Cyclopropane-Derived Peptidomimetics. Design, Synthesis, and Evaluation of Novel Ras Farnesyltransferase Inhibitors

Abstract

Trisubstituted cyclopropanes have previously been established as rigid replacements of dipeptide arrays in several biological systems. Toward further evaluating the utility of these dipeptide mimics in the design of novel CA(1)A(2)X-based inhibitors of Ras farnesyltransferase (FTase), the conformationally constrained, diastereomeric pseudopeptides CAbuPsi[COcpCO]FM 7-9, the flexible analogue CAbuPsi[CHOHCH(2)]FM (10), and the tetrapeptide CAbuFM (6) were prepared. The orientations of the two peptide backbone substituents and the phenyl group on the cyclopropane rings in 7-9were specifically designed to probe selected topological features of the hydrophobic binding pocket of the A(2) subsite of FTase. The syntheses of the requisite trisubstituted cyclopropane carboxylic acid 22 and the diastereomeric cyclopropyl lactones 32a,b featured diastereoselective intramolecular cyclopropanations of chiral allylic diazoacetates and a new method for introducing side chains onto the C-terminal amino acid of cyclopropane-derived dipeptide replacements via the opening of an N-Boc-aziridine with an organocuprate. These cyclopropane intermediates were then converted into the targeted FTase inhibitors 7-9 by standard peptide coupling techniques. The pseudopeptides 7-9 were found to be competitive inhibitors of Ras FTase with IC(50)s of 1055 nM for 7, 760 nM for 8, and 7200 nM for 9. The flexible analogue 10 of these constrained inhibitors exhibited a IC(50) of 320 nM and hence was slightly more potent than 7 and 8. All of these pseudopeptides were less potent than the tetrapeptide parent CAbuFM (6), which had an IC(50) of 38 nM. Because 7 and 8 are approximately equipotent, it appears that the orientation of the peptide backbone substituents on the cyclopropane rings in 7 and 8 do not have any significant effect on binding affinity and that multiple binding modes are possible without significant changes in affinity. On the other hand, this flexibility does not extend to the orientation of the side chain of the A(2) residue as 7 and 8 were both nearly 1 order of magnitude more potent than 9. Comparison of the relative potencies of 6 and 10 suggests that the amide linkage between the A(1) and the A(2) residues of CA(1)A(2)X-derived FTase inhibitors is important.

Design, Synthesis, and Evaluation of Matrix Metalloprotease Inhibitors Bearing Cyclopropane-Derived Peptidomimetics as P1‘ and P2‘ Replacements

“…We previously found that rigidified pseudopeptides incorporating replacements derived from 2 were either equipotent or less active than their flexible derivatives. [5][6][7][8]11 The present results thus clearly signal that further investigations are necessary to understand the basis of these differences and to establish the scope and utility of cyclopropane-derived isosteres related to 3.…”

“…To evaluate 1,2,3-trisubstituted cyclopropane derivatives of 2 and 3 as peptide isosteres, we developed a number of efficient methods for the enantioselective syntheses of cyclopropanes bearing functionally diverse substituents . Cyclopropanes, primarily those related to 2 , were then incorporated as rigid replacements into biologically active inhibitors of renin, HIV-1 protease, and Ras farnesyltransferase, as well as enkephalin analogues 8 and SH2 antagonists . Cyclopropanes have also been used by others as peptide mimics .…”

Natural Products and Their Mimics as Targets of Opportunity for Discovery

“…In subsequent work, we studied conformationally constrained analogues of matrix metalloprotease inhibitors, 190 Ras-farnesyltransferase inhibitors, 191 and enkephalins. 192 In each of these investigations, we never observed more than a 10-fold enhancement in potency for the constrained analogue over its more flexible control.…”

Synthesis of Fluorinated Cyclopropyl Amino Acid Analogues: Toward the Synthesis of Original Fluorinated Peptidomimetics.

“…For example, fluorinated amino acids (trifluoroleucine and trifluoromethionine, in particular) have recently emerged as valuable building blocks for designing hyperstable proteins folds as well as directing highly specific protein–protein interactions . Moreover, the design of small rigid molecules, such as cyclopropane peptidomimetics, that replicate the essential features of oligopeptide secondary structure is a central goal in efforts to identify peptide-like ligands having high affinity for biological targets . The incorporation of cyclopropyl amino acids has already been reported in the literature showing interesting results in terms of biological activity and conformational induction. ,,, To our knowledge, the synthesis of peptidomimetics incorporating within their structure a fluorinated cyclopropyl amino acid analogue has never been reported in the literature.…”