Synthesis, Pharmacological Evaluation, and Molecular Modeling Studies of Novel Peptidic CAAX Analogues as Farnesyl-Protein-Transferase Inhibitors

(L)-Monomethyl Tyrosine (Mmt): New Synthetic Strategy via Bulky 'Forced-Traceless' Regioselective Pd-Catalyzed C(sp2)-H Activation

The enormous influence in terms of bioactivity, affinity, and selectivity represented by the replacement of (L)-2,6-dimethyl tyrosine (Dmt) instead of Phenylalanine (Phe) into Nociceptin/orphanin (N/OFQ) neuropeptide analogues has been well documented in the literature. More recently, the non-natural amino acid (L)-2-methyl tyrosine (Mmt), with steric hindrance included between Tyr and Dmt, has been studied because of the modulation of steric effects in opioid peptide chains. Here, we report a new synthetic strategy to obtain Mmt based on the well-known Pd-catalyzed ortho-C(sp2)-H activation approach, because there is a paucity of other synthetic routes in the literature to achieve it. The aim of this work was to force only the mono-ortho-methylation process over the double ortho-methylation one. In this regard, we are pleased to report that the introduction of the dibenzylamine moiety on a Tyr aromatic nucleus is a convenient and traceless solution to achieve such a goal. Interestingly, our method provided the aimed Mmt either as N-Boc or N-Fmoc derivatives ready to be inserted into peptide chains through solid-phase peptide synthesis (SPPS). Importantly, the introduction of Mmt in place of Phe1 in the sequence of N/OFQ(1-13)-NH2 was very well tolerated in terms of pharmacological profile and bioactivity.

Rapid analysis of protein farnesyltransferase substrate specificity using peptide libraries and isoprenoid diphosphate analogues

Protein farnesytransferase (PFTase) catalyzes the farnesylation of proteins with a carboxy-terminal tetrapeptide sequence denoted as a Ca₁a₂X box. To explore the specificity of this enzyme, an important therapeutic target, solid-phase peptide synthesis in concert with a peptide inversion strategy was used to prepare two libraries, each containing 380 peptides. The libraries were screened using an alkyne-containing isoprenoid analogue followed by click chemistry with biotin azide and subsequent visualization with streptavidin-AP. Screening of the CVa₂X and CCa₂X libraries with Rattus norvegicus PFTase revealed reaction by many known recognition sequences as well as numerous unknown ones. Some of the latter occur in the genomes of bacteria and viruses and may be important for pathogenesis, suggesting new targets for therapeutic intervention. Screening of the CVa₂X library with alkyne-functionalized isoprenoid substrates showed that those prepared from C₁₀ or C₁₅ precursors gave similar results, whereas the analogue synthesized from a C₅ unit gave a different pattern of reactivity. Lastly, the substrate specificities of PFTases from three organisms (R. norvegicus, Saccharomyces cerevisiae, and Candida albicans) were compared using CVa₂X libraries. R. norvegicus PFTase was found to share more peptide substrates with S. cerevisiae PFTase than with C. albicans PFTase. In general, this method is a highly efficient strategy for rapidly probing the specificity of this important enzyme.

Novel route to chaetomellic acid A and analogues: serendipitous discovery of a more competent FTase inhibitor

A new practical route to chaetomellic acid A (ACA), based on the copper catalysed radical cyclization (RC) of (Z)-3-(2,2-dichloropropanoyl)-2-pentadecylidene-1,3-thiazinane, is described. Remarkably, the process entailed: (i) a one-pot preparation of the intermediate N-α-perchloroacyl-2-(Z)-alkyliden-1,3-thiazinanes starting from N-(3-hydroxypropyl)palmitamide, (ii) a two step smooth transformation of the RC products into ACA and (iii) only one intermediate chromatographic purification step. The method offers a versatile approach to the preparation of ACA analogues, through the synthesis of an intermediate maleic anhydride with a vinylic group at the end of the aliphatic tail, a function that can be transformed through a thiol-ene coupling. Serendipitously, the disodium salt of 2-(9-(butylthio)nonyl)-3-methylmaleic acid, that we prepared as a representative sulfurated ACA analogue, was a more competent FTase inhibitor than ACA. This behaviour was analysed by a molecular docking study.

Zinc metalloproteins as medicinal targets

Zinc bioinorganic chemistry has emphasized the role of the metal ion on the structure and function of the protein. There is, more recently, an increasing appreciation of the role of zinc proteins in a variety of human diseases. This critical review, aimed at both bioinorganic and medicinal chemists, shows how apparently widely-diverging diseases share the common mechanistic approaches of targeting the essential function of the metal ion to inhibit activity. Protein structure and function is briefly summarized in the context of its clinical relevance. The status of current and potential inhibitors is discussed along with the prospects for future developments (162 references).

Understanding the antitumor activity of novel tricyclicpiperazinyl derivatives as farnesyltransferase inhibitors using CoMFA and CoMSIA

3D-QSAR studies of some tricyclicpiperazinyl derivatives as farnesyltransferase inhibitors were performed by comparative molecular field analysis (CoMFA) and comparative molecular similarity indices (CoMSIA) methods to rationalize the structural requirements responsible for the inhibitory activity of these compounds. The global minimum energy conformer of the template molecule 35, the most active and pharmacokinetically stable molecule of the series, was obtained by simulated annealing method and used to build structures of the molecules in the dataset. The CoMFA model obtained after the removal of outliers produced statistically significant results with cross-validated and conventional correlation coefficients of 0.550 and 0.969, respectively. The combination of steric, electrostatic, hydrogen bond acceptor and hydrophobic fields in CoMSIA gave the best results with cross-validated and conventional correlation coefficients of 0.611 and 0.986, respectively. The predictive ability of CoMFA and CoMSIA were determined using a test set of 24 tricyclicpiperazinyl derivatives giving predictive correlation coefficients of 0.543 and 0.663, respectively, indicating good predictive power. Further the robustness of the model was verified by bootstrapping analysis. Based on the CoMFA and CoMSIA analysis we have identified some key features in the tricyclicpiperazinyl series that are responsible for farnesyltransferase inhibitory activity that may be used to design more potent tricyclicpiperazinyl derivatives and predict their activity prior to synthesis.