Showing papers by "Burkhard König published in 2006"
TL;DR: Metal complexes with open coordination sites serve as binding sites in the development of chemosensors to study metalloenzyme function in bioinorganic chemistry or to direct supramolecular self-assembly.
Abstract: Metal complexes with open coordination sites have found
wide use in molecular recognition. They serve as binding
sites in the development of chemosensors to study metalloenzyme
function in bioinorganic chemistry or to direct
supramolecular self-assembly. Lewis-acidic metal complexes can target a large variety of Lewis basic functional groups,
which makes them very suitable for the design of synthetic
receptors. Coordination to metal ions occurs typically with large enthalpies compared to those for hydrogen bond
formation, salt-bridges, or dipole-dipole interactions.
203 citations
TL;DR: In this article, the polarity of the melts was estimated using solvatochromic dyes and found to be in the range of DMF or water, depending on the sensitivity of the dye for hydrogen bonds.
160 citations
123 citations
TL;DR: In this paper, a low-melting mixtures of sugar, urea and inorganic======salt as solvent, a fast and efficient palladium-catalyzed catalyzed alkyl transfer with tetraalkyltin reagents was observed.
Abstract: The transfer of simple alkyl groups in
Stille reactions usually requires special solvents
(HMPA) or certain organotin reagents (stannatranes,
monoorganotin halides) to be efficient.
Using low-melting mixtures of sugar, urea and inorganic
salt as solvent, a fast and efficient palladiumcatalyzed
alkyl transfer with tetraalkyltin reagents
was observed. The high polarity and nucleophilic
character of the solvent melt promotes the reaction.
Stille biaryl synthesis using electron-poor and electron-
rich aryl bromides proceeds with quantitative
yields in the sugar-urea-salt melt. Catalyst loading
may be reduced to 0.001 mol% and the catalyst
melt mixture remains active in several reaction
cycles. Showing the same or improved performance
for Stille reactions than organic solvents and allowing
a very simple work up, sugar-urea-salt melts are
a non-toxic and cheap alternative reaction medium
available in bulk quantities for the catalytic process.
96 citations
TL;DR: A simple flavin-based catalytic system is able to transform light into chemical output with amplified response utilizing a Cu(I)-catalyzed cycloaddition reaction.
64 citations
TL;DR: In this article, an efficient strategy for the synthesis of functionalized 2,2′-bipyridines was proposed based on readily available 3-pyridyl-1,2,4-triazine 4-oxides and uses a reaction sequence of nucleophilic substitution of hydrogen and aza Diels-Alder reaction.
47 citations
TL;DR: An extraction method was established to determine the concentration of tattoo pigments and decomposition products quantitatively and, despite the poor solubility of the pigments, a nearly complete recovery from aqueous suspension or skin showing a recovery of up to 100%, except for the very volatile 1,4-DCB.
Abstract: Tattooing is a widespread process of puncturing pigments into skin, whereas the resulting concentration inside the skin remains unknown. Many tattoo colorants are organic pigments, such as azo pigments, manufactured for other uses. To remove tattoos from skin, laser pulses at very high intensities are applied to the skin to destroy the tattoo pigments. Recent investigations have shown that several azo compounds are cleaved by laser light leading to potentially toxic or carcinogenic compounds. To assess the risk of tattooing and laser treatment of tattoos, the concentration of the pigments and their decomposition products in the skin must be determined. Therefore, an extraction method was established to determine the concentration of tattoo pigments and decomposition products quantitatively. The extraction of two widely used azo compounds, Pigment Red 22 and Pigment Red 9, and their laser-induced decomposition products, 2-methyl-5-nitroaniline, 4-nitrotoluene, 2,5-dichloraniline, and 1,4-dichlorobenzene, w...
45 citations
TL;DR: The guanidinium group is a typical functional group in molecules with physiological or biological activity as mentioned in this paper, and its geometry and physiochemical properties are of importance for molecular recognition processes.
Abstract: The guanidinium group is a typical functional group in molecules with physiological or biological activity. Its geometry and physiochemical properties are of importance for molecular recognition processes. We discuss modern synthetic methods for the introduction of the guanidinium group and focus our survey on examples from natural product synthesis and drug synthesis.
40 citations
TL;DR: A two-dimensional chemical system in which a divalent “template” guides and controls the stepwise and cooperative self-assembly mediated by base pairing of adenosine and uridine nucleotides is described.
