Concerning the Diastereomerization of Stilbenoid Hypericin Derivatives

Summary.  Experiments on a newly prepared (E)-configured ω-benzal-hypericin derivative using TLC and ¹H NMR together with quantum chemical calculations revealed that in stilbenoid hypericin derivatives photodiastereomerization between the (E)- and (Z)-diastereomers occurs in principle. However, due to its low diastereomerization quantum yield and photo and thermal equilibria, which reside mostly on the side of the (E)-diastereomer, this photoreaction is only of marginal importance to the photochemistry of stilbenoid hypericin derivatives. Thus, photodiastereomerization does not appreciably interfere with the photoreactions important for photodynamic therapy. This was demonstrated by comparing the sensitized bilirubin photodestruction of hypericin and the ω-benzal-hypericin derivative. Received December 6, 2001. Accepted December 21, 2001     

The Protonation and Deprotonation Equilibria of Hypericin Revisited

Summary.  The protonation and deprotonation behaviour and the assignment of pK _a values of hypericin are reviewed and discussed. Three experiments (electrospray MS, ¹H NMR, acid–base indicator equilibria) provided additional evidences for the assignment of pK _a values of −5 and −6 to mono- and diprotonation at the carbonyl groups of hypericin, of pK _a = 2 to monodeprotonation at the bay-region, and of pK _a = 11 to dideprotonation at the bay- and peri-regions. Received September 26, 2001. Accepted October 1, 2001     

On the homo- and heteroassociation of hypericin

Summary Hypericin exhibits rather complicated homo- and heteroassociation behavior. Whereas in common polar solvents hypericin dissolves monomolecularly up to concentrations of 10^–3 mol/l, the presence of water in these solvents leads to homoassociation. As derived by spectroscopic measurements, these homoassociates exhibit a stacking pattern similar to the one observed for the crystalline material. Tetrahydrofuran seems to be an exception, as it is the only solvent which results in 1,6-dioxo tautomer formation. Heteroassociation of hypericin involves two distinct types of behavior. In the majority of cases, hypericin forms homoassociates which then heteroassociate with the co-solvate to yield stabilized solutions of these homoassociates. Only with human serum albumin a specific heteroassociate is formed. By means of competition experiments it could be established that hypericin is binding to the active site of the IIIA subdomain of the protein.Dedicated to Prof. Dr.Karl Schlöpl on the occasion of his 70th birthday     

Concerning the Absorption and Photochemical Properties of an ω-4-Dimethylaminobenzal Hypericin Derivative

Summary.  A hypericin derivative containing ω,ω ′-4-dimethylaminobenzal residues was shown to undergo an intramolecular [2 + 2] cycloaddition upon irradiation leading to a cyclobutane derivative whose main absorption band is hardly shifted as compared to hypericin. The corresponding ω-substituted derivative displayed a 34 nm bathochromic shift and a strongly reduced fluorescence quantum yield rendering it a nice candidate for a photodynamic therapy agent. Unfortunately, however, it produced virtually no photosensitized active oxygen species, making it thus unsuited for this purpose. Received July 11, 2001. Accepted July 18, 2001     

Analysis of the Solid-State Rearrangementof Hydrido-Alkynyl Ruthenium Complexesto their Vinylidene Tautomers

Summary.  The solid-state tautomerization of the hydrido-alkynyl derivatives [Cp ^*RuH(C&*CR)-(dippe)][BPh₄] (Cp^* = C₅Me₅; R = SiMe₃, Ph, H; dippe = 1,2-bis-(diisopropylphosphino)-ethane) to their vinylidene isomers [Cp ^*Ru*C*CHR(dippe)][BPh₄] was studied by IR spectroscopy. Characteristic isothermic αvs. t curves for each individual rearrangement process were recorded. Their shape, and hence the isomerization mechanism, depends strongly on the nature of the substituent R. The kinetic analysis of the above curves using the Avrami-Erofeev provided some mechanistic information about the isomerization process in the solid. Received July 7, 2000. Accepted August 29, 2000     

