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PubMed2005

Microwave-promoted Suzuki reactions of aryl chlorides in aqueous media.

[reaction: see text] The microwave-promoted Suzuki coupling reaction of aryl chlorides with boronic acids performed in an aqueous media was studied using the air- and moisture-stable catalyst POPd2 (dihydrogen di-mu-chlorodichlorobis(di-tert-butylphosphinito-kappaP)dipalladate (2-)). This catalyst system under microwave conditions (150 degrees C, 15 min) provided coupled products with yields ranging from 64% to 99%. This method tolerated a variety of substituents and sterically hindered substrates.

Biphenyl Compounds↗
PubMed2002

Facile synthesis of N-aryl pyrroles via Cu(II)-mediated cross coupling of electron deficient pyrroles and arylboronic acids.

N-Arylation of electron-deficient pyrroles has been achieved by cross-coupling with arylboronic acids at room temperature in the presence of stoichiometric amounts of copper(II) acetate. The generality of this reaction has been established with variously substituted pyrroles as well as boronic acids. A key intermediate in the synthesis of a matrix metalloprotease inhibitor has been achieved using this methodology.

Biphenyl Compounds↗
PubMedDate not supplied

The cytotoxicity of 3'-aminocyanoborane-2', 3'-dideoxypyrimidines in murine and human tissue cultured cell lines.

3'-Aminocyanoborane-2', 3'-dideoxythymidine (VIIa) and 3'-aminocyanoborane-2', 3'-dideoxyuridine (VIIIb) were successfully synthesized. The thymidine derivative (VIIIa) was shown to be a potent cytotoxic agent in murine and selected human suspended and solid tumor cell lines. Compound VIIIa inhibited L-1210 leukemia DNA and RNA synthesis with the protein synthesis requiring a higher concentration of drug for inhibition within 60 min. The purine pathway appeared to be the major target of Compound VIIIa with inhibition of IMP dehydrogenase and dihydrofolate reductase activities. The compound affected metabolic enzyme activities in the pyrimidine pathway as well as the nucleoside kinase activities. The DNA molecule did not appear to be target of the 3'-aminocyanoborane-2', 3'-dideoxythymidine (VIIIa), in that there was no change in ct-DNA viscosity, thermal denaturation or absorption of nucleosides of DNA nor was there any L-1210 DNA strand scission or inhibition of L-1210 DNA topoisomerase II activity when compound VIIIa was incubated at 100 microM.

Animals↗
PubMed2005

Boron deficiency and concentrations and composition of phenolic compounds in Olea europaea leaves: a combined growth chamber and field study.

Boron deficiency is the most frequent micronutrient disorder in olive (Olea spp.) orchards. We tested the hypothesis that plant boron status affects phenolic metabolism, which, in turn, influences several ecophysiological traits of olive (Olea europaea L.) trees, by studying the effects of boron deficiency on leaf phenolic compounds of olive in a growth chamber experiment (CE) and a field experiment (FE). In the CE, a semi-hydroponic system was used to control nutrient supply. Plants received complete nutrient solution containing either 23 (control) or 0 microM H3BO3 (boron-deficient treatment). In the FE, boron-deficient trees were chosen based on visible boron-deficiency symptoms and analysis of their leaf boron concentration. Boron deficiency caused significant accumulation of phenolic compounds in leaves of CE plants (1.7 to 5.8 times more, depending on leaf age), but not in leaves of FE plants. However, in both experiments, the concentration of an unidentified phenolic compound, with a UV-spectrum resembling that of caffeic acid, increased in response to boron deficiency (by a factor of 40 to 184 in the CE and by a factor of three in the FE). Regression analysis showed that the concentration of this compound was negatively correlated to leaf boron concentration, irrespective of growth conditions and treatment. We conclude that, under field conditions, boron deficiency may not be the only factor determining the concentration of total phenolics, but it may be responsible for the accumulation of a distinct phenolic metabolite in olive leaves.

Boron↗
PubMed2000

Borato-1,2-diaminocyclohexane platinum (II), a novel anti-tumor drug.

Borato-1,2-diaminocyclohexane platinum (II) (BDP) was synthesized and compared to cisplatin (cisPt) as a potential anti-tumor drug. BDP and cisPt (0.2-20 microM) dose-dependently inhibited DNA synthesis in L1210 murine leukemia cells, DU-145 prostate cancer cells, A549 lung carcinoma cells, and MCF-7 breast cancer cells, as judged by measuring [(3)H]-thymidine incorporation. BDP and cisPt induced killing of L1210 murine cells by 97 and 78%, respectively. The LD(50) was 35 and 14 mg/kg for BDP and cisPt, respectively. Interestingly, while cisPt (at optimal dose) induced a 100% increase in life span (ILS) of BDF1 mice bearing L1210 tumor cells, BDP (at optimal dose) induced a 200% increase in ILS in the same tumor model. In conclusion, BDP is a novel platinum derivative compound that appears more effective in increasing the ILS than cisplatin against the leukemia tumor mouse model.

