Small-Molecule Inhibitors of Protein Geranylgeranyltransferase Type I

Abstract

Small molecules that inhibit the geranylgeranylation of K-Ras4B and RhoA by protein geranylgeranyltransferase type I (GGTase-I) were identified from chemical genetic screens of heterocycles synthesized through phosphine catalysis of allenes. To further improve the efficacy of the GGTase-I inhibitors (GGTIs), 4288 related compounds bearing core dihydropyrrole/pyrrolidine and tetrahydropyrdine/piperidine scaffolds were synthesized on SynPhase Lanterns in a split-pool manner through phosphine-catalyzed [3+2] and [4+2] annulations of resin-bound allenoates. Testing of the 4288 analogs resulted in several GGTIs exhibiting submicromolar IC 50 values. Because proteins such as Ras and Rho GTPases are implicated in oncogenesis and metastasis, these GGTIs might ultimately lead to the development of novel antitumor therapeutics.Although library approaches to the discovery of small-molecule enzyme inhibitors or receptor ligands are well established, 1 many reactions continue to pose challenges when applied to solid phase synthesis for the generation of compound libraries. From our development of phosphine catalysis of allenoates, 2 we envisioned that these reactions might be adaptable to solid phase synthesis for the generation of heterocycle libraries using resin-bound allenoates. Before embarking on the potentially time-consuming development of solid phase processes, however, we decided to screen our model compounds synthesized through solution-phase reactions. If we could identify a biologically important molecule from the preliminary screen, it would then be worthwhile pursuing a library generated through solid phase split-pool synthesis. Herein, we report the first example of phosphine catalysis of polymer-bound allenoates and a combinatorial library approach to the development of potent inhibitors of protein geranylgeranyltransferase type I (GGTase-I).Protein prenylation, a posttranslational modification of nascent proteins by either the farnesyl or geranylgeranyl isoprenoid at the C-terminus cysteine residue, is a key event in the regulation of many protein functions. 3 Of particular interest is the farnesylation of the oncogenic forms E-mail: ohyun@chem.ucla With this premise in mind, we screened a collection of 138 heterocycles 9 for their ability to inhibit the activity of human GGTase-I to geranylgeranylate K-Ras4B or RhoA. Purified GGTase-I was incubated with its substrate protein K-Ras4B or RhoA, [ 3 H]GGPP, and the 138 compounds. After 30 min, the degree of incorporation of tritiated geranylgeranyl groups was measured using a scintillation counter. We identified a number of compounds as GGTIs ( Figure 1).This discovery of promising lead GGTI compounds and their moderate activity warranted the development of efficient and rapid syntheses and evaluations of analogous structures in the search for better inhibitors; we envisioned a short, modular synthetic route (Scheme 1), using SynPhase™ lanterns as the solid support. 10 Validation of the synthetic route on the polymer support commenced with formation o...

Recent applications of aziridine ring expansion reactions in heterocyclic synthesis

“…53 Gold catalysts have been applied in cascade-type reactions for the conversion of various 2-(aryloxyprop-1-ynyl)aziridines 74a-h to spiro[isochroman-4,2'-pyrrolines] 75a-h (Scheme 23). 54 The reaction exploited both the σ-and π-Lewis acid properties of the gold salt for a Friedel-Crafts type intramolecular rearrangement followed by the cyclization of an aminoallene intermediate.…”

Inhibitors of Protein Geranylgeranyltransferase I and Rab Geranylgeranyltransferase Identified from a Library of Allenoate-derived Compounds

“…, we reported the construction of a library of allenoate-derived compounds and the identification of novel GGTI compounds (28). The library construction involved the use of allenoates as multireactive core molecules.…”

“…In this study, we first report the identification and characterization of novel inhibitors of GGTase-I that were identified from a chemical compound library that we constructed through diversity-oriented synthesis using allenoic acid-derived starting materials (28). A specific modification that improves their cellular activity has been identified.…”

“…Other chemicals were obtained from Sigma. The allenoate-derived compound library, including P3-E5 and P5-H6, were synthesized as described (28). Detailed methods for the synthesis of P63-F10, P63-C7, P63-E11, P62-A5, P62-C11, P62-E4, and modified P5-H6 compounds (P61-A2, P61-A5, P61-A6, P61-A7 and P61-B4) will be described elsewhere.…”

Chemical Biology/ Chemical Genetics/ Chemical Genomics: Importance of Chemical Library

“…For example, 10,000 compounds with 44 different scaffolds can be obtained from chemical reactions based on this chemistry [26]. We have screened the library constructed by Dr. Kwon and identified novel GGTI compounds [27]. Screening results are summarized in Figure 1.…”