An Unusual Photoreaction of 3,4-Di-O-benzyl-hypericin

Summary.  Upon irradiation of 3,4-di-O-benzyl-hypericin and proton sponge (bis-1,8-N,N-dimethylamino-naphthalene) in benzene solution, a stable radical ion pair formed which exhibited an intense absorption band around 800 nm. This was advanced by UV/Vis, NMR, and ESR spectroscopy. In presence of oxygen, irradiation of this photoproduct led to an activated oxygen species which then attacked the proton sponge. Received July 17, 2000. Accepted July 20, 2000     

On the Chemistry of a Dibenzohypericin Derivative

Summary.  A hypericin derivative was synthesized in which instead of the methyl groups two benzene rings were condensed to the chromophoric system in order to extend its conjugation. This derivative showed lowered fluorescence and concomitantly enhanced sensitized production of active oxygen species as compared to hypericin. However, in contrast to intuition its long wavelength band remained unshifted in comparison to its parent compound hypericin. Geometry and absorption properties were also investigated by means of semiempirical calculations. Received July 27, 2001. Accepted August 9, 2001     

Concerning the Solvent Effect in the Aldol Condensation

Summary.  Except for the catalyst and the temperature, the nature of the solvent also affects the aldol condensation, favouring α,β-unsaturated carbonyl compounds in alcoholic solvents or β-hydroxyl carbonyl compounds in tetrahydrofuran. Received November 22, 1999. Accepted (revised) December 21, 1999     

Microanalysis of Glass Containing Alkali Ions

 The common problems connected with alkali ion migration during EPMA were studied on glasses containing nearly all possible alkali ions (Na, K, Rb, Cs). Binary silica glasses were prepared by melting from a very pure batch in Pt crucible. The glasses were carefully polished using alcohol to prevent surface corrosion by water and they were stored in vacuum. The specimens were coated with carbon layers approximately 30-nm thick and exposed to a 50- keV electron beam of 100 μm diameter. It was found that all alkali ions migrate under the electron beam, but the rate of the migration depends on the current density. The decay curves (characteristic X-ray intensity versus time) are similar in shape in all cases. The decay curve shows two transport regimes, the first being linear-like, the second being the exponential-like. The first transport regime busts into the rapid alkali migration after a time known as the incubation period. The period is in general longer for the larger-alkali ions size. It was found that even large rubidium and caesium ions migrate inside the glass with the same mechanism as sodium and potassium ions. While for K, Rb, and Cs ions the incubation periods were observed under the suitable experimental conditions, binary glass containing Na exhibits no observable incubation period. Except for the binary Na₂O + SiO₂ glass, the suitable experimental conditions for reliable quantitative EPMA can be found.     

金丝桃素的合成工艺改进

以大黄素为原料,经还原,Aldol缩合和光照反应合成了金丝桃素,总收率58.6%,其结构经1H NMR, IR和MS表征.     

The Products of Vicarious Nucleophilic Substitution and Annelation in the Reactions of α-Haloalkyl Carbanions with Benzonaphthyridines and their N-Oxides

Summary.  Carbanions of chloromethyl 4-tolylsulfone, bromo- and chloromethanesulfomorpholide, and neopentyl chloromethanesulfonate react with benzonaphthyridines and their N-oxides via two pathways: vicarious nucleophilic substitution of hydrogen and annelation. The results are rationalized in terms of the negative charge delocalization in the intermediate σ-adducts. Received October 15, 2001. Accepted (revised) November 26, 2001     

On the Molecularity of Bilirubins and their Esters and Anions in Chloroform Solution

Summary.  Bilirubins with propionic acids at C-8 and C-12 engage in intramolecular hydrogen bonding and are thought to be monomeric in solution, although the latter is unproven. In contrast, their dimethyl esters and etiobilirubin analogs (with the C-8 and C-12 propionic acids replaced by alkyl residues) favor intermolecular hydrogen bonding and are thought to be dimeric in nonpolar solvents. There is little information on the molecularity of the bilirubin dianion in solution. In this work, vapor pressure osmometry studies of chloroform solutions of bilirubins, their dimethyl esters, and etio-analogs clearly indicate that the diacids and dianions are monomeric, whereas the diesters and dialkyls are dimeric. However, the presence of a C-10 gem-dimethyl group causes the ester and the etiobilirubin to become monomeric. Received May 9, 2000. Accepted May 19, 2000     

Flame Atomic Absorption Spectrometric Determination of Arsenic After Volatilization of As(III) with Chloride Ions

 The generation of volatile species of As(III) as a means to introduce arsenic into a flame atomic absorption spectrometer has been studied. The method is based on the reaction between As(III) and chloride ions in sulphuric acid medium. The reaction is performed in a discontinuous or batch mode. With this method 130 μl of a solution containing 17.5% (w/v) sodium chloride and As(III) are injected by a 500 ml.min⁻¹ N₂ carrier gas flow into 1 ml of concentrated sulphuric acid. The gaseous compounds generated are introduced into the spectrometer through the nebulizer and As is determined. Received October 3, 1998. Revision January 6, 1999.     

