Metal complex amino acid synthons: syntheses, structures and stereoselective reactions of (iminoacetato)cobalt(III) complexes.
Date
2002
Authors
Bendahl, Lars
Hammershoi, Anders
Jensen, Dan
Larsen, Sine
Riisager, Anders
Sargeson, Alan
Sorensen, Henning
Journal Title
Journal ISSN
Volume Title
Publisher
Royal Society of Chemistry
Abstract
Amino acid anions (AAO-) chelated to cobalt(III) in [(en)2Co(AAO)](O3SCF3)2 (AA = Gly, Sar, Ala and Glu) were selectively oxidized to their imine derivatives by a new general procedure utilizing PBr3 and N-bromosuccinimide in dmf. The new iminoacetato complexes, Λ- and Δ-[(en)2Co(O2CCH=NH)](O3SCF 3)2, constitute chiral glycine equivalents which can serve as synthons for stereoselective α-amino acid synthesis. In alkaline EtOH, quantitative addition of CH2(COMe)2, CH2(CO2Et)2 or MeCOCH2CO2Et to the imine of the iminoacetate ligand initially produced both diastereomers of the product α-amino acid cobalt(III) complexes. However, subsequent crystallization-induced asymmetric transformations in the heterogeneous reaction mixtures led to better than 90% excess of a single diastereomer after five days, and the diastereopure product triflate salts were obtained after recrystallization. Both enantiomers of isotopically substituted (3-13C, 98%)aspartic acid were produced by facile synthesis from Δ-[(en)2Co(O2CCH=NH)](O3SCF 3)2 and diethyl (2-13C)malonate. The new N-methyliminoacetato complex, rac-[(en)2Co(O2CCH=NMe)](O3SCF3) 2, also yielded to imine addition reactions providing a route to the α-N-methylamino acid subclass. The molecular structures of the new imine complexes, Λ-(+)578-[(en)2Co(O2CCH=NH)]Br 2·H2O and rac-[(en)2Co(O2CCH=NMe)]S2O6 ·1.5H2O, and the diethyl carboxy-aspartate addition product, (ΛS,ΔR)-[(en)2Co{O2CCH(CH(CO2 Et)2)NH2}](ClO4)2, were determined by X-ray crystallography.
Description
Keywords
Keywords: Chelation; Complexation; Crystallization; Derivatives; Molecular structure; Oxidation; Stereochemistry; Synthesis (chemical); X ray crystallography; Stereoselective reactions; Amino acids
Citation
Collections
Source
Dalton Transactions
Type
Journal article