Reduced Schiff Base Research Articles

Synthesis and structural behavior of ternary copper(II) complexes containing reduced Schiff base N-(2-hydroxybenzyl)-4-aminobutyric acid and 1,10-phenanthroline

Ternary copper(II) complexes containing reduced Schiff base ligand N-(2-hydroxybenzyl)-4-aminobutyric acid (H 2Sab4) and 1,10-phenanthroline (phen) have been synthesized and characterized. Compound [Cu(Sab4)(phen)(H 2O)] · 5H 2O ( 1) was prepared from Cu(OAc) 2 · H 2O, H 2Sab4, phen, and LiOH in the ratio 1:1:1:2 in H 2O–MeOH. Green crystals of [Cu 3(Sab4) 2(phen)(H 2O) 2](ClO 4) 2 · 0.5H 2O ( 2) were isolated first from Cu(ClO 4) 2 · H 2O, H 2Sab4, phen, and LiOH in the ratio of 1:1:1:1. The filtrate furnished dark blue rhombohedral crystals of [Cu(H 2Sab4) 2(phen)](ClO 4) 2 ( 3), within a week. When the ratio of base was doubled, [Cu 2(Sab4)(phen) 3](ClO 4) 2 · 3H 2O ( 4) was the only product isolated. The crystal structures of 1, 3 and 4 have been determined. In the zwitterionic mononuclear complex 1 the Cu(II) has square pyramidal geometry with a water molecule at the apical position and the carboxylate anion hydrogen bonded to the lattice water molecules. Five highly ordered water molecules present in the lattices in 1 generate an interesting 3D hydrogen bond network in the solid state. In 3, the carboxylic acid is deprotonated by the secondary amino group of the ligand to form a zwitterion. The carbonyl O atoms and the protons of phenolic and –NH 2 + groups of the ligands are involved in extensive hydrogen bond network. The presence of intra and intermolecular π⋯π interactions between the two ligands is evident in 4.

Enantioselective Catalysis;150:Chiral-at-Metal (η6-p-Cymene)Ruthe­nium(II) Complexesof Binaphthyl Ligands - Synthesis, Characterization, andEnantioselective Catalysis

Neutral and cationic half-sandwich (η 6 -p-cymene)ruthe-nium complexes 9-12 with chiral Schiff base ligands derived from binaphthylamino derivatives and salicylaldehyde, diphenyl(2-formylphenyl)phosphane, and 2-pyridinealdehyde form two diastereomers which only differ in the metal configuration. From the diastereomeric mixtures of compounds 10 and 12 the major diastereomers crystallize, whereas for compound 9 both diastereomers co-crystallize in a 1:1 ratio in the same single crystal. In compounds 13 and 14 containing the reduced Schiff base ligands, the nitrogen atom of the secondary amine functionality becomes another chiral center. In solution at room temperature the various diastereomers interconvert rapidly. The new compounds were used as catalysts in the enantioselective transfer hydrogenation of acetophenone with 2-propanol and in the Diels-Alder reaction of cyclopentadiene with methacrolein.

Six-coordinated oxovanadium(V) complexes of reduced Schiff bases derived from amino acids: synthesis, reactivity and redox studies

New oxovanadium(V) complexes, [VOL(hq)] (1)–(4) have been prepared by the reaction of [VO(acac)2] with ligands LH2 in the presence of 8-hydroxyquinoline (Hhq). LH2 is the dibasic tridentate ONO Mannich base [(S)-H2glysal, (S)-H2alasal, (S)-H2leusal and (S)-H2ileusal; S represents the S-enantiomer] obtained by the reduction of the Schiff bases of salicylaldehyde (sal) and the amino acids: glycine (gly), DL-alanine (ala), leucine (leu) and isoleucine (ileu), respectively. Spectral studies suggest an octahedral structure for these complexes. The complexes exhibit a single 51V-n.m.r. signal at −464.6 to −468.0 p.p.m. due to the existence of a single isomeric species in solution. In the presence of L-ascorbic acid under aerobic conditions [VO(S-glysal)(hq)] (1) and [VO(S-isoleusal)(hq)] (4) are converted into the corresponding dioxo species possible via intermediate reduction. A time- dependent 51V-n.m.r. study has also been carried out in order to investigate the possible isomerisation and/or further reaction in solution.

