A method for the determination of the pKa of the .alpha.-hydrogen in amino acids using racemization and exchange studies

Stroud, Eric D.; Fife, Dennis J.; Smith, Grant Gill

doi:10.1021/jo00174a045

Cited by 31 publications

(23 citation statements)

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“…Ionic mechanisms of racemization and epimerizationwere proposed by G. G. Smithand co-workers 6,[12][13][14][15][16][17][18][19][20] , whoshowed that the rates of racemization of peptides were faster than those of free amino acids. However, this research wasmainly restricted to the epimerization of linear peptides and the racemization of 2,5-diketopiperazines bearing one chiral center, and did not consider cyclic diastereomeric peptides.…”

Section: Oriental Journal Of Chemistrymentioning

confidence: 99%

Epimerization of Cyclic Alanyl-Alanine in Basic Solutions

Munegumia¹,

Fujimoto²,

MichioTakada³

et al. 2014

Orient. J. Chem

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Alanine anhydrides (Cyclo-(Ala-Ala)) are the simplest dipeptides that have two chiral centers and three diastereomers: Cyclo-(L-Ala-L-Ala), Cyclo-(D-Ala-D-Ala), and Cyclo-(L-Ala-D-Ala).Analysis of the epimerization of these peptides may throw light on the development of homochirality in proteins. We show that the epimerization rate of Cyclo-(L-Ala-L-Ala) and Cyclo-(D-Ala-D-Ala) is higher than that of Cyclo-(L-Ala-D-Ala), while the ring-opening rates of Cyclo-(L-Ala-L-Ala) and Cyclo-(D-Ala-DAla) arelower than that of Cyclo-(L-Ala-D-Ala) in basic aqueous solutions. The total reaction resulted in the preferred stability of Cyclo-(L-Ala-L-Ala) and Cyclo-(D-Ala-D-Ala) to Cyclo-(D-Ala-L-Ala).

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Section: Oriental Journal Of Chemistrymentioning

confidence: 99%

Epimerization of Cyclic Alanyl-Alanine in Basic Solutions

Munegumia¹,

Fujimoto²,

MichioTakada³

et al. 2014

Orient. J. Chem

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“…Isovaline, 2-methylbutyric acid, and sec -butylamine contain analogous chiral centers; however, although isovaline has been found to contain an l ee , only racemic compositions of 2-methylbutyric acid and sec -butylamine have been reported in Murchison, Orgueil, and various Antarctic carbonaceous chondrites. ,,, Recent anisotropy studies show that UV CPL can induce enantiomeric excesses in amino acids, but not in amines and carboxylic acids, , perhaps explaining these observations. The contrast between the observed l ee of isovaline and the racemic nature of its analogous acid and amine suggest that either (1) an initial imbalance was induced in the amino acid enantiomers but not the carboxylic acid or amine; (2) degradation of a chiral amino acid led to loss of stereochemistry at the chiral carbon; (3) racemization occurred in the carboxylic acids and amines at a faster rate than in the amino acids, although the lower acidity of the α-hydrogen in these compounds argues against this possibility; − or (4) physical properties of amino acids (e.g., higher polarity) led to the amplification of a small imbalance through aqueous processes inside carbonaceous chondrites . Further studies of these aliphatic compounds from other meteorites may provide additional information on the origins of enantiomeric excesses in amino acids.…”

Section: Introductionmentioning

confidence: 99%

Meteoritic Amino Acids: Diversity in Compositions Reflects Parent Body Histories

et al. 2016

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The analysis of amino acids in meteorites dates back over 50 years; however, it is only in recent years that research has expanded beyond investigations of a narrow set of meteorite groups (exemplified by the Murchison meteorite) into meteorites of other types and classes. These new studies have shown a wide diversity in the abundance and distribution of amino acids across carbonaceous chondrite groups, highlighting the role of parent body processes and composition in the creation, preservation, or alteration of amino acids. Although most chiral amino acids are racemic in meteorites, the enantiomeric distribution of some amino acids, particularly of the nonprotein amino acid isovaline, has also been shown to vary both within certain meteorites and across carbonaceous meteorite groups. Large l-enantiomeric excesses of some extraterrestrial protein amino acids (up to ∼60%) have also been observed in rare cases and point to nonbiological enantiomeric enrichment processes prior to the emergence of life. In this Outlook, we review these recent meteoritic analyses, focusing on variations in abundance, structural distributions, and enantiomeric distributions of amino acids and discussing possible explanations for these observations and the potential for future work.

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“…The pK a of the α proton of Phg is 14.9 9 and racemization of this residues is often encountered in peptide synthesis. 10 The peptides were cleaved from the resin and analyzed by LC-MS without purification.…”

Section: Resultsmentioning

confidence: 99%

Solid-Phase Synthesis of Diverse Peptide Tertiary Amides By Reductive Amination

Pels

Kodadek

2015

ACS Comb. Sci.

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The synthesis of libraries of conformationally-constrained peptide-like oligomers is an important goal in combinatorial chemistry. In this regard an attractive building block is the N-alkylated peptide, also known as peptide tertiary amide (PTA). PTAs are strongly biased conformationally due to allylic 1,3 strain interactions. We report here an improved synthesis of these species on solid supports through the use of reductive amination chemistry using amino acid-terminated, bead-displayed oligomers and diverse aldehydes. The utility of this chemistry is demonstrated by the synthesis of a library of 10,000 mixed peptoid-PTA oligomers.

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A method for the determination of the pKa of the .alpha.-hydrogen in amino acids using racemization and exchange studies

Cited by 31 publications

References 0 publications

Epimerization of Cyclic Alanyl-Alanine in Basic Solutions

Epimerization of Cyclic Alanyl-Alanine in Basic Solutions

Meteoritic Amino Acids: Diversity in Compositions Reflects Parent Body Histories

Solid-Phase Synthesis of Diverse Peptide Tertiary Amides By Reductive Amination

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