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11
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84914087916
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α-Amino-β-hydroxy carboxylic acids are naturally occuring compounds. Some of them being proteinogenic and/or essential amino acids are involved in various physiological processes in living organisms therefore, analogs of these amino acids are very interesting as biomedical tools or potential inhibitors. Other α-amino-β-hydroxy carboxylic acids are constituents of complex natural products such as cyclosporin, bouvardin, peptides and glycopeptides, which usually posses high antibiotic activity. In addition, these amino acids are valuable precursors to β-lactam antibiotics.
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13
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0028355337
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For stoicheiometric asymmetric synthesis see:
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(1994)
Tetrahedron
, vol.50
, pp. 1539
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Duthaler1
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15
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84986730833
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Benzyl (R)- and (S)-2-tert-butyl-5-oxo-oxazolidine-3-carboxylate for convenient preparation ofD- andL-threonine analogs from aldehydes
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(1991)
Liebigs Annalen der Chemie
, pp. 1067
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Blaser1
Seebach2
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18
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85077759504
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Asymmetric Syntheses via Heterocyclic Intermediates; XIX1. On the Enantioselective Synthesis of β-Fluorovaline Methyl Ester and Related α-Amino-β-fluorocarboxylic Esters
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(1983)
Synthesis
, pp. 673
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Groth1
Schollkopf2
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19
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0012476236
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Asymmetric Syntheses via Heterocyclic Intermediates; XV1. Enantioselective Synthesis of (R)-(-)-β-Hydroxyvaline using L,-Valine or (S)-O,O-Dimethyl-α-methyldopa as Chiral Auxiliary Reagents
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(1982)
Synthesis
, pp. 868
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Schollkopf1
Nozulak2
Groth3
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31
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84914087915
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Available from Merck (cat. no. 814473) and Jansen Chimica (now Acros Chimica, cat. no. 2691950).
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49
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84914087913
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Mechanistic model of this aldol reaction had been studied on the examples of acetone, formaldehyde, acetaldehyde, benzaldehyde, and 3,4-(methylenedioxy)benzaldehyde condensations with complex (S)-1; see ref. 10a.
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50
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84914087912
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The electrostatic repulsion between trifluoromethyl (or in general perfluoroalkyl) group and negatively charged ionized carboxylic group, and electrostatic attraction between the positively charged Ni(II)-ion and fluorine atoms of fluoroalkyl group of an amino acid moiety was suggested with some hesitation by us to explain this unexpected result; see ref. 11a.
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51
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84914087911
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3. Full crystallographic data have been deposited at the Cambridge Crystallographic Data Center and are available from the principal authors.
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53
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84914087910
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As has been shown previously (see refs 10,11), CD and ORD spectra of Ni(II)-complexes of this type in neutral solutions exhibit two maxima in the region of metal d-d transition (Cotton effects at 450 and 550 nm). In ORD spectra, the sign of Cotton effects in this region strictly depends upon the conformation of polycyclic system of chelate rings, that in turn, is the result of orientation of bulkier α-substituent in the amino acid formed. Thus, in the case of complexes containing α-monosubstituted α-amino acid, pseudoaxial orientation of amino acid side chain, that corresponds to α-(L) configuration of α-amino acid, causes positive sign of Cotton effect at 500–700 nm region and negative sign at 400–450 nm. Consequently, pseudoequatorial orientation of amino acid side chain brings about opposite signs of Cotton effects at 400–450 (positive) and at 500–700 nm (negative) region. As was established in [[Truncated]]
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58
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84914087908
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Physical properties and reactivity of complex 1 give grounds to believe that the metal ion bears a positive charge. Recently we have shown that molecular mechanic calculations with electrostatic terms included are more accurate in evaluation of relative stability of diastereomeric Ni(II)-complexes. See ref. 11a.
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