Biomedical subjects

Ulrik Boas

Publications and source records attributed to Ulrik Boas.

8 recordsLinked to original sources

PubMed2006

Carbocations in action. Design, synthesis, and evaluation of a highly acid-sensitive naphthalene-based backbone amide linker for solid-phase synthesis.

The design, synthesis, and properties of an extremely acid-labile backbone amide linker based on a regiospecifically substituted tetraalkoxy naphthaldehyde core are presented. This handle enables cleavage of peptide backbone amides (secondary amides) off a solid support using as little as 0.5% TFA in CH2Cl2. This proceeds without cleavage of tert-butyl ethers and tert-butyl esters. The design is based on a DFT study that predicted the most stabile alkoxy-substituted methyl naphthyl carbocation. [structure: see text]

Journal Article↗

PubMed2006

Thiophene backbone amide linkers, a new class of easily prepared and highly acid-labile linkers for solid-phase synthesis.

Solid-phase synthesis is of tremendous importance for small-molecule and biopolymer synthesis. Linkers (handles) that release amide-containing products after completion of solid-phase synthesis are widely used. Here we present a new class of highly acid-labile backbone amide linkers (BAL handles) based on 3,4-ethylenedioxythiophene (EDOT), which we have termed T-BAL. These thiophene linkers are synthesized in three convenient steps from commercially available EDOT. In the linker design, the spacer was introduced to the EDOT core either via a carbon-carbon bond or via a thioether linkage. Introduction of the spacer via a C-C bond was performed by a chemoselective Negishi coupling without transient protection of the aldehyde group to provide the T-BAL1 handle. Introduction via a thioether linkage was performed by a facile nucleophilic aromatic substitution between the brominated EDOT aldehyde and unprotected mercapto acids to provide T-BAL2 and T-BAL3 handles. The minimal use of protecting groups gave the corresponding linker molecules in few synthetic steps and in good yields. After anchoring of the linker to a polymeric support, introduction of the first amino acid was achieved by reductive amination, giving a secondary amine. A following acylation of the secondary amine with a symmetrical amino acid anhydride resulted in a backbone amide linkage between the handle and the growing substrate (e.g., peptide chain). After solid-phase synthesis, the substrates could be released from the resin by either low acid conditions using 1% TFA in CH2Cl2 or high acid conditions such as 50% TFA in CH2Cl2. Peptide thioesters could be released from the T-BAL1 handle under very mild conditions using aqueous acetic acid. Tert-butyl based protecting groups, tert-butyl esters, tert-butyl ethers, and Boc groups, as well as dimethyl acetals were relatively stable to these mild conditions for release of the peptides.

Amides↗

PubMed2004

Role of the peri-effect in synthesis and reactivity of highly substituted naphthaldehydes: a novel backbone amide linker for solid-phase synthesis.

Handles (linkers) with an aldehyde functionality that permits the anchoring of substrates by reductive amination have, since their first report in the mid-1990s, become widely-used tools in solid-phase synthesis. In the synthesis of peptides, they allow anchoring of the growing peptide chain through a backbone amide, thus giving easy access to C-terminal modified or cyclic peptides. Recently, we described two new handles (NAL-1 and NAL-2) with dialkoxynaphthaldehyde core structures. Here, we describe the design, synthesis and properties of a novel trialkoxynaphthalene-based backbone amide linker (NAL-3). The NAL-3 handle is based on a trialkoxynaphthaldehyde (NALdehyde-3) that was synthesized in nine high-yielding steps from 3-methoxyphenylacetic acid in 51% overall yield. The naphthalene ring system was constructed using a regioselective methanesulfonic acid-catalyzed ring-closing reaction. The tetra-substituted naphthalene derivative 1,3,6-trimethoxynaphthalene-2-carbaldehyde (7) was selectively demethylated in the 1 position using BBr(3). The selectivity of this reaction is discussed, based on the crystal structures of reactant and product, 1-hydroxy-3,6-dimethoxy-naphthalene-2-carbaldehyde (8), and in the context of the peri-effect. The new handle was anchored to an aminomethylated poly(styrene) solid support, followed by assembly of a model dipeptide, then a study of the cleavage properties under acidic conditions was carried out. Surprisingly, the trialkoxynaphthaldehyde-based handle proved less acid-labile than the dialkoxynaphthaldehyde handles, and this fact is discussed with respect to handle design.

Aldehydes↗

PubMed2004

Amyloid aggregates of the prion peptide PrP106-126 are destabilised by oxidation and by the action of dendrimers.

The prion protein (PrP) peptide 106-126 forms amyloid aggregates in vitro and this sequence is speculated to be involved in the formation of amyloid fibrils by the abnormally folded PrP protein (PrPSc) found in spongiform encephalopathies. It is shown here by incubation experiments in water using Thioflavin T (ThT) as a fluorescent probe for amyloid formation that changes in C-terminal charge, oxidation state and conformational stabilisation lead to large changes in amyloid forming behaviour (amyloidogenicity) of this peptide. Amyloid formation is favoured by a charged C-terminus and is strongly inhibited by oxidation. Furthermore, cationic dendrimers are shown to perturb peptide fibrillation in a process dependent on the nature of the charged groups on the dendrimer surface.

