A novel formula for location of double bond in alkenyl acetates and alcohols based on mass spectral data of dimethyl disulfide derivatives

A new formula was presented for locating double bond position in dodecenols, tetrade-cenols, hexadecenols and their acetates, based on mass spectral data of dimethyl disulfide derivatives. In this procedure, molecular ion and base peak ion were utilized as characteristic parameters to identify the positional isomers. The method was tested with mass spectra of 25 dimethyl disulflde derivatives of mono-unsaturated acetates and alcohols, and the original double-bond position in each isomer was located unambiguously.     

β-环糊精及其衍生物对Al(Ⅲ)-铁试剂的荧光增强效应及机理

Effect of β-cyclodextrin and its derivatives on the fluorescence intensities o f Al(Ⅲ)-Ferron were investigated in detail.The results indicated that sensitizin g effect and enhanced selectivity of the system as CTMAB and HP-β-CD are in c oexistence,there is obvious synergistie senzitizing effect.Byusing pyrene as p robe,the mechanism of the effect was discussed in the light of inclusion effect principle of the cyclodextrins.     

N-ALKYLPHENOTHIAZINE RADICAL CATIONS GENERATED IN THE CAVITY OF β-CYCLODEXTRINS IN A(?)UEOUS SOLUTION

Phenothiazine and i~+s derivatives were oxidized by l_2 and 2,2,6,6-tetrametbyl-4-acetyloxypiperidine oxoammonium hexachloroantimonate to the corresponding radical cationsin the cavity of β-cyclodextrins in aqueous solution.The mechanism of electron transferbetween substrates and oxidants is discussed in terms of association of β-CDs.     

A Facile Synthesis of 4-Alkyl-2-Quinolones

The derivatives of 4-alkyl-2-quinolones possess a variety of biological activities. The general synthetic method of 4-alkyl-2-quinolones is the reaction of aryl amines with β-ketoesters to form β-ketoamides, which are then heated in concentrated sulfuric acid to complete the ring closure. Although a number of its 4-methyl and aryl derivatives have been obtained, other 4-alkyl-2-quinolones are rarely mentioned for lack of a convenient method to prepare the appropriate β-ketoesters used in condensation.     

Theoretical Study on Enol-keto Tautomerism of α-Fluorine-β-diketones

1 INTRODUCTION β-diketones are a class of high functional com- pounds with outstanding optical, electric and magne- tic properties[1], and the negative ion may act as an excellent chelating agent. Hall[2] have studied β-di- ketone/metal ion complexes and indicated that the ability of combination correlates with the keto-enol distribution in solution. The enol-keto equilibrium existing in β-diketones has been extensively studied over several decades[3~9]. Burdett[10] have investiga- ted…     

Analysis of the linkage positions and isomers of monosaccharide units in oligosaccharides by negative secondary ion mass spectrometry in combination with the stereoselective reaction with substituted boronic acid

The negative secondary ion mass spectrometry,in combination with the stereoselectivederivatizations with substituted boronic acid RB(OH)_2,was used in the analysis of fourteen oligosac-charides.The mass spectra of the derivatives provide information on their linkage Positions and iso-merism of the individual monoscaccharide units.The results indicated that among the derivativesof the oligosaccharides analyzed,those with 1—4 and 1—6 linkages all presented the ion peaks at m/z287,sometimes one more peak at m/z 449.Furthermore,a relationship was found between the linkagepositions and the intensity orders of the derivative ions.Finally,the derivatives of the disaccharideswith a galactose presented an intense ion peak at m/z 347,and those of oligosaccharides with 1—6linkage to a galactose at terminal presented the ion at m/z 317.In the case of oligosaccharides witha fructose residue,characteristic ion of m/z 155 was produced.The conditions of stereoselectivederivatizations and mass spectrometry were studied,in order to obtain a better reproducibility of themass spectra.     

Interfacial Behaviors of Azocalixarene Derivatives at the Air/Water Interface and Photochromism in the Langmuir-Blodgett Films

The azocalixarenes is a novel chromogenic compound and their spectra properties have been reported. A number of them have been applied as selective ionophores in extractive process1 or as selective ligands in ion selective electrodes and optical sensors based on spectra changes2. Some amphiphilic azocalixarene derivatives with hydrophobic long alkyl chains were synthesized and their interfacial behaviors at the air / water interface have also been investigated3. However, the photochromism of t…     

Are the Nitro-and Amino-substituted Piperidine High-energy-density Compounds?

