Identification of potent type I MetAPs inhibitors by simple bioisosteric replacement. Part 2: SAR studies of 5-heteroalkyl substituted TCAT derivatives

Design, synthesis and biological evaluation of substituted 3-amino-N-(thiazol-2-yl)pyrazine-2-carboxamides as inhibitors of mycobacterial methionine aminopeptidase 1

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb) is the number one cause of deaths due to a single infectious agent worldwide. The treatment of TB is lengthy and often complicated by the increasing drug resistance. New compounds with new mechanisms of action are therefore needed. We present the design, synthesis, and biological evaluation of pyrazine-based inhibitors of a prominent antimycobacterial drug target - mycobacterial methionine aminopeptidase 1 (MtMetAP1). The inhibitory activities of the presented compounds were evaluated against the MtMetAP1a isoform, and all derivatives were tested against a broad spectrum of myco(bacteria) and fungi. The cytotoxicity of the compounds was also investigated using Hep G2 cell lines. Overall, high inhibition of the isolated enzyme was observed for 3-substituted N-(thiazol-2-yl)pyrazine-2-carboxamides, particularly when the substituent was represented by 2-substituted benzamide. The extent of inhibition was strongly dependent on the used metal cofactor. The highest inhibition was seen in the presence of Ni²⁺. Several compounds also showed mediocre in vitro potency against Mtb (both Mtb H37Ra and H37Rv). Despite the structural similarities of bacterial and fungal MetAP1 to mycobacterial MtMetAP1, title compounds did not exert antibacterial nor antifungal activity. The reasons behind the higher activity of 2-substituted benzamido derivatives, as well as the correlation of enzyme inhibition with the in vitro growth inhibition activity is discussed.

Targeting Metalloenzymes for Therapeutic Intervention

Metalloenzymes are central to a wide range of essential biological activities, including nucleic acid modification, protein degradation, and many others. The role of metalloenzymes in these processes also makes them central for the progression of many diseases and, as such, makes metalloenzymes attractive targets for therapeutic intervention. Increasing awareness of the role metalloenzymes play in disease and their importance as a class of targets has amplified interest in the development of new strategies to develop inhibitors and ultimately useful drugs. In this Review, we provide a broad overview of several drug discovery efforts focused on metalloenzymes and attempt to map out the current landscape of high-value metalloenzyme targets.

Inhibitors of Selected Bacterial Metalloenzymes

The utilization of bacterial metalloenzymes, especially ones not having mammalian (human) counterparts, has drawn attention to develop novel antibacterial agents to overcome drug resistance and especially multidrug resistance. In this review, we focus on the recent achievements on the development of inhibitors of bacterial enzymes peptide deformylase (PDF), metallo-β-lactamase (MBL), methionine aminopeptidase (MetAP) and UDP-3-O-acyl- N-acetylglucosamine deacetylase (LpxC). The state of the art of the design and investigation of inhibitors of bacterial metalloenzymes is presented, and challenges are outlined and discussed.

Improved Total Synthesis of Tubulysins and Design, Synthesis, and Biological Evaluation of New Tubulysins with Highly Potent Cytotoxicities against Cancer Cells as Potential Payloads for Antibody-Drug Conjugates

Improved, streamlined total syntheses of natural tubulysins such as V (Tb45) and U (Tb46) and pretubulysin D (PTb-D43), and their application to the synthesis of designed tubulysin analogues (Tb44, PTb-D42, PTb-D47-PTb-D49, and Tb50-Tb120), are described. Cytotoxicity evaluation of the synthesized compounds against certain cancer cell lines revealed a number of novel analogues with exceptional potencies [e.g., Tb111: IC₅₀ = 40 pM against MES SA (uterine sarcoma) cell line; IC₅₀ = 6 pM against HEK 293T (human embryonic kidney cancer) cell line; and IC₅₀ = 1.54 nM against MES SA DX (MES SA with marked multidrug resistance) cell line]. These studies led to a set of valuable structure-activity relationships that provide guidance to further molecular design, synthesis, and biological evaluation studies. The extremely potent cytotoxic compounds discovered in these investigations are highly desirable as potential payloads for antibody-drug conjugates and other drug delivery systems for personalized targeted cancer chemotherapies.