Animals↗
PubMed2006

Ruthenium-catalyzed regiospecific borylation of methyl C-H bonds.

We report the regiospecific, ruthenium-catalyzed borylation of saturated terminal C-H bonds. Alkylboronates were obtained in 78-98% yields. The borylations of alkanes, trialkylamines, protected alcohols, and fluoroalkanes occurred regiospecifically at the methyl group that is least sterically hindered. In contrast to most organometallic C-H activation, the reactions of alkanes occurred in higher yields than the reactions of arenes. Reactions were conducted that probed steric and electronic effects on the alkyl borylation. These reactions showed that the borylation occurred preferentially at the methyl group that is least sterically hindered and most electron-deficient. Ruthenium compounds containing boryl ligands were synthesized, and one was characterized by X-ray crystallography. One of these compounds contained a rare bridging boryl ligand and served as a catalyst precursor for the borylation of octane.

Boron Compounds↗
PubMed2003

2-aminoethoxydiphenyl borane activates a novel calcium-permeable cation channel.

The membrane-permeable, noncompetitive inositol 1,4,5-trisphosphate (IP3)-receptor inhibitor 2-aminoethoxydiphenyl borane (2-APB) has been widely used to probe for IP3-receptor involvement in calcium signaling pathways. However, a number of recent studies in different cell types revealed other sites of action of 2-APB. In this study, we examined the influence of 2-APB on capacitative calcium entry and intracellular Ca2+ concentrations in rat basophilic leukemia (RBL-2H3 m1) cells. 2-APB was found to inhibit capacitative calcium entry, but at concentrations greater than 50 microM, a new effect of 2-APB was observed. When capacitative calcium entry was blocked with Gd3+, 2-APB caused an increase in cytoplasmic Ca2+. This increase in intracellular Ca2+ was not caused by altered buffering of cytoplasmic Ca2+ and was not caused by or in any way affected by the depletion of intracellular Ca2+ stores. Associated with the increase in intracellular Ca2+, in the presence of 2 mM Ca2+, 2-APB activated single channels in the plasma membrane with a conductance of approximately 50 pS. These channels seem to be nonselective cation channels; monovalent cations are the major carriers of current, but finite permeability to Ca2+ leads to a significant intracellular Ca2+ signal. Experiments with excised patches indicate that 2-APB activates these channels from the outer aspect of the cell membrane. This effect of 2-APB further illustrates the complex actions of this compound and reveals the presence in RBL-2H3 m1 cells of a novel, ligand-gated calcium-permeable channel.

Animals↗
PubMed2000

4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) dyes modified for extended conjugation and restricted bond rotations.

Five new, constrained, aryl-substituted 4,4-difluoro-4-bora-3a, 4a-diaza-s-indacene (BODIPY) dyes (3f,g and 4h-j) were prepared and investigated to see if they have more favorable fluorescence characteristics than the unconstrained systems 2 that were prepared in previous studies. Dye types 3 and 4 have relatively rigid conformations caused by the heteroatom (3f and 3g) or ethylene bridge (4h-j) linkers that preclude free rotation of the substituted-benzene molecular fragments. In the event, the new dye types 3 and 4 have longer lambda(max abs) (620-660 nm) and lambda(max)(fluor) (630-680 nm) values than compounds 2. They also exhibit higher extinction coefficients (>100 000 M(-1) cm(-1), except for 3g). Their fluorescent quantum yields are high (up to 0.72 for 4j), with the exception of compound 3g, which has a quantum yield of only 0.05. The redox properties of dyes 3 and 4 have also been examined.

Boron Compounds↗
PubMed2006

Synthesis and reactivity of dichloroboryl complexes of platinum(II).