Nitro and amino groups were introduced into piperidine skeleton to design derivatives of piperidine(labeled as α, β_1, β_2, β_3, γ and δ). Heats of formation(HOFs) are calculated in detail at the B3PW91/6-311+G(d,p) level for these aminonitropiperidines. The results show that all derivatives have negative heats of formation, which were affected by the positions of substituted groups. The molecular stability is estimated and analyzed based on bond dissociation energies(BDE) and characteristic heights(H_(50)). All derivatives designed in this paper are confirmed with lower impact sensitivity than 1,3,5-trinitro-1,3,5-triazinane(RDX) and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane(HMX). Furthermore, the detonation velocities(D) and the detonation pressures(P) are predicted via the Kamlet-Jacobs equation. In all these molecules, δ has comparable detonation character with that of RDX and HMX and can be the candidate of high-energy-density compounds(HEDCs).     

Design and Synthesis of p/m-[p-（un）Substituted Phenylsulfonamido]phenyl β-Diketo Acids and Quinoxalone Derivatives

Diketo acid derivatives are potent and selective HIV-1 integrase inhibitors. To investigate the detailed synthesis of those derivatives, a series of p/m-[p-（un）substituted phenylsulfonamido]phenyl β-diketo acid derivatives have been designed and synthesized. The quinoxalone derivatives as the potential bioisosteres of the biologically labile β-diketoacid pharmacophores have also been synthesized from reactions of the corresponding diketo acids with o-phenylenediamine. The structures of all diketo acid （ester） and quinoxalone derivatives were confirmed by 1^H NMR, 13^C NMR, IR, HRMS and/or MS （ESI）. X-ray crystallographic analysis of 11b demonstrates a similar arrangement of the side chain of quinoxalone derivatives with the parent diketoacids due to the intramolecular hydrogen bond （O…H-N） and the sp^2 hybridization configuration of the two nitrogen atoms of the quinoxalone ring.     

高效可回收催化剂In(OTf)_3用于无溶剂条件下Pechmann缩合反应(英文)

In(OTf)3 plays the role of a Lewis acid catalyst in the Pechmann condensation of phenols with β-ketoesters under solvent-free conditions to give coumarin derivatives. This novel and inexpensive method has advantages such as short reaction time, excellent product yields, and avoids the use of organic solvents in agreement with green chemistry principles. Catalyst loadings can be as low as 1 mol% to give high yields of the corresponding coumarins at 80 °C. The catalyst can be recovered after the reaction, and reused with only a slight decrease in the yield.     

Microwave‐Assisted Synthesis of β‐Lactams and Cyclo‐β‐dipeptides

Different cyclo‐β‐dipeptides were prepared from corresponding N‐substituted β‐alanine derivatives under mild conditions using PhPOCl₂ as activating agent in benzene and Et₃N as base. To evaluate β³‐substituent influence, the amino acids 7 – 26 were synthesized, and a β‐lactam formation reaction was carried out instead of cyclo‐β‐dipeptide formation. The crystal structures of three derivatives of cyclo‐β‐peptides and one β‐lactam are presented.     

Nucleo‐β‐Amino Acids: Synthesis and Oligomerization to β‐Homoalanyl‐PNA

The synthesis of thyminyl‐, uracilyl‐, cytosinyl‐, and guaninyl‐β³‐amino acids and the oligomerization of the cytosinyl‐ and guaninyl‐β³‐amino acids to β‐homoalanyl‐PNA are presented. The pyrimidinyl nucleobases were connected to the γ‐position of β‐homoalanine by Mitsunobu reaction with a β‐homoserine derivative or by nucleophilic substitution of methanesulfonates. For the preparation of the guaninyl‐β³‐amino acid, a β‐lactam route was established that might be of interest also for the synthesis of other β³‐amino acid derivatives. The cytosinyl and guaninyl building blocks were oligomerized to hexamers. They form quite stable self‐pairing complexes in H₂O as indicated by temperature dependent UV and CD spectroscopy.     

Preparation of β2‐Homotryptophan Derivatives for β‐Peptide Synthesis

In view of the prominent role of the 1H‐indol‐3‐yl side chain of tryptophan in peptides and proteins, it is important to have the appropriately protected homologs H‐β² HTrp OH and H‐β³ HTrp OH (Fig.) available for incorporation in β‐peptides. The β²‐HTrp building block is especially important, because β²‐amino acid residues cause β‐peptide chains to fold to the unusual 12/10 helix or to a hairpin turn. The preparation of Fmoc and Z β²‐HTrp(Boc) OH by Curtius degradation (Scheme 1) of a succinic acid derivative is described (Schemes 2–4). To this end, the (S)‐4‐isopropyl‐3‐[(N‐Boc‐indol‐3‐yl)propionyl]‐1,3‐oxazolidin‐2‐one enolate is alkylated with Br CH₂CO₂Bn (Scheme 3). Subsequent hydrogenolysis, Curtius degradation, and removal of the Evans auxiliary group gives the desired derivatives of (R)‐H β²‐HTrp OH (Scheme 4). Since the (R)‐form of the auxiliary is also available, access to (S)‐β²‐HTrp‐containing β‐peptides is provided as well.     

Preparation of Protected β2‐ and β3‐Homocysteine, β2‐ and β3‐Homohistidine,and β2‐Homoserine for Solid‐Phase Syntheses

The Ser, Cys, and His side chains play decisive roles in the syntheses, structures, and functions of proteins and enzymes. For our structural and biomedical investigations of β‐peptides consisting of amino acids with proteinogenic side chains, we needed to have reliable preparative access to the title compounds. The two β³‐homoamino acid derivatives were obtained by Arndt–Eistert methodology from Boc‐His(Ts)‐OH and Fmoc‐Cys(PMB)‐OH (Schemes 2–4), with the side‐chain functional groups' reactivities requiring special precautions. The β²‐homoamino acids were prepared with the help of the chiral oxazolidinone auxiliary DIOZ by diastereoselective aldol additions of suitable Ti‐enolates to formaldehyde (generated in situ from trioxane) and subsequent functional‐group manipulations. These include OH→O^tBu etherification (for β²hSer; Schemes 5 and 6), OH→STrt replacement (for β²hCys; Scheme 7), and CH₂OH→CH₂N₃→CH₂NH₂ transformations (for β²hHis; Schemes 9–11). Including protection/deprotection/re‐protection reactions, it takes up to ten steps to obtain the enantiomerically pure target compounds from commercial precursors. Unsuccessful approaches, pitfalls, and optimization procedures are also discussed. The final products and the intermediate compounds are fully characterized by retention times (t_R), melting points, optical rotations, HPLC on chiral columns, IR, ¹H‐ and ¹³C‐NMR spectroscopy, mass spectrometry, elemental analyses, and (in some cases) by X‐ray crystal‐structure analysis.     

Preparation of the β2‐Homoselenocysteine Derivatives Fmoc‐(S)‐β2hSec(PMB)‐OH and Boc‐(S)‐β2hSec(PMB)‐OH for Solution and Solid‐Phase Peptide Synthesis

Fmoc‐β²hSer(^tBu)‐OH was converted to Fmoc‐β²hSec(PMB)‐OH in five steps. To avoid elimination of HSeR, the selenyl group was introduced in the second last step (Fmoc‐β²hSer(Ts)‐OAll→Fmoc‐β²hSec(PMB)‐OAll). In a similar way, the N‐Boc‐protected compound was prepared. With the β²hSe‐derivatives, 21 β²‐amino‐acid building blocks with proteinogenic side chains are now available for peptide synthesis.     

