Synthesis and properties of derivatives of 1,4-dihydropyrimidine-5-carboxylic acid

1,4-Dihydropyrimidines were synthesized by reductive dethionation of the corresponding 2-thiono-4-aryl-1,2,3,4-tetrahydropyrimidine-5-carboxylic acid derivatives, and some of their properties were studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1223–1227, September, 1986.     

Photophysical properties of ruthenium bipyridine (4-carboxylic acid-4'-methyl-2,2'-bipyridine) complexes and their acid-base chemistry

Photophysical properties such as absorption and emission spectra, lifetimes, and redox potentials of eight ruthenium complexes, Ru(LL)2(MebpyCOOH)2+, where LL represents bpy, phen, Me2bpy, Me4bpy, (MeO)2bpy, (EtO)2bpy, Cl2bpy, and NO2phen, have been measured. The acid dissociation constants of ground and excited states have been determined. The ground-state pKa values were obtained from the pH dependence of the complex absorbance changes. The excited-state pKa* values were extracted from the emission titration curve and corrected for the excited-state lifetime of both protonated and deprotonated species. The largest DeltapKa, pKa*-pKa, found for Ru(Me2bpy)2(MebpyCOOH)2+ and Ru(Me4bpy)2(MebpyCOOH)2+ of 1.7 indicate that MebpyCOOH gains most of the MLCT excited-state electron. The big negative DeltapKa found for Ru(Cl2bpy)2(MebpyCOOH)2+, -4.2, clearly indicates the metal-to-ligand charge transfer to the Cl2bpy ligands.     

Photophysical properties of lanthanide complexes with 5-nitro-1,10-phenanthroline

Abstract  

Five novel lanthanide (Eu³⁺, Tb³⁺, Sm³⁺, Dy³⁺, and Gd³⁺) complexes with 5-nitro-1,10-phenanthroline (phenNO₂) have been synthesized and characterized by elemental analysis, IR, UV, and luminescence spectra. The triplet state energy of phenNO₂ was determined to be 20,048 cm⁻¹ via the phosphorescence spectra of phenNO₂ and its gadolinium complex. The photophysical properties of these complexes indicated that the triplet state energy of the ligand is suitable for the sensitization of the luminescence of Eu³⁺ and Sm³⁺, especially the former.     

Synthesis of novel quinoxaline-5-carboxylic acid derivatives

This paper describes the synthesis of several new 2,3-dimethoxy-6-methyl-7-nitro-quinoxaline-5-carboxylic acid derivatives ( 13a-m ) via a multistep synthetic route from 5-methyl-1H-benzo[d][1,3]oxazine-2,4-dione ( 1 ).     

Oxidation of some derivatives of tetrahydropyrimidine-5-carboxylic acid with selenium dioxide

The oxidation of derivatives of 2-oxo-4-phenyl-6-methyl-1,2,3,4-tetrahydropyrimidine-5-carboxylic acid with selenium dioxide was studied. It was observed that the 6-methyl group is oxidized to a hydroxymethyl, formyl, or carboxy group (in the latter case probably after dehydrogenation of the ring). The structure of the final product depends on the degree of substitution of the ring with respect to the nitrogen atom and on the substituent in the 5 position.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 535–538, April, 1982.     

Synthesis and properties of derivatives of 4-aminofuroxan-3-carboxylic acid

4-Amino-3-cyanofuroxan, obtained by the oxidation of aminocyanoglyoxime, reacts with hydrazine and hydroxylamine to form the amidrazone and amidoxime respectively of 4-aminofuroxan-3-carboxylic acid. The reaction of the amidoxime with triethyl orthoformate can lead to closure of both the pyrimidine and the 1,2,4-oxadiazole ring.Latvian Institute of Organic Synthesis, Riga. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1115–1119, August, 1997.     

Photophysical, electrochemical and anion sensing properties of Ru(II) bipyridine complexes with 2,2'-biimidazole-like ligand

A new anion sensor [Ru(bpy)(2)(DMBbimH(2))](PF(6))(2) (3) (bpy is 2, 2'-bipyridine and DMBbimH(2) is 7,7'-dimethyl-2,2'-bibenzimidazole) has been developed. Its photophysical, electrochemical and anion sensing properties are compared with two previously investigated systems, [Ru(bpy)(2)(BiimH(2))](PF(6))(2) (1) and [Ru(bpy)(2)(BbimH(2))](PF(6))(2) (2) (BiimH(2) is 2,2'-biimidazole and BbimH(2) is 2,2'-bibenzimidazole). The high acidity of the N-H fragments in these complexes make them easy to be deprotonated by strong basic anions such as F(-) and OAc(-), and they form N-H···X hydrogen bonds with weak basic anions like Cl(-), Br(-), I(-), NO(3)(-), and HSO(4)(-). Complex 3 displays strong hydrogen bonding with these 5 weak basic anions, with binding constants between 17,000 and 21,000, which are larger than those observed in complex 1, with binding constants between 3300 and 5700, and in complex 2, which shows no hydrogen bonding toward Cl(-), Br(-), I(-), and NO(3)(-), and forms considerable hydrogen bonds with HSO(4)(-) with a binding constant of 11,209. These hydrogen bonding behaviours give different NMR, emission and electrochemical responses. The different anion binding affinity of these complexes may be mainly attributed to their different pK(a1) values, 7.2 for 1, 5.7 for 2, and 6.2 for 3. The additional methyl groups at the 7 and 7' positions of complex 3 may also play an important role in the enhancement of anion binding strength.     

