TOF-SIMS evidence of intercalated molecular gases and diffusion-limited reaction kinetics in an alpha particle-irradiated PTFE matrix

The chemical evolution of poly(tetrafluoroethylene) (PTFE) that is brought about by increasing levels of irradiation with alpha particles is accompanied by the emergence and proliferation of functionalized moieties. Families of reaction products specifically identified in the alpha-irradiated polymer matrix include hydride-, hydroxide-, and oxide-functionalized fluorocarbons. The data also indicate the emergence of hydrogen peroxide (H2O2) and hydrazine (N2H4), but no distinct evidence suggesting the formation of perfluorinated amines, amides, or cyanogens is found. In this article we substantiate the speciation of emergent species and reveal evidence of intercalated molecular gases with which alpha particle-generated radicals may react to form the observed products. Furthermore, we present evidence to suggest that the kinetics of alpha particle-induced reaction is limited by the diffusion of radicals within the polymer matrix. That is to say, chemical additives in the polymer matrix are shown to be scavengers of H*, O*, and F* radicals and limit the rates of reaction that produce functionalized fluorocarbon moieties. Above a threshold dose of alpha particles, the concentration of radicals exceeds that of the scavenger species, and free radical diffusion commences as evidenced by a sudden increase in the yield of reaction products. Samples of PTFE were irradiated to alpha doses in the range of 10(7) to 5 x 10(10) rad with 5.5 MeV 4He2+ ions from a tandem accelerator. Residual gas analysis (RGA) was utilized to monitor the liberation of molecular gases from PTFE during alpha particle irradiation of samples in vacuum. Static time-of-flight SIMS (TOF-SIMS), equipped with a 20 keV C60+ source, was employed to probe chemical changes as a function of alpha particle irradiation. Chemical images and high-resolution mass spectra were collected in both the positive and negative polarities.     

Stereoselective alkylation of alpha,beta-unsaturated imines via C-H bond activation

The stereoselective alkylation of alpha,beta-unsaturated imines via C-H activation followed by imine hydrolysis produces tri- and tetrasubstituted alpha,beta-unsaturated aldehydes. In the presence of a rhodium catalyst, alpha,beta-unsaturated N-benzyl imines derived from methacrolein, crotonaldehyde, and tiglic aldehyde undergo directed C-H activation at the beta-position and react with terminal alkenes and alkynes to form the tri- and tetrasubstituted alpha,beta-unsaturated imines with very high stereoselectivity. Hydrolysis to provide alpha,beta-unsaturated aldehydes can be performed under carefully controlled conditions that maintain the stereochemistry of the beta-alkylated imine products. Alternatively, for beta-alkylation products of the N-benzyl imine of methacrolein, hydrolysis can be performed under conditions that provide complete isomerization to the E isomer.     

Stereoselective desymmetrisation of prochiral alpha,alpha-dicyanoalkenes via domino Michael-Michael addition reactions

The desymmetrisation of prochiral alpha,alpha-dicyanoalkenes via tandem Michael-Michael addition reactions with alpha,beta-unsaturated ketones catalysed by 9-amino-9-deoxyepicinchona alkaloids was investigated, from which bicyclic products bearing four stereogenic centers were afforded in a single operation with high stereoselectivities (>99% de, up to >99.5% ee).     

Extremely Efficient Chiral Induction in Conjugate Additions of p-Tolyl alpha-Lithio-beta-(trimethylsilyl)ethyl Sulfoxide and Subsequent Electrophilic Trapping Reactions

Reaction of p-tolyl alpha-lithio-beta-(trimethylsilyl)ethyl sulfoxide with alpha,beta-unsaturated esters gave the conjugate addition products as a single diastereomer. The intermediate enolates were subsequently trapped with various alkyl halides or aldehydes to give the products with extremely high stereoselectivity. The reaction with alpha,beta-unsaturated ketones also proceeded with high diastereoselectivity. Protolysis of the enolates derived from the alpha-methyl-alpha,beta-unsaturated esters gave the products with high stereoselectivity. The stereo- and regioselective elimination of the sulfinyl group gave chiral homoallylic carboxylates.     