Oxovanadium(iv and v) and copper(ii) complexes of N-salicyl-glycylglycine and N-salicyl-glycylglycylglycine

By reaction of salicylaldehyde and GlyGly or GlyGlyGly, followed by reduction with NaBH4, N-salicyl-glycylglycine 1 and N-salicyl-glycylglycylglycine 2, the reduced Schiff bases H2sal-RGG and H2sal-RGGG, containing the GlyGly or GlyGlyGly moities, are prepared and characterised. Their acid–base properties and complexation with VIVO2+ and CuII are studied by pH-potentiometry, visible absorption and EPR spectrometries, and the protonation and complex formation constants are determined. Vanadium and copper complexes are also prepared and characterised. Differences in the metal binding abilities of 1 and 2 are found. Amide deprotonation is proved but its extent depends on the system, being particularly important in the M–H2sal-RGG systems with the formation of the (O-phenolate, N-amine, N-amide, COO−) (6+5+5)-membered joined chelate system. Depending on the system, at physiological pH this binding mode and/or 2 × (O-phenolate, N-amine) are dominant. The aminophenolate chelates formed with sal-RGG and sal-RGGG behave as anchoring donor sites and the ML and ML2 complexes, involving O-phenolate, N-amine chelation, form in higher relative concentration than in the corresponding M–GlyGly or M–GlyGlyGly systems. Moreover, while for the VIVO–H2sal-RGG system the N-amide deprotonation/co-ordination is strongly promoted, it is not so favoured in the CuII–H2sal-RGG and CuII–H2sal-RGGG systems. The increased stability induced by the additional O-phenolate donor is particularly relevant for sal-RGG and hydrolysis of the MLH−1 complexes starts several pH units higher than in the GlyGly systems. In contrast to VIV, the VV complexes formed with sal-RGGG were found to be more stable than those of sal-RGG.

Interconversion of a monomer and two coordination polymers of a copper(II)-reduced Schiff base ligand-1,10-phenanthroline complex based on hydrogen- and coordinative-bonding.

Two compounds, [Cu(3)(Sbal)(2)(phen)(H(2)O)(2)](ClO(4))(2)-3H(2)O (1) and [Cu(H(2)Sbal)(2)(phen)](ClO(4))(2) (2), were isolated in successive steps from the reaction mixture containing Cu(ClO(4))(2)-6H(2)O, 1,10-phenanthroline, N-(2-hydroxybenzyl)-beta-alanine (H(2)Sbal), and LiOH in the ratio of 1:1:1:1. When the ratio of the base was doubled, the neutral monomer [Cu(Sbal)(phen)]-2H(2)O (3) was obtained. The cation in 1 exists as a one-dimensional polymer in the solid state, while weak O--H...O hydrogen bonds in the cation of 2 generate Delta Lambda Delta Lambda. type one-dimensional spiral chains. Addition of HClO(4) to 3 furnished 1 and 2, and this mixture can be converted back to 3 by the addition of a base. This conversion of a monomer to two 1-D polymers was found to be reversible. Crystal data for 1: triclinic space group P one macro, a = 12.0353(5) A, b = 12.2848(5) A, c = 15.3185(6) A, alpha = 84.993(1) degrees, beta = 89.411(1) degrees, gamma = 67.414(1) degrees, V = 2082.5(2) A(3), Z = 2, rho(calcd) = 1.668 g cm(-3). Crystal data for 2: tetragonal space group P4(1)/a, a = 10.8095(1) A, c = 59.0159(4) A, V = 6895.7(1) A(3), Z = 8, rho(calcd) = 1.605 g cm(-3). Crystal data for 3: monoclinic space group Pn, a = 10.6344(3) A, b = 5.3953(1) A, c = 18.1983(1) A, V = 1029.26(4) A(3), Z = 2, rho(calcd) = 1.526 g cm(-3). When Cu(NO(3))(2) was used in the place of Cu(ClO(4))(2), [Cu(2)(Sbal)(phen)(3)](NO(3))(2)-2.5H(2)O (4) was the only isolable product for the 1:1:1:1 ratio, and 3 was the only isolable product for the 1:1:1:2 ratio. Crystal data for 4: triclinic space group P one macro, a = 10.8063(8) A, b = 13.919(1) A, c = 16.564(1) A, alpha = 88.957(2) degrees, beta = 71.008(1) degrees, gamma = 69.829(2) degrees, V = 2198.9(3) A(3), Z = 2, rho(calcd) = 1.556 g cm(-3). Variable temperature magnetic measurements showed that the polymeric structure in 1 behaves, magnetically, as a strongly coupled micro-phenoxo dimer (2J = -390 cm(-1)) plus an isolated monomer.

