A good imitation: Aryl‐1‐indanyl ketones are found to be highly efficient, reversible, cell‐penetrating inhibitors of the human peptidyl prolyl cis/trans isomerase Pin1. Owing to their structure 1, they are assumed to mimic the transition state 2 of the enzymatically catalyzed rotation about the imidic peptide bond preceding a proline residue.

The novel 3H-spiro[1-benzofuran-2-cyclopentan]-3-one skeleton has been made accessible by different routes. One- and two-step protocols lead to tricyclic and tetracyclic benzofuranones 2 and 3, respectively. A four-step synthesis to spirocompound 4 is described. The novel spirocyclic benzofuranones display modest to no inhibition of the human peptidyl prolyl cis/trans isomerase Pin1.

Geschickt imitiert: Aryl‐1‐indanylketone erweisen sich als hocheffiziente, reversible und zellgängige Inhibitoren der humanen Peptidyl‐Prolyl‐cis/trans‐Isomerase Pin1. Aufgrund ihrer Struktur 1 wird angenommen, dass sie den Übergangszustand 2 der enzymatisch katalysierten Rotation um die imidische Peptidbindung vor dem Prolin nachahmen.