Ether Bridged Dimers

Further studies by the same researchers suggested that these compounds exert their effect on tumour cells by growth inhibition and that the endoperoxide bridge is essential for activity. They also investigated the influence that the stereochemistry of the ether bridge had on cytotoxicity towards EN2 tumour cells and found that the non-symmetrical dimer was more cytotoxic than the symmetrical one. 

Dimeric carbonato-bridged complexes A4[Cr2(C03)4(H20)2] (A = NH4, Li, Na, K, Rb, Cs A2 = Mg) can be precipitated166 from aqueous suspensions of the acetate, and the ammonium salt (or CrC03)157 suspended in ether will react with the stronger acids CF3C02H164 and CF2HC02H167 to give dinuclear carboxylates (equation 17). 

Many dimeric piperidine alkaloids also occur in nature, e.g., carpaine which has been isolated from papaya leaves (Carica papaya) 175 the absolute configuration has been determined.176 Naturally occurring isoquinoline alkaloids177 exist in dimeric forms in some cases, e.g., the bisbenzylisoquinoline alkaloids which have two benzylisoquinoline nuclei joined together through one, two, or even three ether bridges an example is epistephanine isolated from Stephania japonica.178... 

Reaction of dimeric, bromo-bridged Co2Br2(NO)4 with NaCN (1 4 mole ratio) in EtOH produces Na[Co(CN)2(NO)2], which may be obtained in pure form by evaporating the solution to dryness, followed by recrystallization from THF-petroleum ether. This compound is also prepared from CoBr(L)(NO) (L = PPh3, SPPhj, SePPhj) with xs NaCN in EtOH at 40-60°C. The same starting materials in a 1 1 mole ratio give instead single bromide-by-cyanide substitution, with formation of Co(CN)L(NO) °. 

The Lehn group synthesised the trinuclear copper(I) complex of the substituted 2,2 -bipyridyl/ether derivative 29 and confirmed its helical structure by X-ray diffraction (Figure 6.15). A dinuclear copper(I) complex of 30 (Figure 6.15) was also synthesised and subsequently the corresponding dimeric ethane-bridged bipyridine and phenanthroline ligands were also demonstrated to yield similar di-helicate copper(I) species. These results thus indicate that helicate formation is tolerant towards minor modification of ligand structure. ... 

Curare alkaloids are dimers of 1-benzyl-l,2,3,4-tetrahydroisoquinolines linked by one, two, or even three ether bridges positioned in a most varied manner. Discussing them in a... 

Reaction Mechanism of Boron Modified Prepolymer Synthesis. The Source for the Dimethylene Ether Bridge is a Dimer and higher Oligomers, as Shown in the Transition State. 

Phytanyl residues bound by an ether bridge to glycerol (or to the polyol calditol) are important constituents of the ether lipids of archaebacteria membranes. In addition dimeric compounds occur in which two phytanyl residues are interlinked tail-to-tail . The phytanyl moieties may be desaturated and contain one to four cyclopentane rings (Fig. 113). 

Crystal stmctures of Grignard reagents do not necessarily correspond to their stmcture in solution. In general, the crystal stmctures (61—64) indicate the reagents are ligated with THF or diethyl ether and are frequentiy observed to be dimers. The Mg atoms in the dimers do not have a Mg—Mg bond instead the dimers are typically held together by a haUde bridge. 

Adventitious water is responsible for the formation of the dimeric hydroxo complex 31 obtained by reaction of AuCb with 1,4-dilithiotetraphenylbutadiene in ether solution [97[. The hydroxo-bridged complex [Au(C6H4N02-2)2( i-0H)[2 (32) was obtained either by reaction of Na[Au(C6H4N02-2)2(0Ph)2] with traces of water in CH2Cl2/n-hexane solution or by treatment of the dichloroaurated complex with NaOH [98[. The crystal structure of 32 2Et20 shows that it is a centrosymmetric... 

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