Sensitized photooxidation of furanoeremophilane with singlet oxygen and their biogenetic relationship

In an attempt to explore the biogenetic relationship of furanoeremophilane derivatives and eremophilan-8alpha,12-olides, produced in Ligularia and their structure-activity relationship, we studied the photosensitized oxidation of furanoeremophilane-type sesquiterpenes. Under the condition of several solvents solution Irradiation with a 200 W incandescent lamp of furanoeremophilan-14beta,6alpha-olide isolated from Ligularia vellerea, in various solutions with methylene blue, rose bengal, toluidine blue and safranine T gave several products. The products were isolated by chromatographic procedure and their structures were elucidated as eremophilan-14beta,6alpha,8alpha,12-diolide derivatives by NMR, IR and MS methods. A reaction mechanism has been proposed.     

Metabolism of three trichothecene mycotoxins, T-2 toxin, diacetoxyscirpenol and deoxynivalenol, by bovine rumen microorganisms

The three trichothecene mycotoxins T-2 toxin, diacetoxyscirpenol (DAS) and deoxynivalenol (DON) were incubated in vitro for 12, 24 and 48 h with rumen microorganisms obtained from a fistulated dairy cow. Gas chromatographic and gas chromatographic-mass spectrometric analyses of extracts indicated all three toxins were biotransformed to a variety of deepoxy and deacylated products. DON was partially converted to a product identified as deepoxy DON. DAS was rapidly converted to four products including 15-monoacetoxyscirpenol (MAS), scirpentriol and two new compounds identified as 15-acetoxy-3 alpha,4 beta-dihydroxytrichothec-9,12-diene (deepoxy MAS) and 3 alpha,4 beta,15-trihydroxytrichothec-9,12-diene (deepoxy scirpentriol). T-2 toxin was also completely biotransformed to the products HT-2, T-2 triol and two new metabolites identified as 15-acetoxy-3 alpha,4 beta-dihydroxy-8 alpha-(3-methylbutyryloxy) trichothec-9,12-diene (deepoxy HT-2) and 3 alpha,4 beta,15-trihydroxy-8 alpha-(3-methylbutyryloxy)trichothec-9,12-diene (deepoxy T-2 triol).     

Synthesis of highly enantioenriched all-carbon quaternary centers: conjugate additions of chiral organolithium nucleophiles to alpha,alpha-dinitrile beta,beta-disubstituted olefins

[reaction: see text]. Highly enantioenriched quaternary centers are obtained by the reaction of chiral lithiated intermediates complexed to (-)-sparteine with tetrasubstituted, alpha,alpha-dinitrile activated olefins. Lithiated N-Boc-N-Aryl benzylamine furnishes products with drs from 78:22 to 95:5, with ers exceeding 94:6. Lithiated N-Boc-N-Aryl allylamine reactants provide enecarbamate products with drs from 55:45 to 99:1, with ers ranging from 87:13 to 97:3.     

7-Oxodihydrokarounidiol [7-oxo-D:C-friedo-olean-8-ene-3 alpha,29-diol], a novel triterpene from Trichosanthes kirilowii.

The structure of 7-oxodihydrokarounidiol [7-oxo-D:C-friedo-olean-8-ene-3 alpha,29-diol], isolates from the seeds of Trichosanthes kirilowii (Cucurbitaceae), was determined by chemical correlation with karounidiol [D:C-friedo-oleana-7,9(11)-diene-3 alpha,29-diol] from the same source. Two other natural products, viz. bryonolic acid (3 beta-hydroxy-D:C-friedo-olean-8-en-29-oic acid) and bryononic acid (3-oxo-D:C-friedo-olean-8-en-29-oic acid), were also correlated with karounidiol.     

Identification of reaction products from the pyridinium dichromate derivatization of prostaglandins by high-performance liquid chromatography and direct chemical ionization mass spectrometry

The reaction products from the oxidation of prostaglandins with pyridinium dichromate have been identified by direct chemical ionization mass spectrometry of the underivatized compounds after separation by reversed-phase high-performance liquid chromatography and ultraviolet diode-array detection. The thermal influence on the reproducibility of the dehydration patterns of the mass spectra was studied. The main products from the prostaglandins E1, E2, F1 alpha and F2 alpha were the corresponding 15-oxo derivatives. Minor amounts of the 9,11,15-trioxoprostaglandin were formed from PGE, while the oxidation of PGF was less selective, yielding additional dioxo derivatives. Addition of water to the reagent reduced the reactivity, but increased the selectivity in favour of the formation of 15-oxo-PGF during the oxidation of PGF.     

