Amino carbon number

Melting Point. Amino acids are soHds, even the lower carbon-number amino acids such as glycine and alanine. The melting points of amino acids generally He between 200 and 300°C. Frequentiy amino acids decompose before reaching their melting points (Table 2). 

Oxidation. Oxidizing agents easily decompose a-amino acids, forming tile corresponding fatty acid with one less carbon number ... 

Acetal (4) undergoes 5 N 1 hydrolysis in aqueous solution at high pH, it is easily monitored via the /7-nitrophcnoxidc chromophore produced.3 The reaction has been used to probe hydration effects in co-solvents alcohols, ammo acids, and peptides— the last two as models for such effects in enzymes. Primary alcohols retard the reaction in proportion to their carbon number, but the ammo acids and peptides show more complex effects, which are interpreted in tenns of interactions between the overlapping hydration shells of the amino and carboxylate groups. 

CycUc polyamides were reported to be isolated from Nylon 6 polymers in 1956 [18,19]. Thermal polycondensation of co-amino acid (carbon number > 6) gave a cycUc and linear polymer [82]. Moreover, upon heating polyamide in the presence of a transamidation catalyst, the cyclization equilibrium is eventually reached, and both Unear and cyclic constituents are present [83]. The proportion of the latter depends on the concentration, and cycUc compounds predominate in high dilute solutions. 

Figure 2 shows that the C1-C5 aliphatic hydrocarbons, amino acids, carboxylic acids, and sulfonic acids from the Murchison meteorite appear to follow a common trend when their values are plotted against carbon number, values generally decrease as the amount of carbon in the molecules increases. This trend has been interpreted as the result of a kinetic isotope effect during the sequential formation of higher-molecular-weight compounds from simpler precursors (Yuen et al., 1984). The more reactive is preferentially added during the synthesis of the carbon skeleton of these compounds. 

Figure 2 Carbon stable-isotope compositions of low-molecular-weight hydrocarbons, amino acids, and monocarboxylic acids from the Murchison meteorite plotted against carhon number. Carbon number 1 denotes methane and CO2, 2 denotes ethane, ethanoic acid, glycine, etc. (source Yuen et al., 1984).

Scheme 4.1 Chemical sketch of ethyl 3- 3-[((2/ )-3- [2-(2,3-dihydro-1H-inden-2-yl)-1, 1-dimethylethyl] amino -2-hydroxypropyl) oxy]-4,5-difluorophenyl propanoate hydrochloride molecule showing the carbon numbering used in the text.

Figure 2.7 Basal spacing of montmoriUonite versus carbon number of amino acid [55] (reproduced with permission from Wiley-VCH).

Following up on the allylic oxidation and the interesting requirement of an ester solvent, the Yeung group attempted the allylic oxidation reaction in the absence of the alkene, and noticed some oxidation of the ester solvent. Development of this as its own reaction demonstrated the successful oxidation of a number of 0-alkyl and A-alkyl esters such as 23 and amides 24. The oxidation typically occurred on a methylene carbon on the alkoxy- or amino-carbon chain several carbons away from the ester center. Attempts to oxidize n-octane resulted in no reaction, further corroborating the necessity of carbonyl coordination to the iodine center. 

The final unique stage in the metabolism of L-isoleucine involves the cleavage of 2-methylacetoacetyl-CoA to acetyl-CoA and propionyl-CoA (Section 10.4). The propionyl-CoA is further metabolized to methylmalonyl-CoA by a biotin-dependent carboxylase and subsequently via succinyl-CoA into the tricarboxylic acid cycle. L-Valine is also metabolized ultimately to methylmalonyl-CoA (Section 10.4), and thus these two branched-chain amino acids form the major precursors of propionyl-CoA and methylmalonyl-CoA. Other precursors of propionyl-CoA include methionine, threonine, odd-carbon-number fatty acids and cholesterol. The methyhnalonyl-CoA produced by propionyl-CoA carboxylase occurs as the D(5)-enantiomer and is racemized to the L(/ )-enantiomer by methylmalonyl-CoA racemase. l(/ )-Methylmalonyl-CoA is then metabolized to succinyl-CoA by a vitamin B12-dependent mutase prior to introduction of the modified molecule into the tricarboxylic acid cycle. 

The condensation may occur one to three times, depending on the number of hydrogen atoms on the a-carbon of the nitroparaffin, giving rise to amino alcohols with one to three hydroxyl groups. A comprehensive review of these compounds has been pubUshed (1). 

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