Enantioselective Total Synthesis and Structural Revision of Dysiherbol†A.

A 12-step total synthesis of the natural product dysiherbol A, a strongly anti-inflammatory and anti-tumor avarane meroterpene isolated from the marine sponge Dysidea sp., was elaborated. As key steps, the synthesis features an enantioselective Cu-catalyzed 1,4-addition/enolate-trapping opening move, an Au-catalyzed double cyclization to build up the tetracyclic core-carbon skeleton, and a late installation of the C5-bridgehead methyl group via proton-induced cyclopropane opening associated with spontaneous cyclic ether formation. The obtained pentacyclic compound (corresponding to an anhydride of the originally suggested structure for dysiherbol A) showed identical spectroscopic data as the natural product, but an opposite molecular rotation. CD-spectroscopic measurements finally confirmed that both the constitution and the absolute configuration of the originally proposed structure of (+)-dysiherbol A need to be revised.

Less is more: Unstable foams clean better than stable foams.

HYPOTHESIS: Foamed surfactant solutions can clean surfaces! We hypothesise that the cleaning efficiency depends on the liquid fraction and on the stability of the foam. We also hypothesise that the cleaning efficiency is the better the smaller the average bubble size is. EXPERIMENTS: The double syringe technique was used to generate foams with varying liquid fractions but the same, very small bubble sizes with and without perfluorohexane in the gas phase. We performed cleaning tests in which the foams were applied to glass substrates contaminated with a fluorescent oil. FINDINGS: We found that unstable foams clean better than stable foams. Three cleaning mechanisms were identified: (1) imbibition at low liquid fractions, (2) wiping, i.e., shifting of the contact line between oil, foam and glass, at all liquid fractions, and (3) drainage at high liquid fractions. The change of the liquid fraction and of the foam stability lead to different combinations of these mechanisms and thus to different cleaning results.

Novel ethoxylated inositol derivatives--hybrid carbohydrate/oligoethylene oxide surfactants.

Carbohydrate- and oligoethylene oxide-based surfactants behave quite differently despite the fact that they are both classes of nonionic surfactants. Intensive studies of a mixture at fixed molar ratio (1:1) of two very common sugar- and oligoethylene oxide-based surfactants, namely n-dodecyl-ß-D-maltoside (ß-C(12)G(2)) and n-dodecyl hexaethylene oxide (C(12)E(6)), revealed that most properties of the mixture are similar to those of the oligoethylene oxide-based surfactant. In the present work, this mixture is compared to respective "hybrid surfactants". Such hybrid surfactants are surfactants whose head group contains chemically linked carbohydrate and oligoethylene oxide units. In order to study the behaviour of this sort of compounds, we synthesised a new class of surfactants whose head group consists of one carbohydrate-like unit (myo-inositol) and three ethylene oxide units. New regiochemically defined ethoxylated inositol derivatives (referred to as C(12)I(1)E(3) and C(12)E(3)I(1) in the following) were synthesised and studied for their thermotropic and lyotropic liquid crystalline properties as well as for their surface activities. The results are compared with those of the reference systems ß-C(12)G(2) and C(12)E(6), and their 1:1 mixture, respectively, and are discussed in terms of structure-property relations.

On the photophysical properties of new luminol derivatives and their synthetic phthalimide precursors.

The photophysical properties of a series of structurally related 4-aminophthalimides and the corresponding 5-aminophthalic hydrazides (luminols) are reported. Absorption, steady-state, and time-resolved fluorescence spectra of luminols exhibited substitution, solvent, and pH dependence. Singlet lifetimes have been determined by time-resolved laser flash spectroscopy. UV spectra in gas phase and DMSO solution were calculated by TD-DFT which revealed the existence of two low-energy excited singlet states with strong pH-sensitivity.

Liquid crystallinity and supramolecular organization of regioisomeric isatin derivatives: an experimental and theoretical study.

