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PubMedDate not supplied

Modification of the thiourea linkage of a fluorescein-oligonucleotide conjugate to a guanidinium motif during ammonia deprotection.

During the preparation of a fluorescent conjugate based on a manganese cationic porphyrin carboxylate derivative linked to a 5'-amino-3'-fluorescein-labeled oligonucleotide, we observed the chemical transformation of the thiourea linkage to a guanidinium function during the deprotection in ammonia of the 3'-fluorescein-oligonucleotide from CPG support. We also noted a secondary reactivity of the activated carboxylate group of the metalloporphyrin precursor with the fluorescein entity of the conjugated oligonucleotide.

Ammonia↗
PubMedDate not supplied

Solid-phase synthesis of substituted imidazoline-tethered 2,3-diketopiperazines, cyclic ureas, and cyclic thioureas.

Efficient methods for the solid-phase synthesis of imidazoline-tethered 2,3-diketopiperazines, cyclic ureas, and cyclic thioureas are described. Following the exhaustive reduction of resin-bound dipeptides derived from orthogonally protected diamino acids, the primary amine of the resulting tetraamines was selectively protected with Dde. The compounds were then selectively cyclized via their secondary amines with three different diimidazole derivatives ((COIm)(2), COIm(2), CSIm(2)). Upon Dde removal, the compounds were selectively N-acylated and dehydratively cyclized with POCl(3) to afford the imidazoline-tethered analogues in moderate yield and high purity. These procedures have been extended to prepare mixture-based combinatorial libraries. Details of the selection of building blocks for preparation of the positional scanning libraries based on the "libraries from libraries" approach are discussed.

Combinatorial Chemistry Techniques↗
PubMed2005

Lewis acid properties of zinc(II) in Its cyclen complex. The structure of [Zn(cyclen)(S=C(NH2)2](ClO4)2 and the bonding of thiourea to metal ions. Some implications for zinc metalloenzymes.

The structure of the complex [Zn(cyclen)Tu](NO(3))(2) (1) is reported (cyclen = 1,4,7,10-tetraazacyclododecane; Tu = thiourea): orthorhombic, space group P2(1)2(1)2(1), a = 11.4170(11) A, b = 12.1995(11) A, c = 12.5299(12) A, Z = 4, R = 0.0504. The coordination of the cyclen is the same as that found for other similar Zn(II) complexes, with square pyramidal coordination around the Zn(II) and mean Zn-N bond lengths of 2.16 A. The coordinated Tu occupies the axial coordination site, with Zn-S = 2.31 A. The Zn-S-C-N torsion angle, involving the coordinated Tu, of 75.4 degrees is unusually large, because such torsion angles involving coordinated Tu are normally closer to 0 degrees. The bonding between Zn and S is discussed in terms of overlap with the p orbitals on S, which favors the eclipsed (Zn-S-C-N torsion = 0 degrees) mode of coordination of Tu. The energies of eclipsed and staggered modes (Zn-S-C-N = 90 degrees) of coordination of Tu to metal ions are examined by means of ab initio calculations, using the STO-3G basis set. It is concluded that the rather low formation constant for the Tu complex with Zn(II)/cyclen reported in this work was due to steric effects in 1, which prevent the adoption of the lower energy eclipsed conformation. These steric effects, because of clashes that would occur between Tu in the eclipsed conformation and the cyclen ring, cause the coordination of Tu with a higher energy conformation, with Zn-S-C-N = 75.4 degrees. The latter approaches the high energy staggered conformation that has Zn-S-C-N = 90 degrees. log K(1) values for Cl(-), Br(-), I(-), and CN(-) are reported and shown to be consistent with the binding site on the Zn(II) in the Zn(II)/cyclen complex being softer in the hard and soft acids and bases (HSAB, Pearson 1997) sense than the Zn(II) aqua ion, but not as soft as Zn(II) in triaza macrocycles that promote tetrahedral coordination. The change in HSAB character from intermediate in the Zn(II) aqua ion to softer in the cyclen complex, and softer still in tridentate N-donor ligands in model complexes, and in the Zn(II) active site of carbonic anhydrase as representative of Zn(II) metalloenzymes in general, is discussed in terms of the role of such effects in the functioning of metalloenzymes.

Binding Sites↗
PubMed2006

Cu(I) dinuclear complexes with tripodal ligands vs monodentate donors: triphenylphosphine, thiourea, and pyridine. A 1H NMR titration study.