Synthesis of 3-arylsulfonylmethyl-1,2,4-oxadiazole-5-carboxylic acid derivatives

Several new 3-arylsulfonylmethyl-1,2,4-oxadiazole-5-carboxylic acid derivatives have been synthesized. A typical example, 3-[(4-chlorophenylsulfonyl)methyl]-1,2,4-oxadiazole-5-carboxylic acid ethyl ester ( 2c ), was prepared from the reaction of 2-(4-chlorophenylsulfonyl)acetamide oxime ( 1c ) with ethyl oxalyl chloride. The hydrazide derivative ( 3f ) showed antihypertensive activity in rats. Various structural modifications to improve activity are discussed.     

Synthesis of 2,2-disubstituted pyrrolidine-4-carboxylic acid derivatives and their incorporation into beta-peptide oligomers

[reaction: see text] We have recently shown that members of a new class of beta-peptides, containing 2,2-disubstituted pyrrolidine-4-carboxylic acid residues, display discrete conformational preferences despite the impossibility of internal hydrogen bonding (Huck et al. J. Am. Chem. Soc. 2003, 125, 9035). Here we describe the synthesis of a variety of 2,2-disubstituted pyrrolidine-4-carboxylic derivatives that bear a diverse set of side chains and protecting groups suitable for oligomer synthesis. In addition, we discuss coupling methods for construction of oligomers in solution and on solid phase. Non-hydrogen bonded foldamers such as those generated from 2,2-disubstituted pyrrolidine-4-carboxylic acids may be useful in biomedical applications because the low intrinsic polarity of their backbones may promote bioavailability.     

Synthesis of some bifunctional derivatives of 8-methylquinoline-5-carboxylic acid

Derivatives of 8-methylquinoline-5-carboxylic acid were synthesized. Alcoholysis of 8-methyl-5-cyanoquinoline gave methyl and ethyl 8-methylquinoline-5-carboxylates, which were converted to the corresponding 8-bromomethyl derivatives. The latter were used for the introduction of a methylamino group and the synthesis of N-acyl derivatives. The hydrazide, amide, and anilide of 8-methylquinoline-5-carboxylic acid were obtained as model compounds.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 785–788, June, 1982.     

Reaction of zinc enolates prepared from 2,2-dibromoindan-1-one or 2,2-dibromo-1-tetralone and zinc with 2-oxochromen-3-carboxylic acid derivatives

Zinc enolates obtained from 2,2-dibromonidan-1-one or 2,2-dibromo-1-tetralone and zinc reacted with alkyl esters and amides of 2-oxochromen-3-carboxylic acid giving the corresponding derivatives of 2,1′-dioxo-spiro(1a,7b-dihydrocyclopropa[c]chromen-1,2′-indan)-or 1′,2′,3′,4′-tetrahydro-2,1′-dioxospiro(1a,7b-dihydrocyclopropa[c]chromen-1,2′-naphthalene)-1a-carboxylic acids prevailingly in the form of a single geometric isomer.     

Photophysical and antimicrobial properties of new double-armed benzo-15-crown-5 ligands and complexes

Research on Chemical Intermediates - New double-armed crown ether ligands linked to pyridine derivatives have been synthesized and characterized. These macrocyclic ligands (1–5) have been...     

Synthesis, structures and properties of Cu(II) and Mn(II) complexes with 1,10-phenanthroline-2-carboxylic acid and 2,2'-bipyridine ligands

Four new 2,2'-bipyridine and 1,10-phenanthroline complexes, namely [Mn(phenca)(2)]·(H(2)O)(2) (1), [Cu(4)(phen)(4)(OH-)(4)(H(2)O)(2)](DMF)(4)(ClO(4)-)(4)(H(2)O) (2), [Cu(2)(2,2-bipy)(2)(C(2)O(4)2-)(H(2)O)(2)(NO(3))(2)] (3) and [Cu(2,2-bipy)(2)(ClO(4)-)](ClO(4)-) (4) (2,2'-bpy = 2,2'-bipyridine, Hphenca = 1,10-phenanthroline-2-carboxylic acid) have been synthesized by a hydrothermal reaction. The products were characterized by elemental analysis, infrared spectroscopy and X-ray crystal diffraction. While strong hydrogen bonds play central roles in the formation of the 3D structure, the combined influence of the weak interactions such as π···π interactions is also evident in the structures. A preliminary investigation on the ion exchange properties of the complexes is presented.     

