A Fluorogenic Molecule for Probing Islet Amyloid Using Flavonoid as a Scaffold Design.

Aggregation of polypeptides and proteins is commonly associated with human and other vertebrate diseases. For example, amyloid plaques consisting of amyloid-ß proteins are frequently identified in Alzheimer's disease and islet amyloid formed by islet amyloid polypeptide (IAPP, amylin) can be found in most patients with type 2 diabetes (T2D). Although many fluorescent dyes have been developed to stain amyloid fibrils, very few examples have been designed for IAPP. In this study, a series of environmentally sensitive fluorescent probes using flavonoid as a scaffold design are rationally designed and synthesized. One of these probes, namely 3-HF-ene-4'-OMe, can bind to IAPP fibrils but not nonfibrillar IAPP by exhibiting a much stronger fluorescent enhancement at 535 nm. In addition, this probe shows better detection sensitivity to IAPP fibrils compared with that of conventionally used thioflavin-T. We demonstrate that 3-HF-ene-4'-OMe can be used to monitor the kinetics of IAPP fibril formation in vitro even in the presence an amyloid inhibitor. To test the specificity of the probe, we attempt to incubate this probe with amyloid fibrils formed from other amyloidogenic proteins. Interestingly, this probe shows different responses when mixed with these fibrils, suggesting the mode of binding of this probe on these fibrils could be different. Moreover, we show that this probe is not toxic to pancreatic mouse ß-cells. Further structural optimization based on the structure of 3-HF-ene-4'-OMe may yield a specific probe for imaging islet amyloid in the pancreas. That would improve our understanding of the relationship between islet amyloid and T2D.

Synthesis of 4-thiol-furanosidic uronate via hydrothiolation reaction.

Uronic acids are not only important building blocks of polysaccharides and oligosaccharides but also are widely used in the food and pharmaceutical industries. Inspired by the structure of natural products, here, we disclosed base-mediated and radical-mediated hydrothiolation reactions for the preparation of thiol-contained uronates. In comparison with base-mediated reaction, radical-mediated hydrothiolation is inefficient due to the electron-withdrawing group on the ethylene group; nevertheless, the adduct had excellent stereoselectivity at both C-4 and C-5 positions. For the alkaline approach, thiols as nucleophiles can regioselectively and stereoselectively attach to the C-4 position of Δ-4,5-unsaturated uronate with moderate to good yields. However, poor stereoselectivity at the C-5 position was observed due to retro thiol-Michael addition. After removing the protecting group of the thiol, the thiol adduct was isomerized to the furanosidic form and the 4-thiol-furanosidic uronate derivative was synthesized for the first time.