Transfer hydrogenation of acetophenone promoted by (arene)ruthenium(II) reduced Schiff base complexes: an X-ray structure of [(η 6- p-cymene)RuCl(OC 6H 4-2-CH 2NHC 6H 4- p-Me)

Arene ruthenium(II) reduced Schiff base complexes of formulation [(η 6- p-cymene)RuCl(L n )] ( 1– 5, n=1–5) were prepared by reacting [(η 6- p-cymene)RuCl 2] 2 with HL n in the presence of sodium carbonate in CH 2Cl 2. The complexes contain an η 6- p-cymene group, a chloride and a bidentate chelating N,O-donor ligand. The molecular structure of [(η 6- p-cymene)RuCl(OC 6H 4-2-CH 2NHC 6H 4- p-Me)] ( 1) has been determined by X-ray crystallography. The complexes are found to be catalytically active for transfer hydrogenation of acetophenone to (±)1-phenylethanol in the presence of KOH and isopropanol showing percent conversion of 98 with the catalysts having a bulky substituent adjacent to the O- and N-donor sites of the auxiliary ligand.

Elevated levels of protein-bound p-hydroxyphenylacetaldehyde, an amino-acid-derived aldehyde generated by myeloperoxidase, are present in human fatty streaks, intermediate lesions and advanced atherosclerotic lesions

Reactive aldehydes might have a pivotal role in the pathogenesis of atherosclerosis by covalently modifying low-density lipoprotein (LDL). However, the identities of the aldehyde adducts that form on LDL in vivo are not yet clearly established. We previously demonstrated that the haem protein myeloperoxidase oxidizes proteins in the human artery wall. We also have shown that p-hydroxyphenylacetaldehyde (pHA), the aldehyde that forms when myeloperoxidase oxidizes L-tyrosine, covalently modifies the Nε-lysine residues of proteins. The resulting Schiff base can be quantified as Nε-[2-(p-hydroxyphenyl)ethyl]lysine (pHA-lysine) after reduction with NaCNBH3. Here we demonstrate that pHA-lysine is a marker for LDL that has been modified by myeloperoxidase, and that water-soluble, but not lipid-soluble, antioxidants inhibit the modification of LDL protein. To determine whether myeloperoxidase-generated aldehydes might modify LDL in vivo, we used a combination of isotope-dilution GC-MS to quantify pHA-lysine in aortic tissues at various stages of lesion evolution. We also analysed LDL isolated from atherosclerotic aortic tissue. Comparison of normal and atherosclerotic aortic tissue demonstrated a significant elevation (more than 10-fold) of the reduced Schiff base adduct in fatty streaks, intermediate lesions and advanced lesions compared with normal aortic tissue. Moreover, the level of pHA-lysine in LDL recovered from atherosclerotic aortic intima was 200-fold that in plasma LDL of healthy donors. These results indicate that pHA-lysine, a specific covalent modification of LDL, is generated in human atherosclerotic vascular tissue. They also raise the possibility that reactive aldehydes generated by myeloperoxidase have a role in converting LDL into an atherogenic lipoprotein.

Elevated levels of protein-bound p-hydroxyphenylacetaldehyde, an amino-acid-derived aldehyde generated by myeloperoxidase, are present in human fatty streaks, intermediate lesions and advanced atherosclerotic lesions