Photophysical and electrochemical properties of chlorophyll a-cyclodextrins complexes

In this work, we have studied the interactions between two different cyclodextrins (CDs) and chlorophyll a (Chl a) in the presence of electrolyte by means of absorption, fluorescence spectroscopy, circular dichroism and cyclic voltammetry. The results obtained indicate that the presence of both CDs gives rise to an increase of Chl a solubility in water. In particular, heptakis-(2,3,6-tri-O-methyl)-beta-cyclodextrin (TRIMEB) favours the dissolution of Chl a monomer in aqueous solution, whereas the presence of hydroxypropyl-beta-cyclodextrin (beta-HP-CD) promotes the pigment aggregation.     

A facile synthesis of 3-amino-5-substitutedaminoisothiazole-4-carboxylic acid derivatives

A facile, general and one-pot method for the preparation of 3-amino-5-substituted-aminoisothiazole-4-carboxylic acid derivatives, in high yields, by the aminative cyclization of 3-amino-3-mercaptoacrylonitriles is described.     

Photophysical properties of ruthenium(II) tris(2,2'-bipyridine) complexes bearing conjugated thiophene appendages

A small series of ruthenium(II) tris(2,2'-bipyridine) complexes has been synthesized in which ethynylated thiophene residues are attached to one of the 2,2'-bipyridine ligands. The photophysical properties depend on the conjugation length of the thiophene-based ligand, and in each case, dual emission is observed. The two emitting states reside in thermal equilibrium at ambient temperature and can be resolved by emission spectral curve-fitting routines. This allows the properties of the two states to be evaluated in both fluid butyronitrile solution and a transparent KBr disk. It is concluded that both emitting states are of metal-to-ligand charge-transfer (MLCT) character, and despite the presence of conjugated thiophene residues, there is no indication for a low-lying pi,pi*-triplet state that promotes nonradiative decay of the excited-state manifold. A key feature of these systems is that the conjugation length imposed by the thiophene-based ligand helps to control the rate constants for both radiative and nonradiative decay from the two MLCT triplet states.     

Alkylation and reductive dethionation of 2-thioxo- and 1,2,3,4-tetrahydropyrimidine-5-carboxylic acid derivatives

2-Methylthio-1,4-dihydropyrimidines were obtained by methylation of 2-thioxo-4-phenyl-5-methoxycarbonyl-6-methyl-1,2,3,4-tetrahydropyrimidine or its 1-methyl derivative in a neutral medium. The alkylation of tetrahydropyrimidine-2-thiones in the anionic form leads to S- and S,N-methylation products. Iodoacetamide alkylates pyrimidine-2-thione with the formation of thiazolidino[3,2-a]pyrimidine derivatives. The reductive dethionation of derivatives of tetrahydropyrimidine-2-thiones and 2-methylthio derivatives of 1,4- and 3,4-dihydropyrimidines was accomplished.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1076–1082, August, 1989.     

Photophysical and electrochemical properties of new ortho-metalated complexes of rhodium(III) containing 2,2'-dipyridylketone and 2,2'-dipyridylamine. An experimental and theoretical study

Two new ortho-metalated rhodium(III) complexes of the formula [Rh(ppy)(2)(L)](+), ppy = 2-phenylpyridine and L = 2,2'-dipyridylketone (dpk) (), 2,2'-dipyridylamine (HDPA) () have been synthesized and subjected to X-ray diffraction crystal structural, photophysical and electrochemical studies. Density functional theory calculations have also been performed to get rationalizations of the optical orbitals and redox orbitals concerning photophysical and electrochemical data. Complex exhibits the triplet ligand-to-ligand charge transfer ((3)LLCT) [pi(ppy)-pi*(dpk)] phosphorescence at 77K (520 nm) and at room temperature (555 nm), while complex shows triplet ligand centred ((3)LC) [pi-pi*(ppy)] phosphorescence only at 77K (460 nm). Both complexes and have similar irreversible oxidation potentials (+1.19 V for and +1.15 V for vs. Fc/Fc(+)). These two complexes show different characteristics in the reduction process: a reversible process occurs for at -1.31 V, while an irreversible process is observed for 2 at -1.85 V.     

Magnetic properties of transition metal complexes with 2,2′-bipyridin-5-yl t-butyl nitroxide

Complexes [Mn^II(5bpno)₃(ClO₄)₂], [Mn^II(5bpno)(CH₃OH)₂Cl₂], [Cu^II(5bpno)₂(ClO₄)₂], and [Cu^II(5bpno)Cl₂] were prepared, where 5bpno stands for 2,2′-bipyridin-5-yl t-butyl nitroxide. X-ray crystallographic analysis clarified that the Cu ion in [Cu(5bpno)₂(ClO₄)₂] was tetra-coordinate with four nitrogen atoms forming two chelate rings. Magnetic measurements revealed the presence of ferromagnetic couplings in the Mn complexes, whereas the Cu complexes showed antiferromagnetic couplings. Magnetic exchange couplings between the metal and radical spins through the intervening pyridine ring can be explained in terms of the spin-polarization mechanism.