Synthesis of enantiopure alpha,alpha-disubstituted amino acids from the asymmetric Strecker reaction products of aldehydes

Treatment of the enolates of 4 generated from the asymmetric Strecker reaction products with alkyl halides or aldehydes provided the corresponding functionalized products with high diastereoselectivity. Deprotection of these products afforded the corresponding enantiopure alpha,alpha-dialkyl amino acids.     

Potential bile acid metabolites. 25. Synthesis and chemical properties of stereoisomeric 3alpha,7alpha,16- and 3alpha,7alpha,15-trihydroxy-5beta-cholan-24-oic acids

Epimeric 3alpha,7alpha,16- and 3alpha,7alpha,15-trihydroxy-5beta-cholan-24-oic acids and some related compounds were synthesized from chenodeoxycholic acid (CDCA) and ursodeoxycholic acid (UDCA), respectively. The key reaction involved one-step remote oxyfunctionalization of unactivated methine carbons at C-17 of CDCA and at C-14 of UDCA as their methyl ester-peracetate derivatives with dimethyldioxirane (DMDO). After dehydration of the resulting 17alpha- and 14alpha-hydroxy derivatives with POCl(3) or conc. H(2)SO(4), the respective Delta(16)- and Delta(14)-unsaturated products were subjected to hydration via hydroboration followed by oxidation to yield the 3,7,16- and 3,7,15-triketones, respectively. Stereoselective reduction of the respective triketones with tert-butylamine-borane complex afforded the epimeric 3alpha,7alpha,16- or 3alpha,7alpha,15-trihydroxy derivatives exclusively. A facile formation of the corresponding epsilon-lactones between the side chain carboxyl group at C-24 and the 16alpha- (or 16beta-) hydroxyl group in bile acids is also clarified.     

Diastereo- and enantioselective direct catalytic aldol reaction of 2-hydroxyacetophenones with aldehydes promoted by a heteropolymetallic complex: catalytic asymmetric synthesis of anti-1,2-diols

An anti-selective direct catalytic asymmetric aldol reaction of 2-hydroxyacetophenones with aldehydes is described. The reaction is catalyzed by a heteropolymetallic complex to afford anti-alpha,beta-dihydroxy ketones as the major diastereomer with excellent enantioselectivity. The use of 2-hydroxyacetophenones bearing electron-donating groups at the phenyl moiety enabled efficient transformation of the aldol products (alpha,beta-dihydroxy ketones) into the corresponding alpha,beta-dihydroxy ester derivatives via Baeyer-Villiger oxidation. A plausible reaction mechanism is also discussed based on the stereochemistry of the products.     

Asymmetric synthesis of beta-amino acid derivatives incorporating a broad range of substitution patterns by enolate additions to tert-butanesulfinyl imines

Addition of Ti(Oi-Pr)(3) ester enolates to tert-butanesulfinyl aldimines and ketimines provided beta-substituted, alpha,beta- and beta,beta-disubstituted, alpha,beta,beta- and alpha,alpha,beta-trisubstituted, and alpha,alpha,beta,beta-tetrasubstituted beta-amino acid derivatives in high yields and with high diastereoselectivites. The N-sulfinyl-beta-amino ester products were further employed as versatile intermediates for both standard solution-phase and solid-phase synthetic transformations, including the synthesis of beta-peptide foldamers.     

Automated structure elucidation of two unexpected products in a reaction of an alpha,beta-unsaturated pyruvate

The reaction between an alpha,beta-unsaturated pyruvate and ethyl diazoacetate (EDA) yielded two unexpected products. The structures of these products were determined by automated elucidation of the chemical structures using spectroscopic inputs of a series of 1D and 2D NMR data using the computer program ACD/Structure Elucidator, StrucEluc. The formation of these products is rationalised. Their structures were also confirmed by x-ray crystallography.     