Abstract: This paper describes a two-dimensional chemical system in
which a divalent “template” guides and controls the stepwise
and cooperative self-assembly mediated by base pairing of
adenosine and uridine nucleotides.
28 citations
TL;DR: In this paper, the authors used potentiometric titration of a series of metal complexes with vacant coordination sites in the presence of molecules resembling amino acid side chain functionalities to screen for new affinities.
27 citations
TL;DR: In this paper, a review summarizes recent work on the synthesis, reactions and applications of α, β-dehydroamino acids, α,β-deh-amino esters, and protected α,α,βdehydronino acids.
Abstract: Dehydroamino acids are versatile intermediates in organic
synthesis and occur as frequent structural motives in natural products and biologically active compounds. This review summarizes recent work (since 1999) on the synthesis, reactions and applications of acyclic and cyclic α,β-dehydroamino acids, α,β-dehydroamino esters, and protected α,β-dehydroamino acids.
TL;DR: The synthesis of guanidino amino acids (GuAA), which are structurally related to Arg and resemble a dipeptide consisting of alpha- and gamma-amino acid with a Guanidinium group in the main chain, are reported.
Abstract: We report the synthesis of guanidino amino acids (GuAA), which are structurally related to Arg and resemble a dipeptide consisting of α- and γ-amino acid with a guanidinium group in the main chain. The compounds are available with different protecting groups in gram amounts and are intended as synthetic building blocks for the construction of synthetic oxoanion or peptide receptors. Tyr, Trp or dansyl-functionalized Lys can be introduced as the α-amino acid part, which leads to luminescent GuAAs. The compounds signal carboxylate binding in MeOH, DMSO and buffered water by change of the emission intensity. The property may find use in the construction of chemosensors.
TL;DR: The scope of the Negishi cross-coupling reaction of organozinc compounds derived from chiral amino acids was extended to electron rich iodoanilines and iodobenzylamines as coupling reagents, allowing the direct modification of serine into phenylalanine derivatives bearing metal ion chelating ligands in their side chain.
TL;DR: The modular synthesis of pyrimidine oligohydrazides and their peptide binding ability are reported and show emission at 423 nm if either excited with light of 320 nm or by a FRET process from a nearby Trp residue.
TL;DR: In this article, the Buchwald-Hartwig coupling reaction was used to synthesize calixarenes with one or two cyclen (1,4,7,10-tetraazacyclododecane) moieties directly connected to the upper rim.
TL;DR: In this article, unsaturated macrocycles were obtained by [2 + 2] photoaddition of acyclic biscinnamates by ortho-xylyl (2) or aryl-1,2-diynyl (6) spacers.
Abstract: Unsaturated macrocycles were obtained by [2 + 2] photoaddition of acyclic biscinnamates. The orientation of the chromophores by ortho-xylyl (2) or aryl-1,2-diynyl (6) spacers leads to the formation of photoproducts in solution as single stereoisomers in high yield. The analogous photocyclization of a cis-enediyne biscinnamate 4 was less efficient, because of a rapid photochemical isomerization of the central double bond.
TL;DR: The synthesis and peptide-binding properties of a Zn(II)nitrilotriacetate complex substituted with pyrimidine hydrazine amides are reported, showing millimolar binding affinity in aqueous buffer to peptides bearing N-terminal His.
TL;DR: The synthesis of a novel chiral dipeptide β-sheet mimic based on aminomethyl-3-oxo-2,3-dihydropyrrole carboxylic acids using a palladium-catalyzed allylation with the chiral Trost ligand as a key step for the construction of a quaternary chiral center.
Abstract: We describe the synthesis of a novel chiral dipeptide β-sheet mimic based on aminomethyl-3-oxo-2,3-dihydropyrrole carboxylic acids. The synthesis uses a palladium-catalyzed allylation with the chiral Trost ligand as a key step for the construction of a quaternary chiral center. This allows the enantioselective conversion of 2-carboxy-3-hydroxy-pyrrole into 3-oxo-2,3-dihydropyrrole-2-allyl-2-carboxylate. The allyl group is subsequently converted into an aldehyde or ester group. Peptide coupling of the 3-oxo-2,3-dihydropyrrole amino acid leads to more extended systems with partially constrained dipeptide units.