Exploration of pipecolate sulfonamides as binders of the FK506-binding proteins 51 and 52.

FK506-binding proteins (FKBP) 51 and 52 are cochaperones that modulate the signal transduction of steroid hormone receptors. Single nucleotide polymorphisms in the gene encoding FKBP51 have been associated with a variety of psychiatric disorders. Rapamycin and FK506 are two macrocyclic natural products, which tightly bind to most FKBP family members, including FKBP51 and FKBP52. A bioisosteric replacement of the α-ketoamide moiety of rapamycin and FK506 with a sulfonamide was envisaged with the retention of the conserved hydrogen bonds. A focused solid support-based synthesis protocol was developed, which led to ligands with submicromolar affinity for FKBP51 and FKBP52. The molecular binding mode for one sulfonamide analogue was confirmed by X-ray crystallography.