ISSN:0018-019X    

DOI:10.1002/hlca.19860690102

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

Separation of Enantiomers by Partition between Liquid Phases. Enantioselectivity of Diastereoisomeric Dimenthyl Tartarates towards α‐Aminoalcohol SaltsThe enantioselectivity of the easily obtainable diastereoisomeric dimenthyl tartaratesIandIItowards the salts of a series of α‐aminoalcohols1‐10was investigated by partition between aqueous and lipophilic phase. The measured enantiomer distribution constantsQ(=KA/KB) confirm the previously observed configurational relationships between the lipophilic tartarates and the preferentially extracted enantiomer of the hydrophilic ammonium slat. However, the (R,R)‐esterIis appreciably more selective than its (S,S)‐diastereoisomerIIor other previously investigated esters. The tartaratesI‐IIItransport norephedrin salts through bulk lipophilic membranes with enantioselectivity comparable to that observed in partition experiments. The most enantioselective esterIcan be used as an efficient mobile phase for preparative separation of norephedrine enantiomers by flash partition c

ISSN:0018-019X    

DOI:10.1002/hlca.19860690103

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

AbstractFour carotenoids (zeaxanthin1, astaxanthin2, and their C50synthetic isoprene‐homologues3und4) have been incorporated into bilayer unilamellar vescles of dimyristoylphospatidylcholine as proved by coelution on aSepharosecolumn. The incorporation into the bilayer proper has been proved by the sensitivity to phase transition of UV/VIS spectra and circular dichroism. The UV/VIS absorptions of the carotenoids are typical of a lipidic environment. At the temperature of phase transition occur both intermolecular phenomena (aggregation of carotenoid molecules) and intramolecular changes (conformational change). The relative solubilities of the various carotenoids in this phospholipid membrane can be fitted with molecular parameters (length of the lipophilic carotenoid segmentvs.lipid bilayer thickness

ISSN:0018-019X    

DOI:10.1002/hlca.19860690104

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

AbstractA synthesis of 1,2‐cis‐configurated, non‐isosteric phosphonate analogues of aldose‐1‐phosphates is described. Treatment of 1‐O‐acyl‐glycoses1,7,13, and19with trialkyl phosphite in the presence of trimethylsilyl trifluoromethanesulfonate gave the 1,2‐cis‐configurated glycosylphosphonates2,4,8,10,14,16,20, and22as the major anomers and the 1,2‐trans‐configurated glycosylphosphonates3,5,9,11,15,17,21, and23as the minor anomers. The 1,2‐cis‐configurated phosphonates4,10,16, and22were deprotected to give the (β‐D‐glucopyranosyl)phosphonate6, the (β‐D‐mannopyranosyl)phosphonate12, the (β‐D‐ribofuranosyl)phosphonate18, and the (β‐D‐arabinofuranosyl)phosphonate24, respectively, in high yields. The preferred formation of 1,2‐cis‐configurated phosphonates is explained by postulating an equilibrium between the anomeric phosphonium‐salt intermediates (such as25and26) and a stabilization of thecis‐configurated salts thro

ISSN:0018-019X    

DOI:10.1002/hlca.19860690105

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

AbstractMössbauerdata recorded at room temperature and 78 K for several binary and two new ternary vanadium sulfides are presented. The results are discussed in comparison with the structures and magnetic susceptibility measurements. A change in the spin state of the Fe‐atoms from the Fe2+high‐spin state to the low‐spin state is observed in the binary vanadium sulfides. This change is due to a shortening of the crystallographicc‐axis which is nearly parallel to short metal‐metal distances. In one ternary thallium vanadium sulfide the Fe is in the unusual trivalent low‐spin state at room

ISSN:0018-019X    

DOI:10.1002/hlca.19860690106

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

AbstractThe synthesis of the cyclopropyl silyl ketones1–4is described. The trimethylsilyl ketone1was prepared from geraniol ((E)‐5) inca.10% overall yield by cyclopropanation leading to6, CrO3oxidation to the aldehyde8, reaction of the latter with trimethylsilyl anion to14A+B, and CrO3oxidation to1. Also for the (t‐butyl)dimethylsilyl ketones2–4, an efficient four‐step synthesis with overall yields of 48%, 85%, and 13%, respectively, was elaborated, starting from the allylic alcohols (E)‐5, and23. The method of preparation involves as the key step aWittigrearrangement of the silylallyl ethers ((E/Z)‐20,24) to the silyl alcohols ((E/Z)‐21,25), subsequent cyclopropanation (19A+B,22A+B,26), and oxidation to the cyclopropyl s

ISSN:0018-019X    

DOI:10.1002/hlca.19860690107

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

AbstractThe two bis‐macrocycles4and5in which the tetraaza units are separated by a chain of different length, have been synthesized using 1,4,7‐tritosyl‐1,4,7,11‐tetraazacyclotetradecane as starting compound and bifunctional alkylating agents. The bis‐macrocycles give binuclear complexes with Ni2+and Cu2+, the properties of which have been studied to obtain information about the interaction of the two subunits as a function of the distance. The VIS spectra of the Ni2+and Cu2+complexes indicate that both metal ions are in a square‐planar geometry as expected from the results of the analogous complexes with 1,4,7,11‐tetraazacyclotetradecane7. Cyclic voltammetry and differential pulse polarography of the binuclear Ni2+complexes in CH3CN show a single two‐electron step for ligand5, whereas two distinct one‐electron redox processes can be observed for ligand4, indicating that the two metal ions interact with each other when the chain length is shorter. Similarly, the EPR studies of frozen solutions of the binuclear Cu2+complexes clearly show that a magnetic dipolar interaction between the two paramagnetic centers exists, and that the strength of it depends upon the length of the bridge. Finally, from the X‐ray structures of the binuclear Ni2+complexes with4and5, it is seen that the two rings are kept apart as far as possible, the distances between the two metal ions determined in the solid correlate well with the obser

ISSN:0018-019X    

DOI:10.1002/hlca.19860690108

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

C45‐and C50‐Carotenoids: Synthesis of (S)‐TrisanhydrobacterioruberinThe Synthesis of (S)‐trisanhydrobacterioruberin ((S)‐1) is

ISSN:0018-019X    

DOI:10.1002/hlca.19860690109

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

AbstractChiral metals are so far practically unknown. The synthesis of a chiral substrate for possible organic conductors and superconductors is described.

ISSN:0018-019X    

DOI:10.1002/hlca.19860690110

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

AbstractThe synthesis of 1,5‐dimethyltricyclo[3.3.0.02,8]octane‐3,7‐dione (2), 1,5‐dimethyltetracyclo[3.3.0.02,804,6]‐octane‐3,7‐dione (3), the corresponding dienes5and6as well as the mixed enones13–15is reported. Using He(I) photoelectron spectroscopy (PE) as a tool, a considerable interaction between the n orbitals on the O‐atoms and the σ frame in2and3as well as of the double bonds in5and6and the σ frame is found. These interactions are also traced back by the electronic absorption spectra of these compounds. The molecular structures of2and3have been investigate

ISSN:0018-019X    

DOI:10.1002/hlca.19860690111

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY