Intramolecular electrophilic rearrangements in saturated acyclic systems. Reactivity of the zwitterion derived from triisopropylphosphine and ethyl 2-cyanoacrylate with respect to different types of electrophiles

The reactions of the zwitterion derived from triisopropylphosphine and ethyl 2-cyanoacrylate with mercuric chloride and aryl isothiocyanates containing Cl atoms in the ortho positions of the benzene ring follow an unusual pathway because this zwitterion represents latent triisopropylphosphine due to the reversibility of the reaction of triisopropylphosphine with ethyl 2-cyanoacrylate. The molecular structures of the adducts of triisopropylphosphine with 2,6-dichloro- and 2,4,6-trichlorophenyl isothiocyanates were confirmed by X-ray diffraction study. Protonation of the adduct of triisopropylphosphine with 2,6-dichlorophenyl isothiocyanate occurred at the nitrogen atom, whereas methylation with methyl trifluoromethanesulfonate afforded an S-methylation product. The results of X-ray diffraction study of the resulting compounds are presented.     

DPPH (= 2,2‐Diphenyl‐1‐picrylhydrazyl = 2,2‐Diphenyl‐1‐(2,4,6‐trinitrophenyl)hydrazyl) Radical‐Scavenging Reaction of Protocatechuic Acid Esters (= 3,4‐Dihydroxybenzoates) in Alcohols: Formation of Bis‐alcohol Adduct

Protocatechuic acid esters (= 3,4‐dihydroxybenzoates) scavenge ca. 5 equiv. of radical in alcoholic solvents, whereas they consume only 2 equiv. of radical in nonalcoholic solvents. While the high radical‐scavenging activity of protocatechuic acid esters in alcoholic solvents as compared to that in nonalcoholic solvents is due to a nucleophilic addition of an alcohol molecule at C(2) of an intermediate o‐quinone structure, thus regenerating a catechol (= benzene‐1,2‐diol) structure, it is still unclear why protocatechuic acid esters scavenge more than 4 equiv. of radical (C(2) refers to the protocatechuic acid numbering). Therefore, to elucidate the oxidation mechanism beyond the formation of the C(2) alcohol adduct, 3,4‐dihydroxy‐2‐methoxybenzoic acid methyl ester ( 4 ), the C(2) MeOH adduct, which is an oxidation product of methyl protocatechuate ( 1 ) in MeOH, was oxidized by the DPPH radical (= 2,2‐diphenyl‐1‐picrylhydrazyl) or o‐chloranil (= 3,4,5,6‐tetrachlorocyclohexa‐3,5‐diene‐1,2‐dione) in CD₃OD/(D₆)acetone 3 : 1). The oxidation mixtures were directly analyzed by NMR. Oxidation with both the DPPH radical and o‐chloranil produced a C(2),C(6) bis‐methanol adduct ( 7 ), which could scavenge additional 2 equiv. of radical. Calculations of LUMO electron densities of o‐quinones corroborated the regioselective nucleophilic addition of alcohol molecules with o‐quinones. Our results strongly suggest that the regeneration of a catechol structure via a nucleophilic addition of an alcohol molecule with a o‐quinone is a key reaction for the high radical‐scavenging activity of protocatechuic acid esters in alcoholic solvents.     

12-钨磷酸希土盐DMF、DMSO加合物的合成、性质及其热分解动力学常数研究

合成了8种钨磷酸希土盐LnPW₁₂O₄₀·xH₂O(Ln=Y、La、Nd、Sm、Gd、Dy、Ho、Yb)的DMF、DMSO加合物,对加合物进行了组成分析,通过IR光谱、TG-DTA曲线对加合物进行了性质表征,并着重研究了加合物热分解过程的动力学,给出了热分解反应级数n和活化能E.     

Supramolecular framework adducts constructed of hexamethylenetetramine,aquated alkali metal cationic clusters,and hexacyanoferrates(II/III)

The reaction of alkali metal hexacyanoferrate(II/III) with (CH₂)₆N₄ (hexamethylenetetramine, abbreviated HMT) in an acidic medium yielded crystalline compounds of stoichiometries HK₂[Fe¹¹¹(CN)₆]·2HMT·4H₂O, H₂K₂[Fe¹¹(CN)₆]·2HMT·4H₂O, and HNa₂[Fe¹¹¹(CN)₆]· 2HMT·5H₂O. Their crystal structures are based on a packing of three molecular components: neutral and/orprotonated HMT, hexacyanoferrate, and an alkali metal ion-water cluster. The resulting three-dimensional supramolecular framework is constructed from the coordination of the alkali metal ion by aqua ligands as well as [Fe(CN)₆]{n–} and HMT units, and further stabilization is achieved by hydrogen bonding between water molecules and the noncoordinated nitrogen atoms of HMT and hexacyanoferrate.     

Interaction between peroxide ion and phenol group which are coordinated to the same iron(III) ion

We have prepared several new iron(III) complexes with ligands which contain a phenol group; these are tetradentate [(X-phpy)H, X and H(phpy) represent the substituents on the phenol ring and N,N-bis(2-pyridylmethyl)-N-(2-hydroxybenzyl)amine, respectively] and pentadentate ligands [(R-enph-X)H; R=ethyl(Et) or methyl(Me) derivative and H(Me-enph) denotes N,N-bis(2-pyridylmethyl)-N″-methyl-N″-(2″-hydroxyl-benzylamine)ethylenediamine] and have determined the crystal structures of Fe(phpy)Cl₂, Fe(5-NO₂-phpy)Cl₂, and Fe(Me-enph)ClPF₆, which are of a mononuclear six-coordinate iron(III) complex with coordination of one or two chloride ion(s). These compounds are highly colored (dark violet) due to the coordination of phenol group to an iron(III) atom. When hydrogen peroxide was added to the solution of the iron(III) complex, a color change occurs with bleaching of the violet color, indicating that oxidative degradation of the phenol moiety occurred in the ligand system. The bleaching of the violet color was also observed by the addition of t-butylhydroperoxide. The rate of the disappearance of the violet color is highly dependent on the substituent on the phenol ring; introduction of an electron-withdrawing group in the phenol ring decreases the rate of bleaching, suggesting that disappearance of the violet band should be due to a chemical reaction between the phenol group and a peroxide adduct of the iron(III) species with an η¹-coordination mode and that in this reaction the peroxide adduct acts as an electrophile towards phenol ring. The intramolecular interaction between the phenol moiety and an iron(III)-peroxide adduct may induce activation of the peroxide ion, and this was supported by several facts that the solution containing an iron(III) complex and hydrogen peroxide exhibits high activities for degradation of nucleosides and albumin.     

钴希夫碱配合物的合成及其氧合机制的研究——Ⅰ.配合物及其氧加合物的合成和表征

本文合成了一系列以水杨醛或萘酚醛同多胺缩合的四齿(N₂O₂)或五齿(N₃O₂)希夫碱为配体的钴希夫碱配合物及它们的氧加合物,用元素分析、红外光谱、磁化率以及ESR谱进行了表征,在续篇中将继续讨论配合物的吸氧行为和氧合机制。     

Palladium-catalyzed addition of hydroxylamine derivatives to Baylis-Hillman acetate adducts

The first use of hydroxylamine derivatives as the aminoxy equivalent of nucleophiles in palladium catalyzed addition to Baylis-Hillman acetate adducts is described. The reaction proceeds smoothly to give the substituted allyloxy amines in good yield and selectivity.     

