Discovery of hybrid Glypromate conjugates with neuroprotective activity against paraquat-induced toxicity

Neurodegenerative disorders comprise a series of heterogeneous conditions that affect millions of people worldwide, representing a significant health burden in both developed and developing countries. Without disease-modifying treatments currently available, the development of effective neurotherapeutics is a health priority. In this work, a new series of peptide-conjugates of the Glypromate neuropeptide is reported to determine the interplay of annular constriction and neuroprotective activity. To this end, (1R,3S,4S)-2-azanorbornane-3-carboxylic acid was used as an l-proline and l-pipecolic acid surrogate in addition to functionalization of the glutamate residue with relevant active pharmaceutical ingredients (APIs), namely amantadine, memantine, and (R)-1-aminoindane. Using non-differentiated SH-SY5Y cells, conjugates 14a and 15a, functionalized with amantadine, significantly reduced protein aggregation, with 15a outperforming both Glypromate (2-fold enhancement, p < 0.05) and an equimolar mixture of Glypromate and amantadine (p < 0.0001). On the other hand, in SH-SY5Y differentiated cells, conjugate 18c functionalized with (R)-1-aminoindane counteracted the toxicity elicited by paraquat (p < 0.0001), while Glypromate was found to exacerbate the neurotoxicity. Altogether, this work adds new insights into Glypromate research by demonstrating that chemical conjugation and annular constriction are effective strategies to tune neuroprotective responses against different neurotoxic stimuli, paving the way for the development of new neurotherapeutics.