Spatially organized chromophores can be beneficial for advanced applications like for example, organic solar cells, laser technology or non-linear optic devices as well as supramolecular photochemistry. Of particular interest are non-static ordered forms of molecular organization as for example, liquid crystals. With this in mind we synthesised four new regioisomeric isatin derivatives by Suzuki-Miyaura coupling of 4-dodecyloxyphenylboronic acid with all four possible regioisomers of bromoisatin. Liquid crystalline properties are found for 5-(4-dodecyloxyphenyl)isatin, while the other regioisomers do not display a mesomorphic behaviour. The synthesis, physicochemical investigations including polarization microscopy, differential scanning calorimetry and X-ray investigations are discussed and accompanied with density functional theory calculations with respect to the target molecules and their possible H-bonded aggregates. Two distinct setups of supramolecular assemblies for such isatin derivatives are discussed and a model for the mesophase is proposed.

Systematic study of the structures of potassiated tertiary amino acids: salt bridge structures dominate.

The gas-phase structures of a series of potassiated tertiary amino acids have been systematically investigated using infrared multiple photon dissociation (IRMPD) spectroscopy utilizing light generated by a free electron laser, ion mobility spectrometry (IMS), and computational modeling. The examined analytes comprise a set of five linear N,N-dimethyl amino acids derived from N,N-dimethyl glycine and three cyclic N-methyl amino acids including N-methyl proline. The number of methylene groups in either the alkyl chain of the linear members or in the ring of the cyclic members of the series is gradually varied. The spectra of the cyclic potassiated molecular ions are similar and well resolved, whereas the clear signals in the respective spectra of the linear analytes increasingly overlap with longer alkyl chains. Measured IRMPD spectra are compared to spectra calculated at the B3LYP/6-311++G(2d,2p) level of theory to identify the structures present in the experimental studies. On the basis of these experiments and calculations, all potassiated molecular ions of this series adopt salt bridge structures in the gas phase, involving bidentate coordination of the potassium cation to the carboxylate moiety. The assigned salt bridge structures are predicted to be the global minima on the potential energy surfaces. IMS cross-section measurements of the potassiated systems show a monotonic increase with growing system size, suggesting that the precursor ions adopt the same type of structure and comparisons between experimental and theoretical cross sections are consistent with salt bridge structures and the IRMPD results.

Syntheses, amphitropic liquid crystallinity, and surface activity of new inositol-based amphiphiles.

Carbohydrates are interesting starting materials for scientific and industrial syntheses as they allow a versatile chemistry. Moreover, they are of natural origin and environmentally benign. During the past few years, inositol, a rather "exotic" carbohydrate, and its derivatives have gained increasing attention. Here, we describe the syntheses of new regiochemically defined inositol monoethers and monoesters as well as regioisomeric inositol ester mixtures and investigate their amphitropic liquid crystallinity. Furthermore, first results on their surface activity in aqueous solutions are given and compared with classical sugar surfactants.

Kinetic determination of potassium affinities by IRMPD: elucidation of precursor ion structures.

Dissociation kinetics of the K(+) loss reaction of three potassiated tertiary amino acids (Scheme 1) were studied by infrared multiple photon dissociation (IRMPD) in a Fourier transform ion cyclotron resonance (FT ICR)-MS instrument. The aim of the study was to probe if a kinetic study by IRMPD can yield useful information on the ion structure of the precursor ion species. The measured activation energy values determined by IRMPD are related to the potassium affinity, DeltaH(K(+)), of N-methyl proline determined by threshold collision-induced dissociation experiments. By appropriate scaling with this reference value, the experimentally determined activation energy values for the K(+) loss are transformed into respective potassium affinities, DeltaH(K(+))(IRMPD). These values match the calculated potassium affinity values for salt bridge (SB) structures, DeltaH(K(+))(SB), substantially better than those for canonical structures with a single formal charge site (charge solvation (CS)), thereby allowing structure identification. This conclusion is consistent with other spectroscopic data, which yielded unambiguous evidence of these tertiary amino acids adopting SB structures in the gas phase. This study demonstrates that IRMPD can be applied to determine individual ion structures in the gas phase, given that adequate reference values are available for proper scaling.

