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PubMed1999

Catalytic Approach for the Formation of Optically Active Allyl alpha-Amino Acids by Addition of Allylic Metal Compounds to alpha-Imino Esters.

A new catalytic enantioselective approach for the formation of allyl alpha-amino acid derivatives by reaction of N-tosyl alpha-imino esters with allyl stannanes and silanes catalyzed by chiral copper(I) complexes has been developed. A series of different BINAP and phosphine-oxazoline (P,N) ligands have, in combination with various Lewis acids, been tested as chiral catalysts for allylation of N-tosyl alpha-imino esters. It has been found that both type of ligands, in combination with copper(I) salts, give highly valuable unsaturated alpha-amino acid derivatives. The reaction has been investigated for different allyl stannanes and silanes, and it has been found that tri-n-butyl allyl stannane gives the best results of the simple allyl compounds tested, leading to gamma,delta-unsaturated alpha-amino acid derivatives in up to 94% yield and with up to 83% ee, which can be improved to be >95% ee by recrystallization. The reaction has also been investigated using different acyclic and cyclic allyl stannanes leading to various types of unsaturated alpha-amino acid derivatives in very high yield (up to 95%) and with up to 98% ee. The stereochemistry and absolute configurations of the allyl alpha-amino acid derivatives have been determined by X-ray analysis, and it is suggested that the reaction takes place as an ene-like reaction.

Journal Article↗
PubMed2004

Nitrogen heterocycles via palladium-catalyzed carbocyclization. Formal synthesis of (+)-alpha-allokainic acid.

[reaction: see text] The Pd-catalyzed carbocyclization of ketoamides was investigated and found to be highly dependent on the phosphine ligand as well as the presence of coordinating counterions. Nitrogen heterocycles were formed without erosion of the stereochemical integrity. The utility of the lactam products was demonstrated by the formal synthesis of (+)-alpha-allokainic acid.

Catalysis↗
PubMed2001

Acidity trends in alpha,beta-unsaturated alkanes, silanes, germanes, and stannanes.

The gas-phase acidity of ethyl-, vinyl-, ethynyl-, and phenyl-substituted silanes, germanes, and stannanes has been measured by means of FT-ICR techniques. The effect of unsaturation on the intrinsic acidity of these compounds and the corresponding hydrocarbons was analyzed through the use of G2 ab initio and DFT calculations. In this way, it was possible to get a general picture of the acidity trends within group 14. As expected, the acid strength increases down the group, although the acidity differences between germanium and tin derivatives are already rather small. As has been found before for amines, phosphines, and arsines, the carbon, silicon, germanium, and tin alpha,beta-unsaturated compounds are stronger acids( )than their saturated analogues. The acidifying effect of unsaturation is much larger for carbon than for Si-, Ge-, and Sn-containing compounds. The allyl anion is better stabilized by resonance than its Si, Ge, and Sn analogues, [CH(2)(-)(delta)--CH(+)(delta)(') --CH(2)(-)(delta)](-) vs [CH(2)(-)(delta)()II = CH(-)(delta)()III - XH(2)(-)(delta)()IV](-) (X = Si, Ge, Sn). The enhanced acid strength of unsaturated compounds is essentially due to a greater stabilization of the anion with respect to the neutral, because the electronegativity of the alpha,beta-unsaturated carbon group increases with its degree of unsaturation. The phenyl derivatives are systematically weaker acids than the corresponding ethynyl derivatives by 15-20 kJ mol(-)(1). Experimentally, toluene acidity is very close to that of propyne, because the deprotonation of propyne takes place preferentially at the =CH group rather than at the -CH(3) group.

Journal Article↗
PubMed2003

Resolved chiral 3,4-diazaphospholanes and their application to catalytic asymmetric allylic alkylation.

One-pot condensation of PhPH2, phthaloyl chloride, and the azine of 2-carboxybenzaldehyde (1) results in the new phosphine, rac-N,N'-phthaloyl-2,3-(2-carboxyphenyl)-phenyl-3,4-diazaphospholane (rac-2), in 88% yield. Resolution via selective crystallization of the diastereomeric alpha-methylbenzylamine salts followed by coupling with amino acids and other amines provides rapid access to new collections of chiral phosphines (3). Pd-catalyzed alkylation of 1,3-dimethylallyl acetate and 1,3-diphenylallyl acetate at room temperature in the presence of 3 exhibits enantioselectivities as high as 92% ee and 97% ee, respectively, with strong sensitivity to the nature of the amino acid appendages. The presence of PF6- salts profoundly affects both the yield and the selectivity of catalytic allylic alkylation.