Reactive aldehydes might have a pivotal role in the pathogenesis of atherosclerosis by covalently modifying low-density lipoprotein (LDL). However, the identities of the aldehyde adducts that form on LDL in vivo are not yet clearly established. We previously demonstrated that the haem protein myeloperoxidase oxidizes proteins in the human artery wall. We also have shown that p-hydroxyphenylacetaldehyde (pHA), the aldehyde that forms when myeloperoxidase oxidizes L-tyrosine, covalently modifies the N(epsilon)-lysine residues of proteins. The resulting Schiff base can be quantified as N(epsilon)-[2-(p-hydroxyphenyl)ethyl]lysine (pHA-lysine) after reduction with NaCNBH(3). Here we demonstrate that pHA-lysine is a marker for LDL that has been modified by myeloperoxidase, and that water-soluble, but not lipid-soluble, antioxidants inhibit the modification of LDL protein. To determine whether myeloperoxidase-generated aldehydes might modify LDL in vivo, we used a combination of isotope-dilution GC-MS to quantify pHA-lysine in aortic tissues at various stages of lesion evolution. We also analysed LDL isolated from atherosclerotic aortic tissue. Comparison of normal and atherosclerotic aortic tissue demonstrated a significant elevation (more than 10-fold) of the reduced Schiff base adduct in fatty streaks, intermediate lesions and advanced lesions compared with normal aortic tissue. Moreover, the level of pHA-lysine in LDL recovered from atherosclerotic aortic intima was 200-fold that in plasma LDL of healthy donors. These results indicate that pHA-lysine, a specific covalent modification of LDL, is generated in human atherosclerotic vascular tissue. They also raise the possibility that reactive aldehydes generated by myeloperoxidase have a role in converting LDL into an atherogenic lipoprotein.

Synthesis, Structure, and Magnetic Properties of Tetranuclear Copper(II) Complexes of Tridentate Dianionic Ligands with an ONO Donor Set

Tetranuclear complexes [CuL2H]4 (1), [CuL2Me]4 (2), and [CuL2Cl]4 (3) with a reduced Schiff base type tridentate ligand H2L2H and its homologous with a substituent on the 2-hydroxymethylphenyl moiety (4-Me, H2L2Me; 4-Cl, H2L2Cl) were prepared and characterized by elemental analyses and magnetic measurements. The crystal structure of 1 was determined by X-ray crystallography. Tetracopper core is represented as a dimer-of-dimers structure by the stacking of two dicopper units bridged by alcoholic oxygens. One of the dicopper units contains square pyramidal (SP) Cu(II) ions, whereas the geometry of each Cu(II) ion in the other unit is described as essentially distorted trigonal bipyramid (TBP). Magnetic behaviors of the complexes are explained by modified equation based on the theoretical Spin Hamiltonian. The exchange integrals (-2J) are evaluated at 292–366 cm−1 for SP dicopper cores and 104–120 cm−1 for TBP, respectively, indicating the existence of different type of antiferromagnetic interaction-pathways corresponded to each copper geometry.

Molecular and Electronic Structure of a Reduced Schiff Base Cryptand: Characterization by X-ray Crystallography and Optical and EPR/ENDOR Spectroscopy

The macrobicyclic Schiff base cryptand, 1, with a m-phenyl group in each of the arms was reduced in tertrahydrofuran with the alkali metals Na through Cs to yield mono-, di-, and trianions. The crystal structure of a salt of 1-, formed by reduction of 1 with potassium metal in mixed dimethyl ether−methylamine solutions, shows that K+ is not encapsulated in the cavity of the cryptand. Instead, it forms methylamine-separated ion pairs arranged in symmetric fashion to give overall C3 symmetry. Solution studies by optical and EPR/ENDOR spectroscopies revealed complex ion pair equilibria that are compatible with external contact ion pair and solvent-separated ion pair formation. The rate of electron (and cation) transfer between strands is <4 × 107 s-1 for contact pairs, but faster for solvent-separated pairs. The addition of cryptand [2.2.2] to complex K+ breaks up the contact ion pairs and yields behavior similar to that of solvent-separated ion pairs. Cyclic voltammetry revealed three partially reversible reduction waves. Both the dianion and trianion were formed in solution by reduction with potassium and studied by optical and EPR spectroscopies. Two compounds, 2 and 3, which model a single strand of the macrobicycle, were used to deconvolute the spectra of 1-. The monoanions, 2- and 3-, are in equilibrium with a diamagnetic dimer that may be related to the pinacolate structure of the analogous ketyl dimers.

Titanium(IV) complexes of the crystallographically characterised fluorene-Schiff base N-2-fluorenyl(salicylideneimine) and related bi- and tetradentate ligands

