Potent and selective active-site-spanning inhibitors have been designed for cathepsin K, a cysteine protease unique to osteoclasts. They act by mechanisms that involve tight binding intermediates, potentially on a hydrolytic pathway. X-ray crystallographic, MS, NMR spectroscopic, and kinetic studies of the mechanisms of inhibition indicate that different intermediates or transition states are being represented that are dependent on the conditions of measurement and the specific groups f lanking the carbonyl in the inhibitor. The species observed crystallographically are most consistent with tetrahedral intermediates that may be close approximations of those that occur during substrate hydrolysis. Initial kinetic studies suggest the possibility of irreversible and reversible active-site modification. Representative inhibitors have demonstrated antiresorptive activity both in vitro and in vivo and therefore are promising leads for therapeutic agents for the treatment of osteoporosis. Expansion of these inhibitor concepts can be envisioned for the many other cysteine proteases implicated for therapeutic intervention.
Loss-of-function mutations in the ligand-binding domain of human peroxisome proliferator-activated receptor gamma (PPARgamma) are associated with a novel syndrome characterized by partial lipodystrophy and severe insulin resistance. Here we have further characterized the properties of natural dominant-negative PPARgamma mutants (P467L, V290M) and evaluated the efficacy of putative natural ligands and synthetic thiazolidinedione (TZD) or tyrosine-based (TA) receptor agonists in rescuing mutant receptor function. A range of natural ligands failed to activate the PPARgamma mutants and their transcriptional responses to TZDs (e.g. pioglitazone, rosiglitazone) were markedly attenuated, whereas TAs (e.g. farglitazar) corrected defects in ligand binding and coactivator recruitment by the PPARgamma mutants, restoring transcriptional function comparable with wild-type receptor. Transcriptional silencing via recruitment of corepressor contributes to dominant-negative inhibition of wild type by the P467L and V290M mutants and the introduction of an artificial mutation (L318A) disrupting corepressor interaction abrogated their dominant-negative activity. More complete ligand-dependent corepressor release and reversal of dominant-negative inhibition was achieved with TA than TZD agonists. Modeling suggests a structural basis for these observations: both mutations destabilize helix 12 to favor receptor-corepressor interaction; conversely, farglitazar makes more extensive contacts than rosiglitazone within the ligand-binding pocket, to stabilize helix 12, facilitating corepressor release and transcriptional activation. Farglitazar was a more potent inducer of PPARgamma target gene (aP2) expression in peripheral blood mononuclear cells with the P467L mutation. Having shown that rosiglitazone is of variable and limited efficacy in these subjects, we suggest that TAs may represent a more rational therapeutic approach.
The tritium exchange labeling of a variety of complex compounds is achieved in the presence of catalyst precursor [(cod)Ir(PPh3)2]BF4 and limited amounts of tritium gas. The regioselectivity of exchange is high and consistent with empirical rules previously observed. High specific activity levels are often achieved, usually with specific aryl C‐H bonds. However, remarkably efficient exchange occurs in certain N‐alkyl groups. Studies of intermolecular inhibition of catalytic exchange suggest reasons why larger amounts of complex are sometimes required to label complex molecules; nevertheless, significant amounts of label incorporation into substrates can be achieved even starting with small amounts of labeling gas. © 1997 John Wiley & Sons, Ltd.
Carvedilol (SK&F 1055 17) possesses unique cardiovascular activity, and is under development for indications such as angina and hypertension. Tritium labeled enantiomers of Carvedilol and racemates of three metabolites were needed for phannacologic and drug metabolic studies. These compounds were synthesized by catalytic tritium-halogen exchange using tritium gas and 10% palladium-on-carbon catalyst. The precursors were polyhalogenated in the carbazole ring. Direct electrophilic bromination of the enantiomers of Carvedilol gave precursors that were converted to the corresponding mtiated final products by catalytic tritium halogen exchange. Bromination of 4-(2,3-epoxypropyloxy)-9H-carbazole gave an intermediate that was converted to the halogenated precursors of the racemic metabolites. Elaboration of this intermediate, 1,3,6-tribromo-4-(2,3-epoxypropyloxy)-9H-carbazole, to the desired metabolite precursors was achieved by nucleophilic epoxide opening with suitably functionalized U-benzyl aryloxyethylamines. Catalytic tritium-halogen exchange upon the brominated metabolite precursors was accompanied by cleavage of u-and Q-benzyl protecting groups. Radiochemical purities of all tritiated final products were greater than 98% after preparative HPLC. Specific activities of the final products, determined by mass spectrometry, ranged from 35 to 76 Ci/mmol. Optical purity of the Carvedilol enantiomers, determined by chiral HPLC, was greater than 99%
The pyridinyl imidazole cytokine-suppressing anti-inflammatory drug (CSAID"), SB 206718 (1) was required in 1251-labeled form for photoaffinity ligand studies. The target compound (SB 206718-[1251], [1*5I]l) was obtained via conversion of the highly functionalized 1 to a tributylstannyl derivative. Radioiododestannylation using Na125I in the presence of chloramine-T gave good radiochemical yields of the title compound (42-69%, four radiosyntheses) at high radiochemical purity (>98%) after HPLC purification at specific activities of 1670-1736 Ci/mmol. Key Words: Pyridinyl imidazole, CSAIDTM, iodine-125, photoaffinity labelling 206718 (1) belongs to a class of novel antiinflammatory agents with the potential to modify the course of chronic inflammatory disease by inhibition of IL-1 and TNF-a. An iodine-125 labeled analog of 1 was critical for pharmacologic studies aimed at identifying the cytokinesuppressing anti-inflammatory drug (CSAIDTM) binding protein. SB 206718-[125I] has now been prepared in high yield and successfully used to identify, purify and characterize the CSAID binding protein (4).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.