The reaction between [Pt(nbe)3] (nbe=norbornene), two equivalents of the phosphines PPh3, PMePh2 or PMe2Ph and 1 equivalent of BCl3 affords the platinum dichloroboryl species [PtCl(BCl2)(PPh3)2], [PtCl(BCl2)(PMePh2)2] and [PtCl(BCl2)(PMe2Ph)2]. All three complexes were characterised by X-ray crystallography and reveal that the boryl group lies trans to the chloride. With PMe3 as the phosphine, the complex [PtCl(BCl2)(PMe3)2] is isolated in high yield as a white crystalline powder although crystals suitable for X-ray crystallography were not obtained. Crystals were obtained of a product shown by X-ray crystallography to be the unusual dinuclear species [Pt2(BCl2)2(PMe3)4(micro-Cl)][BCl4] which reveals an arrangement in which two square planar platinum(II) centres are linked by a single bridging chloride which is trans to a BCl2 group on each platinum centre. The reaction of [PtCl(BCl2)(PMe3)2] with NEt3 or pyridine (py) affords the adducts [PtCl{BCl2(NEt3)}(PMe3)2] and [PtCl{BCl2(py)}(PMe3)2], respectively, both characterised spectroscopically. The reaction between [PtCl(BCl2)(PMe3)2] and either 4 equivalents of NHEt2 or piperidine (pipH) results in the mono-substituted boryl species [PtCl{BCl(NEt2)}(PMe3)2] and [PtCl{BCl(pip)}(PMe3)2], respectively, the former characterised by X-ray crystallography. Treatment of either [PtCl(BCl2)(PMe3)2] (in the presence of excess NEt3) or [PtCl{BCl(NEt2)}(PMe3)2] with catechol affords the B(cat) (cat=catecholate) derivative [PtCl{B(cat)}(PMe3)2] which is also formed in the reaction between [Pt(PMe3)4] and ClB(cat) and also from the slow decomposition of [Pt{B(cat)}2(PMe3)2] in dichloromethane over a period of months. The compound [Pt{B(cat)}2(PMe3)2] was prepared from the reaction between [Pt(PMe3)4] and B2(cat)2.

Boron Compounds↗
PubMed2006

Comparative molecular field analysis and comparative molecular similarity indices analysis of boron-containing human thymidine kinase 1 substrates.

Three-dimensional quantitative structure-activity relationship (3D-QSAR) using CoMFA and CoMSIA techniques was applied to evaluate 56 pyrimidine nucleosides as substrates of human thymidine kinase 1 (hTK1), 27 of them containing a carborane substituent either at the 3-, 5-, or 3'-position of the 2'-deoxyuridine scaffold. This is the first report describing 3D-QSAR studies of compounds containing boron atoms. Both CoMFA and CoMSIA models were derived from a training set of 47 molecules and the predictive capacity of the CoMSIA model was successfully validated by accurately calculating known phosphorylation rates of both boronated and non-boron hTK1 substrates that were not included in the training set. The optimal CoMSIA model provided the following values: q(2) 0.622, r(2) 0.983, s 0.165, and F 187.5. Contour maps obtained from the CoMSIA model were in agreement with the experimentally determined biological data.

Boron↗
PubMed1990

The selective inhibition of thrombin by peptides of boroarginine.

Peptides containing alpha-aminoboronic acids with neutral side chains are highly effective reaction intermediate analog inhibitors of the serine proteases leukocyte elastase, pancreatic elastase, and chymotrypsin. A protocol has been developed for the synthesis of peptides containing alpha-aminoboronic acids with a basic, 3-guanidinopropyl side chain (boroArg) to extend the range of these compounds to trypsin-like proteases. Ac-(D)Phe-Pro-boroArg-OH, Boc-(D)Phe-Pro-boroArg-OH, and H-(D)Phe-Pro-boroArg-OH were prepared as inhibitors of thrombin based on earlier observations that it has a high affinity for this sequence. All three boronic acids are highly effective, slow-binding inhibitors of thrombin, inhibiting it with final inhibition constants and association rates of: 41 pM, 5.5 x 10(6) M-1 s-1; 3.6 pM, 9.3 x 10(6) M-1 s-1; less than 1 pM, 8.0 x 10(6) M-1 s-1, respectively. Comparison of their binding at equilibrium to thrombin, plasma kallikrein, factor Xa, plasmin, and two-chain tissue plasminogen activator has shown that all three inhibitors have at least 2 orders of magnitude greater affinity for thrombin, with the exception of the acetyl derivative which has a 40-fold greater affinity for thrombin than kallikrein. The boroarginine peptides are effective in inhibiting the action of thrombin in rabbit plasma against its physiological substrates. Activated partial thromboplastin time was significantly prolonged in vitro by all of the inhibitors at concentrations of 50-200 nM. Prolongations of activated partial thromboplastin time were also observed in rabbits after intravenous (40-80 micrograms/kg or subcutaneous (0.20-2 mg/kg) injections of Ac-(D)Phe-Pro-boroArg-OH. Results indicate that this new class of synthetic thrombin inhibitors may be clinically useful as antithrombotic agents.

