A series of macrocyclic 3-aminopyrrolidinone farnesyltransferase inhibitors (FTIs) has been synthesized. Compared with previously described linear 3-aminopyrrolidinone FTIs such as compound 1, macrocycles such as 49 combined improved pharmacokinetic properties with a reduced potential for side effects. In dogs, oral bioavailability was good to excellent, and increases in plasma half-life were due to attenuated clearance. It was observed that in vivo clearance correlated with the flexibility of the molecules and this concept proved useful in the design of FTIs that exhibited low clearance, such as FTI 78. X-ray crystal structures of compounds 49 and 66 complexed with farnesyltransferase (FTase)-farnesyl diphosphate (FPP) were determined, and they provide details of the key interactions in such ternary complexes. Optimization of this 3-aminopyrrolidinone series of compounds led to significant increases in potency, providing 83 and 85, the most potent inhibitors of FTase in cells described to date.

The optimization of enzyme inhibitor potency and specificity is an important goal of drug design since both properties contribute to clinical efficacy and safety. Restricting an inhibitor's conformation to one recognized by the enzyme increases potency by lowering the entropic barrier to complex formation, and could potentially enhance specificity by limiting its interactions with other macromolecules. 1 In lieu of detailed structural characterization of enzyme-inhibitor interactions, the transferred nuclear Overhauser effect (trNOE) NMR method has proven valuable in defining conformations of ligands weakly associated with macromolecules. 2 However, despite the considerable implications of the trNOE technique for drug design, there are few instances of the method playing an influential role in inhibitor optimization, 3 and none is directed at designing specific conformational constraints. This report describes the design of a highly potent macrocyclic enzyme inhibitor based on the trNOE structure of a conformationally flexible analogue. Farnesyltransferase (FTase) is an important posttranslational processing enzyme that prenylates proteins using farnesylpyrophosphate (FPP) and enables the participation by some in signal transduction during cell proliferation. 4 Inhibitors of this enzyme (FTIs) are promising antitumor agents, and several are currently being evaluated in human clinical trials. 5 In our investigations of structure-activity relationships of the clinical candidate 1, 6 we found that the related FTI 2, with diminished inhibitory activity (FTase IC 50 475 nM vs 2 nM), was an appropriate ligand for the trNOE experiment.In the absence of added enzyme, NMR spectroscopic evaluation of 2 reveals no defined solution conformation. NMR-derived intramolecular distance constraint data was generated in the presence of the putative FTase‚FPP complex. Ligand-competition experiments with a potent peptidomimetic FTI served to disqualify non-active-site bound contributions. The calculated lowest-energy structures depict folded conformations with the cyanophenyl group flanking the piperazinone ring (Figure 1). 7a Stabilization of this orientation by covalent linkage of the cyanophenyl and piperazinone N-aryl substituent in a macrocycle appeared to be an attractive approach to optimize the properties of 1.The synthesis of a macrocyclic version of 1 is described in Scheme 1. The piperazinone 8, prepared by a Mitsunobu cyclodehydration reaction, 8 was reductively coupled with aldehyde 5 to give 9. Compound 9 was subjected to a tandem basepromoted arylmethanesulfonate deprotection and S N Ar cyclization 9 to give the cyclophane 10 in good yield. Interestingly, 10 exhibits planar chirality, and its enantiomeric conformers are readily resolved by chiral HPLC, due to a sufficient activation energy for their interconversion. 10 The calculated lowest-energy structure of (+)-10 7c (Figure 2, gray) bears close resemblance to available FTase-bound conformations of 2 (Figure 1), especially with regard to the relative positions of ...

Incorporation of polar functionality into a series of highly potent calcitonin gene-related peptide (CGRP) receptor antagonists was explored in an effort to improve pharmacokinetics. This strategy identified piperazinone analogues that possessed improved solubility at acidic pH and increased oral bioavailability in monkeys. Further optimization led to the discovery of the clinical candidate 2-[(8R)-8-(3,5-difluorophenyl)-10-oxo-6,9-diazaspiro[4.5]dec-9-yl]-N-[(2R)-2 0-oxo-1,1 0 ,2 0 ,3-tetrahydrospiro[indene-2,3 0-pyrrolo[2,3-b]pyridin]-5-yl]acetamide (MK-3207) (4), the most potent orally active CGRP receptor antagonist described to date.