Journal Article↗
PubMed2004

First derivatives of myo-inositol 1,4,6-trisphosphate modified at positions 2 and 3: structural analogues of D-myo-inositol 1,4,5-trisphosphate.

Novel, structurally modified potential mimics of the second messenger D-myo-inositol 1,4,5-trisphosphate, based on the biologically active regioisomer D-myo-inositol 1,4,6-trisphosphate, were synthesised. DL-5-O-Benzyl-1,4,6-tri-O-p-methoxybenzyl-myo-inositol was the key intermediate for the preparation of the following compounds: DL-3-deoxy-, DL-3-deoxy-2-O-methyl-, DL-3-O-(2-hydroxyethyl)-, DL-3-O-(3-hydroxypropyl)- and DL-3-O-(4-hydroxybutyl)-myo-inositol 1,4,6-trisphosphate. DL-1,4,6-Tri-O -allyl-5-O-benzyl-myo-inositol was used to prepare DL-2-O-methyl-myo-inositol 1,4,6-trisphosphate. Deoxy-compounds were prepared by reduction of the corresponding tosylated intermediate using Super Hydride. The hydroxyalkyl groups were introduced at the C-3 of myo-inositol using the corresponding benzyl protected hydroxy alkyl bromide via the cis-2,3-O-dibutylstannylene acetal. Methylation and benzylation at C-2 was accomplished using methyl iodide and benzyl bromide, respectively, in the presence of sodium hydride. Deblocking of p-methoxybenzyl groups was accomplished with TFA in dichloromethane and the allyl groups were removed by isomerisation to the cis-prop-1-enyl derivative, which was hydrolysed under acidic conditions to give the corresponding 1,4,6-triol. The 1,4,6-triols were phosphitylated with the P(III) reagent bis(benzyloxy)(diisopropylamino)phosphine in the presence of 1H-tetrazole then oxidised with 3-chloroperoxybenzoic acid followed by deblocking by hydrogenolysis to give DL-2-O-methyl-, DL-3-O-deoxy-, DL-3-O-deoxy-2-O-methyl-, DL-3-O-(2-hydroxyethyl)-, DL-3-O-(3-hydroxypropyl)- and DL-3-O-(4-hydroxybutyl)-myo-inositol 1,4,6-trisphosphate, respectively.

Benzyl Compounds↗
PubMed2007

Evaluation of microwave irradiation for analysis of carbonyl sulfide, carbon disulfide, cyanogen, ethyl formate, methyl bromide, sulfuryl fluoride, propylene oxide, and phosphine in hay.

Fumigant residues in hay were "extracted" by microwave irradiation. Hay, in gastight glass flasks, was placed in a domestic microwave oven, and fumigants were released into the headspace by microwave irradiation. Power settings for maximum release of fumigants were determined for carbonyl sulfide (COS), carbon disulfide (CS(2)), cyanogen (C(2)N(2)), ethyl formate (EF), methyl bromide (CH(3)Br), sulfuryl fluoride (SF), propylene oxide (PPO), and phosphine (PH(3)). Recoveries of fortified samples were >91% for COS, CS(2), CH(3)Br, SF, PPO, and PH(3) and >76% for C(2)N(2) and EF. Completeness of extraction was assessed from the amount of fumigant retained by the microwaved hay. This amount was determined from further microwave irradiation and was always small (<5% of the amount obtained from the initial procedure). Limits of quantification were <0.1 mg/kg for COS, CS(2), C(2)N(2), EF, and PH(3) and <0.5 mg/kg for CH(3)Br, SF, and PPO. These low limits were essentially due to the absence of interference from solvents and no necessity to inject large-volume gas samples. The microwave method is rapid and solvent-free. However, care is required in selecting the appropriate power setting. The safety implications of heating sealed flasks in microwave ovens should be noted.

Animal Feed↗
PubMed1985

18-Substituted steroids: synthesis of 18-hydroxycortisol (11 beta,17 alpha,18,21-tetrahydroxy-4-pregnene-3,20-dione) and 18-hydroxycortisone (17 alpha,18,21-trihydroxy-4-pregnene-3,11,20-trione).