Infrared multiple photon dissociation spectroscopy of potassiated proline.

The structure of proline in [proline + K]+ has been investigated in the gas phase using high level DFT and MP2 calculations and infrared photo dissociation spectroscopy with a free electron laser (FELIX). The respective FELIX spectrum of [proline + K]+ matches convincingly the calculated spectra of two structurally closely related and nearly iso-energetic zwitterionic salt bridge (SB) structures. An additional unresolved band at approximately 1725 cm(-1) matching with the characteristic CO stretching mode of charge solvation (CS) structures points toward the presence of a minor population of these conformers of proline in [proline + K]+. However, theory predicts a significant energy gap of 18.9 kJ mol(-1) (B3LYP/6-311++G(2d,2p)) or 15.6 kJ mol(-1) (MP2) between the lowest CS conformer of proline and the clearly favored SB structure.

1,2,5,10,11,14-hexaoxadispiro[5.2.5.2]hexadecanes: novel spirofused bis-trioxane peroxides.

A set of new bis-spirofused 1,2,4-trioxanes 4a-d was obtained from the reaction of cyclohexane-1,4-dione with allylic hydroperoxides 2a-d, bearing an additional hydroxy group in the homoallylic position, by diastereoselective photooxygenation of allylic alcohols 1a-d and subsequent BF(3)-catalyzed peroxyacetalization with the diketone. From the reaction of a monoprotected cyclohexane-1,4-dione 5 with the allylic hydroperoxide 6 derived from the singlet oxygenation of methyl hydroxytiglate, one monospiro compound was obtained, the 1,2,4-trioxane ketone 7, as well as a mixture of the diastereoisomeric syn- and anti bis-1,2,4-trioxanes 8. The structures of bis-1,2,4-trioxanes were examined theoretically by DFT methods and compared with X-ray structural data in order to evaluate the preferential trioxane ring conformational orientation.

Photochemistry of allyloxybenzophenones: a pseudo-Paternò-Büchi rearrangement accompanied by hydrogen transfer induced 1,5-cyclization.

The solution photochemistry of the ortho allyloxy-substituted benzophenone has been investigated in detail. Product analysis revealed formation of a diastereomeric mixture of dihydrobenzofuran derivatives by cyclization via a short-lived intermediate 1,5-biradical and an unusual acetal by a pseudo-Paternò-Büchi rearrangement. The latter reaction pathway was supported by means of laser flash photolysis, where a long-lived intermediate with a maximum absorption band at 380 nm was observed. Besides, theoretical calculations (TD-DFT) of this UV-transient resulted in a band with maximum intensity at 390 nm showing a good correlation between experimental results and theoretical calculations. For comparison, the meta-substituent substrate was also investigated showing preferred triplet-triplet energy transfer.

New ethoxylated inositol surfactant.

Carbohydrates are an attractive class of starting materials for organic syntheses because they are of natural origin, environmentally friendly, and highly functionalized, in this way promoting a sustainable chemistry. A somewhat exotic but nevertheless readily available family of carbohydrates allowing a fascinating chemistry are inositols (cyclohexane-1,2,3,4,5,6-hexols), which we currently use for the synthesis of new surfactants. In our previous work, we reported on the synthesis of a number of new regiochemically defined myo-inositol ethers and esters and studied their surface activity in aqueous solution as well as their ability to form thermotropic liquid crystals. It turned out that the hydrophilicity of the myo-inositol head group alone does not ensure sufficient water solubility of these surfactants. To improve the water solubility, we increased the inositol head group by the introduction of a tri(ethylene oxide) unit. The resulting surfactant is the first representative of a new class of inositol-based surfactants (CiEjIk) that combine the properties of classical sugar surfactants (CnGm) and oligo(ethylene oxide) alkyl ether surfactants (CiEj).