Branched carbon chains formation

Suresh et al. investigated the extraction of uranium and thorium by TsBP and TiBP (isomers of TBP with branched carbon chain) as an alternative choice for TBP (47). Higher homologues of TBP, for example, THP and TEHP, were reported to have higher extraction ability with reduced tendency toward third-phase formation (50, 51). The esters with bulkier substituents in place of the butyl group were proposed to be of practical value for the process applications in uranium and thorium separation (54). The LOC of thorium in equilibrium with aqueous nitric acid-thorium nitrate was reported to decrease in the order THP > TAP > TBP. Pathak et al. showed that TEHP can be a better choice for U/Th separation compared to TBP and TsBP (55). 

Cyanohydrin Synthesis. Another synthetically useful enzyme that catalyzes carbon—carbon bond formation is oxynitnlase (EC 4.1.2.10). This enzyme catalyzes the addition of cyanides to various aldehydes that may come either in the form of hydrogen cyanide or acetone cyanohydrin (152—158) (Fig. 7). The reaction constitutes a convenient route for the preparation of a-hydroxy acids and P-amino alcohols. Acetone cyanohydrin [75-86-5] can also be used as the cyanide carrier, and is considered to be superior since it does not involve hazardous gaseous HCN and also virtually eliminates the spontaneous nonenzymatic reaction. (R)-oxynitrilase accepts aromatic (97a,b), straight- (97c,e), and branched-chain aUphatic aldehydes, converting them to (R)-cyanohydrins in very good yields and high enantiomeric purity (Table 10). 

In these formulae it is assumed that the (NH3) group has a capacity for forming homologous chains much like the methylene (CII2) group in the carbon compounds. The metal-ammines were represented, therefore, as built up of chains of ammonia molecules. By adopting such formulae he recognised that two different forms of chain formation are possible just as in the case of the carbon compounds, namely, the normal form and the iso or branched form. Thus ... 

The synthesis of type II branched-chain sugars should seem a more difficult task because it needs activation of a carbon atom on the sugar template and a control of the stereochemical course of the carbon-carbon bond formation. Probably because of this apparent difficulty several methods have been devised in the last decade, in particular, in the field of organo-metallic and free radical reactions. 

The synthesis of doubly branched-chain sugars should, in principle, follow the same principles through two successive formations of carbon-carbon bonds as described in the foregoing. However, additional methods especially designed to introduce two carbon chains on the same carbon (type IV) or on two vicinal carbons (type V) are now available. 

Branched carbon skeletons are formed by standard reaction types but sometimes with addition of rearrangement steps. Compare the biosynthetic routes to three different branched five-carbon units (Fig. 17-19) The first is the use of a propionyl group to initiate formation of a branched-chain fatty acid. Propionyl-CoA is carboxylated to methylmalonyl-CoA, whose acyl group is transferred to the acyl carrier protein before condensation. Decarboxylation and reduction yields an acyl-CoA derivative with a methyl group in the 3-position. 

Treede I, Hauser G, Muhlenweg A et al (2005) Genes involved in formation and attachment of a two-carbon chain as a component of eurekanate, a branched-chain sugar moiety of avilamycin A. Appl Environ Microbiol 71 400-406... 

The low molecular weight analogs, 3-chloropentane (3-CP) and 1-chloropentane (1-CP) were treated in exactly the same manner as the polymer glasses. Since these analogs were small molecules, no solvent was necessary to enhance resolution in the ESR. On irradiation, cleavage of the carbon-chlorine bond is expected for both. The 3-CP should serve as a model to indicate carbon-chlorine cleavage in the main PVC chain. The 1-CP molecule could be used to indicate formation of any primary radicals in PVC from branch points, chain cleavage, etc. 

Apart from sotolon, the other compounds in Fig. 5 can be explained as the products of a Maillard reaction, and their carbon skeletons simply originate from the active Amadori intermediate in other words, they still preserve the straight carbon chain structure of monosaccharides. In spite of being a simple Cg lactone, sotolon has a branched carbon skeleton, which implies another formation process in the Maillard reaction. Sulser e al.(6) reported that ethyl sotolon (ll) was prepared from threonine with sulfuric acid, and that 2-oxobutyric acid, a degradation product of threonine, was a better starting material to obtain II. This final reaction is a Claisen type of condensation, which would proceed more smoothly under alkaline conditions. As we(lO) obtained II from 2-oxobutyric acid (see figure 6) with a high yield in the presence of potassium carbonate in ethanol, a mixed condensation of 2-oxobutyric and 2-oxo-propanoic (pyruvic) acids was attempted under the same conditions, and a mixture of sotolon (22% yield) and II were obtained however, the... 

Free methylerythritol is a widespread polyol in plants. The formation of the isoprene skeleton via the alternative route involves an intramolecular rearrangement. The branched carbon skeleton of ME can be deduced from the rearrangement of the straight chain DX (Fig. 4). Deuterium-labeled ME isotopomers were synthesized chemically and were incorporated into the prenyl chains of the E. coli quinones (2). 

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