Synthesis of Alamandine Glycoside Analogues as New Drug Candidates to Antagonize the MrgD Receptor for Pain Relief

Abstract

Two series of putatively brain-penetrant alamandine glycosides have been prepared for screening against the MrgD receptor. One series has retained the first 6 residues of the alamandine sequence (ARVYIH), replacing the terminal proline (P) with serine (S) glycosides at the C-terminus. In the second series, the alteration of the steric bulk was performed by changing the initial alanine (A) residue with glycine (G); D-alanine (a); nor-valine (norV); D-nor-valine (D-norV); valine (V); and D-nor-valine (v) with keeping the serine-beta-D-glucoside (S-Glc) at the C-terminus. All the peptides and glycopeptides were synthesized as their C-terminal amide. The purity of native alamandine and its eleven selected derivatives was confirmed using analytical HPLC. Also, the molecular weight and chemical composition were confirmed using mass spectroscopy. The MrgD receptor expression was evaluated in rationally chosen human cell lines, A549 and HEK 293. Both cell lines showed the presence of the MrgD receptor around 35 kDa, as confirmed by western blot analysis. The effect of varying concentrations of some alamandine derivatives on cell viability was evaluated on HEK 293 and A549 cell lines.