Identification of (3R)-7-Hydroxy-N-((1S)-1-{[(3R,4R)-4-(3-hydroxyphenyl)- 3,4-dimethyl-1-piperidinyl]methyl}-2-methylpropyl)-1,2,3,4-tetrahydro- 3-isoquinolinecarboxamide as a Novel Potent and Selective Opioid κ Receptor Antagonist