Induced polycycle

A Pd11- or Ptn-induced polycyclization of compounds containing two or even three C=C-double bonds and a hydroxyl group was described by Gagne and coworkers [179]. Thus, reaction of6/1-377 with equimolar amounts of the Ptn complex 6/1-378 led to the Pt-alkyl complex 6/1-379. Treatment of6/1-379 with NaBH4 provided the tetracyclic 6/1-380 as a 96 3 1 mixture in 86% yield (Scheme 6/1.95). It was proposed that, in the domino process, carbocations are formed as intermediates. 

The Pauson-Khand reaction is the Co-induced formation of cyclopentenones from ene-ynes and CO. One impressive example of a domino Pauson-Khand process is the synthesis of fenestrane 6/4-15, as reported by Keese and colleagues [278]. The transformation is initiated by a double Grignard reaction of 4-pentynoic acid 6/4-12, followed by protection of the formed tertiary hydroxyl group to give 6/4-13. The Co-induced polycyclization of 6/4-13 led directly to the fenestrane 6/4-15... 

Call an (r, < )-boundary sequence ambiguous if it admits at least two different (r, q)-fillings. Call it irreducible if its (r, -filling does not contain, as induced polycycle, the (r, )-fillings of other ambiguous (r, -boundary sequences. 

Guzii, A.G., Makarieva, T.N., Denisenko, V.A., Dmitrenok, P.S., Kuzmich, A.S., Dyshlovoy, S.A., Krasokhin, V.B., and Stonik, V.A. (2010) Monanchocidin A new apoptosis-inducing polycyclic guanidine alkaloid from the marine sponge Morumchora pulchra. Org. Lett., 12, 4292-4295. 

A large number of polycyclic aromatic hydrocarbons are known Many have been synthesized m the laboratory and several of the others are products of com bustion Benzo[a]pyrene for example is present m tobacco smoke contaminates food cooked on barbecue grills and collects m the soot of chimneys Benzo[a]pyrene is a carcinogen (a cancer causing substance) It is converted m the liver to an epoxy diol that can induce mutations leading to the uncontrolled growth of certain cells... 

The aqueous micellai solutions of some surfactants exhibit the cloud point, or turbidity, phenomenon when the solution is heated or cooled above or below a certain temperature. Then the phase sepai ation into two isotropic liquid phases occurs a concentrated phase containing most of the surfactant and an aqueous phase containing a surfactant concentration close to the critical micellar concentration. The anionic surfactant solutions show this phenomenon in acid media without any temperature modifications. The aim of the present work is to explore the analytical possibilities of acid-induced cloud point extraction in the extraction and preconcentration of polycyclic ai omatic hydrocai bons (PAHs) from water solutions. The combination of extraction, preconcentration and luminescence detection of PAHs in one step under their trace determination in objects mentioned allows to exclude the use of lai ge volumes of expensive, high-purity and toxic organic solvents and replace the known time and solvent consuming procedures by more simple and convenient methods. 

Polycyclic aromatic hydrocarbons have been classified as human carcinogens because they induce cancers in experimental animals and because smoking and exposure to mixtures of chemicals containing polycyclic aromatic hydrocarbons in the workplace increase the risk of lung cancer in exposed individuals. In experimental animals, benzo(a)pyrene induces cancer in different organs depending on the route of administration.Furthermore, exposure to polycyclic aromatic hydrocarbons commonly occurs in occupations related to traffic (use of diesel engines in transportation and railways). 

Biomimetic synthesis of natural nonfused polycyclic ethers by metal oxide-induced. syn-oxidative polycyclizations of hydropolyenes 98PAC355. 

Polyene cyclizations are of substantial value in the synthesis of polycyclic terpene natural products. These syntheses resemble the processes by which the polycyclic compounds are assembled in nature. The most dramatic example of biosynthesis of a polycyclic skeleton from a polyene intermediate is the conversion of squalene oxide to the steroid lanosterol. In the biological reaction, an enzyme not only to induces the cationic cyclization but also holds the substrate in a conformation corresponding to stereochemistry of the polycyclic product.17 In this case, the cyclization is terminated by a series of rearrangements. 

