NMR-assisted biometal chelation study of new L-Carnosine mimics: promising neuroprotective agents

Alzheimer's Disease (AD) is a neurodegenerative syndrome that slowly destroys memory and thinking skills, resulting from the loss of brain cells and their connections. [1] It has a multifactorial etiology stemming from both accumulation and aggregation of misfolded proteins, and an imbalance of metal ions that promotes aggregation and neuroinflammation. L-Car is a dipeptide (Figure 1) widely distributed in mammalian tissues and serves as a potential drug candidate [2] for neurodegenerative syndromes due to its radical scavenger, anti-inflammatory, antiaggregant, antiglycation, and well-known zinc-chelating activities. [3] Since the therapeutic potential of L-Car is limited by its low bioavailability, we synthesized new L-Car mimics characterized by phosphate isosteres of the carboxylic group (Figure 1). Therefore, here we illustrate the capability of the novel mimics to chelate the Zn(II) ion through titration experiments carried out by using the NMR presaturation sequence ZGESGP and to compare it with that of L-Car. The NMR analyses were performed at pH 7 and T 310 K to simulate physiological conditions, revealing two main consistent events in the spectra: a variation in chemical shift, common to both L-Car and the mimics, and broadening until complete flattening of the signals, occurring only for Carolp. Based on the regions of shift and/or broadening, we anticipated the structures of the complexes, which will be confirmed by further experiments. Replacing the carboxylic group with the phosphate group enhances interaction with Zn(II), and this finding provides a basis for further experiments involving co-titration and diffusion and for designing and synthesizing novel isosteres with improved chelating profiles.