Formation of Ketimines from Aldimines in Schiff Base Condensation of Amino Acids and Imidazole-2-Carboxaldehydes: Tautomerization of Schiff Bases of Amino Acids Resulting in the Loss of Stereogenic Center
The Schiff base reaction of imidazole-2-carboxaldehydes with the anion of alanine, leucine and phenylalanine in the presence of nickel(II) ion gives the neutral NiL<sub>2</sub> complexes. The Schiff base ligand, L, binds through an imidazole nitrogen, N<sub>Im</sub>, the amin...
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MDPI AG
2023-09-01
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| Series: | Inorganics |
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| Online Access: | https://www.mdpi.com/2304-6740/11/10/381 |
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| author | Greg Brewer Cynthia Brewer Raymond J. Butcher Peter Zavalij |
| author_facet | Greg Brewer Cynthia Brewer Raymond J. Butcher Peter Zavalij |
| author_sort | Greg Brewer |
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| description | The Schiff base reaction of imidazole-2-carboxaldehydes with the anion of alanine, leucine and phenylalanine in the presence of nickel(II) ion gives the neutral NiL<sub>2</sub> complexes. The Schiff base ligand, L, binds through an imidazole nitrogen, N<sub>Im</sub>, the amino acid nitrogen, N<sub>AA</sub>, and a carboxylate oxygen, O, atom. The two N<sub>2</sub>O ligands bind to the nickel(II) in a meridional fashion with the N<sub>Im</sub> and O of each ligand in trans positions. These ligands can exist as the anticipated aldimine, Im − CH = N<sub>AA</sub> − CH(R) − CO<sub>2</sub><sup>−</sup>, or the ketimine, Im − CH<sub>2</sub>N<sub>AA</sub> = C(R) − CO<sub>2</sub><sup>−</sup>, tautomer. Tautomerization of the initially formed aldimine Schiff base results in movement of the hydrogen atom of the alpha carbon of the amino acid to the aldehyde carbon, C<sub>Ald</sub>, atom of the imidazole carboxaldehyde with resultant relocation of the imine double bond in the reverse direction. Ten structures of the structurally unprecedented ketimine tautomer, prepared from imidazole-2-carboxaldehydes and a pyrazole-3-carboxaldehyde, were presented. The structural data supported the formation of the ketimines in each case, while the aldimine tautomer was observed with imidazole-4-carboxaldehydes. A rationale of this can be explained on the basis of charge distribution in the likely intermediate in the tautomerization. |
| first_indexed | 2024-03-10T21:10:55Z |
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| language | English |
| last_indexed | 2024-03-10T21:10:55Z |
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| spelling | doaj.art-88ed3629691c458a87140268462f7afe2023-11-19T16:48:52ZengMDPI AGInorganics2304-67402023-09-01111038110.3390/inorganics11100381Formation of Ketimines from Aldimines in Schiff Base Condensation of Amino Acids and Imidazole-2-Carboxaldehydes: Tautomerization of Schiff Bases of Amino Acids Resulting in the Loss of Stereogenic CenterGreg Brewer0Cynthia Brewer1Raymond J. Butcher2Peter Zavalij3Department of Chemistry, The Catholic University of America, Washington, DC 20064, USADepartment of Chemistry, The Catholic University of America, Washington, DC 20064, USADepartment of Chemistry, Howard University, Washington, DC 20059, USADepartment of Chemistry, University of Maryland, College Park, MD 20742, USAThe Schiff base reaction of imidazole-2-carboxaldehydes with the anion of alanine, leucine and phenylalanine in the presence of nickel(II) ion gives the neutral NiL<sub>2</sub> complexes. The Schiff base ligand, L, binds through an imidazole nitrogen, N<sub>Im</sub>, the amino acid nitrogen, N<sub>AA</sub>, and a carboxylate oxygen, O, atom. The two N<sub>2</sub>O ligands bind to the nickel(II) in a meridional fashion with the N<sub>Im</sub> and O of each ligand in trans positions. These ligands can exist as the anticipated aldimine, Im − CH = N<sub>AA</sub> − CH(R) − CO<sub>2</sub><sup>−</sup>, or the ketimine, Im − CH<sub>2</sub>N<sub>AA</sub> = C(R) − CO<sub>2</sub><sup>−</sup>, tautomer. Tautomerization of the initially formed aldimine Schiff base results in movement of the hydrogen atom of the alpha carbon of the amino acid to the aldehyde carbon, C<sub>Ald</sub>, atom of the imidazole carboxaldehyde with resultant relocation of the imine double bond in the reverse direction. Ten structures of the structurally unprecedented ketimine tautomer, prepared from imidazole-2-carboxaldehydes and a pyrazole-3-carboxaldehyde, were presented. The structural data supported the formation of the ketimines in each case, while the aldimine tautomer was observed with imidazole-4-carboxaldehydes. A rationale of this can be explained on the basis of charge distribution in the likely intermediate in the tautomerization.https://www.mdpi.com/2304-6740/11/10/381Schiff basetautomerizationamino acidaldimineketimineimidazole |
| spellingShingle | Greg Brewer Cynthia Brewer Raymond J. Butcher Peter Zavalij Formation of Ketimines from Aldimines in Schiff Base Condensation of Amino Acids and Imidazole-2-Carboxaldehydes: Tautomerization of Schiff Bases of Amino Acids Resulting in the Loss of Stereogenic Center Inorganics Schiff base tautomerization amino acid aldimine ketimine imidazole |
| title | Formation of Ketimines from Aldimines in Schiff Base Condensation of Amino Acids and Imidazole-2-Carboxaldehydes: Tautomerization of Schiff Bases of Amino Acids Resulting in the Loss of Stereogenic Center |
| title_full | Formation of Ketimines from Aldimines in Schiff Base Condensation of Amino Acids and Imidazole-2-Carboxaldehydes: Tautomerization of Schiff Bases of Amino Acids Resulting in the Loss of Stereogenic Center |
| title_fullStr | Formation of Ketimines from Aldimines in Schiff Base Condensation of Amino Acids and Imidazole-2-Carboxaldehydes: Tautomerization of Schiff Bases of Amino Acids Resulting in the Loss of Stereogenic Center |
| title_full_unstemmed | Formation of Ketimines from Aldimines in Schiff Base Condensation of Amino Acids and Imidazole-2-Carboxaldehydes: Tautomerization of Schiff Bases of Amino Acids Resulting in the Loss of Stereogenic Center |
| title_short | Formation of Ketimines from Aldimines in Schiff Base Condensation of Amino Acids and Imidazole-2-Carboxaldehydes: Tautomerization of Schiff Bases of Amino Acids Resulting in the Loss of Stereogenic Center |
| title_sort | formation of ketimines from aldimines in schiff base condensation of amino acids and imidazole 2 carboxaldehydes tautomerization of schiff bases of amino acids resulting in the loss of stereogenic center |
| topic | Schiff base tautomerization amino acid aldimine ketimine imidazole |
| url | https://www.mdpi.com/2304-6740/11/10/381 |
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