The isolation of 18-hydroxycortisol from the urine of patients with primary aldosteronism was recently described and no synthetic procedure was available for its preparation. The C-13 angular methyl group of prednisolone-17 alpha,21-acetonide-11 beta-nitrite was functionalized by photolysis in the presence of oxygen to give the product 18-hydroxy-prednisolone-17 alpha,21-acetonide-18-nitrate. The 18-nitrate was reduced with zinc and ammonium acetate to the corresponding 18-hydroxy compound, 18-hydroxy-prednisolone-17 alpha,21-acetonide. Homogeneous hydrogenation with Tris(triphenyl-phosphine)rhodium (I) chloride as catalyst resulted in the formation of 18-hydroxy-cortisol-17 alpha,21-acetonide. Acid hydrolysis of the latter compound gave 18-hydroxycortisol. Oxidation of 18-hydroxycortisol-17 alpha,21-acetonide with pyridinium dichromate followed by acid hydrolysis gave 18-hydroxycortisone. The 18-hydroxylated steroids exist as the 18,21-hemiacetals. Catalytic reduction with tritium gas with Tris(triphenyl-phosphine)rhodium (I) chloride of 18-hydroxyprednisolone-17 alpha,21-acetonide and acid hydrolysis gave [1,2(3)H]18-hydroxycortisol.

Chemical Phenomena↗
PubMed2004

Pentacoordinate nickel(II) complexes double bridged by phosphate ester or phosphinate ligands: spectroscopic, structural, kinetic, and magnetic studies.

The bis(phosphatediester)-bridged complexes [[Ni([12]aneN(3))(mu-O(2)P(OR)(2))](2)](PF(6))(2) [[12]aneN(3)=Me(3)[12]aneN(3), 2,4,4-trimethyl-1,5,9-triazacyclododec-1-ene; R=Me (1), Bu (2), Ph (3), Ph-4-NO(2) (4); [12]aneN(3)=Me(4)[12]aneN(3), 2,4,4,9-tetramethyl-1,5,9-triazacyclododec-1-ene; R=Me (5), Bu (6), Ph (7), Ph-4-NO(2) (8)] were prepared by hydrolysis of the phosphate triester with the hydroxo complex [[Ni([12]aneN(3))(mu-OH)](2)](PF(6))(2) or by acid-base reaction of the dialkyl or diaryl phosphoric acid and the above hydroxo complex. The acid-base reaction was also used to synthesise the phosphinate-bridged complexes [[Ni([12]aneN(3))(mu-O(2)PR(2))](2)](PF(6))(2) [[12]aneN(3)=Me(3)[12]aneN(3), R=Me (9), Ph (10); [12]aneN(3)=Me(4)[12]aneN(3), R=Me (11), Ph (12)]. The molecular structures of complexes 2, 3 and 12 were established by single crystal X-ray diffraction studies. The eight-membered rings defined by the nickel atoms and the bridging ligands show distorted twist-boat, chair and boat-boat conformations in 2, 3 and 12, respectively. The experimental susceptibility data for compounds 2, 3 and 12 were fitted by least-squares methods to the analytical expression given by Ginsberg. The best fit was obtained with values of J=-0.11 cm(-1), D=-9.5 cm(-1) and g=2.20 for 2; J=-0.97 cm(-1), D=-9.3 cm(-1) and g=2.21 for 3; and J=-0.14 cm(-1), D=-11.9 cm(-1) and g=2.195 for 12. The magnetic-exchange pathways must involve the phosphate/phosphinate bridges, because these favour antiferromagnetic interactions. The observation of a higher exchange parameter for compound 3 is a consequence of a favourable disposition of the O-P-O bridges. The kinetics for the hydrolysis of TNP (tris(4-nitrophenyl)phosphate) with the dinuclear nickel(II) hydroxo complex [[Ni(Me(3)[12]aneN(3))(mu-OH)](2)](PF(6))(2) was studied by UV-visible spectroscopy. The proposed mechanism for TNP-promoted hydrolysis can be described as one-substrate/two-product, and can be fitted to a Michaelis-Menten equation.

Esters↗
PubMedDate not supplied

Phosphine-containing HYNIC derivatives as potential bifunctional chelators for (99m)Tc-labeling of small biomolecules.

