Figure 1.

Chemical structures of aminosalicylates and their colon-targeting prodrugs. A: 5-ASA; B: Sulfasalazine; colon-targeting prodrug of 5-ASA with sulfapyridine; C: 4-ASA; D: Amide prodrug of 4-ASA with glycine; E: L-arginine salts of 4-ASA and 5-ASA; F: H₂S-releasing prodrugs of 5-ASA and 4-ASA; G: Prodrugs of 4-ASA with salicylic acid, hydroxybenzene and N-salicyloyl glycine; H: Prodrugs of 4-ASA with substituted phenols; I: amide conjugate of 4-ASA with D-phenylalanine; J: Amide conjugate of 4-ASA with L-tryptophan; K: Amide prodrug of 4-ASA with D-glucosamine; L: Polymeric prodrug of 4-ASA; M: Prodrug of 4-ASA with 4-ASA (4A-4AAz).