Amino Acid Sequence↗

PubMed2003

Dendrimers in drug research.

Dendrimers are versatile, derivatisable, well-defined, compartmentalised chemical polymers with sizes and physicochemical properties resembling those of biomolecules e.g. proteins. The present critical review (citing 158 references) briefly describes dendrimer design, nomenclature and divergent/convergent dendrimer synthesis. The characteristic physicochemical features of dendrimers are highlighted, showing the effect of solvent pH and polarity on their spatial structure. The use of dendrimers in biological systems are reviewed, with emphasis on the biocompatibility of dendrimers, such as in vitro and in vivo cytotoxicity, as well as biopermeability, biostability and immunogenicity. The review deals with numerous applications of dendrimers as tools for efficient multivalent presentation of biological ligands in biospecific recognition, inhibition and targeting. Dendrimers may be used as drugs for antibacterial and antiviral treatment and have found use as antitumor agents. The review highlights the use of dendrimers as drug or gene delivery devices in e.g. anticancer therapy, and the design of different host-guest binding motifs directed towards medical applications is described. Other specific examples are the use of dendrimers as 'glycocarriers' for the controlled multimeric presentation of biologically relevant carbohydrate moieties which are useful for targeting modified tissue in malignant diseases for diagnostic and therapeutic purposes. Finally, the use of specific types of dendrimers as scaffolds for presenting vaccine antigens, especially peptides, for use in vaccines is presented.

Amines↗

PubMed2002

New dendrimer-peptide host-guest complexes: towards dendrimers as peptide carriers.

Adamantyl urea and adamantyl thiourea modified poly(propylene imine) dendrimers act as hosts for N-terminal tert-butoxycarbonyl (Boc)-protected peptides and form chloroform-soluble complexes. Investigations with NMR spectroscopy show that the peptide is bound to the dendrimer by ionic interactions between the dendrimer outer shell tertiary amines and the C-terminal carboxylic acid of the peptide, and also through host-urea to peptide-amide hydrogen bonding. The hydrogen-bonding nature of the peptide-dendrimer interactions was further confirmed by using Fourier transform IR spectroscopy, for which the NH- and CO-stretch signals of the peptide amide moieties shift towards lower wavenumbers upon complexation with the dendrimer. Spatial analysis of the complexes with NOESY spectroscopy generally shows close proximity of the N-terminal Boc group of the peptide to the peripheral adamantyl groups on the dendrimer host. The influence of side-chain motif on interactions with the host is analyzed by using seven different N-Boc-protected tripeptides as guests for the dendrimer. Downfield shifts of up to 1.3 ppm were observed for the guest amide NH-proton signals. These shifts decreased with increasing 'bulkiness' of the amino acid side chains. Despite this, the dendrimer was capable of making multiple peptide-dendrimer complexes when presented with a library of seven peptides. The different peptides were all present in the host, which did not show specific preferences, and could be released under mild acidic conditions. These results show the general nature of the peptide-dendrimer interactions in the formation of either single- or multiple-peptide-dendrimer complexes.

Amines↗

PubMedDate not supplied

The ortho backbone amide linker (o-BAL) is an easily prepared and highly acid-labile handle for solid-phase synthesis.

The tris(alkoxy)benzyl backbone amide linker (BAL) has found widespread application in solid-phase synthesis. The key intermediate for preparation of para BAL (p-BAL) is 2,6-dimethoxy-4-hydroxybenzaldehyde; several reports on its synthesis have appeared. However, the ortho analogue of the handle (o-BAL) has successfully been used by us for the synthesis of C-terminal-modified peptides, oligosaccharides, and substituted anilines. Here, we present a new and convenient synthesis of the key intermediate for o-BAL, 4,6-dimethoxy-2-hydroxybenzaldehyde, by a highly regioselective demethylation with BBr3, followed by purification through steam distillation. Cleavage studies of Leu-enkephalin anchored to either o-BAL or p-BAL handles revealed that both handles were surprisingly acid-labile and released the peptide with dilute TFA (5% and even 1% TFA in CH2Cl2). This useful property allowed the synthesis of fully protected Leu-enkephalin. The very convenient synthesis of 4,6-dimethoxy-2-hydroxybenzaldehyde combined with the benign properties of the o-BAL handle may make it the preferred regioisomer.

Acids↗

PubMedDate not supplied

Two dialkoxynaphthalene aldehydes as backbone amide linkers for solid-phase synthesis.

Two new solid-phase handles for backbone amide anchoring based on regioisomeric dialkoxynaphthalene aldehydes (NALdehydes) were synthesized in five convenient steps from the corresponding commercially available dihydroxynaphthalenes. The two NALdehydes were coupled to an aminomethyl polystyrene support, the first monomer attached by efficient reductive amination, and the secondary amine acylated to form naphthalene amide linker (NAL-1 and NAL-2) anchoring. After on-resin synthesis, release of peptides was effected with TFA/H(2)O (95:5), TFA/DCM (50:50), or low TFA concentrations. The properties of the NAL handles were evaluated in the solid-phase synthesis of a series of peptides, in which NAL-2 showed the best cleavage properties.

Acylation↗