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Görgen JJ Comfort JR Tinsley JR Averett T DeKorse J Franklin B Ritchie BG Kyle G Klein A Berman B Burleson G Cranston K Faucett JA Jarmer JJ Knudson JN Penttilä S Tanaka N Brinkmöller B Dehnhard D Yen YF Hoibråten S Breuer H Flanders BS Khandaker MA Naples DL Zhang D Barlett ML Hoffmann GW Purcell M 《Physical review letters》1991,66(17):2193-2196
246.
Sekino E Kumamoto T Tanaka T Ikeda T Ishikawa T 《The Journal of organic chemistry》2004,69(8):2760-2767
(-)-Quinine-catalyzed intramolecular oxo-Michael addition (IMA) of 7-hydroxy-5-methoxy-8-tigloylcoumarins was developed for the enantioselective construction of 2,3-dimethyl-4-chromanone systems in the context of the asymmetric synthesis of anti-HIV-1 active Calophyllum coumarins. Combination of the IMA and MgI(2)-assisted demethylation of the 5-methoxy group along with isomerization of the formed chromanone systems as key steps successfully led to the concise synthesis of (+)-inophyllum B and (+)-calanolide A, possible candidates for AIDS drugs. Further examination of the asymmetric IMA with cinchona alkaloids lacking a methoxy group on the quinoline skeleton suggested the influence of the methoxy substituent on stereoselectivity at the stereogenic centers of the chromanone systems. 相似文献
247.
Tanaka K Ohta K Haddad PR Fritz JS Miyanaga DA Hu W Hasebe K 《Journal of chromatography. A》2000,884(1-2):167-174
A simple, selective, and sensitive method for the simultaneous determination of anions (sulfate, nitrate, and chloride) and cations (sodium, ammonium, potassium, magnesium, and calcium) in acid rain waters was developed using ion-exclusion/ cation-exchange chromatography with conductimetric detection. A weakly acidic cation-exchange resin column (Tosho TSKgel OA-PAK-A) and a sulfosalicylic acid-methanol-water eluent was used. With a mobile phase comprising 1.25 mM sulfosalicylic acid in methanol-water (7.5:92.5) at 1.2 ml/min, simultaneous separation and detection of the above anions and cations was achieved in about 30 min. Linear calibration plots of peak area versus concentration were obtained over the concentration ranges 0-1.0 mM for anions (R=0.9991) and 0-0.5 mM for cations (R=0.9994). Detection limits calculated at S/N=3 ranged from 4.2 to 14.8 ppb for the anions and from 2.4 to 12.1 ppb for the cations. The reproducibility of retention times was 0.14-0.15% relative standard deviation (RSD) for anions and 0.18-0.31% for cations, and reproducibility of chromatographic peak areas was 1.22-1.75% RSD for anions and 1.81-2.10% for cations. The method was applied successfully to the simultaneous determination of anions and cations in aerosols transported from mainland China to central Japan, as determined by a meteorological satellite data analyzer. 相似文献
248.
Fujishima H Takeshita H Toyota M Kim HS Wataya Y Tanaka M Sasaki T Ihara M 《Chemical & pharmaceutical bulletin》2001,49(5):572-575
Biological evaluations of bicyclo[6.4.0]dodecenone derivatives on antimalarial activity in vitro against Plasmodium falciparum and cytotoxicity against human KB cells were made. (+/-)-(1R*,4S*,7R*,8S*)-4-tert-Butyl-dimethylsiloxy-5,5-dimethyl-1-methyl-9-methylene-7-phenylsulfonylbicyclo[6.4.0]dodec-2,11-dien-10-one (15) exhibited potent antimalarial activity, whereas (+/-)-(1R*,7R*,8S*)-1-methyl-9-methylene-7-phenylsulfonylbicyclo[6.4.0]dodec-2,11-dien-10-one (14) showed significant cytotoxic activity in human KB cells. Both 14 and 15 possess, as a structural character, the exo-methylene moiety in their 6-membered ring of the 8-6 fused ring system. 相似文献
249.
The asymmetric hydroformylation of 2‐ and 3‐vinylfurans ( 2a and 2b , resp.) was investigated by using [Rh{(R,S)‐binaphos}] complexes as catalysts ((R,S)‐binaphos = (11bS)‐4‐{[1R)‐2′‐phosphino[1,1′‐binaphthalen]‐2‐yl]oxy}dinaphtho[2,1‐d:1′,2′‐f][1,3,2]dioxaphosphepin; 1 ). Hydroformylation of 2 gave isoaldehydes 3 in high regio‐ and enantioselectivities (Scheme 2 and Table). Reduction of the aldehydes 3 with NaBH4 successfully afforded the corresponding alcohols 5 without loss of enantiomeric purity (Scheme 3). 相似文献
250.
Ohno H Ando K Hamaguchi H Takeoka Y Tanaka T 《Journal of the American Chemical Society》2002,124(51):15255-15266
The base-mediated intramolecular amination of bromoallenes having an axial chirality is described. The treatment of (4S,aR)-4-alkyl-4-[N-(arylsulfonyl)amino]-1-bromobuta-1,2-dienes with NaH in DMF affords 2,3-cis-2-ethynylaziridines in good to excellent selectivity (2,3-cis:trans = 92:8-99:1). The reaction of (4S,aS)-bromoallenes with NaH/DMF also gives 2,3-cis-2-ethynylaziridines selectively (79:21-91:9). These experimental results have been rationalized by B3LYP density functional calculations together with the 6-31+G(d) basis set and the Onsager solvation model. The transition structures for cis-aziridine formation of both (4S,aR)- and (4S,aS)-bromoallenes in DMF are favored over the corresponding trans transition structures by 4.35 and 1.41 kcal/mol, respectively. Furthermore, the calculations predicted that a less polar solvent gives higher cis selectivity for (4S,aS)-bromoallenes. In fact, improvement of the cis selectivity to 99:1 has been realized by using a less polar solvent such as THF. The cyclization of bromoallenes bearing a beta- or gamma-amino group also affords four- and five-membered azacycles in a highly cis-selective manner. 相似文献