Schiff base ligands have been prepared by the condensation of 2-aminofluorene with salicylaldehyde ( 1, flusalH) or 3-methoxy-2-hydroxybenzaldehyde ( 2, MeOflusalH). Compound 1 reacts with TiCl 4 in a 1:1 stoichiometry to afford [TiCl 3(flusal)] ( 3) and in a 2:1 ratio to yield [TiCl 4(flusalH) 2] ( 4). The reaction of excess TiBz 4 with compound 1 results in the isolation of the octahedral Ti(IV) complex [Ti(flusal) 2(flusalaBz) 2] ( 5). Crystallographic and spectroscopic data for the latter indicate a complex containing two Schiff base ligands present as conventional N,O chelates and a further two ligands in which the CN function is reduced by the addition of benzyl and hydrogen moieties producing an O-bound species with pendant amine. The single crystal X-ray diffraction structure of compound 1 has been obtained and compared with the published data for compound 5. Similar ligand alkylation to that observed in compound 5 is also achieved by the reaction of organolithium reagents with compounds 1 and 2; the reaction of PhLi and compound 2 followed by aqueous hydrolysis affords MeOflusalaPhH ( 6). Although reactivity does occur between TiCl 4 and compound 6, the products could not be fully characterised. Thus tetradentate reduced Schiff base ligands were synthesised by the reaction of salenH 2 with MeLi or PhLi, giving salenaMe 2H 2 ( 7) and salenaPh 2H 2 ( 8), respectively. Reaction of compound 8 and TiCl 4 affords the quadruply deprotonated amido complex [Ti(salenamidoPh 2)] ( 9), which hydrolyses in air to the μ-oxo amine complex [Ti(salenaPh 2)O] ( 10).

Rapid complexing of oxoacylglycerols with amino acids, peptides and aminophospholipids.

We prepared model Schiff bases from 2-[9-oxo]nonanoyl glycerol (2-MAG-ALD) and various amino compounds. 2-MAG-ALD was obtained by pancreatic lipase hydrolysis of trioleoyl glycerol and reductive ozonolysis of the resulting 2-monooleoyl glycerol. The reaction products were purified by thin-layer chromatography. Schiff bases were synthesized in greater than 50% yield by reacting 2-MAG-ALD with twofold molar excess of valine, Nalpha-acetyl-L-lysine methyl ester and the tripeptides glycyl-glycyl-glycine, glycyl-glycyl-histidine, and glycyl-histidyl-lysine in aqueous methanol and with 1-palmitoyl-2-stearoyl glycerophosphoethanolamine (PE) in chloroform/methanol for 16 h at room temperature. Prior to analysis the bases were reduced with sodium cyanoborohydride in methanol for 30 min at 4 degrees C. Reaction products were analyzed by high-performance liquid chromatography/electrospray ionization/mass spectrometry (HPLC/ESI/MS). Reduced Schiff bases of 2-MAG-ALD with PE and amino acids were analyzed by normal-phase HPLC/ESI/MS and those with peptides by reversed-phase HPLC/ESI/MS. Single adducts were obtained in all cases and both the alpha-amino group of valine and the epsilon-amino group of Nalpha-acetyl-L-lysine methyl ester were reactive. Molecular ions of reaction products were the only detected ions in the negative ionization mode, whereas in the positive ion mode sodiated molecular ions were also detected. The present study suggests that 2-MAG-ALD may form Schiff base adducts with amino compounds in other aqueous media, such as the intestinal lumen and in the hydrophobic environment of cell membranes.

Synthesis, isolation, and characterization of the adduct formed in the reaction of p-hydroxyphenylacetaldehyde with the amino headgroup of phosphatidylethanolamine and phosphatidylserine.

The adducts that form when aldehydes modify proteins have been implicated in the pathogenesis of vascular disease and aging. Our previous studies indicated that p-hydroxyphenylacetaldehyde (pHA), the major product of L-tyrosine oxidation by the myeloperoxidase/hydrogen peroxide/chloride system of phagocytes, covalently modifies the epsilon-amino group of lysine residues at sites of inflammation. Here, we report that pHA also reacts with the amino group of synthetic phospholipids and red blood cell model systems. Using fast atom bombardment mass spectrometric analysis of ethanolamine glycerophospholipid or serine glycerophospholipid incubated with pHA and NaBH3CN, we detected products that were consistent with reduced phospholipid Schiff base adducts. We confirmed the reaction of the aldehyde with the amino group through 1H NMR and mass spectrometric analysis of polar headgroups recovered from the modified and reduced parent lipid. When phospholipid model systems and cell membranes were exposed to physiological levels of L-tyrosine and the myeloperoxidase/hydrogen peroxide/chloride system followed by treatment with NaBH3CN, reduced Schiff base adducts of pHA with ethanolamine glycerophospholipid and serine glycerophospholipid (pHA-PE and pHA-PS, respectively) were produced. The reaction required myeloperoxidase, hydrogen peroxide, L-tyrosine, and chloride ion; it was inhibited by catalase or heme poisons, implicating hydrogen peroxide and peroxidase in the pathway. Collectively, these results demonstrate that an aldehyde generated by the myeloperoxidase system of phagocytes can covalently modify the amino groups of phosphatidylethanolamine and phosphatidylserine. Because amino glycerophospholipids are critical components of cell membranes and circulating lipoproteins such as LDL, similar reactions may play important roles in the initiation or progression of disease at sites of inflammation.

