From serendipitous reaction discovery to antimycobacterial opportunities: general access to scarcely reported 2-((pyrrolin-5-yl)amino)phenols.

The rearrangement reaction of 3-(benzoxazol-2-yl)propan-1-amines into 2-((pyrrolin-5-yl)amino)phenols was revealed during an X-ray crystallography fragment screening against PptAb, a phosphopantetheinyl transferase from Mycobacterium abscessus. Mechanistic and methodological studies offered access to a scarcely exemplified scaffold and prompted revision of the commercial fragment structure. The relevance of this series for the design of PptAb inhibitors was confirmed by the co-crystallization of synthetic samples within the enzyme active site.