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Transition metal-catalyzed racemization of amino acids

Author: DuBaoTong
Tutor: TianLaiJin；SunYuXi
School: Qufu Normal University
Course: Inorganic Chemistry
Keywords: Amino acids DL Experimental and theoretical studies M (u ¨) lliken charge Charge transfer NBO analysis
CLC: TQ460.1
Type: Master's thesis
Year: 2011
Downloads: 61
Quote: 0
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Abstract


In recent years, with the life sciences and chiral drug development in-depth study, previously thought to have no effect on the human body D-amino acids in life activities and drug preparation having L-amino acids can not replace the role of the D-amino acid As a series of chiral synthesis of chiral drugs with special therapeutic efficacy. Thus, D-amino acid preparation and application has become a research focus. For the current D-amino acid in the preparation of racemic conversion rate, racemic slower rate and other issues, this paper common transition metals as catalysts in organic acid catalyzed by L-amino acid racemization, and Gaussian 03 program which make theoretical simulation studies reveal racemization regularity. Main text as follows: First, take into account the shape of the amino acid R-group (linear or cyclic), suction electron repulsion and pH and other factors on the impact of racemization from 19 kinds of optically active amino acids selected four kinds of the representative amino acids - tryptophan, phenylalanine, glutamic acid and lysine for the study. Secondly, from the economic point of view and to consider the catalytic effect, select the manganese, iron, zinc, cadmium acetate four metals as a catalyst. Experimental section, the first test higher temperature (boiling acetic acid, 117.9 ℃) racemization of 4 amino acids. Found that the basic amino acid at this temperature, racemization does not occur, and thus can eliminate the influence of temperature on the amino acid racemization; then at the same temperature, the four kinds of metal were catalyzed racemization of four amino acids. Contrast manganese, iron, zinc, cadmium ion catalyzed racemization rate, can be found in four metallic catalytic effect of the catalytic amino acids: Mn2 gt; Fe2 gt; Zn2 gt; Cd2, which Mn2 tryptophan, phenylalanine, glutamic acid and lysine racemic conversion rate reached 49.7%, 60.1%, 81.1% and 70.8%, higher than the literature alkali conditions racemization rate. Racemization reaction rate in terms, Fe2 fastest catalytic rate of 1 to 1.5 hours to complete racemization, Mn2 and Cd2 are relatively slow, 2.5 to 3 hours to complete racemization, which relative to the alkali or aldehyde catalyzed time -5 to 8 hours, has a great advantage. Since the R-group side chain indole ring and benzene ring of electron-withdrawing effect, tryptophan and phenylalanine racemic ratio has significantly improved but still difficult to achieve complete racemization. Theoretical research component, racemic tryptophan research, first to the crystal database four kinds of metal complexes with tryptophan based on the crystal structure using the Gaussian 03 program at the B3LYP, LANL2DZ level structure optimization and frequency analysis. Calculated based on the frequency of the complex thermodynamic data to thereby obtain racemic reaction standard free energy ΡrG (?), Described in thermodynamics of metal ion catalyzed conversion of racemic amino acid α: αFe2 gt; αMn2 gt; αCd2 gt; αZn2; based on the obtained racemic reaction ΔrHF, illustrate the catalytic metal ion rate r: rFe2 gt; rMn2 gt; rCd2 gt; rZn2. By comparing the before and after racemisation Mulliken charge of each atom was found L-Trp on the chiral carbon atom the negative charge decreases after the racemization reaction, according to four kinds of complexes on the chiral carbon atom law known negative charge, metal ion catalyzed conversion of racemic α as: αFe2 gt; αMn2 gt; αCd2 gt; αZn2. Finally, according to the natural bond orbital method, the color and the amino acid complexes were NBO analysis, comparison and move out by the chiral carbon atom of the second electronic stabilization energy ΔE (2) knowledge, metal ion catalyzed conversion of racemic α is: αMn2 gt; αFe2 gt; αZn2 gt; αCd2. Comprehensive analysis of three theoretical knowledge four kinds of metal ion catalyzed conversion of racemic α as: αMn2 gt; αFe2 gt; αZn2 gt; αCd2; racemization reaction rate r: rFe2 gt; rMn2 gt; rCd2 gt; rZn2, which with the experimental results with good consistency. For data not obtained crystals phenylalanine, glutamic acid and lysine, tryptophan program this paper GaussView metal complexes optimized structure made based on metal complexes corresponding amino acid with the initial configuration, and then conduct structural optimization and frequency calculations. Then follow the Rule of racemic tryptophan method first thermodynamic analysis, the results show that metal-catalyzed conversion of three amino acids racemic more consistent: racemization of standard free energy ΔrG (?) Described in thermodynamics, metal ion catalyzed conversion of the amino acid racemization: αFe2 gt; αZn2 gt; αMn2 gt; αCd2; atomic charges from the perspective of knowledge, metal ion catalyzed conversion of the amino acid racemization: αMn2 gt; αFe2 gt; αZn2 gt; αCd2; NBO analysis by the second-order statistics of the stabilization energy ΔE (2) knowledge, racemization conversion rate: αMn2 gt; αFe2 gt; αZn gt; αCd2. Therefore, the above three analysis methods, different metal catalytic effect of three amino acids more consistent racemic, racemic reaction conversion rate: αMm2 gt; αFe2 gt; αZn2 gt; αCd2, which is consistent with the experimental results. The metal-catalyzed amino acid racemization rate is slightly different, but similar catalytic effect on tryptophan, Fe2 catalytic fastest, Cd2 catalytic rate of the slowest. In summary, this paper four kinds of amino acids is represented both by chemical experiments to find a method of racemic amino acids quickly, and in the level of theory to statistical thermodynamics means of atomic charge analysis, NBO analysis methods reveal the amino acid racemization of the law. Has broad application prospects for the preparation of D-amino acids has a certain significance.

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