Cobalt-Catalyzed Cross-Dehydrogenative C(sp2 )-C(sp3 ) Coupling of Oxazole/Thiazole with Ether or Cycloalkane

Direct C5-alkylation of oxazole/thiazole with ether or cycloalkane has been achieved through a cobalt-catalyzed cross-dehydrogenative coupling (CDC) process in moderate to good yields. This transformation represents the first C(sp² )-C(sp³ ) cross-coupling at the C5-position of the oxazole/thiazole via double C-H bond cleavages. Various functional groups on oxazole/thiazole substrates, as well as water and air, are well-tolerated with this concise and practical protocol, constituting straightforward access to heterocycles with great medicinal significance. A preliminary mechanism involving a radical process has also been proposed.

Highly efficient triphenyl(3-sulfopropyl)phosphonium functionalized phosphotungstic acid on silica as a solid acid catalyst for selective mono-allylation of acetals

A silica-supported zwitterion-functionalized phosphotungstic acid catalyst developed for the selective Hosomi–Sakurai reaction giving 93–99% yield of homoallyl ethers.

Metallo-aminopeptidase inhibitors

Aminopeptidases are enzymes that selectively hydrolyze an amino acid residue from the N-terminus of proteins and peptides. They are important for the proper functioning of prokaryotic and eukaryotic cells, but very often are central players in the devastating human diseases like cancer, malaria and diabetes. The largest aminopeptidase group include enzymes containing metal ion(s) in their active centers, which often determines the type of inhibitors that are the most suitable for them. Effective ligands mostly bind in a non-covalent mode by forming complexes with the metal ion(s). Here, we present several approaches for the design of inhibitors for metallo-aminopeptidases. The optimized structures should be considered as potential leads in the drug discovery process against endogenous and infectious diseases.

Synthesis of barbiturate-based methionine aminopeptidase-1 inhibitors

The syntheses of a new class of barbiturate-based inhibitors for human and Escherichia Coli methionine aminopeptidase-1 (MetAP-1) are described. Some of the synthesized inhibitors show selective inhibition of the human enzyme with high potency.

Elucidation of the function of type 1 human methionine aminopeptidase during cell cycle progression

Processing of the N-terminal initiator methionine is an essential cellular process conserved from prokaryotes to eukaryotes. The enzymes that remove N-terminal methionine are known as methionine aminopeptidases (MetAPs). Human MetAP2 has been shown to be required for the proliferation of endothelial cells and angiogenesis. The physiological function of MetAP1, however, has remained elusive. In this report we demonstrate that a family of inhibitors with a core structure of pyridine-2-carboxylic acid previously developed for the bacterial and yeast MetAP1 is also specific for human MetAP1 (HsMetAP1), as confirmed by both enzymatic assay and high-resolution x-ray crystallography. Treatment of tumor cell lines with the MetAP1-specific inhibitors led to an accumulation of cells in the G(2)/M phase, suggesting that HsMetAP1 may play an important role in G(2)/M phase transition. Overexpression of HsMetAP1, but not HsMetAP2, conferred resistance of cells to the inhibitors, and the inhibitors caused retention of N-terminal methionine of a known MetAP substrate, suggesting that HsMetAP1 is the cellular target for the inhibitors. In addition, when HsMetAP1 was knocked down by gene-specific siRNA, cells exhibited slower progression during G(2)/M phase, a phenotype similar to cells treated with MetAP1 inhibitors. Importantly, MetAP1 inhibitors were able to induce apoptosis of leukemia cell lines, presumably as a consequence of their interference with the G(2)/M phase checkpoint. Together, these results suggest that MetAP1 plays an important role in G(2)/M phase of the cell cycle and that it may serve as a promising target for the discovery and development of new anticancer agents.