Study of Mono- and Bi-nuclear Copper(ii) Complexes of Tridentate Reduced Schiff Bases

Spectral, electrochemical and magnetic studies of mononuclear complexes CuL·nH2O, Cu(L)A and binuclear complexes Cu2L2·nH2O and Li(Cu2L22A–H) where L is a tridentate reduced Schiff base ligand and A is imidazole, reveal strong antiferromagnetic interactions in the binuclear complexes.

Chemical Trapping of Ternary Complexes of Human Immunodeficiency Virus Type 1 Integrase, Divalent Metal, and DNA Substrates Containing an Abasic Site: IMPLICATIONS FOR THE ROLE OF LYSINE 136 IN DNA BINDING

We report a novel assay for monitoring the DNA binding of human immunodeficiency virus type 1 (HIV-1) integrase and the effect of cofactors and inhibitors. The assay uses depurinated oligonucleotides that can form a Schiff base between the aldehydic abasic site and a nearby enzyme lysine epsilon-amino group which can subsequently be trapped by reduction with sodium borohydride. Chemically depurinated duplex substrates representing the U5 end of the HIV-1 DNA were initially used. We next substituted an enzymatically generated abasic site for each of 10 nucleotides normally present in a 21-mer duplex oligonucleotide representing the U5 end of the HIV-1 DNA. Using HIV-1, HIV-2, or simian immunodeficiency virus integrases, the amount of covalent enzyme-DNA complex trapped decreased as the abasic site was moved away from the conserved CA dinucleotide. The enzyme-DNA complexes formed in the presence of manganese were not reversed by subsequent addition of EDTA, indicating that the divalent metal required for integrase catalysis is tightly bound in a ternary enzyme-metal-DNA complex. Both the N- and C-terminal domains of integrase contributed to efficient DNA binding, and mutation of Lys-136 significantly reduced Schiff base formation, implicating this residue in viral DNA binding.

Model for the Reduced Schiff Base Intermediate between Amino Acids and Pyridoxal: Copper(II) Complexes of N-(2-Hydroxybenzyl)amino Acids with Nonpolar Side Chains and the Crystal Structures of [Cu(N-(2-hydroxybenzyl)-D,L-alanine)(phen)].H(2)O and [Cu(N-(2-hydroxybenzyl)-D,L-alanine)(imidazole)

Copper(II) complexes with reduced Schiff base ligands of amino acids possessing nonpolar side chains with salicylaldehyde have been synthesized. Ternary complexes with imidazole, 1,10-phenanthroline, and pyridine have been prepared and characterized for N-(2-hydroxybenzyl)-D,L-alanine. The crystal structures of [(N-(2-hydroxybenzyl)-D,L-alanine)(1,10-phenanthroline)Cu(II)] monohydrate ([Cu(SAla)phen].H(2)O) and [(N-(2-hydroxybenzyl)-D,L-alanine)(imidazole)Cu(II)] ([Cu(SAla)Him]), have been determined. [Cu(SAla)phen].H(2)O crystallized in space group P&onemacr;, with a = 8.718(2) Å, b = 10.886(3) Å, c = 11.693(2) Å, alpha = 71.32(2) degrees, beta = 85.27(2) degrees, gamma = 70.21(2) degrees, and Z = 2. The copper atom is five coordinate, with SAla acting as a tridentate ONO chelator through the carboxylato and phenolato oxygens and the amine nitrogen. The remaining donors are provided by the phen nitrogens. [Cu(SAla)Him] crystallized in space group P2(1)/n, with a = 10.353(1) Å, b = 6.714(1) Å, c = 18.769(2) Å, beta = 91.71(1) degrees, and Z = 4. The copper atom is four coordinate, with SAla acting as a tridentate ONO chelator with the neutral imidazole moiety coordinated through nitrogen. In both complexes the ligand has two chiral centers due to the coordination of the N. Molecular mechanics calculations show that unfavorable steric interactions would occur in the nonobserved R,R and S,S diastereomers. Compounds prepared have been characterized by a range of physicochemical techniques. The complexes may serve as stable models for the intermediates in enzymatic amino acid transformations.

