,S,S,S)-6 and the corresponding (R)-beta-amino alcohols at 0 degrees C. Furthermore, absorbance inversion temperatures (AIT) were observed within the range of 0-50 degrees C in many cases. 相似文献
183.
Kaoru Ikeda 《Letters in Mathematical Physics》1991,23(2):121-126
We consider the Hamiltonian systems on the Poisson structure of GL() which is introduced from the quantum group GL
q
() by the so-called quasi-classical limit of GL
q
(). Furthermore, we show that the Toda lattice hierarchy is a Hamiltonian system of this structure. 相似文献
184.
An alternative synthetic route to 1,4,5-trisubstituted imidazoles from α-imino ketone, which can be prepared from imidoyl chlorides and aromatic aldehydes via N-heterocycle carbene-catalyzed aroylation was developed. This methodology consists of simple transformations, allowing a rapid access to imidazole derivatives with various aryl substituents at the desired positions. 相似文献
185.
Hitoshi Kamauchi Masahiro Noji Kaoru Kinoshita Toshikatsu Takanami Kiyotaka Koyama 《Tetrahedron》2018,74(23):2846-2856
The unprecedented tetracyclic coumarin derivatives 1 and 2 and the coumarin dimers 3–5 were isolated from chemically engineered extracts (coumarin dimerization of natural extract) of the marine-derived fungus Eurotium rubrum. The structures of these compounds were established using NMR, MS and IR methods. The absolute configuration of 1 was determined by ECD calculations. The unprecedented tetracyclic coumarin skeleton was generated by domino-Knoevenagel-Diels-Alder reactions. Compounds 1–5 showed tyrosinase inhibitory activity (IC50?=?1.7, 1.2, 4.9, 1.8 and 2.9?μM, respectively). The isolated coumarin derivatives 1–5 were not observed by HPLC analysis in crude extracts of E. rubrum, suggesting that chemically engineered extract generated these new coumarin derivatives with tyrosinase inhibitory activity. 相似文献
186.
T. Takeda M. Fujiwara M. Kurosawa N. Takahashi M. Tamura T. Kawabata Y. Fujikawa K. N. Suzuki N. Abe T. Kubota T. Takahashi 《Journal of Radioanalytical and Nuclear Chemistry》2018,317(2):811-824
In this paper, cheap liquorice residue was used to prepare activated carbon (AC), thioacetamide (TAA) was used to modify the AC, and the adsorption experiments were conducted in the simulated acid radioactive wastewater with low uranium concentration to study the adsorption behavior and mechanism for uranium by TAA modified AC (TAA–AC). The removal efficiency by TAA–AC was 92.1–98.2% from the 1 mg L?1 uranium solution at pH 2–6. The adsorption equilibrium data were well fitted by Dubinin–Radushkevich model, and the maximum adsorption capacity was estimated to be 340 mg g?1. TAA–AC showed an enhanced selectivity for uranium in the presence of competitive ions. Furthermore, the adsorption experiments were conducted in the actual acid radioactive wastewater with low uranium concentration from an in situ leach uranium mine. The high adsorption rate (98.3%) and selectivity (Kd?=?3.78×104 mL g?1) for uranium were observed in the actual acid radioactive wastewater, and the adsorption rate was found to maintain 96.2% over six cycles of adsorption–desorption. 相似文献
187.
Yamamoto A Nakamura K Furukawa K Konishi Y Ogino T Higashiura K Yago H Okamoto K Otsuka M 《Chemical & pharmaceutical bulletin》2002,50(1):47-52
To find new tachykinin NK1 receptor antagonists from natural sources, we examined the tachykinin antagonist activity in the extracts of approximately 200 species of plants by the use of isolated guinea pig ileum. As a result, we discovered a novel and potent NK1 receptor antagonist in the extract of dried flowers of Matricaria chamomilla L. (chamomile). The structure of the antagonist was established as N1,N5,N10,N14-tetrakis[3-(4-hydroxyphenyl)-2-propenoyl]-1,5,10,14-tetraazatetradecane (tetracoumaroyl spermine, 1a). The Ki values of 1a, estimated from the inhibitory action on the substance P (SP)-induced contraction of the guinea pig ileum and the inhibition of the binding of [3H][Sar9, Met(O2)11]SP to human NK1 receptors, were 21.9 nM and 3.3 nM, respectively. 1a is the first potent NK1 receptor antagonist from natural sources and it has a unique structure of a polyacylated spermine. 1a was concentrated in pollen of Matricaria chamomilla L. and was also found in the extracts of flowers of other four species of Compositae. In addition, we found N1,N5,N10-tris[3-(4-hydroxyphenyl)-2-propenoyl]-1,5,10,14-tetraazatetradecane (2) as a new compound in the extract of flowers of Matricaria chamomilla L., which did not exhibit any tachykinin antagonist activity. A number of related compounds were synthesized, and the structure-activity relationship was studied. 相似文献
188.
Hydrogenolytic asymmetric transamination between alkyl (R)-phenylglycinate and ethyl pyruvate was studied. The effect of the asymmetric moieties and of the solvents used in the asymmetric synthesis were explained by the substrate-catalyst complex. 相似文献
189.
Oxidation of a mixture of diketene and a 1,1-diarylethene 1 with manganese(III) acetate dihydrate gave an equilibrium mixture of 5-hydroxy-2-pentanone 2 and a tetrahydrofuran-2-ol, which was subsequently dehydrated in glacial acetic acid to yield 4-penten-2-one 4 in good yield. A similar reaction in the presence of alcohols or amines afforded 2-alkoxy-2-methyltetrahydrofurans 5 or 3-acetyl-2-aminodihydrofurans 9 in moderate yields. Diketene reacted with manganese(III) acetate in the presence of nucleophiles, such as water and alcohols, to give a mixture of unconjugated manganese(III) enolate A and conjugated manganese(III) enolate B. Major products 4 and 5 were formed by the oxidation of the conjugated manganese(III) enolate B. Tetrahydrofurylideneacetates 3 and 7 derived from the unstable unconjugated enolate A were also obtained as minor products. The reaction pathways are discussed. 相似文献
190.
Optically active 3-butyn-2-ol, an important building block, was synthesized successfully using lipase-catalyzed kinetic resolution. Starting from the thus obtained 3-butyn-2-ol, several 4-aryl-substituted compounds were synthesized enantioselectively. 相似文献