Reports of a high-affinity ligand for E-selectin, sialyl di-Lewis(x) (sLe(x)Le(x), 1), motivated us to incorporate modifications to previously reported biphenyl-based inhibitors that would provide additional interactions with the protein. These compounds were assayed for the ability to inhibit the binding of sialyl Lewis(x) (sLe(x), 2) bearing HL-60 cells to E-, P-, and L-selectin fusion proteins. We report that dimeric or trimeric compounds containing multiple components of simple nonoligosaccharide selectin antagonists inhibit sLe(x)-dependent binding with significantly enhanced potency over the monomeric compound. The enhanced potency is consistent with additional binding interactions within a single selectin lectin domain; however, multivalent interaction with multiple lectin domains as a possible alternative cannot be ruled out. Compound 15e (TBC1269) showed optimal in vitro activity from this class of antagonists and is currently under development for use in the treatment of asthma.
The calcium dependent E-selectin/sialyl Lewisx (sLex) interaction plays a key role in inflammation where it mediates the rolling of leukocytes prior to firm adhesion and extravasation from the vasculature. A model of E-selectin/sLex binding, along with previously reported structure-activity relationships of sLex-related oligosaccharide, was used in the rational design of non-oligosaccharide inhibitors of this pivotal interaction. A palladium-mediated biaryl-coupling (Suzuki) reaction was used as the key step to prepare a number of substituted biphenyls which were assayed for their ability to inhibit the binding of E-, P-, and L-selectin-IgG fusion proteins to sLex expressed on the surface of HL60 cells. Some of the compounds developed had greater in vitro potency than the parent sLex tetrasaccharide and are currently being evaluated in in vivo models of inflammation to select a candidate for clinical development.
We have previously disclosed the discovery of 2,4-disubstituted anilinothiophenesulfonamides with potent ET(A)-selective endothelin receptor antagonism and the subsequent identification of sitaxsentan (TBC11251, 1) as a clinical development compound (Wu et al. J. Med. Chem. 1997, 40, 1682 and 1690). The orally active 1 has demonstrated efficacy in a phase II clinical trial of congestive heart failure (Givertz et al. Circulation 1998, 98, Abstr. #3044) and was active in rat models of myocardial infarction (Podesser et al. Circulation 1998, 98, Abstr. #2896) and acute hypoxia-induced pulmonary hypertension (Chen et al. FASEB J. 1996, 10 (3), A104). We now report that an additional substituent at the 6-position of the anilino ring further increases the potency of this series of compounds. It was also found that a wide range of functionalities at the 3-position of the 2,4,6-trisubstituted ring increased ET(A) selectivity by approximately 10-fold while maintaining in vitro potency, therefore rendering the compounds amenable to fine-tuning of pharmacological and toxicological profiles with enhanced selectivity. The optimal compound in this series was found to be TBC2576 (7u), which has approximately 10-fold higher ET(A) binding affinity than 1, high ET(A)/ET(B) selectivity, and a serum half-life of 7.3 h in rats, as well as in vivo activity.
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