Complexes [PPh3Cu(Tr(Mes,Me))] (1), [PPh3Cu(Tr(Me,o-Py))] (2), and [PPh3Cu(Br(Mes)pz(o-Py))] (3) (Tr(Mes,Me) = hydrotris[1,4-dihydro-3-methyl-4-mesityl-5-thioxo-1,2,4-triazolyl]borate; Tr(Me,o-Py) = hydrotris[1,4-dihydro-4-methyl-3-(2-pyridyl)-5-thioxo-1,2,4-triazolyl]borate; Br(Mes)pz(o-Py) = hydro[bis(thioxotriazolyl)-3-(2-pyridyl)pyrazolyl]borate; PPh3 = triphenylphosphine) were synthesized by the reaction of dinuclear complexes [Cu(Tr(Mes,Me))]2, [Cu(Tr(Me,o-Py))]2, [Cu(Br(Mes)pz(o-Py))]2, and PPh3. 1-3 were characterized by 1H, 13C, and 31P NMR spectroscopy and ESI-mass spectrometry. Crystal structure analyses were performed for 1 and 2. Both complexes crystallize in the triclinic P space group with the metal in a slightly distorted tetrahedral geometry (S3P coordination) bound by a kappa3-S3 ligand and a PPh3 molecule. The solution molecular structures were investigated by means of variable-temperature (210-310 K, CDCl3, 1-2; 200-310 K, CD2Cl2, 3) and NOESY NMR spectroscopy. The solution structures of 1-2 are in accordance with the X-ray structures, and the complexes do not exhibit fluxional behavior. On the other hand, 3 is subject to an equilibrium between two species with a coalescing temperature of approximately 260 K. DFT geometry optimizations suggest that the major species of 3 consists of the Br(Mes)pz(o-Py) ligand bound to Cu(I) in the kappa3-S2H fashion with two C=S groups and a [Cu...H-B] interaction. A PPh3 completes the copper coordination (S2HP coordination). The complex [TuCu(Tr(Mes,Me))] (4) (Tu = thiourea) was crystallized using an excess of Tu with respect to [Cu(Tr(Me,2-Py))]2 (approximately a 6:1 ratio). The metal adopts a distorted tetrahedral geometry with an overall S3H coordination determined by the bound kappa3-S2H ligand (two C=S groups and a [B-H...Cu] interaction) and by a Tu. The reactivity of dinuclear complexes [Cu(Tr(Mes,Me))]2, [Cu(Tr(Me,o-Py))]2, and [Cu(Br(Mes)pz(o-Py))]2 with monodentate ligands was investigated by means of NMR titrations with PPh3, Tu. and pyridine (Py), and formation constants for the adducts [DCu(L)] (D = monodentate donor, L = tripodal ligand) were determined.

Copper↗
PubMed1995

New analogs of burimamide as potent and selective histamine H3 receptor antagonists: the effect of chain length variation of the alkyl spacer and modifications of the N-thiourea substituent.

Burimamide was one of the first compounds reported to antagonize the activation of the histamine H3 receptor by histamine. We have prepared a large series of burimamide analogs by variation of the alkyl spacer length of burimamide from two methylene groups to six methylene groups and also by replacement of the N-methyl group with other alkyl and aryl groups. All analogs are reversible, competitive H3 antagonists as determined on the guinea pig intestine. Elongation of the alkyl chain from an ethylene chain to a hexylene chain results in an increase of the H3 antagonistic activity. The H3 selective pentylene and hexylene analogs of burimamide are about 10 times more potent than burimamide. The N-thiourea substituents, however, have no beneficial influence on the affinity.

Animals↗
PubMed1992

Structure-activity studies of potassium channel opening in pinacidil-type cyanoguanidines, nitroethenediamines, thioureas, and ureas.

Potassium channel opening activity for pinacidil-type cyanoguanidines, nitroethenediamines, thioureas, and ureas, has been assessed through simultaneous measurement of spontaneous contractile activity and stimulation of 86Rb+ efflux from rat portal veins loaded with 86Rb+. The good correlation between these two effects suggests that the vasodilator activity of the compounds is directly attributable to an increased opening of potassium channels. The resulting quantitative in vitro data has been used to analyze the structure-activity relationships for potassium channel opening, allowing the biological activity to be rationalized in terms of a pharmacophore involving a hydrogen-bond-acceptor element, a hydrogen-bond-donor element, and a lipophilic binding group. A model for the binding of pinacidil-related compounds to their potassium channel receptor has been developed, and compounds designed to test this model have been synthesized and tested. Prototropic equilibria are implicated as playing a fundamental role in determining the hydrogen-bonding ability of the compounds, and conformational changes in the receptor are invoked to explain disparities in the chiral recognition of lipophilic groups in different compounds.

Animals↗
PubMed1981

Cyclic urea and thiourea derivatives as inducers of murine erythroleukemia differentiation.

A series of derivatives of tetramethylurea, a known inducer of the differentiation of Friend erythroleukemia cells, has been synthesized and tested for its capacity to induce erythroid maturation, as measured by the synthesis of hemoglobin. Cyclic urea and thiourea derivatives consisting of five-, six-, and seven-membered ring systems containing N-alkyl substituents were prepared. Most of these agents were relatively effective inducers od differentiation, with N-alkyl substitution appearing to be essential for maximum response. The most potent agents developed were N,N'-dimethyl cyclic ureas. Exposure to concentrations of 2 to 4 mM of these derivatives resulted in more than 90% of the cell population achieving a differentiated state. Under these conditions, the parent compound, tetramethylurea, was slightly less efficacious, causing differentiation of only 68% of the population at its maximum effective level of 4 mM.

