Analysis of 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine and Its Phase I and Phase II Metabolites in Mouse Urine Using LC�CUV�CMS�CMS

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is an abundantly present heterocyclic aromatic amine which is found to be carcinogenic in rodents, mice and rats. The biotransformation of PhIP is extensive and involves both the formation of bioactivated as well as detoxification metabolites. In order to understand its carcinogenicity, the metabolism of PhIP needs to be studied. Numerous metabolites of PhIP have been described but, so far, assays for their quantitative determination in biological matrices are scarce. We present the development and application of an assay, using reversed phase liquid chromatography coupled to ultraviolet and mass spectrometry detectors for the quantification of PhIP, three phase I and nine phase II metabolites in urine. Additionally, the identification of two PhIP-sulfates by the use of NMR is presented. Sample pretreatment consisted of straightforward dilution of urine. PhIP and its metabolites were shown to be stable in diluted urine for at least 22 h when stored at 2?C8 °C. Precision of the analysis was within 15%. The assay has been successfully applied for the quantification of PhIP and 12 of its metabolites in urine from mice that received 200 mg kg^?1 PhIP via oral gavage.     

A facile strategy to prevent trifluoroacetylation of N-terminal proline peptides

Unwanted trifluoroacetylation occurred at the N-terminus of prolinyl peptides during detachment from the solid phase. This was observed when the N-α-Fmoc protecting group had been removed prior to the final TFA treatment. Subtly changing the SPPS protocol and incorporating Boc- in place of the Fmoc-protected proline as the N-terminal building block efficiently suppressed this side reaction.     

Modular Columnar Supramolecular Polymers as Scaffolds for Biomedical Applications

Self‐assembly of discotic molecules into supramolecular polymers offers a flexible approach for the generation of multicomponent one‐dimensional columnar architectures with tuneable biomedical properties. Decoration with ligands induces specific binding of the self‐assembled scaffold to biological targets. The modular design allows the easy co‐assembly of different discotics for the generation of probes for targeted imaging and cellular targeting with adjustable ligand density and composition.     

Pre- and postfunctionalized self-assembled π-conjugated fluorescent organic nanoparticles for dual targeting

There is currently a high demand for novel approaches to engineer fluorescent nanoparticles with precise surface properties suitable for various applications, including imaging and sensing. To this end, we report a facile and highly reproducible one-step method for generating functionalized fluorescent organic nanoparticles via self-assembly of prefunctionalized π-conjugated oligomers. The engineered design of the nonionic amphiphilic oligomers enables the introduction of different ligands at the extremities of inert ethylene glycol side chains without interfering with the self-assembly process. The intrinsic fluorescence of the nanoparticles permits the measurement of their surface properties and binding to dye-labeled target molecules via F?rster resonance energy transfer (FRET). Co-assembly of differently functionalized oligomers is also demonstrated, which enables the tuning of ligand composition and density. Furthermore, nanoparticle prefunctionalization has been combined with subsequent postmodification of azide-bearing oligomers via click chemistry. This allows for expanding ligand diversity at two independent stages in the nanoparticle fabrication process. The practicability of the different methods entails greater control over surface functionality. Through labeling with different ligands, selective binding of proteins, bacteria, and functionalized beads to the nanoparticles has been achieved. This, in combination with the absence of unspecific adsorption, clearly demonstrates the broad potential of these nanoparticles for selective targeting and sequestration. Therefore, controlled bifunctionalization of fluorescent π-conjugated oligomer nanoparticles represents a novel approach with high applicability to multitargeted imaging and sensing in biology and medicine.     

Stable helical beta 3-peptides in water via covalent bridging of side chains

An on-bead cyclization protocol of beta 3-peptides was developed, providing easy access to cyclic beta 3-peptides. With this methodology, a small library of helical cyclic beta 3-peptides was synthesized and investigated with CD spectroscopy. Covalent bridging of two side chains in beta 3-peptides significantly stabilized their helical conformation in aqueous solutions and turned out to be superior to the previously described electrostatic interactions.     

Designed Asymmetric Protein Assembly on a Symmetric Scaffold

Cellular signaling is regulated by the assembly of proteins into higher‐order complexes. Bottom‐up creation of synthetic protein assemblies, especially asymmetric complexes, is highly challenging. Presented here is the design and implementation of asymmetric assembly of a ternary protein complex facilitated by Rosetta modeling and thermodynamic analysis. The wild‐type symmetric CT32–CT32 interface of the 14‐3‐3–CT32 complex was targeted, ultimately favoring asymmetric assembly on the 14‐3‐3 scaffold. Biochemical studies, supported by mass‐balance models, allowed characterization of the parameters driving asymmetric assembly. Importantly, our work reveals that both the individual binding affinities and cooperativity between the assembling components are crucial when designing higher‐order protein complexes. Enzyme complementation on the 14‐3‐3 scaffold highlighted that interface engineering of a symmetric ternary complex generates asymmetric protein complexes with new functions.     

Self‐Assembled Fluorescent Organic Nanoparticles for Live‐Cell Imaging

Fluorescent, cell‐permeable, organic nanoparticles based on self‐assembled π‐conjugated oligomers with high absorption cross‐sections and high quantum yields have been developed. The nanoparticles are generated with a tuneable density of amino groups for charge‐mediated cellular uptake by a straightforward self‐assembly protocol, which allows for control over size and toxicity. The results show that a single amino group per ten oligomers is sufficient to achieve cellular uptake. The non‐toxic nanoparticles are suitable for both one‐ and two‐photon cellular imaging and flow cytometry, and undergo very efficient cellular uptake.     

Site‐Specific Protection and Dual Labeling of Human Epidermal Growth Factor (hEGF) for Targeting,Imaging, and Cargo Delivery

Well‐defined human epidermal growth factor (hEGF) constructs featuring selectively addressable labels are urgently needed to address outstanding questions regarding hEGF biology. A protein‐engineering approach was developed to provide access to hEGF constructs that carry two cysteine‐based site‐specific orthogonal labeling sites in multi‐milligram quantities. Also, a site‐selective (de)protection and labeling approach was devised, which allows selective modification of these hEGF constructs. The hEGF, featuring three native disulfide bonds, was expressed featuring additional sulfhydryl groups, in the form of cysteine residues, as orthogonal ligation sites at both the N and C termini. Temporary protection of the N‐terminal cysteine unit, in the form of a thiazolidine ring, avoids interference with protein folding and enables sequential labeling in conjunction with the cysteine residue at the C terminus. Based on thus‐generated hEGF constructs, sequential and site‐specific labeling with a variety of molecular probes could be demonstrated, thus leading to a biological fully functional hEGF with specifically incorporated fluorophores or protein cargo and native cellular targeting and uptake profiles. Thus, this novel strategy provides a robust entry to high‐yielding access of hEGF and rapid and easy site‐specific and multifunctional dual labeling of this growth factor.