Blood Coagulation↗
PubMed1995

(+/-)-(N-alkylamino)benzazepine analogs: novel dopamine D1 receptor antagonists.

(+/-)-(N-Alkylamino)benzazepine analogs were prepared as novel dopamine D1 receptor antagonists to further elucidate the role of these receptor subtypes in the pharmacology and toxicology of cocaine. In the first series of compounds, (+/-)-7-chloro-8-hydroxy-3- [6-(N,N-dimethylamino)-hexyl]-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepi ne (15) showed the highest affinity (Ki = 49.3 nM) and subtype-selectivity for dopamine D1 over dopamine D2, 5-HT2a, and 5-HT2c receptors. Compounds 7a [(+/-)-7-Chloro-8-hydroxy-3-[4-(N,N-dimethylamino)butyl]-1-phenyl- 2,3,4,5-tetrahydro-1H-3-benzazepine], 11 [(+/-)-7-chloro-8-hydroxy-3-[6-[(N,N-dimethylamino)hexyl]-1- phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine-cyanoborane], and 15 were moderately potent dopamine D1 receptor antagonists as evidenced by their ability to block dopamine-stimulated adenylyl cyclase activity in rat caudate (predicted Ki values = 60, 34, and 21 nM, respectively). Compound 7a appears to be unique in that, despite its relatively potent inhibition of dopamine stimulated adenylyl cyclase, it demonstrated relatively weak binding affinity at the dopamine D1 receptors (Ki = 811 nM). Unlike previously reported N-alkylbenzazepines, where a significant loss in dopamine D1 receptor binding affinity was observed when successive increases in the alkyl side chain size at the benzazepine nitrogen were made, several of these novel N-alkylamino analogs demonstrated high-affinity binding with an optimal chain length of six carbons. This initial series of compounds appears to be identifying another binding domain on the dopamine D1 receptor protein that has not previously been characterized and that accepts an amino function. Further, these compounds may serve as templates for the design of peripherally active dopamine D1 receptor antagonists.

Animals↗
PubMed1999

Protein kinase C modulators bearing dicarba-CLOSO-dodecaborane as a hydrophobic pharmacophore.

The size and position of a hydrophobic moiety on a benzolactam skeleton, which reproduces the active conformation and biological activity of teleocidins, play an important role in the appearance of the activity. We have designed and synthesized benzolactams bearing dicarba-closo-dodecaborane. These compounds showed potent binding affinity to protein kinase C, providing a further example of the application of carborane as the hydrophobic pharmacophore of biologically active molecules.

Boron Compounds↗
PubMed2002

Molecular color sensors for monosaccharides.

[structure: see text] Boronic acid color sensor 2 undergoes a visible color change, from purple to pink, on the addition of monosaccharides in aqueous methanol at pH 8.21.

Aniline Compounds↗
PubMedDate not supplied

Boron-enriched streptavidin potentially useful as a component of boron carriers for neutron capture therapy of cancer.

A boron-enriched streptavidin has been prepared by chemical conjugation of a boron-rich compound, B(12)H(11)SH(2)(-) (BSH), to a genetically engineered streptavidin variant. The streptavidin variant used has 20 cysteine residues per molecule, derived from a C-terminal cysteine stretch consisting of five cysteine residues per subunit. Because natural streptavidin has no cysteine residues, the reactive sulfhydryl groups of the cysteine stretch serve as unique conjugation sites for sulfhydryl chemistry. BSH was conjugated irreversibly to the sulfhydryl groups of the streptavidin variant via a sulfhydryl-specific homobifunctional chemical cross-linker. Quantitative boron analysis indicates that the resulting streptavidin-BSH conjugate carries approximately 230 boron atoms/molecule. This indicates that the chemical conjugation of BSH to the streptavidin variant was highly specific and efficient because this method should allow the conjugation of a maximum of 240 boron atoms/streptavidin molecule. This boron-enriched streptavidin retained both full biotin-binding ability and tetrameric structure, suggesting that the conjugation of BSH has little, if any, effect on the fundamental properties of streptavidin. This boron-enriched streptavidin should be very useful as a component of targetable boron carriers for neutron capture therapy of cancer. For example, a monoclonal antibody against a tumor-associated antigen can be attached tightly to the boron-enriched streptavidin upon simple biotinylation, and the resulting conjugate could be used to target boron to tumor cells on which the tumor-associated antigen is overexpressed.

Animals↗