Short-chain dehydrogenases/reductases (SDR)

Short-chain dehydrogenases/reductases (SDR) constitute a large protein family. Presently, at least 57 characterized, highly different enzymes belong to this family and typically exhibit residue identities only at the 15-30% level, indicating early duplicatory origins and extensive divergence. In addition, another family of 22 enzymes with extended protein chains exhibits part-chain SDR relationships and represents enzymes of no less than three EC classes. Furthermore, subforms and species variants are known of both families. In the combined SDR superfamily, only one residue is strictly conserved and ascribed a crucial enzymatic function (Tyr 151 in the numbering system of human NAD(+)-linked prostaglandin dehydrogenase). Such a function for this Tyr residue in SDR enzymes in general is supported also by chemical modifications, site-directed mutagenesis, and an active site position in those tertiary structures that have been characterized. A lysine residue four residues downstream is also largely conserved. A model for catalysis is available on the basis of these two residues. Binding of the coenzyme, NAD(H) or NADP(H), is in the N-terminal part of the molecules, where a common GlyXXXGlyXGly pattern occurs. Two SDR enzymes established by X-ray crystallography show a one-domain subunit with seven to eight beta-strands. Conformational patterns are highly similar, except for variations in the C-terminal parts. Additional structures occur in the family with extended chains. Some of the SDR molecules are known under more than one name, and one of the enzymes has been shown to be susceptible to native, chemical modification, producing reduced Schiff base adducts with pyruvate and other metabolic keto derivatives. Most SDR enzymes are dimers and tetramers. In those analyzed, the area of major subunit contacts involves two long alpha-helices (alpha E, alpha F) in similar and apparently strong subunit interactions. Future possibilities include verification of the proposed reaction mechanism and tracing of additional relationships, perhaps also with other protein families. Short-chain dehydrogenases illustrate the value of comparisons and diversified research in generating unexpected discoveries.

High-field NMR and restrained molecular modeling studies on a DNA heteroduplex containing a modified apurinic abasic site in the form of covalently linked 9-aminoellipticine.

Two-dimensional NMR methods were used to model the possible solution structure of an intercalative complex of 9-aminoellipticine (Aell), a polycyclic pyridocarbazolamine, covalently bound to an apurinic ring-opened deoxyribose site of a duplex DNA fragment in the reduced Schiff base form. The required oligonucleotide single strand containing covalently attached aminoellipticine was obtained by reductive amination in the presence of sodium cyanoborohydride. The combined NMR-energy minimization methods were employed to refine the model structures of two distinct forms, intrahelical and extrahelical, of a control 9-mer duplex DNA, d(CGTG.dr.GTGC).d(GCACTCACG), which contains an apurinic site positioned opposite a dT residue on the complementary strand. The model structure of an aminoellipticine conjugate with the same DNA sequence, derivatized via the aforementioned covalent attachment, was also obtained by incorporating intermolecular drug-DNA and intra- and internucleotide NOE-derived proton-proton distance estimates as restraints in energy minimization routines. The indole ring system of aminoellipticine, which is inserted at the apurinic site, intercalates between and is parallel to flanking GC base pairs. The pyridinic ring of aminoellipticine, in protonated form, also stacks between cytidine and thymidine bases on the complementary strand, which is consistent with the observation that the normal sequential NOE connectivity at the 5'-C13-T14 step is broken and indeed diverted through the ellipticine moiety, e.g., C13-Aell-T14 connectivities through the Aell-H4/C5Me protons. Interestingly, the partial stacking of the pyridinic ring is observed only between the 5'-CT step vs an adjacent 5'-TC step, owing to inherently weak stacking interactions associated with the former. In the absence of any potential groups that can participate in electrostatic or hydrogen-bonding interactions with the nucleic acid, pi-pi stacking and hydrophobic contacts at the intercalation site appear to be the important factors in determining stability and conformation of the aminoellipticine-DNA conjugate. Stacking interactions in such a bistranded intercalative complexation of aminoellipticine apparently govern the formation of a single intrahelical form of a right-handed B-type DNA duplex. The overall structural features lead us to propose working models for an enzyme-like DNA cleavage activity of 9-aminoellipticine and the observed inhibition of the AP endonuclease-dependent DNA excision-repair pathway.

