Nat. Chem. Biol. 10, 1066–1072 (2014); published online 26 October 2014; corrected after print 22 December 2014

In the version of this article initially published, the scaffold structure shown for compounds 33 and 34 was incorrect in Figure 4a, with a nitrogen atom misplaced within the five-membered ring moiety. The error has been corrected in the HTML and PDF versions of the article.