1188-01-8Relevant academic research and scientific papers
Neighboring Residue Effects: Evidence for Intramolecular Assistance to Racemization or Epimerization of Dipeptide Residues
Smith, Grant Gill,Evans, Robert C.,Baum, Rocky
, p. 7327 - 7332 (1986)
Dipeptides, their methyl esters, diketopiperazines (DKP), and N-substituted derivatives were racemized at high temperatures (approximately 120 deg C) in aqueous phosphate buffered solutions at pH values close to pH of maximum racemization (approximately 8).The racemization of the dipeptides Ala-Gly and Gly-Ala followed reversible first-order kinetics.The initial rate of racemization of DKP was very fast but soon slowed down, supposedly due to hydrolysis.The resulting rate was similar to that of the dipeptides.Esters of dipeptides followed racemization patterns similar to DKP.The racemization rate constants of the dipeptides studied were shown to be independent of the concentration of the dipeptide and the concentration of buffer.A carboxy-terminal proline residue greatly increased the rate of racemization (epimerization) of the amino-terminal residue.Increasing the basicity of the N-terminal amino acid residue increased the rate of racemization (or epimerization) of the C-terminal residue unless the C-terminal was sterically hindered as the Ile and Val.Decreasing the basicity of the N-terminal amino acid residue decreased racemization or epimerization for nonhindered C-terminal amino acids.These results support the influence of neighboring groups in the racemization or epimerization of dipeptides.DKP formation is a competing reaction allowing racemization or epimerization in dipeptides.Dipeptide racemization or epimerization is proposed to be the result of combination of intramolecular base assistance and DKP formation.
Peptide Synthesis Using the Pyrrole Ring as an Amino Protecting Group
Kashima, Choji,Maruyama, Tatsuya,Harada, Kazuo,Hibi, Shigeki,Omote, Yoshimori
, p. 601 - 645 (2007/10/02)
The utility of a pyrrole ring as an amino protecting group for amino acids in peptide synthesis has been studied.The N-termini of various amino acids (1) were protected with a pyrrole ring by treatment with 2,5-dimethoxytetrahydrofuran (10) to give 2-substituted 2-(1-pyrrolyl)acetic acids (11).The peptide bond between (11) and amino acid methyl ester (2) was formed using N,N'-dicyclohexylcarbodiimide, and the pyrrole ring was cleaved by ozonolysis and hydrolysis without the cleavage of a peptide bond to give the corresponding dipeptide compounds (26) in good yields.
Flow 1H nmr study of the rapdid nucleophilic addition of amino acids to 4-formylpyridine
Tan, Liang K.,Cocivera, Michael
, p. 772 - 777 (2007/10/02)
Rapid addition of primary amino acids and imidazole to 4-formylpyridine to form carbinolamine intermediates in water has been studied by means of stopped-flow 1H nuclear magnetic resonance spectroscopy.The equilibrium constant Kn for this process was determined using stopped-flow uv spectroscopy.For the amino acid D,L-alanine and its derivatives , D,L-alanine methyl ester and D,L-alanylglycine Kn does not appear to correlate with Ka, the acid dissociation constant.Values of kn, the addition rate constant, appear to be independent of pH and bufferconcentration fo these nucleophiles.The limited data indicate that the variation in rates of nucleophilic addition to 4-formylpyridine cannot be accounted for in terms of pKa, Kn or related to systematic changes in structure of the nucleophile.As a group, the primary amino acid D,L-alanine and its derivatives have comparable kn values within a factor of two in spite of their different pKa values.Imidazole, an aromatic secondary diamine, has a kn value that is 10 to 20 times larger than these primary amines and has a relatively small Kn value.At the same time , its kn value is comparable to that found previously for sarcosine, a secondary acyclic amino acid having substantially larger pKa and Kn values.The nucleophilic addition step of primary amino acid and derivatives is rapid relative to the subsequent dehydration and prototropic shift steps.It occurs in a pH range at which pyridine nitrogen protonation is negligible.