Alkyl radicals generated efficiently from allylsulfones in 80% aqueous formic acid induced a cyclization reaction on aromatic and heteroaromatic compounds to provide polycyclic aromatic and heteroaromatic derivatives (Eq. 7.17).37... 

Knowledge regarding biosyntheses has induced several biomimetic approaches towards steroids, the first examples being described by van Tamelen [10] and Corey [11]. A more efficient process was developed by Johnson [12] who, to synthesize progesterone 0-10 used an acid-catalyzed polycyclization of the tertiary allylic alcohol 0-7 in the presence of ethylene carbonate, which led to 0-9 via 0-8 (Scheme 0.3). The cyclopentene moiety in 0-9 is then transformed into the cyclohexanone moiety in progesterone (0-10). 

Oxidation is intimately linked to the activation of polycyclic aromatic hydrocarbons (PAH) to carcinogens (1-3). Oxidation of PAH in animals and man is enzyme-catalyzed and is a response to the introduction of foreign compounds into the cellular environment. The most intensively studied enzyme of PAH oxidation is cytochrome P-450, which is a mixed-function oxidase that receives its electrons from NADPH via a one or two component electron transport chain (10. Some forms of this enzyme play a major role in systemic metabolism of PAH (4 ). However, there are numerous examples of carcinogens that require metabolic activation, including PAH, that induce cancer in tissues with low mixed-function oxidase activity ( 5). In order to comprehensively evaluate the metabolic activation of PAH, one must consider all cellular pathways for their oxidative activation. 

A potentially powerful probe for sorting out the contribution of hydroperoxide-dependent and mixed-function oxidase-dependent polycyclic hydrocarbon oxidation is stereochemistry. Figure 9 summarizes the stereochemical differences in epoxidation of ( )-BP-7,8-dihydrodiol by hydroperoxide-dependent and mixed-function oxidase-dependent pathways (31,55,56). The (-)-enantiomer of BP-7,8-dihydrodiol is converted primarily to the (+)-anti-diol epoxide by both pathways whereas the (+)-enantiomer of BP-7,8-dihydrodiol is converted primarily to the (-)-anti-diol epoxide by hydroperoxide-dependent oxidation and to the (+)-syn-diol epoxide by mixed-function oxidases. The stereochemical course of oxidation by cytochrome P-450 isoenzymes was first elucidated for the methycholanthrene-inducible form but we have detected the same stereochemical profile using rat liver microsomes from control, phenobarbital-, or methyl-cholanthrene-induced animals (32). The only difference between the microsomal preparations is the rate of oxidation. 

Wattenberg LW and Loub WD. 1978. Inhibition of polycyclic aromatic hydrocarbon-induced neoplasia by naturally occurring indoles. Cancer Res 38 1410-1413. 

There are several chemical compounds found in the waste waters of a wide variety of industries that must be removed because of the danger they represent to human health. Among the major classes of contaminants, several aromatic molecules, including phenols and aromatic amines, have been reported. Enzymatic treatment has been proposed by many researchers as an alternative to conventional methods. In this respect, PX has the ability to coprecipitate certain difficult-to-remove contaminants by inducing the formation of mixed polymers that behave similarly to the polymeric products of easily removable contaminants. Thus, several types of PX, including HRP C, LiP, and a number of other PXs from different sources, have been used for treatment of aqueous aromatic contaminants and decolorization of dyes. Thus, LiP was shown to mineralize a variety of recalcitrant aromatic compounds and to oxidize a number of polycyclic aromatic and phenolic compounds. Furthermore, MnP and a microbial PX from Coprinus macrorhizus have also been observed to catalyze the oxidation of several monoaromatic phenols and aromatic dyes (Hamid and Khalil-ur-Rehman 2009). 

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