Two prototype phosphine-containing HYNIC chelators, HYNIC-Kp-DPPB and HYNIC-Ko-DPPB (HYNIC = 6-hydrazinonicotinamide; K = lysine; and DPPB = diphenylphosphine-benzoic acid), have been synthesized and characterized by NMR ((1)H, (13)C, and (31)P) and LC-MS. Macrocyclic (99m)Tc complexes, [(99m)Tc(HYNIC-Ko-TPPB)(tricine)] and [(99m)Tc(HYNIC-Kp-DPPB)(tricine)], were prepared by reacting the phosphine-containing HYNIC chelator with (99m)TcO(4)(-) in the presence of excess tricine and stannous chloride. Results from this study clearly demonstrated that both HYNIC-Kp-DPPB and HYNIC-Ko-DPPB are able to form highly stable macrocyclic (99m)Tc complexes, [(99m)Tc(HYNIC-Ko-TPPB)(tricine)] and [(99m)Tc(HYNIC-Kp-DPPB)(tricine)], when tricine is used as the coligand. Radio-HPLC data suggest that the complex [(99m)Tc(HYNIC-Kp-DPPB)(tricine)] exists as only one detectable isomer in solution while the complex [(99m)Tc(HYNIC-Ko-DPPB)(tricine)] has three isomers. It was also found that three isomers of [(99m)Tc(HYNIC-Ko-DPPB)(tricine)] interconvert at elevated temperatures, suggesting that the presence of these isomers might be due conformational changes in the macrocyclic Tc chelate. The LC-MS data for both macrocyclic (99m)Tc complexes are completely consistent with the proposed composition. The phosphine-containing HYNIC chelators described in this study may have the potential as bifunctional chelators for (99m)Tc labeling of small biomolecules.

Chromatography, High Pressure Liquid↗
PubMed2004

Intramolecular hydroboration of unsaturated phosphine boranes.

Homoallylic phosphine boranes undergo intramolecular hydroboration upon activation by triflic acid. The reaction occurs via an intermediate B-trifluorosulfonyloxyborane complex such as 15, followed by S(N)1-like or S(N)2-like displacement of the triflate leaving group, apparently leading to the formation of a four-center transition state. In the case of trisubstituted double bonds, as in the substrates 29 and 32, ionic hydrogenation of the alkene competes with internal hydroboration.

Journal Article↗
PubMed2000

Phosphine generation by mixed- and monoseptic-cultures of anaerobic bacteria.

A microbial basis for bioreductive generation of phosphine is proposed, which could account at least in part for the presence of this toxic gas in natural anaerobic environments and in sewage and landfill gases. Phosphine generation under anaerobic growth conditions was dependent upon both the culture inoculum source (animal faeces) and enrichment culture conditions. Phosphine was detected in headspace gases from mixed cultures under conditions promoting fermentative growth of mixed acid and butyric acid bacteria, either in the presence or absence of methane generation. Monoseptic cultures of certain mixed acid fermentors (Escherichia coli, Salmonella gallinarum, and Salmonella arizonae) and solvent fermentors (Clostridium sporogenes, Clostridium acetobutyricum and Clostridium cochliarium) also generated phosphine. Such fermentative bacteria participate in the multi-stage process of methanogenesis in nature. Generation of phosphine by these bacteria, rather than by methanoarchaea themselves, could explain the apparent correlation between methanogenesis and the formation of phosphine in nature.

Bacteria, Anaerobic↗
PubMed2003

Rhodium-catalyzed addition of arylboronic acids to alkynyl aza-heteroaromatic compounds in water.

Alkynyl heteroaromatic compounds reacted with arylboronic acids to give addition products in the presence of a rhodium catalyst. The best results were obtained when a novel pyridine-substituted water-soluble phosphine ligand was used. The reactions proceed to give trisubstituted alkenes from various arylboronic acids and alkynyl heteroaromatic compounds with high regioselectivity. Only alkynes with a nitrogen atom in proximity to the triple bond were converted to the corresponding alkenes, as expected for a chelation-controlled addition.

Journal Article↗
PubMed2005

Synthesis and pharmacological activities of amine-boranes.

