Anders Hammershøi

Macrotricyclic hexaamine cage complexes of cobalt(III): synthesis, characterization and properties

Synthese au coordinat hexadente tris(amino-2 ethyl)-1,4,7 triaza-1,4,7 cyclononane et de [CoL] 3+ . Synthese des complexes ou L est egalement: amino-9 hexaazatricyclodocosane, heptaazatricyclodocosane. Etude de configuration et electrochimique

Reactivity studies of chelated maleate ion: stereoselectivity and structural correlations

Etude des structures cristallines des complexes Λ [Co(en) 2 (maleato)] PF 6 •2H 2 O, [Co(en)(aca)(H 2 O)] ClO 4 •2H 2 O et Δ-fac (5,5)-[Co(en)(aea)] BCS•3H 2 O (BCS=anion bromocamphresulfonate) pour determiner leurs connectivites et leurs configurations absolues

Synthesis of 2-(nitromethyl)ornithine from ornithine mediated by cobalt(III)

Abstract Rac.-p-(tris(2-aminoethyl)amine-2-(nitromethyl)ornithine)cobalt(III) trichloride (2d) was obtained by a simple three-step procedure from ornithine using cobalt template chemistry. p-(Tris(2-aminoethyl)amine-ornithine)cobalt(III) trichloride (2a) was obtained from tris(2-aminoethyl)amine (tren) and (S)-ornithine in the presence of cobalt(II), which was oxidised to cobalt(III) during the reaction. Complex 2a was selectively oxidised with thionyl chloride–dimethyl formamide to p-(tris(2-aminoethyl)amine-dehydro-ornithine)cobalt(III) trichloride 2b. Complex 2c, in which reaction of thionyl chloride–dimethyl formamide has also occurred at the δ-amine of ornithine, was obtained at longer reaction times. Complex 2b reacted with nitromethane anion to give rac.-p-(tris(2-aminoethyl)amino-2-(nitromethyl)ornithine)cobalt(III) trichloride (2d). The amino acid rac.-2-(nitromethyl)ornithine (1b) was released by reducing complex 2d with aqueous ammonium sulfide. Complex 2d was expected to release 2-(nitromethyl)ornithine (1b) in hypoxic cells, where the amino acid could act as an inhibitor of ornithine decarboxylase. Preliminary data indicated that complex 2d was weakly cytotoxic in one cell type studied.

Oxidation of amino acids co-ordinated to cobalt(III)

Rapid oxidation of chelated amino acids to imines and amides by thionyl chloride in N,N-dimethylformamide is described.

Metal complex amino acid synthons: syntheses, structures and stereoselective reactions of (iminoacetato)cobalt(III) complexes

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(O2CCHNH)](O3SCF3)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(O2CCHNH)](O3SCF3)2 and diethyl (2-13C)malonate. The new N-methyliminoacetato complex, rac-[(en)2Co(O2CCHNMe)](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(O2CCHNH)]Br2·H2O and rac-[(en)2Co(O2CCHNMe)]S2O6·1.5H2O, and the diethyl carboxy-aspartate addition product, (ΛS,ΔR)-[(en)2Co{O2CCH(CH(CO2Et)2)NH2}](ClO4)2, were determined by X-ray crystallography.

The binding of a complex cobalt ruthenium polyamine by deoxyribonucleic acid and a lipopolysaccharide: A model for a novel class of drugs

In this paper we discuss the following: 1. Synthesis of [Co(H3CsarNHCH2pyRu(NH3)5)] (PF6)5, (CoRu). 2. Interaction of CoRu with calf thymus DNA and with lipopolysaccharide from Escherichia coli C (LPS) has been estimated using the absorption of the complex at 242 and 420 nm. 3. DNA and LPS increase the rate of fall of absorption at 420 nm due to autooxidation of the complex. 4. The fall in absorption of CoRu(II) at 420 nm can be used to give an approximate measure of binding to DNA and to LPS. 5. Both macromolecules are aggregated by CoRu at high concentrations and the cation and macromolecule complex can be removed by low speed centrifugation. 6. The DNA-CoRu complex can also be removed by high speed centrifugation when the cation concentration is too low to cause aggregation (20 microM CoRu/155 microM DNA-P). Absorption of redissolved complex at 420 nm is restored by reduction with ascorbic acid. 7. At saturation the ratio of mole CoRu bound/mole DNA-P is 0.16.

A simple regiospecific strategy for labelling hydrogen atoms in α-amino acids

Simple methods for the regioselective introduction of deuterium labels at the α- and β-carbon atoms of leucine using a Co(III) imino acid complex are described which have a general applicability to the synthesis of a range of labelled amino acids.

Chiral template amino acid syntheses using a 2-iminoacetatocobalt(III) chelate as a synthon

Chelated glycinate on cobalt(III) is readily oxidized to 2-iminoacetate to give a useful synthon for stereoselective syntheses of α-amino acids by the addition of carbanions and through asymmetric transformations of the second kind.

Conversion of chelated hydroxy-L-proline into pyrrole-2-carboxylate

Oxidation of chelated hydroxy-L-proline by thionyl chloride gives substituted dihydropyrroles, which undergo subsequent base-induced elimination to give chelated pyrrole-2-carboxylate complexes.

Diastereoisomeric β-ethyl aspartate–cobalt(III) complexes: Λ(+)578- and Δ(−)578-bis­(ethane-1,2-diamine)[β-ethyl (S)-aspartato]cobalt(III) bis­(perchlorate) monohydrate

The structures of the diastereoisomers Λ(+)(578)-, (I), and Δ(-)(578)-bis(ethane-1,2-diamine)[β-ethyl (S)-aspartato-κ(2)N,O(1)]cobalt(III) bis(perchlorate) monohydrate, (II), both [Co(C(6)H(10)N(2)O(4))(C(2)H(8)N(2))(2)](ClO(4))(2)·H(2)O, are compared. In both structures, the ester group of the amino acid side chain is engaged only in intramolecular hydrogen bonding to coordinated amine groups. This interaction is stronger in (I) and correlates with previously observed diastereoisomeric equilibrium ratios for related metal complex systems in aqueous media. The two perchlorate anions of (II) are located on twofold axes. Both perchlorates in (I) and one of the perchlorates in (II) are affected by disorder. Both structures exhibit extensive three-dimensional hydrogen-bonding networks.