- Total syntheses of cathepsin D inhibitory izenamides A, B, and C and structural confirmation of izenamide B
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The first total syntheses of izenamides A, B, and C, which are depsipeptides inhibitor of cathepsin D, were accomplished. In addition, the stereochemistry of izenamide B was confirmed by our syntheses. The key features of our synthetic route involve the avoidance of critical 2,5-diketopiperazine (DKP) formation and the minimization of epimerization during the coupling of amino acids for the target peptides.
- Lim, Changjin
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- tert-Butyloxycarbonyl and Benzyloxycarbonyl Amino Acid Fluorides. New, Stable Rapid-Acting Acylating Agents for Peptide Synthesis
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A new class of rapid-acting acylating agents, α-BOC and Z amino acid fluorides are obtained as stable, often crystalline, compounds by treatment of the protected amino acid cyanuric fluoride.
- Carpino, Louis A.,Mansour, El-Sayed M. E.,Sadat-Aalaee, Dean
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p. 2611 - 2614
(2007/10/02)
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- Neighboring Residue Effects: Evidence for Intramolecular Assistance to Racemization or Epimerization of Dipeptide Residues
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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.
- Smith, Grant Gill,Evans, Robert C.,Baum, Rocky
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p. 7327 - 7332
(2007/10/02)
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