Revised (β-phenyl) stereochemistry of ultrapotent μ opioid BU72

Abstract

In its crystal structure in complex with the μ opioid receptor (μOR), the opioid BU72 exhibits extreme deviations from the expected geometry.¹ Three of these involve the phenyl group. There is also unexplained electron density next to the benzylic carbon. Here I show that inverting the benzylic configuration fills this unexplained density and eliminates the phenyl group outliers, along with all but one of the others. I propose that this is the correct structure of BU72.