Synthesis of N-urethane-protected γ-amino-functionalized butenoates and tautomeric studies by means of NMR, X-ray crystallography and ab initio calculations

N-Urethane-protected γ-amino-α-cyano-β-hydroxybutenoates were synthesized as potential statine analogues and the stability of their possible tautomers was assessed using NMR, X-ray crystallography and ab initio calculations. The results establish that the cis-enol tautomeric form is the most stable one both in solution (CDCl3) and in the solid phase. In full agreement with the experimental data, the theoretical calculations predicted that the cis-enol tautomer would be the minimum energy tautomer

Dielectric studies of a bioactive tetramic acid and its complexes with Cu(II) and Co(II)

The 3-acyl tetramic acids constitute a growing class of natural products displaying a range of biological activities. The β,β′ tricarbonyl moiety present in the 3-acyl tetramic acid provides a suitable site for bidentate complexation to a metal, which increases the biological activity. For the dielectric study of N-acetyl-3-butanoyl tetramic acid and a series of its complexes with Cu(II) and Co(II) in symmetric and asymmetric forms, we used the Thermally Stimulated Depolarization Currents (TSDC) technique. The drastic decrease of the intensity of the TSDC peaks of the symmetric and asymmetric complexes, compared to the above mentioned ligand, suggested that the polarizability of the side groups is considerably reduced. This result enhances the proposed complexation mode of the ligand through oxygen next to carbons 3 and 4 of the 5-member ring

Copper(II), cobalt(II), nickel(II) and zinc(II) complexes containing the enolate of N-acetyl-3-butanoyltetramic acid (Habta) and its phenylhydrazone derivative analogues. Crystal structure of [Cu(abta)2(py) 2]·2H2O

Reaction of N-acetyl-3-butanoyltetramic acid (N-acetyl-3-butanoyl-4- hydroxypyrrolidin-2-one) (Habta) with M(CH3CO2) 2·xH2O (x = 1, 2 or 4; M = CuII, Co II or NiII) in a 1:1 ratio gave M(CH3CO 2)(abta)·yH2O 1, 3, 5 and in 1:2 ratio M(abta) 2·y′H2O 2, 4, 6. A new ligand, the phenylhydrazone of Habta (HPhabta), has been prepared and reacts with M(CH 3CO2)2·xH2O (x = 2 or 4; M = CuII or CoII) in a 1:1 and 1:2 ratio to give the analogous complexes M(CH3CO2)(Phabta)·zH2O 9, 11 and M(Phabta)2·z′H2O 10 respectively. The solid state structure of [Cu(abta)2(py)2]·2H 2O 2a has been determined by single crystal X-ray diffraction. It shows that copper adopts a slightly distorted octahedral co-ordination geometry with the abta enolate ligand adopting an O,O′ mode of co-ordination via the functionalities associated with C4 and the acyl group at C 3 in the pyrrolidine ring. The reaction of Habta with Zn(CH 3CO2)2·2H2O in 1:1 ratio gives a complex 7 with a deacetylated ligand whereas, with 1:2 ratio, Zn(abta)2·2H2O 8 is obtained. In contrast the reaction of HPhabta with Zn(CH3CO2)2· 2H2O, irrespective of the metal to ligand ratio, gives Zn(CH 3CO2)(Phbta)·2H2O 12 containing the deacetylated ligand. © The Royal Society of Chemistry 2001