Zn2+‐Complexation by a β‐Peptidic Helix and Hairpin Containing β3hCys and β3hHis Building Blocks: Evidence from CD Measurements. Preliminary Communication

Two new β³‐homohistidine‐ and β³‐homocysteine‐containing β‐peptides have been prepared by solid‐phase synthesis. A β‐octapeptide ( 2 ) contains seven β³‐amino acids and one β²‐amino acid. The β²/β³ segment has been placed in the middle of this peptide, which contains β³‐amino acids of alternating configuration, to induce the formation of a hairpin secondary structure. A β‐decapeptide ( 3 ) has been designed to fold to a 3₁₄‐helical secondary structure with neighboring His side chains in 6‐ and 9‐positions. Circular‐dichroism (CD) measurements show the capability of both peptides to bind Zn²⁺ ions in aqueous solution. In the case of the β‐octapeptide, binding of Zn²⁺ causes a dramatic change of the CD spectrum, indicating a change or a stabilization of its secondary structure. Zn²⁺ Ions clearly stabilize the 3₁₄‐helix of the β‐decapeptide, in neutral and basic solution. For the construction of the two new β‐peptides, we needed to have a supply of the β‐amino acid derivatives Fmoc‐β³hCys(Trt)‐OH and Fmoc‐β³hHis(Trt)‐OH, the preparation of which is described herein.     

Preparation of the β3‐Homoselenocysteine Derivatives Fmoc‐β3hSec(PMB)‐OH and Boc‐β3hSec(PMB)‐OH for Solution and Solid‐Phase‐Peptide Synthesis and Selenoligation

The title compounds, 4 and 7 , have been prepared from the corresponding α‐amino acid derivative selenocystine ( 1 ) by the following sequence of steps: cleavage of the Se? Se bond with NaBH₄, p‐methoxybenzyl (PMB) protection of the SeH group, Fmoc or Boc protection at the N‐atom and Arndt–Eistert homologation (Schemes 1 and 2). A β³‐heptapeptide 8 with an N‐terminal β³‐hSec(PMB) residue was synthesized on Rink amide AM resin and deprotected (‘in air’) to give the corresponding diselenide 9 , which, in turn, was coupled with a β³‐tetrapeptide thiol ester 10 by a seleno‐ligation. The product β³‐undecapeptide was identified as its diselenide and its mixed selenosulfide with thiophenol (Scheme 3). The differences between α‐ and β‐Sec derivatives are discussed.     

Preparation of β2‐Amino Acid Derivatives (β2hThr, β2hTrp, β2hMet, β2hPro, β2hLys,Pyrrolidine‐3‐carboxylic Acid) by Using DIOZ as Chiral Auxiliary

The title compounds were prepared from valine‐derived N‐acylated oxazolidin‐2‐ones, 1 – 3, 7, 9 , by highly diastereoselective (≥ 90%) Mannich reaction (→ 4 – 6 ; Scheme 1) or aldol addition (→ 8 and 10 ; Scheme 2) of the corresponding Ti‐ or B‐enolates as the key step. The superiority of the ‘5,5‐diphenyl‐4‐isopropyl‐1,3‐oxazolidin‐2‐one’ (DIOZ) was demonstrated, once more, in these reactions and in subsequent transformations leading to various t‐Bu‐, Boc‐, Fmoc‐, and Cbz‐protected β²‐homoamino acid derivatives 11 – 23 (Schemes 3–6). The use of ω‐bromo‐acyl‐oxazolidinones 1 – 3 as starting materials turned out to open access to a variety of enantiomerically pure trifunctional and cyclic carboxylic‐acid derivatives.     

Preparation and Structure of Magnesium Bis(hydrogen β‐glutamate) Hexahydrate

The dissociation equilibria of aqueous solutions of β‐glutamic acid were studied by potentiometric titration and the three pK values determined under standard conditions. The hydrogen β‐glutamate anion β‐GluH⁻ was found to be the dominating species in the physiologically relevant pH range 4.0–9.4. Neutralization of β‐glutamic acid by magnesium oxide affords magnesium bis(hydrogen β‐glutamate) Mg (β‐GluH)₂, which crystallizes as the hexahydrate from dilute aqueous solution. A single‐crystal X‐ray study showed that the β‐GluH⁻ anions are not part of the coordination sphere of the magnesium ion. Instead hexahydrated dications [Mg(H₂O)₆]²⁺ are intimately associated with free β‐GluH⁻ anions through a three‐dimensional network of H‐bonds. This study provides the first structural and conformational reference data for the β‐GluH⁻ anion.