摘要:

AbstractAn alternative synthesis of enantiomerically pure SDZ 220–881(1a)and SDZ EAB 515(1b)starting from L‐Z‐tyrosine is desc

ISSN:0018-019X    

DOI:10.1002/hlca.19980810322

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractThe synthesis of the enantiomerically pure, bridgehead‐functionalized bicyclo[3.2.1]octanes11and16, containing a conformationally fixed trihydroxypropyl (aminodihydroxypropyl) unit, as well as the X‐ray structure of11are described. These compounds are of interest as sugar surrogates in the preparation of DNA analogs. Compounds11and16became available in 10 and 12 steps, respectively, and in an overall yield of 11 and 4% from D‐arabinoseviaa highly stereoselective pinacol coupling as the key

ISSN:0018-019X    

DOI:10.1002/hlca.19980810323

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractBicyclic thiohydantoins were synthesized in a stereoselective manner by reacting (2R)/(2S)‐diastereoisomer mixtures of 1,3‐thiazolidine‐2,4‐dicarboxylic acids or their dimethyl diesters with PhNCS. 5,5‐Dimethyl‐1,3‐thiazolidine‐2,4‐dicarboxylic acid with PhNCS led to a cyclization involving the CO group at the C(2) center of the thiazolidine ring, while the acid's dimethyl diester gave cyclization involving the CO group at C(4). In contrast, reactions involving unsubstituted 1,3‐thiazolidine‐2,4‐dicarboxylic acid or its dimethyl diester led to thiohydantoins in which the ring closure had taken place only with the COO group at C(4). Independently of the direction of the ring closure, all reactions produce exclusively products with the (R)‐configuration at C(2). The configurational assignments were based on1H‐ and13C‐NMR studies, and confirmed b

ISSN:0018-019X    

DOI:10.1002/hlca.19980810324

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractThe CH2Cl2extract ofMonotes engleriGilg. (Dipterocarpaceae) showed antifungal activity against the yeastCandida albicansin our bioautographic TLC assays. After a first fractionation of the crude extract, the bioactivity was located in one of the fractions. To perform an efficient targeted isolation of the active compounds, LC/UV/MS and LC/UV/NMR analyses of the crude extract and the active fraction were performed. LC/UV/, LC/MS, and LC/NMR data (1D and 2D) allowed the identification of1as (2S)‐2,3‐dihydro‐5,7‐dihydroxy–{3‐hydroxy‐4‐[(3‐methylbut‐2‐enyl) oxy]phenyl}‐4H‐1‐benzopyran‐4‐one, a new prenylated flavanone, named monoteson A. Subsequent isolation of1has permitted the determination of its absolute configuration on the basis of CD measurements. Theree other prenylated flavanoes2–4were isolated from the same extract. Compound3was identified as2‐ (3, 5‐dihydroxyphenyl) ‐2,3‐dihydro‐5, 7‐dihydroxy‐6, 8‐bis (3‐methylbut‐2‐enyl)‐4H‐1‐benzopyran‐4‐one, another new natural product, named monotesone B. The structures of2and4were established as selinone and lonchocarpol A, respectively. The antifungal

ISSN:0018-019X    

DOI:10.1002/hlca.19980810325

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractThe first steps, believed to be involved in the highly enantioselective copolymerization of styrene and carbon monoxide to poly[1‐oxo‐2‐phenylpropane‐1,3‐diyl] with phosphinodihydrooxazole‐palladium(II) complexes, were investigated. The insertion of carbon monoxide into [Pd(Me)(PˆN)(solvent)]TfO (PˆN = (S)‐2‐[2‐(5H‐benzo[b]phosphindol‐5‐yl)phenyl]4‐benzyl‐4,5‐dihydrooxazole(1))and of styrene into [Pd(Me)(PˆN)(solvent)] TfO were highly regioselective (alkyl and acyl substituentstransto N); moreover, the olefin insertion took place with essentially com

ISSN:0018-019X    

DOI:10.1002/hlca.19980810326

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractAbsolute rate constants and theirArrheniusparameters are obtained for the addition of a cyclic malonyl radical derived fromMeldrum's acid to 20 mono‐ or 1,1‐disubstituted alkenes in (±)‐propylene oxide and for the addition of the open‐chain di(tert‐butyl)malonyl radical to six mono‐ or 1,1‐disubstituted alkenes in 1,1,2‐trichloro‐1,2,2‐trifluoroethane by time‐resolved electron spin resonance spectroscopy. At room temperature, the radicals add at the unsubstituted C‐atoms with rate constants ranging from 1.1. 105M−1S−1(acrolein) to 2.4. 106M−1S−1(1,1‐diphenylethene). The frequency factors are in the narrow ranges of log (A/M−1S−1) = 8.7 ± 0.1 for the cyclic and log (A/M−1S−1) = 8.2 ± 0.2 for the open‐chain malonyl species, whereas the activation energies vary from 12.9 kJ/mol (1,1‐diphenylethene) to 21.7 kJ/mol (acrylonitrile). They correlate with the alkene ionization potentials and, more weakly, with the reaction enthalpy. No correlation was found between the activation energies and the alkene electron affinities. Hence, the results confirm and quantify the electrophilic

ISSN:0018-019X    

DOI:10.1002/hlca.19980810327

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractThe disubstituted clusters[Ir4(CO)10(μ2‐LL)] with one edge‐bridging ligand have a ground‐state geometry with all COs terminal (LL = (MeS)2CHMe, cluster1) or with three edge‐bridging COs (LL = (Ph2P)2CHMe, cluste2; LL =Ph2P(CH2)3PPh2, cluster3) in the solid state and in solution. A comparative13C‐NMR study of1–3shows that their respective ground‐state geometries are merely relative minima of energy in the same kinetic profile of successive fluxional processes consisting of a merry‐go‐round of six COs about a unique trangular face and the rotation of terminal COs about one Ir‐atom. The factors affecting the activation energy of the merry‐go‐round result from the relative bites of the bidentate ligands in the ground‐state geometry, as shown by a comparison o

ISSN:0018-019X    

DOI:10.1002/hlca.19980810328

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

ISSN:0018-019X    

DOI:10.1002/hlca.19980810329

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

ISSN:0018-019X    

DOI:10.1002/hlca.19980810301

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY