Natesan Murugesan

Dual metalloprotease inhibitors. I. constrained peptidomimetics of mercaptoacyl dipeptides

Abstract A series of benzo-fused lactams were incorporated as conformationally restricted dipeptide mimetics of Ala-Pro in dual-acting ACE/NEP inhibitors 1 and 2. The result of this modification led to compounds possessing excellent inhibitory potency versus ACE and NEP both in vitro and in vivo.

MERCAPTOACYL DIPEPTIDES AS DUAL INHIBITORS OF ANGIOTENSIN-CONVERTING ENZYME AND NEUTRAL ENDOPEPTIDASE PRELIMINARY STRUCTURE-ACTIVITY STUDIES

Abstract Mercaptoacyl dipeptides were prepared as dual-acting ACE/NEP inhibitors. Inhibition of each enzyme may be explained by different binding models. Structure-activity studies determined that, in this series of compounds, the mercaptopropanoyl dipeptide framework leads to increased affinity for NEP but diminished ACE activity in vivo .

Reductions in log P improved protein binding and clearance predictions enabling the prospective design of cannabinoid receptor (CB1) antagonists with desired pharmacokinetic properties.

Several strategies have been employed to reduce the long in vivo half-life of our lead CB1 antagonist, triazolopyridazinone 3, to differentiate the pharmacokinetic profile versus the lead clinical compounds. An in vitro and in vivo clearance data set revealed a lack of correlation; however, when compounds with <5% free fraction were excluded, a more predictable correlation was observed. Compounds with log P between 3 and 4 were likely to have significant free fraction, so we designed compounds in this range to give more predictable clearance values. This strategy produced compounds with desirable in vivo half-lives, ultimately leading to the discovery of compound 46. The progression of compound 46 was halted due to the contemporaneous marketing and clinical withdrawal of other centrally acting CB1 antagonists; however, the design strategy successfully delivered a potent CB1 antagonist with the desired pharmacokinetic properties and a clean off-target profile.

REDUCTION OF SITE-SPECIFIC CYP3A-MEDIATED METABOLISM FOR DUAL ANGIOTENSIN AND ENDOTHELIN RECEPTOR ANTAGONISTS IN VARIOUS IN VITRO SYSTEMS AND IN CYNOMOLGUS MONKEYS

2-{Butyryl-[2′-(4,5-dimethyl-isoxazol-3-ylsulfamoyl)-biphenyl-4-ylmethyl]-amino}-N-isopropyl-3-methyl-butyramide (BMS-1) is a potent dual acting angiotensin-1 and endothelin-A receptor antagonist. The compound was subject to rapid metabolic clearance in monkey and human liver microsomes and exhibited low systemic exposure and marked interanimal variability in cynomolgus monkeys after p.o. administration. The variability pattern was identical to that of midazolam given p.o. in the same monkeys, as measured by area under the curve and Cmax values, suggesting that CYP3A-mediated metabolism might play a role in the rapid clearance and observed interanimal variability. Subsequent in vitro metabolism studies using human liver microsomes and cDNA-expressed human cytochrome P450 (P450) enzymes revealed that BMS-1 was a CYP3A4 substrate and was not metabolized by other human P450 enzymes. Mass spectral and NMR analyses of key metabolites led to the identification of the dimethyl isoxazole group as a major metabolic soft spot for BMS-1. Replacement of the 4-methyl group on the isoxazole ring with halogens not only improved overall metabolic stability but also decreased CYP3A-mediated hydroxylation of the isoxazole 5-methyl group. As exemplified by 2-{butyryl-[2′-(4-fluoro-5-methyl-isoxazol-3-ylsulfamoyl)-biphenyl-4-ylmethyl]-amino}-N-isopropyl-3-methyl-butyramide (BMS-3), a fluorinated analog of BMS-1, the structural modification resulted in an increase in the systemic exposure relative to previous analogs and a dramatic reduction in interanimal variability in the monkeys after p.o. administration. In addition, BMS-3 could be metabolized by both CYP2C9 and CYP3A4, thus avoiding the reliance on a single P450 enzyme for metabolic clearance. Integration of results obtained from in vitro metabolism studies and in vivo pharmacokinetic evaluations enabled the modulation of site-specific CYP3A-mediated metabolism, yielding analogs with improved overall metabolic profiles.

Design and synthesis of nonpeptidal endothelin receptor antagonists based on the structure of a cyclic pentapeptide

Abstract A series of dibenzodiazepine-10-acetic acid derivatives were synthesized as prototypes to mimic the structural features of the cyclopentapeptide endothelin antagonist 1. Some of the analogs showed moderate affinity for both the ETA and ETB receptors.

Synthesis and In Vivo Evaluation of Novel PET Radioligands for Imaging the Endothelin-A Receptor

The endothelin subtype-A (ETA) receptor is a member of a family of G-protein–coupled receptors that plays a central role in vasoconstriction, cell proliferation, and hormone production. The aim of this study was to synthesize and evaluate in vivo 11C- and 18F-labeled analogs of the potent and selective ETA antagonist N-[[2′-[[(4,5-dimethyl-3-isoxazolyl)amino]sulfonyl]-4-(2-oxazolyl)[1,1′-biphenyl]-2-yl]methyl]-N,3,3-trimethylbutanamide (BMS-207940). Methods: Protected precursors and authentic nonradioactive standards were synthesized by reductive amination and subsequent alkylation of protected aldehyde 1. Desmethyl precursor 2 was reacted with 11C-methyl iodide followed by deprotection and high-performance liquid chromatography purification to produce 11C-(N-[[2′-[[(4,5-dimethyl-3-isoxazolyl)amino]sulfonyl]-4-(2-oxazolyl)[1,1′-biphenyl]-2-yl]methyl]-N,1-methylindolecarboxamide) (11C-BMS-5p) 3. Nitro precursor 4 was reacted with 18F-fluoride and purified by high-performance liquid chromatography to produce 18F-(N-[[2′-[[(4,5-dimethyl-3-isoxazolyl)amino]sulfonyl]-4-(2-oxazolyl)[1,1′-biphenyl]-2-yl]methyl]-N,4-fluorobenzamide) (18F-FBzBMS) 5. Biodistribution was determined by injecting male CD-1 mice via the tail vein with either 11C-BMS-5p 3 or 18F-FBzBMS 5. Specific binding was determined by pretreatment with 1 mg of BMS-207940 per kilogram. PET scanning of a baboon using either 11C-BMS-5p 3 or 18F-FBzBMS 5 was performed at baseline and 40 min after intravenous administration of 1 mg of BMS-207940 per kilogram. Results: 11C-BMS-5p 3 was synthesized with 1.5% radiochemical yield in 36 min, with an average specific activity of 1,051 GBq/μmol (28,400 mCi/μmol; n = 5) at the end of synthesis. 18F-FBzBMS 5 was synthesized with 0.54% radiochemical yield in 130 min, with an average specific activity of 12.9 GBq/μmol (349 mCi/μmol, n = 7) at the end of synthesis. In mice, the highest uptake of both radioligands was in the liver, lungs, and heart. Radioactivity in the liver washed out over time, and uptake in the lungs and heart remained relatively stable. Mice pretreated with 1 mg of BMS-207940 per kilogram showed greater than 64% specific binding in the lungs and kidneys at 60 min. Specific binding in the heart was determined to be 63% for 11C-BMS-5p 3 and 81% for 18F-FBzBMS 5. PET studies in a baboon showed high uptake of both radioligands in the myocardium. Between 35 and 85 min, the heart-to-blood ratio was 4.7 to 1. Pretreatment with a 1 mg/kg dose of BMS-207940 showed 85% specific binding in the myocardium at 85 min after injection. Conclusion: Both 11C-BMS-5p 3 and 18F-FBzBMS 5 bind selectively to the ETA receptor in vivo. Further development of these radioligands for imaging the ETA receptor in humans is warranted.

Characterization of a novel and selective CB1 antagonist as a radioligand for receptor occupancy studies

Obesity remains a significant public health issue leading to Type II diabetes and cardiovascular disease. CB1 antagonists have been shown to suppress appetite and reduce body weight in animal models as well as in humans. Evaluation of pre-clinical CB1 antagonists to establish relationships between in vitro affinity and in vivo efficacy parameters are enhanced by ex vivo receptor occupancy data. Synthesis and biological evaluation of a novel and highly selective radiolabeled CB1 antagonist is described. The radioligand was used to conduct ex vivo receptor occupancy studies.