Examples with structures related

For many of the drugs associated with hepatotoxicity, there are examples of structurally related drugs which are latent to bioactivation and toxicity because of the absence of the toxicophore or the existence of alternate metabolic pathways. For example, the hepatotoxicity associated with the use of the anti-Parkinson s agent tolcapone does not occur with the structurally related drug entacapone, despite administration at doses similar to tolcapone (200-1000 mg QD). This disparity may be explained in part by the observation that entacapone does not succumb to the bioactivation reactions of tolcapone in humans (Scheme 15.3) [35]. It is also noteworthy that tolcapone but not entacapone is a potent uncoupler of oxidative... 

Figure 3. Examples of sulfur compounds with structures related to well known biological markers.

The hydroformylation mechanism for phosphine-modified rhodium catalysts follows with minor modifications the Heck-Breslow cycle. HRh(CO)(TPP)3 [11] is believed to be the precursor of the active hydroformylation species. First synthesized by Vaska in 1963 [98] and structurally characterized in the same year [99], Wilkinson introduced this phosphine-stabilized rhodium catalyst to hydroformylation five years later [100]. As one of life s ironies, Vaska even compared HRh(CO)(TPP)3 in detail with HCo(CO)4 as an example of structurally related hy-drido complexes [98]. Unfortunately he did not draw the conclusion that the rhodium complex should be used in the oxo reaction. According to Wilkinson, two possible pathways are imaginable the associative and the dissociative mechanisms. Preceding the catalytic cycle are several equilibria which generate the key intermediate HRh(CO)2(TPP)2 (Scheme 4 L = ligand). 

Ferroelectric properties can be attributed to the presence of medium-sized cations in many oxides with structures related to that of perovskite, for example BaTiOa and KNbOa. These contain ions... 

Naturally occurring compounds with carbon-metal bonds are very rare The best example of such an organometallic compound is coenzyme Bi2 which has a carbon-cobalt ct bond (Figure 14 4) Pernicious anemia results from a coenzyme B12 deficiency and can be treated by adding sources of cobalt to the diet One source of cobalt IS vitamin B12 a compound structurally related to but not identical with coen zyme B12... 

Finally, Vogtle and his coworkers have prepared a number of cascade molecules which are structurally related to the aforementioned systems. These are repeating ring units of increasingly large cavity size and are prepared by repetitive synthetic procedures. Typically, an amine is cyanoethylated, the nitrile reduced to an amine which may then be further cyanoethylated and reduced or cyclized with a diacid halide. The rather elaborate scheme is illustrated in ref. 61 and examples of the structural type are shown in Table 8.4. 

Cyclophanes or 7r-spherands have played a central role in the development of supramolecular chemistry forming an important class of organic host molecules for the inclusion of metal ions or organic molecules via n-n interactions. Particular examples are provided by their applications in synthesis [80], in the development of molecular sensors [81], and the development of cavities adequate for molecular reactions with possible applications in catalysis [82]. The classical organic synthesis of cyclophanes can be quite complex [83], so that the preparation of structurally related molecules via coordination or organometallic chemistry might be an interesting alternative. 

Some related examples with BR2 monocapped ligands are also known [181] and one of these molecules, 129, assembles to an interesting supramolecular structure, in which the cobalt(III) ions in a methylcobaloxime unit are coordinated to the pyridine residues of the bridging B(py)(OMe) group (Fig. 34). The dinuclear complex forms a large rectangular cage that is limited by the two pyridine residues and the cobaloxime moieties. The two pyridine... 

Wherever possible, we have sought a direct comparison of the reactivities of structurally related Crni and q-II alkyls with ethylene. For example, after having established the catalytic activity of complexes of the type [( Cri (L)2R] (see above), we showed that the isostructural neutral compounds Cp Crn(L)2R did not polymerize ethylene instead facile P-hydrogen elimination was observed. [3) This difference in reactivity was not due to the charge of the complexes. Thus, we have subsequently shown that neutral Cr J alkyls are also active polymerization catalysts. For example, Cp Cr I(THF)Bz2 and even anionic Li[Cp Cr H(Bz)3] (Bz = benzyl) polymerized ethylene at ambient temperature and pressure, while the structurally related CpCrD(bipy)Bz proved inert.[5]... 

Structurally related compounds may cross-react with the antibody, yielding inaccurate results. In screening for the herbicide alachlor in well water by immunoassay, a number of false positives were reported when compared with gas chromatography (GC) analysis. A metabolite of alachlor was found to be present in the samples and it was subsequently determined that the cross-reactivity by this metabolite accounted for the false-positive results. On the other hand, cross-reactivity by certain structural analogs may not be an issue. For example, in an assay for the herbicide atrazine, cross-reactivity by propazine is 196% because of atrazine and propazine field use... 

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