Synthesis and supramolecular properties of trimethylene-bridged clips

The novel trimethylene-bridged clips 3 and 4 have been synthesized by using repetitive stereoselective Diels-Alder reactions of the benzo- and naphthobismethylenenorbornenes 8 and 19 as dienes and norbornadiene 9 as bisdienophile, and subsequent dehydrogenation of the primary cyclobisadducts 10 and 20 by using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). Clips 3 and 4 serve as receptors for a variety of electron-deficient neutral and cationic aromatic substrates, comparable to the molecular tweezers 1 and 2. The thermodynamic parameters of the complex formation, K(a) and DeltaG, were determined by (1)H NMR titration experiments and, in the case of the highly stable complex TCNB 32@4, by the use of isothermal titration microcalorimetry. The finding that clip 4 forms more stable complexes than 3 can be explained by the larger van der Waals contact surfaces of the naphthalene sidewalls in 4 compared to the corresponding benzene systems in 3. In the complexes with 4 as receptor, the plane of each aromatic substrate molecule is calculated to be oriented almost parallel to the naphthalene sidewalls. However, in the complexes of tweezers 2, the substrate is usually oriented parallel to the central naphthalene spacer unit. Due to the more open topology of 4, most complexes were calculated to consist of two or more equilibrating noncovalent conformers.     

Beiträge zur Chemie der Pyrrolpigmente, 82. Mitt.: Wasserlösliche Polymere mit kovalent gebundenen violinoiden und 2,3-dihydro-verdinoiden Gallenfarbstoffen

Summary A violinoid and a 2,3-dihydrobilindione chromophore is attachedvia an appendix anchored at rings A of the pigments by means of reacting them with the polyacryl-N-acryloxysuccinimid copolymer to yield water-soluble chromopolymers. They are characterized by a molecular mass of about 4000 to 6000 and a relation of one chromophoric unit per 6 to 22 monomers. Their absorption spectra and circular dichroism recorded in water and dimethylsulfoxide as solvents are discussed with respect to structural aspects, and in comparison with monomeric chromophore derivatives.

Herrn Prof. Dr. K. Schlögl mit den besten Wünschen zum 65. Geburtstag gewidmet     

Beiträge zur Chemie der Pyrrolpigmente, 44. Mitt.: Gallenfarbstoffe als Ionophore

The carrier mediated transport of cations using model compounds of the verdinoid and rubinoid bile pigment structural type as ionophores is studied. Verdinoid bile pigments turn out to be very effective carriers for cations exhibiting a pronounced selectivity for certain transition metal ions like Cr^+-+, Fe⁺⁺, Cu⁺⁺ and Zn⁺⁺. The scope of this behaviour of verdinoid bile pigments is compared to [18]-crown-6 and meso-tetraphenylporphin and is discussed with regard to structural, biological, analytical and technical implications.

     

Complexation of electron donor-acceptor [2.2] paracyclophanes with tetracyanoethylene (TCNE)

For a series of electron donor-acceptor cyclophanes the effect of the acceptor unit on the ionisation potential I_D of the donor part was measured by determining the transition energies of the charge-transfer absorption of intermolecular complexes with TCNE.     

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     

Syntheses and Properties of Two Heterocyclically Substituted Hypericin Derivatives: 10,11-Dibenzothiazolyl-10,11-didemethylhypericin and 10,11-Dibenzoxazolyl-10,11-didemethylhypericin

Summary. The syntheses of the two heterocyclically substituted title hypericin derivatives were achieved starting either from 6-benzothiazolyl-tri-O-methyl-6-demethylemodin or 6-benzoxazolyl-tri-O-methyl-6-demethylemodin. The use of microwave assisted synthesis for the preparation of these anthraquinone synthons and the chemical as well as photochemical properties of the corresponding unique hypericin derivatives, which might constitute new photodynamic therapy agents, are reported. The tautomeric and stereochemical aspects of these hypericin derivatives were investigated by means of semiempirical calculations (AM1).     

The molecular and crystal structures of two diastereomeric 3,4-dihydropyrromethenones

The molecular and crystal structures of the two racemic diastereomeric 3,4-dihydropyrromethenone derivatives1 and2 of configurations (Z) and (E) were determined at 93 K (1, 2) and at room temperature (1). From an analysis of the crystallographically observed temperature coefficients a pseudorotation flexibility of the pyrrolidinone ring in the crystal is deduced. In both compounds a nearly orthogonal arrangement between the two heterocyclic ring systems is observed, which is ascribed to the steric bulk of the substituents in positions 1 and 3 of the pyrrolidinone ring.Herrn Prof.Josef Schurz zum 60. Geburtstag gewidmet.     

Zur regioselektiven nucleophilen Addition an 2,3-Dihydrobilatriene-abc

Donors are added regioselectively to position 10 of 2,3-dihydrobilatrienes-abc in a reversible reaction, which is complicated in case of strongly basic donors due to the easy deprotonation of the partially saturated ring. Compared to the bilatrienes-abc the addition equilibrium is retarded by about two orders of magnitude.

     

Thermal synthesis of the optical pure pentapeptide derivative Z-(L)-Ala-(L)-Phe-Gly-(L)-Phe-Gly-OMe

The pentapeptide Z-(L)-Ala-(L)-Phe-Gly-(L)-Phe-Gly-OMe was obtained by reacting the activated dipeptide derivative Z-(L)-Ala-(L)-Phe-OPcp with the amino peptide derivative TFA·H-Gly-(L)-Phe-Gly-OMe at 100–105°C under reduced pressure (10^?2-10-^?3 Torr) without using solvents. The product obtained by bulk condensation showed no racemization, whereas the product obtained by a matrix mediated condensation contained 5,5 % diastereomer Z-(L)-Ala-(D)-Phe-Gly-(L)-Phe-Gly-OMe. Separation of diastereomers was achieved by HPLC on a silicagel column.     

Umlagerungsreaktionen von (2′-Propinyl)cyclohexadienolen und -semibenzolen

Rearrangements of (2′-Propinyl)cyclohexadienols and -semibenzenes The acid-catalyzed dienol-benzene rearrangement of 3- and 5-methyl-substituted (2′-propinyl)cyclohexadienols has been investigated. Treatment of the dienols with CF₃COOH in CCl₄ yields allenyl- and (2′-propinyl)benzenes via [3,4]- and [1,2]-sigmatropic rearrangements, respectively. The reaction with H₂SO₄ in Et₂O leeds to a mixture of allenyl-, 2′-propinyl-, 3′-butinyl- and (2′,3′-butadienyl)benzenes (Scheme 3). The latter are products of a thermal semibenzene-benzene rearrangement (cf. Scheme 9). The corresponding semibenzenes have been prepared by dehydration of the cyclohexadienols with H₂SO₄ or POCl₃ (Schemes 6 and 7). Under acidic conditions, the p-(2′-propinyl)semibenzenes 33–35 (Scheme 8) undergo [3,4]- and [1,2]-sigmatropic rearrangements to give again allenyl- and (2′-propinyl)benzenes, whereas the thermal rearrangements to the 3′-butinyl- and (2′,3′-butadienyl)benzenes (Scheme 9) involves a radical mechanism. In contrast, the o-(2′-propinyl)semibenzene b (Scheme 7) leads to (2′,3′-butadienyl)benzene 32 via a thermal [3,3]-sigmatropic rearrangement.