Animals↗
PubMed1980

Antihypertensive (2-aminoethyl)thiourea derivatives. 2.

Starting with 2,6-dichlorophenyl isothiocyanate, 1-(2-aminoethyl)-2-cyano-3-(2,6-dichlorophenyl)guanidine (2) was prepared in three steps. In contrast to the corresponding thiourea 1, this compound was essentially inactive as an antihypertensive agent.

Animals↗
PubMed2003

N-(3-acyloxy-2-benzylpropyl)-N'-[4-(methylsulfonylamino)benzyl]thiourea analogues: novel potent and high affinity antagonists and partial antagonists of the vanilloid receptor.

Isosteric replacement of the phenolic hydroxyl group in potent vanilloid receptor (VR1) agonists with the alkylsulfonamido group provides a series of compounds which are effective antagonists to the action of the capsaicin on rat VR1 heterologously expressed in Chinese hamster ovary (CHO) cells. In particular, compound 61, N-[2-(3,4-dimethylbenzyl)-3-pivaloyloxypropyl]-N'-[3-fluoro-4-(methylsulfonylamino)benzyl]thiourea was a full antagonist against capsaicin, displayed a K(i) value of 7.8 nM (compared to 520 nM for capsazepine and 4 nM for 5-iodoRTX), and showed excellent analgesic activity in mice. Structure-activity analysis of the influence of modifications in the A- and C-regions of 4-methylsulfonamide ligands on VR1 agonism/antagonism indicated that 3-fluoro substitution in the A-region and a 4-tert-butylbenzyl moiety in the C-region favored antagonism, whereas a 3-methoxy group in the A-region and 3-acyloxy-2-benzylpropyl moieties in the C-region favored agonism.

Analgesics↗
PubMed2001

Carbohydrate-based receptors with multiple thiourea binding sites. Multipoint hydrogen bond recognition of dicarboxylates and monosaccharides.

The binding properties of multitopic sugar thiourea receptors toward dicarboxylate and monosaccharide guests have been examined taking glutarate and octyl beta-D-glucopyranoside as model ligands. For the anionic hydrogen bond acceptor, both the complex stoichiometry and the association constants (K(as)) were found to be strongly dependent on the relative disposition of recognition elements in the host. In contrast, for the glucoside guest a 1:1 stoichiometry was observed in all cases, the K(as) values being largely independent of the unbound state provided that geometrically equivalent supramolecular topologies can be achieved.

Binding Sites↗
PubMed2000

Regiospecific carbonylative annulation of iodophenol acetates and acetylenes to construct the flavones by a new catalyst of palladium-thiourea-dppp complex.

[reaction: see text] Regiospecific carbonylative annulation of o-iodophenol acetates and acetylenes mediated by palladium-thiourea-dppp complex in the presence of base at 40 degrees C under a balloon pressure of CO generates diversified flavones in high yields. This newly developed synthetic technology provides a highly efficient method for potential application to the combinatorial synthesis of those heterocycles on the solid support.

Acetylene↗
PubMed2000

A general synthetic method for the formation of substituted 5-aminotetrazoles from thioureas: a strategy for diversity amplification.

A general method for the synthesis of 5-aminotetrazoles is outlined using the mercury(II)-promoted attack of azide anion on a thiourea. The reaction proceeds through a guanyl azide intermediate, which undergoes electrocyclization to the tetrazole. The method is high yielding and provides access to mono-, di-, and trisubstituted 5-aminotetrazoles, targets of potential interest for combinatorial library development.

Crystallography, X-Ray↗
PubMed2003

Synthesis of carbocyclic and heterocyclic fused quinolines by cascade radical annulations of unsaturated N-aryl thiocarbamates, thioamides, and thioureas.

[reaction: see text] Tandem radical cyclizations of suitably substituted N-aryl thiocarbamates, thioamides, and thioureas are induced by exposure to tris(trimethylsilyl)silane (TTMSH) and UV light and provide furoquinolines, isofuroquinolines, cyclopentaquinolines, indoloquinolines, and related ring systems. The intermediacy of an alpha-thioalkylamino radical, which is the synthetic equivalent of an imidoyl radical, is invoked.

Cyclization↗
PubMed2005

Anion recognition using preorganized thiourea functionalized [3]polynorbornane receptors.

[structure: see text] A new family of [3]polynorbornane frameworks exhibiting conformationally preorganized aromatic thiourea (cleft-like) receptors have been designed and synthesized for anion recognition. These show excellent affinity for the biologically relevant dihydrogenphosphate (H(2)PO(4)(-)) and dihydrogenpyrophosphate (H(2)P(2)O(7)(2)(-)) anions (among others), which are bound in 1:1 and 2:1 (host:anion) ratio, respectively. Moreover, visually striking color changes accompany guest binding, enabling this family to act as colorimetric anion sensors.

Anions↗