Aliphatic oxidation

A number of the previously cited investigators3->2>5 9 have employed UV spectroscopy as an analytical tool for following PC degradation. We have found the measurement of UV spectra of weathered PC films by difference from an unexposed reference sample to be an extremely simple and useful analytical method. This nondestructive analysis allows the repetitive return of a sample to the exposure conditions and thus enables one to essentially perform continuous analyses on the same sample. This technique, of course, will not detect the formation of non-chromophoric products such as aliphatic oxidation products which may form during the degradation. 

The expulsion of CO from ketocyclohexadienyl radical is also reasonable, not only in view of the data of flow-reactor results, but also in view of other pyrolysis studies [64], The expulsion indicates the early formation of CO in aromatic oxidation, whereas in aliphatic oxidation CO does not form until later in the reaction after the small olefins form (see Figs. 3.11 and 3.12). Since resonance makes the cyclopentadienyl radical very stable, its reaction with an 02 molecule has a large endothermicity. One feasible step is reaction with O atoms namely,... 

Metabolism is the major route of elimination of THC from the body as little is excreted unchanged. In humans, over 20 metabolites have been identified in urine and feces 26 Metabolism in humans involves allylic oxidation, epoxidation, aliphatic oxidation, decarboxylation, and conjugation. The two monohydroxy metabolites (Figure 4.7) 11-hydroxy (OH)-THC and 8-beta-hydroxy THC are active, with the former exhibiting similar activity and disposition to THC, while the latter is less potent. Plasma concentrations of 11-OH-THC are typically <10% of the THC concentration after marijuana smoking. Two additional hydroxy compounds have been identified, namely, 8-alpha-hydroxy-THC and 8,11-dihydroxy-THC, and are believed to be devoid of THC-like activity. Oxidation of 11-OH-THC produces the inactive metabolite, ll-nor-9-carboxy-THC, or THC-COOH. This metabolite may be conjugated with glucuronic acid and is excreted in substantial amounts in the urine. 

Acetal Resins. Acetal resins (qv) are poly (methylene oxide) or polyformaldehyde homopolymers and formaldehyde [50-00-0] copolymerized with aliphatic oxides such as ethylene oxide (42). The homopolymer resin polyoxymethylene [9002-81-7] (POM) is produced by the anionic catalytic polymerization of formaldehyde. For thermal stability, the resin is endcapped with an acyl or alkyl function. 

Animals. Rapidly absorbed. DT50 < 1 hr, extensively metabolized in rodents, much less in dogs, and excreted with metabolites 3-hydroxy (aliphatic oxidation) and 5-hydroxy (O-demethylation) in urine (DT50 54—60 hr in rodents, 73 hr in dogs)... 

Triesters Glyceryl triacetate (triacetin) 8.1 Aliphatic Oxides 433 812 20... 

Capsaicin and capsaicinoids undergo Phase I metabolic conversion involving both oxidative and non-oxidative paths. The liver is the major site of this enzymatic activity. Lee and Kumar (1980) demonstrated the conversion of catechol metabolites via hydroxylation of vanil-lyl ring. In rats, dihydrocapsaicin is metabolized to products that are excreted in the urine as glu-curonides (Kawada and Iwai, 1985). The generation of a quinone derivative occurs via O-demethylation at the aromatic ring with concomitant oxidation of the semiquinone and quinone derivatives or via demethylation of the phenoxy radical intermediate of capsaicin. Additionally, the alkyl side chain of capsaicin is also susceptible to oxidative deamination (Wehmeyer et al., 1990). There is evidence that capsaicinoids can undergo aliphatic oxidation (cu-oxidation) (Surh et al, 1995 Reilly et al, 2003) which is a possible detoxification pathway. Non-oxidative pathways are also involved in the bioconversion of capsaicin, e.g. hydrolysis of the acid-amide bond to yield vanillylamine and fatty acyl moieties (Kawada et al, 1984 Kawada and Iwai, 1985 Oi et al, 1992). 

Among the reactions catalyzed by cytochrome P450 are (a) aliphatic oxidation, (b) aromatic hydroxylation, (c) N-hydroxylation, (d) N-dealkylation, and (e) O-dealkylation. 

Manchee, G.R., et al. The aliphatic oxidation of salmeterol to alpha-hydroxysalmeterol in human liver microsomes is catalyzed by CYP3A. Drug Metab. Dispos. 1996, 24, 555-559. 

Chiral to diastereoisomer transformations a second chiral center is introdueed into the drug either by reaetion at a prochiral center or via conjugation with a chiral conjugating agent. Examples include the side-chain aliphatic oxidation of pentobarbitone and the keto-reduction of warfarin to yield the eorresponding diastereoisomeric alcohol derivatives or the stereoseleetive glueuronidation of oxazepam [113]. 

Nuclearity has a strong impact on reactivity, as evidenced by the different reactivity of mono versus binuclear copper oxidation enzymes (aromatic vs aliphatic oxidation) or the specific roles of the different Zn centers in alkaline phosphatase. Some nuclearities (e.g., binuclear metal complexes) correspond to thermodynamic sinks. In that case, preorganization is not required. Less stable nuclearities require a platform in order to be maintained during the catalytic process. Mononuclear systems correspond to this situation. In particular, monocopper centers need to be embedded to be protected. The funnel complex strategy was developed for that purpose. Porphyrin complexes can be protected from deactivation pathways by grafting them... 

Aliphatic Oxidation and O-Dealkylation - Cytochrome P-450 monoxygenases appear to be involved in a variety of aliphatic hydroxylations. One common pathway involves an initial w-hydroxylation as with pentobarbital, followed by further metabolism to the aldehyde and acid by dehydrogenases. Hydroxylation also frequently occurs at the penultimate carbon as in amobarbital l, at benzylic and allylic positions and at carbons bearing a heteroatom. Many examples of such oxidations are cited in a recent review.Hydroxylation at carbon bearing a heteroatom such as oxygen, nitrogen or sulfur leads to the so-called dealkylation reactions so common in drug metabolism. 

Another class of aliphatic oxidations catalyzed by microsomal monoxygenases is 0-dealkylation. The reaction involves cleavage of the alkyl-oxygen bond as shown by the lack of incorporation of oxygen-18 into the phenolic product, 4-hydroxyacetanilide, when 4-methoxyacetanilide was treated with microsomes in the presence of H2 0 and 18q2. The mechanism of such 0-dealkylations appears to involve hydroxylation of the alkyl moiety to form a hemlacetal or hemiketal which decon oses to form the 0-dealkylated product and, respectively, either an aldehyde or... 

The commercial polyester elastomers are mostly based on poly(tetrameth-ylene oxide) (PTMO) as flexible segment and poly(butylene terephthalate) (PBT) as rigid segment. Yet, many chemical modifications of some particular segments and also segments of totally different chemical structure have been examined and applied. Thus, in addition to PTMO [1,2,11-16], poly(ethylene oxide) (PEO) [17-22], poly(aliphatic oxide) (C2-C4) copolymers [23-30], poly (butylene succinate), and other aliphatic polyesters [31-35], polycaprolac-tone (PCL), polypivalolactone (PVL) [36,37], aliphatic polycarbonates (PC) [38-41], dimerized fatty acid (DFA)-based polyesters [42-50], polyamide 66 and derivatives [47-57], polyolefins [58-60], rubbers [61-63], and polydimethyl-siloxane [64,65] are used as flexible segments of polyester elastomers. 

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