Design and Pharmacology of N -[(3 R )-1,2,3,4-Tetrahydroisoquinolinium- 3-ylcarbonyl]-(1 R )-1-(4-chlorobenzyl)- 2-[4-cyclohexyl-4-(1 H -1,2,4-triazol- 1-ylmethyl)piperidin-1-yl]-2-oxoethylamine ( 1 ), a Potent, Selective, Melanocortin Subtype-4 Receptor Agonist