Structure-based drug design identifies polythiophenes as antiprion compounds.

Prions cause transmissible spongiform encephalopathies for which no treatment exists. Prions consist of PrP(Sc), a misfolded and aggregated form of the cellular prion protein (PrP(C)). We explore the antiprion properties of luminescent conjugated polythiophenes (LCPs) that bind and stabilize ordered protein aggregates. By administering a library of structurally diverse LCPs to the brains of prion-infected mice via osmotic minipumps, we found that antiprion activity required a minimum of five thiophene rings bearing regularly spaced carboxyl side groups. Solid-state nuclear magnetic resonance analyses and molecular dynamics simulations revealed that anionic side chains interacted with complementary, regularly spaced cationic amyloid residues of model prions. These findings allowed us to extract structural rules governing the interaction between LCPs and protein aggregates, which we then used to design a new set of LCPs with optimized binding. The new set of LCPs showed robust prophylactic and therapeutic potency in prion-infected mice, with the lead compound extending survival by >80% and showing activity against both mouse and hamster prions as well as efficacy upon intraperitoneal administration into mice. These results demonstrate the feasibility of targeted chemical design of compounds that may be useful for treating diseases of aberrant protein aggregation such as prion disease.

Spectral discrimination of cerebral amyloid lesions after peripheral application of luminescent conjugated oligothiophenes.

In vivo imaging of pathological protein aggregates provides essential knowledge of the kinetics and implications of these lesions in the progression of proteopathies, such as Alzheimer disease. Luminescent conjugated oligothiophenes are amyloid-specific ligands that bind and spectrally distinguish different types of amyloid aggregates. Herein, we report that heptamer formyl thiophene acetic acid (hFTAA) passes the blood-brain barrier after systemic administration and specifically binds to extracellular ß-amyloid deposits in the brain parenchyma (Aß plaques) and in the vasculature (cerebral ß-amyloid angiopathy) of ß-amyloid precursor protein transgenic APP23 mice. Moreover, peripheral application of hFTAA also stained intracellular lesions of hyperphosphorylated Tau protein in P301S Tau transgenic mice. Spectral profiling of all three amyloid types was acquired ex vivo using two-photon excitation. hFTAA revealed a distinct shift in its emission spectra when bound to Aß plaques versus Tau lesions. Furthermore, a spectral shift was observed for Aß plaques versus cerebral ß-amyloid angiopathy, indicating that different amyloid types and structural variances of a specific amyloid type can be distinguished. In conclusion, by adding spectral signatures to amyloid lesions, our results pave the way for a new area of in vivo amyloid imaging, allowing in vivo differentiation of amyloid (sub)types and monitoring changes of their structure/composition over time.

Synthesis of a library of oligothiophenes and their utilization as fluorescent ligands for spectral assignment of protein aggregates.

Molecular probes for selective identification of protein aggregates are important to advance our understanding of the molecular pathogenesis underlying protein aggregation diseases. Here we report the chemical design of a library of anionic luminescent conjugated oligothiophenes (LCOs), which can be utilized as ligands for detection of protein aggregates. Certain molecular requirements were shown to be necessary for detecting (i) early non-thioflavinophilic protein assemblies of Aß1-42 and insulin preceding the formation of amyloid fibrils and (ii) for obtaining distinct spectral signatures of the two main pathological hallmarks observed in human Alzheimer's diease brain tissue (Aß plaques and neurofibrillary tangles). Our findings suggest that a superior anionic LCO-based ligand should have a backbone consisting of five to seven thiophene units and carboxyl groups extending the conjugated thiophene backbone. Such LCOs will be highly useful for studying the underlying molecular events of protein aggregation diseases and could also be utilized for the development of novel diagnostic tools for these diseases.

Synthetic studies of cephalandole alkaloids and the revised structure of cephalandole A.

A synthesis of the originally proposed 2-(1 H-indol-3-yl)-4 H-3,1-benzoxazin-4-one structure of the alkaloid cephalandole A (1) led to a structural revision, and the isolated natural product has now been identified as the previously known compound 3-(1 H-indol-3-yl)-2 H-1,4-benzoxazin-2-one (7). The structural assignment was corroborated by detailed NMR studies. A short synthesis of the related natural compound cephalandole B (2) has also been performed, confirming its structure. In addition some chemical transformations, involving, for example, the related synthetic molecule 2-(1 H-indol-3-yl)-3 H-quinazolin-4-one (9), are presented.

Total synthesis of luotonin A and 14-substituted analogues.

A new and concise synthesis of luotonin A was achieved from the previously described compounds ethyl 4-oxo-3,4-dihydroquinazoline-2-carboxylate and 1-(2-nitrophenyl)prop-2-en-1-one. New 14-substituted luotonin A analogues were prepared using 14-chloroluotonin A as the key intermediate.