Practical synthesis of optically active alpha,alpha-disubstituted malonamic acids through asymmetric hydrolysis of malonamide derivatives with Rhodococcus sp. CGMCC 0497

A variety of alpha,alpha-disubstituted malonamides undergo enantioselective hydrolysis with Rhodococcus sp. CGMCC 0497 to give challenging enantiopure alpha,alpha-disubstituted malonamic acids with up to >99% enantiomeric excesses and 98% chemical yields. The enantioselectivity originated from the effects of a highly enantioselective amidase. The products could be converted to valuable (R)- or (S)-alpha,alpha-dialkylated amino acids after routine conversions.     

Decomposition of 2-(1-hydroxybenzyl)thiamin. Ruling out stepwise cationic fragmentation

[reaction: see text] The rapid fragmentation of 2-(1-hydroxybenzyl)thiamin (1) is initiated by transfer of a proton from C2alpha to give an enamine. The subsequent irreversible process can be written as a concerted (or stepwise) rearrangement involving migration of the hydroxyl hydrogen to the methylene bridge. An attractive alternative is internal addition of C2alpha to the pyrimidine, generating a carbocation. However, addition of azide to the reaction solution, which could trap the carbocation, has no effect on the rate or products of reaction.     

Asymmetric total syntheses of (+)-3-(z)-laureatin and (+)-3-(z)-isolaureatin by "lone pair-lone pair interaction-controlled" isomerization

The first asymmetric total syntheses of the dihalogenated medium-sized dioxabicyclic marine natural products (+)-3-(Z)-isolaureatin (1) and (+)-3-(Z)-laureatin (2) have been accomplished. Notable features of the highly stereo-, regio-, and chemoselective syntheses of these alpha,alpha'-trans-oxocene natural products include an intramolecular amide enolate alkylation to construct the alpha,alpha'-cis-oxocene, novel "lone pair-lone pair interaction-controlled" epimerizations to the alpha,alpha'-trans-oxocenes, various strategies for stereoselective introduction of halogen atoms, and novel olefin cross-metatheses for construction of the (Z)-enyne systems.     

Organocatalytic asymmetric conjugate addition of nitroalkanes to alpha,beta-unsaturated enones using novel imidazoline catalysts

A new catalytic enantioselective conjugate addition of nitroalkanes to acyclic alpha,beta-unsaturated enones catalyzed by novel organic catalysts has been developed. A series of chiral amines has been tested as catalysts for the addition of 2-nitropropane to benzylideneacetone, and it is found that a novel imidazoline catalyst, prepared from phenylalanine, can catalyze a highly enantioselective 1,4-addition reaction. The reaction of various acyclic and cyclic nitroalkanes was found to proceed well with enantioselectivities up to 86% ee, and enantiopure products can be obtained by recrystallization. The potential of the reaction is documented by the reaction of a series of substituted alpha,beta-unsaturated enones with different nitroalkanes. Furthermore, the synthetic applicability of the reaction is demonstrated by the formation of optically active functionalized pyrrolines and pyrrolidines by reductive amination of the products. On the basis of the absolute configuration of the conjugate addition products, the mechanism for the reaction is discussed and a transition state proposed.     

Kinetic resolution of racemic lactones by conjugate additions of allylic organolithium species: direct formation of three contiguous centers with high diastereo- and enantioselectivities

[reaction: see text] Kinetic resolution of racemic alpha,beta-unsaturated lactones by the organolithium species produced from asymmetric lithiation of N-Boc-N-(p-methoxyphenyl)cinnamylamine provides conjugate addition products with three contiguous stereogenic centers in yields of 62-77% with diastereomeric ratios from 75:25 to >99:1 and enantiomeric ratios for the major diastereomers from 94:6 to 98:2.     

Using 211At as internal alpha radiolysis source allowing for simple detection of radiolysis products

The determination of radiolysis products is an important field both for the basic understanding of the radiolysis process and for process development. The latter case mainly dealing with processes for handling radioactive wastes. There are several kinds of radiolysis processes that originate from the different kinds of radiation. Gamma rays and high-energy beta has a high ability to penetrate barriers while alpha irradiation in principle has to be performed with the radiation emitting nuclide inside the actual sample. This can be a problem since most laboratories able to identify radiolysis products cannot handle alpha contaminated samples. In this paper we suggest the use of ²¹¹At as internal alpha emitting radionuclide. Due to its short half-life and decay to more or less stable daughters the radiolysis products may be examined using normal equipment without causing contamination.