A number of amine-boranes and related derivatives possess a wide range of biological activities including antineoplastic, antiviral, hypolipidemic, anti-inflammatory activities, anti-osteoporotic and dopamine receptor antagonist activities. The compounds include borane complexes of alpha-amino acids, aromatic, aliphatic and heterocyclic amines, and nucleosides. The syntheses of amine-borane derivatives are generally carried out by first preparing a tertiary amine- or phosphine-cyano- or carboxyborane to serve as a borane donor for a subsequent Lewis acid exchange reaction. Borane adducts of simple aliphatic amines, heterocyclic amines and nucleic acids demonstrated potent cytotoxic activity in vitro and in vivo against murine and human tumor models. These boron-containing compounds were shown to inhibit DNA synthesis; such inhibition was caused primarily by reducing de novo purine biosynthesis via inhibition of PRPP amidotransferase, IMP dehydrogenase and dihydrofolate reductase activities. Aliphatic, heterocyclic and nucleoside amine-boranes have also been shown to possess hypolipidemic activity in mice and rats. Many boron derivatives from different chemical classes demonstrated both cytotoxic and hypolipidemic activities. They decreased low-density lipoprotein (LDL) cholesterol while increasing high-density lipoprotein (HDL) cholesterol levels. The mode of action of these compounds in the 50-100 microM concentration range appeared to be by increasing lipid excretion from the body and by inhibiting rate-limiting enzyme activities for the de novo synthesis of lipids and cholesterol (e.g., phosphatidylate phosphohydrolase, ATP-dependent citrate lyase, cytoplasmic acetyl coenzyme A [CoA] synthetase, HMG CoA reductase, and acetyl CoA carboxylase). Selected amine-boranes (e.g., trimethylamine-cyanoborane, N-methylmorpholine-cyanoborane, and the base-boronated 2'-deoxynucleosides) have anti-inflammatory, analgesic, anti-arthritic and anti-osteoporotic activities.

Animals↗
PubMed2000

Modeling of Enterococcus faecalis D-alanine:D-alanine ligase: structure-based study of the active site in the wild-type enzyme and in glycopeptide-dependent mutants.

A model for the 3-D structure of Enterococcus faecalis D-Ala:D-Ala ligase was produced using the X-ray structure of the Escherichia coli enzyme complexed with ADP and the methylphosphinophosphate inhibitor as a template. The model passed critical validation criteria with an accuracy similar to that of the template crystallographic structure and showed that ADP and methylphosphinophosphate were positioned in a large empty pocket at the interface between the central and the C-terminal domains, as in E. coli. It evidenced the residues important for substrate binding and catalytic activity in the active site and demonstrated a large body of conserved interactions between the active sites of the E. faecalis and the E. coli D-Ala:D-Ala ligase, the major differences residing in the balance between the hydrophobic and aromatic environment of the adenine. The model also successfully explained the inactivity of four spontaneous mutants (D295 --> V, which impairs interactions with Mg2+ and R293, which are both essential for binding and catalytic activity; S319 --> I, which perturbs recognition of D-Ala2; DAK251-253 --> E, in which the backbone conformation in the vicinity of the deletion remains unaltered but phosphate transfer from ATP is perturbed because of lack of K253; T316 --> I, which causes the loss of a hydrogen bond affecting the positioning of S319 and therefore the binding of D-Ala2). Since D-Ala:D-Ala ligase is an essential enzyme for bacteria, this approach, combining molecular modeling and molecular biology, may help in the design of specific ligands which could inhibit the enzyme and serve as novel antibiotics.

Adenosine Diphosphate↗
PubMed2003

The effects of oxidative stress on mitochondrial transmembrane potential in retinal ganglion cells.

Retinal ganglion cells (RGCs) are central neurons that undergo apoptosis after axonal injury. As the relationship between mitochondrial and oxidative signaling of apoptosis in neuronal systems is unclear, we sought to achieve a better understanding of the interplay of these two pathways by investigating the effect of direct oxidative stress on mitochondrial membrane potential in cultured RGCs, as measured with the dual-emission probe JC-1. Treatment with hydrogen peroxide caused RGC mitochondrial depolarization. Several pharmacological treatments were used to define the mechanism. Whereas cycloheximide, tris(2-carboxyethyl)phosphine, and cyclosporin A were unable to prevent the depolarization, bongkrekic acid significantly reduced the severity of the depolarization. This suggests that the hydrogen peroxide-induced depolarization may act through mitochondrial permeability transition pore opening independent of thiol oxidation, and may be preventable under certain conditions.

Animals↗