Nat. Chem. Biol. 7, 469–478 (2011); published online 15 May 2011; corrected after print 15 February 2012

In the version of this article initially published, the authors concluded, on the basis of the substantial (approximately five-fold) N1 regioselectivity observed for reactions that form the unsubstituted triazole ureas shown in Figures 1–3, that the major regioisomeric product for the 4-substituted triazole ureas shown in Figures 1 and 3 was also the N1 regioisomer. They have since determined by X-ray crystallography (provided as Supplementary Data Sets 1 and 2) that the N2 regioisomer is the major product for the 4-substituted triazole ureas. The structures have been corrected in the HTML and PDF versions of the article and in the chemical probe table associated with the article.