Publications

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Abstract A series of dodecanuclear highly positively charged homo‐ and heterometallamacrocycles [{Pd(η 3 ‐2‐Me‐C 3 H 4 )} 6 (4‐PPh 2 py) 12 {M 2 (tpbz)} 3 ] 18+ (M=Pd, Pt; tpbz=1,2,4,5‐tetrakis(diphenylphosphanyl)benzene were synthesized by the quantitative self‐assembly of {Pd(η 3 ‐2‐Me‐C 3 H 4 )} + , {M 2 (tpbz)} 4+ and 4‐PPh 2 py moieties in 2:1:4 molar ratio. The cationic assemblies were obtained as salts of different fluorinated anions with diverse sizes and electronic properties, namely BF 4 − , PF 6 − , SbF 6 − and CF 3 SO 3 − . The new crown‐like metallamacrocycles showed remarkable differences in their NMR spectra due to the presence of the different counteranions. On the basis of the observed variations, the metallacycles have been tested as catalytic precursors in allylic alkylation reactions. The anion‐dependent activity and selectivity has been analysed and compared with that of the corresponding monometallic allylic corners [Pd(η 3 ‐2‐Me‐C 3 H 4 )(4‐PPh 2 py) 2 ]X (X=BF 4 − , PF 6 − , SbF 6 − , CF 3 SO 3 − ). DFT calculations have been employed in order to help to the interpretation of the experimental data and to model the anion–crown interactions.

The rubromycins, such as gamma-rubromycin, heliquinomycin, and griseorhodin A, are a family of extensively modified aromatic polyketides that inhibit HIV reverse transcriptase and human telomerase. Telomerase inhibition crucially depends on the presence of a spiroketal moiety that is unique among aromatic polyketides. Biosynthetic incorporation of this pharmacophore into the rubromycins results in a dramatic distortion of the overall polyketide structure, but how this process is achieved by the cell has been obscure. To identify the enzymes involved in spiroketal construction, we generated 14 gene-deletion variants of the griseorhodin A biosynthetic gene cluster isolated from the tunicate-associated bacterium Streptomyces sp. JP95. Heterologous expression and metabolic analysis allowed for an assignment of most genes to various stages of griseorhodin tailoring and pharmacophore generation. The isolation of the novel advanced intermediate lenticulone, which exhibits cytotoxic, antibacterial, and elastase-inhibiting activity, provided direct evidence that the spiroketal is formed by cleavage of four carbon-carbon bonds in a pentangular polyketide precursor. This remarkable transformation is followed by an epoxidation catalyzed by an unusual cytochrome P450/NADPH:ubiquinone oxidoreductase pair that utilizes a saturated substrate. In addition, the absolute configuration of griseorhodin A was determined by quantum-chemical circular dichroism (CD) calculations in combination with experimental CD measurements.

To broaden the applicability of chemically modified DNAs in nano- and biotechnology, material science, sensor development, and molecular recognition, strategies are required for introducing a large variety of different modifications into the same nucleic acid sequence at once. Here, we investigate the scope and limits for obtaining functionalized dsDNA by primer extension and PCR, using a broad variety of chemically modified deoxynucleotide triphosphates (dNTPs), DNA polymerases, and templates. All natural nucleobases in each strand were substituted with up to four different base-modified analogues. We studied the sequence dependence of enzymatic amplification to yield high-density functionalized DNA (fDNA) from modified dNTPs, and of fDNA templates, and found that GC-rich sequences are amplified with decreased efficiency as compared to AT-rich ones. There is also a strong dependence on the polymerase used. While family A polymerases generally performed poorly on "demanding" templates containing consecutive stretches of a particular base, family B polymerases were better suited for this purpose, in particular Pwo and Vent (exo-) DNA polymerase. A systematic analysis of fDNAs modified at increasing densities by CD spectroscopy revealed that single modified bases do not alter the overall B-type DNA structure, regardless of their chemical nature. A density of three modified bases induces conformational changes in the double helix, reflected by an inversion of the CD spectra. Our study provides a basis for establishing a generally applicable toolbox of enzymes, templates, and monomers for generating high-density functionalized DNAs for a broad range of applications.

