Ethyl side chain

Hydrogenation of polybutadiene converts both cis and trans isomers to the same linear structure and vinyl groups to ethyl branches. A polybutadiene sample of molecular weight 168,000 was found by infrared spectroscopy to contain double bonds consisting of 47.2% cis, 44.9% trans, and 7.9% vinyl. After hydrogenation, what is the average number of backbone carbon atoms between ethyl side chains ... 

Short chain branching is negligible with Ziegler and Phillips homopolymers although it is possible to introduce deliberately up to about seven ethyl side chains per 1000 carbon atoms in the Ziegler polymers. 

As pointed out previously, controlled degradation reactions are very difficult with aliphatic or alicyclic hydrocarbons, and most of the relabeling work has been concentrated on aromatic reaction products. Procedures have been extensively described by Pines and co-workers (e.g., 97, 96, also 87, 89-98, 95, 98). For the present purpose, it suffices to note that the 14C contents of the methyl side-chains and the rings in aromatic reaction products are readily estimated by oxidation of the methyl to carboxyl, followed by decarboxylation, while ethyl side-chains may be oxidatively degraded one carbon atom at a time. Radiochemical assays may be made on CO2 either directly in a gas counter, or after conversion to barium carbonate, while other solid degradation intermediates (e.g., benzoic acid or the phthalic acids) may be either assayed directly as solids or burned to CO2. Liquids are best assayed after burning to CO2. 

Ester functions present in molecules tend to be considered labile although steric effects etc. may be utilized to produce drugs without inherent chemical or metabolic problems due to ester lability. For instance a series of antimuscarinic compounds which had selectivity for the M3 receptor (Figure 7.18) were stabilized by the incorporation of a hydroxy ethyl side chain or a cyclic ring system at positions surrounding the ester function. Presumably the proximity of these groups to the ester function (carbonyl) prevents close approach of the attacking nucleophile, in this case probably a serine hydroxyl. 

Polyethylene also contains ethyl side chains. These are formed according to the reactions in Scheme 13.3 leading to 2-ethylhexyl and 1,3-paired diethyl branches.220-222 Formation of such new branching has high probability since the newly formed radical is in close proximity to the chain backbone. 

The synthesis of fluorine-18-labelled receptor-based radiopharmaceuticals carried out before 1986 have been reviewed331 and the methods applied for the synthesis of 18F-butyrophenone neuroleptics such as spiroperidol (spiperone), haloperidol have been critically evaluated. The synthesis for preparing 7V-(2-[18F]fluoroethyl)spiperone330 involving the [18F]fluoride ion displacement of a suitable leaving group on the ethyl side chain was found to be particularly good (>50% yield). 

Two dimeric Vinca alkaloids, vinorelbine and anhydrovinblastine, have also been investigated using the CHCl3-HF-SbF5 system.550-552 In both cases, the corresponding products difluorinated in the ethyl side chain (140) were isolated in modest yields [Eq. (5.206)]. The mechanistic pathway suggested that the transformation includes steps already depicted in Schemes 5.57 and 5.58. 

Figure 5.101. It is apparent that stereochemistries in the 24-methyl, 24-ethyl, and 24-ethylidene derivatives could be controlled by the reduction processes or by proton loss as appropriate. It is more plausible for different stereochemistries in the 24-methyl and 24-ethyl side-chains to arise from reduction of different double bonds, rather than reduction of the same double bond in two different ways. In practice, other mechanisms involving a 25(26)-double bond are also found to operate.

Direct introduction of a vinyl substituent onto an aromatic ring is not a feasible reaction. p-Methoxystyrene must be prepared in an indirect way by adding an ethyl side chain and then taking advantage of the reactivity of the benzylic position by bromination (e.g., with N-bromosuccinimide) and dehydrohalogenation. 

C(19) shifts are also diagnostic of the axial/equatorial nature of the ethyl side chain. (256)... 

Bacillus spp. Atrazine Ethyl side chain Korpraditskul et al. (1993)... 

Nagy et al. (1995a, c) identified an enzyme in R. corallinus NRRLB-15444 that can dechlorinate atrazine, but only after the prior removal of either the isopropyl or ethyl side-chains. The enzyme, however, catalyzes deamination of several less substituted. v-triazincs. 

A study was designed to define the relative rates of dealkylation of selected triazine herbicides and two monodealkylated triazine degradation products in the unsaturated zone and in surface runoff. Atrazine and propazine degrade to DEA by deethylation and deisopropylation, respectively. Similarly, atrazine and simazine can both dealkylate to DIA by removal of an isopropyl and ethyl side chain, respectively (Figure 30.12). Differences in the concentration of the dealkylated degradation product from the two different sources should indicate any preferential removal of ethyl versus isopropyl side chain. Furthermore, because monodealkylated DEA and DIA have different side chains remaining, their relative rate of removal should provide additional information on the liability of the ethyl side chain versus an isopropyl side chain. 

This study showed that under field conditions, the removal of an ethyl side chain from atrazine occurred more readily than the removal of an isopropyl side chain. Furthermore, deethylation rates of atrazine and simazine were comparable, and approximately two to three times more rapid than the rates of deisopropylation from atrazine and propazine, regardless of parent triazine. Continued dealkylation of the monodealkylated degradation products at 1 m in the unsaturated zone also shows a preferential removal of ethyl side chains over isopropyl side chains. Therefore, the small concentrations of DIA commonly reported in the environment do not result purely from a smaller production of the degradation product, but from a rapid removal once produced. This substantial turnover rate or flux of DIA in the environment is evidence for the presence of a didealkylated degradation product in the unsaturated zone (Mills and Thurman, 1994 Thurman et al., 1994). 

The O-deethylation of phenacetin is CYPlA2-mediated and results in the liberation of acetaldehyde that is subsequently metabolized to acetate and then CO2. Thus, a breath test based on the use of phenacetin labeled with 14C in the 1-position of the ethyl side chain could function to assess CYP1A2 activity. Early studies demonstrated the feasibility of this approach and its potential application to evaluating hepatic function (65,66). No extensive validation was attempted, so it is difficult to determine how well this test reflects the enzyme s intrinsic clearance, rather than perhaps some other determinant, such as liver blood flow. However, the situation appears to be moot since phenacetin is no longer an approved dmg worldwide because of its renal side effects following chronic dosing accordingly, further studies of this approach are unlikely. 

Rates of loss of water from the molecular ions of hexanol-3, 3-d2 and hexanol-4, 4-d2 have been measured over the time range from tens of picoseconds to 10 ps [229]. Two distinct reactions were identified, one involving a 5-membered and the other a 6-membered cyclic transition state. The former appeared to have the higher frequency factor, i.e. the looser transition state or higher densities of states in the transition state. It is important to bear in mind that what are being compared here are a five-membered ring with a propyl side chain and a six-membered ring with an ethyl side chain. That the former is looser ... 

Intermolecular isotope effects /c2h4 //c2d4 in the range 1.3 -1.9 have been reported for metastable ion decompositions effecting loss of ethylene from various triazole molecular ions with 7V-ethyl side chains [568, 573]. Subsequent elimination of N2 from the benztriazole fragment ions occurs with an isotope effect of 1.5 (unlabelled vs. perdeuterated ions), perhaps indicating that a hydrogen transfer is involved in the decomposition [573],... 

Thiamine pyrophosphate looks quite like a nucleotide. It has two heterocyclic rings, a pyrimidine similar to those found in DNA and a thiazolium salt. This ring has been alkylated on nitrogen by the pyrimidine part of the molecule. Finally, there is a pyrophosphate attached to the thiazolium salt by an ethyl side chain. 

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