HYDROBORATION OF UNSATURATED AMINES X. HYDROBORATION-HALOGENATION OF ALLYL PHOSPHORAMIDATES ROUTE TO γ-HALOGENOPROPYL PHOSPHORAMIDATES AND γ-HALOGENATED AMINES

Abstract

This paper describes the synthesis of γ-halogenopropyl phosphoramidates I by hydroboration-halogenation reaction of N-phosphorylated allylamines II (phosphoramidates and phosphoramides). Only the use of allyl phosphoramidates leads to a good regioselectivity of the addition of boron atom on the terminal carbon atom of the allyl structure (compounds III).

The absence of N→B complex formation permits a good reactivity of the trialkylboranes III and IV. The breaking of the P[sbnd]N bond, in acidic medium of the compounds I gives corresponding γ-halogenated amines V.     

Lithium adduct as precursor ion for sensitive and rapid quantification of 20 (S)‐protopanaxadiol in rat plasma by liquid chromatography/quadrupole linear ion trap mass spectrometry and application to rat pharmacokinetic study

A novel, rapid and sensitive liquid chromatography/quadrupole linear ion trap mass spectrometry [LC‐ESI‐(QqLIT)MS/MS] method was developed and validated for the quantification of protopanaxadiol (PPD) in rat plasma. Oleanolic acid (OA) was used as internal standard (IS). A simple protein precipitation based on acetonitrile (ACN) was employed. Chromatographic separation was performed on a Sepax GP‐C₁₈ column (50 × 2.1 mm, 5 μM) with a mobile phase consisting of ACN–water and 1.5 μM formic acid and 25 mM lithium acetate (90 : 10, v/v) at a flow rate of 0.4 ml/min for 3.0 min. Multiple‐reaction‐monitoring mode was performed using lithium adduct ion as precursor ion of m/z 467.5/449.4 and 455.6/407.4 for the drug and IS, respectively. Calibration curve was recovered over a concentration range of 0.5–100 ng/ml with a correlation coefficient >0.99. The limit of detection was 0.2 ng/ml in rat plasma for PPD. The results of the intraday and interday precision and accuracy studies were well within the acceptable limits. The validated method was successfully applied to investigate the pharmacokinetic study of PPD after intravenous and gavage administration to rat. Copyright © 2013 John Wiley & Sons, Ltd.     

Sodiation as a tool for enhancing the diagnostic value of MALDI‐TOF/TOF‐MS spectra of complex astaxanthin ester mixtures from Haematococcus pluvialis

The microalga Haematococcus pluvialis produces the pigment astaxanthin mainly in esterified form with a multitude of fatty acids, which results in a complex mixture of carotenol mono‐ and diesters. For rapid fingerprinting of these esters, matrix‐assisted laser desorption ionization time of flight mass spectrometry (MALDI‐TOF/TOF‐MS) might be an alternative to traditional chromatographic separation combined with MS. Investigation of ionization and fragmentation of astaxanthin mono‐ and diester palmitate standards in MALDI‐TOF/TOF‐MS showed that sodium adduct parent masses [M + Na]⁺ gave much simpler MS² spectra than radical / protonated [M]^+● / [M + H]⁺ parents. [M + Na]⁺ fragments yielded diagnostic polyene‐specific eliminations and fatty acid neutral losses, whereas [M]^+● / [M + H]⁺ fragmentation resulted in a multitude of non‐diagnostic daughters. For diesters, a benzonium fragment, formed by polyene elimination, was required for identification of the second fatty acid attached to the astaxanthin backbone. Parents were forced into [M + Na]⁺ ionization by addition of sodium acetate, and best signal‐to‐noise ratios were obtained in the 0.1 to 1.0 mM range. This method was applied to fingerprinting astaxanthin esters in a crude H. pluvialis extract. Prior to MALDI‐TOF/TOF‐MS, the extract was fractionated by normal phase Flash chromatography to obtain fractions enriched in mono‐ and diesters and to remove pheophytin a, which compromised monoester signals. All 12 types of all‐trans esterified esters found in LC were identified with MALDI‐TOF/TOF‐MS, with the exception of two minor monoesters. Copyright © 2013 John Wiley & Sons, Ltd.