*2.1. Peptides*

Synthetic Esc(1-21) (GIFSKLAGKKIKNLLISGLKG-NH2) and its diastereomer, Esc(1- 21)-1c, GIFSKLAGKKIKN(d-Leu)LI(d-Ser)GLKG-NH2, were purchased from Biomatik (Wilmington, NC, USA). Briefly, the peptides were assembled by stepwise solid-phase synthesis using a standard F-moc protocol and purified via reverse-phase high-performance liquid chromatography (RP-HPLC) to a purity of 95%. The molecular mass was verified by mass spectrometry (Figure S1).
