From Proteopediaproteopedia link
STRUCTURAL INSIGHTS INTO THE DESIGN OF NONPEPTIDIC ISOTHIAZOLIDINONE-CONTAINING INHIBITORS OF PROTEIN TYROSINE PHOSPHATASE 1B
[PTN1_HUMAN] Tyrosine-protein phosphatase which acts as a regulator of endoplasmic reticulum unfolded protein response. Mediates dephosphorylation of EIF2AK3/PERK; inactivating the protein kinase activity of EIF2AK3/PERK. May play an important role in CKII- and p60c-src-induced signal transduction cascades. May regulate the EFNA5-EPHA3 signaling pathway which modulates cell reorganization and cell-cell repulsion. 
Publication Abstract from PubMed
Structural analyses of the protein-tyrosine phosphatase 1B (PTP1B) active site and inhibitor complexes have aided in optimization of a peptide inhibitor containing the novel (S)-isothiazolidinone (IZD) phosphonate mimetic. Potency and permeability were simultaneously improved by replacing the polar peptidic backbone of the inhibitor with nonpeptidic moieties. The C-terminal primary amide was replaced with a benzimidazole ring, which hydrogen bonds to the carboxylate of Asp(48), and the N terminus of the peptide was replaced with an aryl sulfonamide, which hydrogen bonds to Asp(48) and the backbone NH of Arg(47) via a water molecule. Although both substituents retain the favorable hydrogen bonding network of the peptide scaffold, their aryl rings interact weakly with the protein. The aryl ring of benzimidazole is partially solvent exposed and only participates in van der Waals interactions with Phe(182) of the flap. The aryl ring of aryl sulfonamide adopts an unexpected conformation and only participates in intramolecular pi-stacking interactions with the benzimidazole ring. These results explain the flat SAR for substitutions on both rings and the reason why unsubstituted moieties were selected as candidates. Finally, substituents ortho to the IZD heterocycle on the aryl ring of the IZD-phenyl moiety bind in a small narrow site adjacent to the primary phosphate binding pocket. The crystal structure of an o-chloro derivative reveals that chlorine interacts extensively with residues in the small site. The structural insights that have led to the discovery of potent benzimidazole aryl sulfonamide o-substituted derivatives are discussed in detail.
Structural insights into the design of nonpeptidic isothiazolidinone-containing inhibitors of protein-tyrosine phosphatase 1B.,Ala PJ, Gonneville L, Hillman M, Becker-Pasha M, Yue EW, Douty B, Wayland B, Polam P, Crawley ML, McLaughlin E, Sparks RB, Glass B, Takvorian A, Combs AP, Burn TC, Hollis GF, Wynn R J Biol Chem. 2006 Dec 8;281(49):38013-21. Epub 2006 Oct 6. PMID:17028182
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.