Synthesis of Hexadentate Hexahydro-1,3,5-triazine-Based Ligands and their Copper(I) Complexes

Summary.  Hexadentate ligands were formed by the reaction of primary dimethylaminoethyl- or methoxyethylamines with formaldehyde. The resulting N, N′, N″-functionalized hexahydro-1,3,5-triazines contain pending amino or ether functionalities which are able to coordinate to metals in addition to the ring nitrogen atoms. Both ligands were reacted with CuBr, and novel tricopper clusters were isolated and characterized by X-ray structure analysis. In these compounds a ring nitrogen atom, the pending amino or ether functionality, and two bridging bromine atoms coordinate each of the copper atoms. Received January 22, 2002; accepted (revised) March 22, 2002     

Synthesis of α-N-Ethylamino Acids and their Derivatives

Summary.  A new synthesis of α-N-ethylamino acids starting from α-amino acids using hexafluoroacetone as protecting and activating agent is described. The hexafluoroacetone-protected N-ethylamino acid derivatives obtained are activated lactons. Therefore, they can be directly transformed without the need of an additional activation step with various nucleophiles into the corresponding carboxylic acid derivatives. Received March 24, 2000. Accepted (revised) April 20, 2000     

On the Reaction between 1-Aza-1,3-dienes and Push-Pull Olefins of the Acyloxymethylidene-malononitrile Type

Summary.  The reaction between push-pull olefins of the acyloxymethylidene-malononitrile type and α, β-unsaturated hydrazones affords selectively 5-alkyl-2-cyano-6-(N′,N′-dimethylhydrazono)-hexa-2,4-dienenitriles. No [4+2]-cycloaddition products were detected. The structure elucidation of the obtained compounds and possible reaction mechanisms are discussed. Received March 9, 2000. Accepted March 20, 2000     

Retention of Some Metal Ions and Their Separation on Silica Gel Modified with Acid Red 88

 Acid Red 88 is strongly extracted by chloroform solutions of Aliquat 336 by an ion exchange mechanism and for its reextraction from the ion pair formed, relatively high concentrations of mineral acids are required. By impregnation of silica with the ion pairs between the cation of Aliquat 336 and the anion of the dye a chelating sorbent for metal ions can be obtained. The sorbent prepared may be successfully used for separation of mixtures of various metal ions by the column extraction chromatography technique, additional purification of sodium and potassium salts from ions of heavy metals and for concentration of trace amounts of ions of various metals from aqueous solutions followed by their quantitative determination. The sorbent can be used repeatedly in the process of sorption and desorption of metal ions (especially those forming less stable complexes with the reagent) after regeneration with solutions of perchloric acid. Received January 28, 1998. Revision March 1, 1999.     

Synthesis of the Racemates of the b-Carboline Alkaloid Chrysotricine and its Diastereomer

Summary.  The racemates of the rubiacea alkaloid Chrysotricine (1) and its diastereomer are synthesized from the isomeric mixture of linalyl oxides 3 and tryptamine in six steps, followed by separation of the diastereomers. Received November 11, 1999. Accepted November 25, 1999     

Vicarious Nucleophilic Substitution of Hydrogen and Formation of Aziridine Rings in Reactions of Benzonaphthyridines and their N-Oxides with Chloromethyl Phenyl Sulfone

Summary.  Treatment of benzonaphthyridines with chloromethyl phenyl sulfone in the presence of base led to the formation of aziridine rings annelated to the benzonaphthyridine skeleton, whereas their N-oxides underwent vicarious nucleophilic substitution of hydrogen (VNS), thus leading to the corresponding phenylsulfonylmethyl derivatives. Received December 11, 2000. Accepted (revised) January 22, 2001