Synthesis of alamandine glycoside analogs as new drug candidates to antagonize the MrgD receptor for pain relief

Two series of putatively brain-penetrant alamandine glycosides have been prepared for screening against the MrgD receptor. The first series retains the initial six residues of the alamandine sequence (ARVYIHP) as the “peptide message,” replacing the C-terminal proline (P) with several serine (S) glycosides at the C-terminus to produce “glycoside addresses”. In the second series, steric bulk was altered to modify the “peptide message”– the N-terminal alanine (A) residue was substituted with glycine (G); D-alanine (a); nor-valine (norV); D-nor-valine (D-norV); valine (V); and D-nor-valine (v), keeping the C-terminal serine-beta-D-glucoside (S-Glc) “glycoside address” constant. All the peptides and glycopeptides were synthesized as their C-terminal amides. The purity of native alamandine and its eleven selected derivatives were each 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. [Figure not available: see fulltext.].