High dosage vitamin E effect on oxidative status and serum lipids distribution in streptozotocin-induced diabetic rats.

This study was performed to determine whether vitamin E supplementation in streptozotocin-induced diabetic rats treated by insulin could reduce serum oxidation markers (malondialdehyde: MDA, Schiff bases, anti-protein-MDA adduct antibodies) and modulate lipid changes. After 10 weeks, diabetes induced in rats a significant increase in Schiff bases (P < 0.006) and anti-protein-MDA adduct antibodies (P < 0.01). These alterations were accompanied by a significant rise in serum free fatty acids (225%), triglycerides (35%), and phospholipids (30%) and changes in fatty acid distribution in these fractions and in cholesterol esters. Vitamin E supplementation in diabetic rats reduced Schiff bases and anti-protein-MDA adduct antibodies and tended to restore the fatty acid profile close to control rats without decreasing quantitatively serum lipids enhanced by diabetes. Concerning fatty acids, vitamin E chiefly reduced stearic acid (C18:0) in free fatty acids, cholesterol esters, and phospholipids and cancelled the decrease in low molecular triglycerides observed in diabetic rats. Furthermore, vitamin E maintained the ratio of monounsaturated and polyunsaturated fatty acids, particularly with respect to oleic acid (C18:1), dihomo-gamma-linolenic acid (C20:3 n-6), eicosapentaenoic (C20:5 n-3), and docosapentaenoic acid (C22:5 n-3), in serum phospholipids. These changes observed in vitamin E supplemented rats, compared to vitamin E-untreated diabetic rats, could favor prevention of accelerated atherogenesis. Particularly, the decrease of serum peroxides and enhancement in phospholipid fatty acids (C20:3 n-6, C20:5 n-3, and C22:5 n-3) could induce the preferential formation of prostaglandins (PGE1, PGI2, PGI3) which are protective in cardiovascular diseases.

Contribution of 4-methylthio-2-oxobutanoate and its transaminase to the growth of methionine-dependent cells in culture: Effect of transaminase inhibitors

The growth in culture of methionine-dependent transformed cells of human, rat and mouse origin was arrested in the absence of L-methionine (Met) but took place in the presence of 4-methylthio 2-oxobutanoic acid (MTOB), the keto acid of Met. From 24 hr after seeding, cells grew in 0.1 mM MTOB medium at a rate comparable to that in 0.1 mM Met medium. Using [ 35S]MTOB, it was found that the Met synthesized was used in normal MRC-5 cells and in transformed HeLa cells to the same extent for protein, adenosylmethionine and adenosylhomocysteine syntheses. However, when the free Met content was examined, it was found to be 3-fold greater in HeLa than in MRC-5 cells. To examine the importance of this free Met for the growth of transformed cells, the transaminase responsible for converting MTOB to Met was chosen as a target enzyme for the synthesis of compounds with potential inhibitory activity. Since this is a multisubstrate enzyme, reduced Schiff bases were prepared containing both pyridoxal or other aromatic groups, as one constituent, and L-Met or other amino-acids in the free acid or ester or amide form, as the other constituent. Only esters containing the pyridoxal moiety and Met or certain of its structural analogues exhibited good selective growth inhibitory activity in that there was little (20%) or no effect on the growth of normal MRC-5 and derm cells, respectively, while that of transformed HeLa, HEp-2 and L1210 cells was strongly inhibited (80%). This inhibition was accompanied by a concomitant decrease in the activity of the MTOB transaminase in both HeLa and MRC-5 cells treated with 3c the most potent inhibitor. However, using [ 35S]MTOB it was found that MTOB itself accumulated 48% in HeLa but only 12% in MRC-5 cells treated with 3c. On the contrary [ 35S]Met formed from [ 35S]MTOB increased 3.7-fold in MRC-5 inhibitor-treated cells showing 20% growth inhibition whereas it decreased 38% in HeLa-treated cells showing 80% growth inhibition. This decrease in cellular Met in HeLa is not responsible for growth arrest. Indeed the growth of HeLa cells could not be restored by adding a 10-fold excess of Met. Since MTOB can alleviate Met-dependence, the intracellular homeostasis of this metabolite may play a hitherto unsuspected role in controlling cell growth.