Abstract An enantiomerically pure diamine based on the 4,15‐difunctionalized [2.2]paracyclophane scaffold and 2‐formylpyridine self‐assemble into an optically pure cyclic metallosupramolecular Fe 4 L 6 helicate upon mixing with iron(II) ions in a diastereoselective subcomponent self‐assembly process. The cyclic assembly results from steric strain that prevents the formation of a smaller linear dinuclear triple‐stranded helicate, and hence, leads to the larger strain‐free assembly that fulfils the maximum occupancy rule. Interestingly, use of the racemic diamine also leads to a racemic mixture of the homochiral cyclic helicates as the major product in a highly diastereoselective narcissistic chiral self‐sorting manner given the fact that the assembly contains ten stereogenic elements, which can in principle give rise to 149 different diastereomers. The metallosupramolecular aggregates could be characterized by NMR, UV/Vis and CD spectroscopy, mass spectrometry, and X‐ray crystallography.

The tetrahedral [Cu(phenAr(2))(py)(2)](+) coordination motif (phen = 1,10-phenanthroline; py = pyridine) conceived on the basis of the HETPYP concept (heteroleptic pyridyl and phenanthroline metal complexes) is a versatile dynamic unit for constructing various heteroleptic metallosupramolecular pseudo-1D, 2D, and 3D structures, both in solution and the solid state. The 2,9-diaryl substituted phenanthroline (phenAr(2)) serves as a capping ligand for copper(I) ions, as its bulky nature prevents formation of the homoleptic complex [Cu(phenAr(2))(2)](+). Combination of the dynamic and concave metal ligand building block [Cu(phenAr(2))](+) with various pyridine (py) ligands, such as bi-, tri-, and tetra-pyridines, opened the way to infinite 1D helicates, 2D networks, and discrete 3D hexanuclear cages, whereas spatial integration of both phenAr(2) and py units into a single ligand resulted in the formation of a Borromean-ring-type hexanuclear cage.

A series of heterometallic metallamacrocycles have been constructed from self-assembly reactions between the fluorinated Au(I) organometallic compounds [(AuC6F4py)2(μ2-diphosphane)] [diphosphane = bis(diphenylphosphanyl)methane (dppm) (1), 1,2-bis(diphenylphosphanyl)ethane (dppe) (2), trans-1,2-bis(diphenylphosphanyl)ethylene (dppet) (3), 1,3-bis(diphenylphosphanyl)propane (dppp) (4), 1,4-bis(diphenylphosphanyl)butane (dppb) (5), and 4,4′-bis(diphenylphosphanyl)-1,1′-biphenyl (dppdph) (6)] and the cis-blocked complexes [M(P–P)(H2O)2](OTf)2 (M = Pd) (P–P = dppp, dppf) (a,c), (M = Pt) (P–P = dppp, dppf) (b,d). Changes of the backbone of the diphosphanes were seen to have an influence on the resulting species. While the self-assembly reactions involving [(AuC6F4py)2(μ2-dppm)] (1), [(AuC6F4py)2(μ2-dppb)] (5), and [(AuC6F4py)2(μ2-dppdph)] (6) donors gave exclusively [2 + 2] heterometallomacrocycles, the assemblies arising from [(AuC6F4py)2(μ2-dppe)] (2) as well as the combinations between [(AuC6F4py)2(μ2-dppp)] (4) and [M(dppp)(H2O)2](OTf)2 (a, b) and [(AuC6F4py)2(μ2-dppet)] (3) and [M(dppf)(H2O)2](OTf)2 (c, d) consisted of an equilibrium between two macrocyclic species ([2 + 2] and a higher-order aggregate [3 + 3], [4 + 4],...). Multinuclear (1H, 19F, 31P) and diffusion NMR spectroscopy in combination with a complete set of ESI-FT-ICR mass spectrometry experiments were used to elucidate the nature of the different assemblies. DFT calculations were performed in order to calculate the molecular geometry and estimate the relative stability of different conformations of [2 + 2], [3 + 3], and [4 + 4] supramolecular species for two of the used diphosphanes.