A simplified analog of debromoaplysiatoxin lacking the B-ring of spiroketal moiety retains protein kinase C-binding and antiproliferative activities.

A simplified analog (3) of aplysiatoxin was synthesized. Compound 3 has only one tetrahydropyran ring at positions 3-7, the A-ring of the spiroketal moiety, which is the conformation-controlling unit for the macrolactone ring. Nuclear magnetic resonance (NMR) analysis and density functional theory (DFT) calculations indicated that 3 existed as an equilibrium mixture of two conformers arising from inversion of the chair conformation of the 2,6-trans-tetrahydropyran ring. The des-B-ring analog 3 binds protein kinase C isozymes and exhibits antiproliferative activity toward human cancer cell lines, comparable to 18-deoxy-aplog-1 with a spiroketal moiety.

Activity to Breast Cancer Cell Lines of Different Malignancy and Predicted Interaction with Protein Kinase C Isoforms of Royleanones.

Plants have been used for centuries to treat several illnesses. The Plectranthus genus has a vast variety of species that has allowed the isolation of cytotoxic compounds with notable activities. The abietane diterpenes 6,7-dehydroroyleanone (DeRoy, 1), 7α-acetoxy-6ß-hydroxyroyleanone (Roy, 2), and Parvifloron D (ParvD, 3) were obtained from Plectranthus spp. and showed promising biological activities, such as cytotoxicity. The inhibitory effects of the different natural abietanes (1-3) were compared in MFC7, SkBr3, and SUM159 cell lines, as well as SUM159 grown in cancer stem cell-inducing conditions. Based on the royleanones' bioactivity, the derivatives RoyBz (4), RoyBzCl (5), RoyPr2 (6), and DihydroxyRoy (7), previously obtained from 2, were selected for further studies. Protein kinases C (PKCs) are involved in several carcinogenic processes. Thus, PKCs are potential targets for cancer therapy. To date, the portfolio of available PKC modulators remains very limited due to the difficulty of designing isozyme-selective PKC modulators. As such, molecular docking was used to evaluate royleanones 1-6 as predicted isozyme-selective PKC binders. Subtle changes in the binding site of each PKC isoform change the predicted interaction profiles of the ligands. Subtle changes in royleanone substitution patterns, such as a double substitution only with non-substituted phenyls, or hydroxybenzoate at position four that flips the binding mode of ParvD (3), can increase the predicted interactions in certain PKC subtypes.

Identification of novel SIRT2-selective inhibitors using a click chemistry approach.

A series of 114 SIRT inhibitor candidates was assembled using 'click chemistry', by reacting two alkynes bearing 2-anilinobenzamide pharmacophore with 57 azide building blocks in the presence of Cu(I) catalyst. Screening identified two SIRT2-selective inhibitors, which were more SIRT2-selective than AGK2, a known SIRT2 inhibitor. These findings will be useful for further development of SIRT2-selective inhibitors.

Tropolones and Thailandepsin B as Lead-like Natural Compounds in the Development of Potent and Selective Histone Deacetylase Inhibitors.

BACKGROUND: Tropolone and thailandepsin B are naturally occurring substances that are primarily isolated from fungi and plants, although they can also be found in certain bacteria. Tropolones belong to an important class of aromatic compounds with a seven-membered nonbenzenoid ring structure. Thailandepsins are a group of natural products that were initially discovered in the culture broth of the Gram-negative bacterium Burkholderia thailandensis. Tropolonebased structures have been identified in over 200 natural compounds, ranging from simple tropolone derivatives to complex multicyclic systems like pycnidione and pyrerubrine A. These natural compounds exhibit a diverse range of pharmacological effects, including antibacterial, antifungal, insecticidal, phytotoxic, anti-inflammatory, antimitotic, anti-diabetic, enzyme inhibitory, anticancer, cytoprotective, and ROS scavenging properties. It is worth noting that thujaplicane, a compound similar to tropolone, displays all of the listed biological activities except for antimitotic action, which has only been observed in one natural tropolone compound, colchicine. Tropolone can be synthesized from commercially available seven-membered rings or derived through various cyclization and cycloaddition reactions. Thailandepsin B, on the other hand, can be synthesized by macro-lactonization of the corresponding secoacid, followed by the formation of internal disulfide bonds. It is important to mention that thailandepsin B exhibits different selective inhibition profiles compared to FK228. OBJECTIVE: We investigated the HDAC inhibitory activity of the Tropolones and Thailandepsin B and discussed the biosynthesis of the naturally occurring compounds and their synthetic scheme. RESULTS AND CONCLUSION: It has been observed that Tropolone derivatives act as isoenzyme-selective inhibitors of proven anticancer drug targets, histone deacetylases (HDACs). Some monosubstituted tropolones show remarkable levels of selectivity for HDAC2 and strongly inhibit the growth of T-lymphocyte cell lines. And Thailandepsins have different selective inhibition profiles than FK228. They exhibit comparable inhibitory activities to FK228 against human HDAC1, HDAC2, HDAC3, HDAC6, HDAC7, and HDAC9, but less potent inhibitory activities than FK228 toward HDAC4 and HDAC8, the latter of which may be useful. Thailandepsins possess potent cytotoxic activities toward some types of cell lines.

DFT-Based QSAR Modelling of Inhibitory Activity of Coumarins and Sulfocoumarins on Carbonic Anhydrase (CA) Isoforms (CA I and CA II).

OBJECTIVE: We present three robust, validated and statistically significant quantitative structure-activity relationship (QSAR) models, which deal with the calculated molecular descriptors and experimental inhibition constant (Ki) of 42 coumarin and sulfocoumarin derivatives measured against CA I and II isoforms. METHODS: The compounds were subjected to DFT calculations in order to obtain quantum chemical molecular descriptors. Multiple linear regression algorithms were applied to construct QSAR models. Separation of the compounds into training and test sets was accomplished using Kennard-Stone algorithm. Leverage approach was applied to determine Applicability Domain (AD) of the obtained models. RESULTS: Three models were developed. The first model, CAI_model1 comprises 30/11 training/test compounds with the statistical parameters of R2=0.85, Q2=0.77, F=27.57, R2 (test) =0.72. The second one, CAII_model2 comprises 30/12 training/test compounds with the statistical parameters of R2=0.86, Q2=0.78, F=30.27, R2 (test) =0.85. The final model, ΔpKi_model3 consists of 25/3 training/ test compounds with the statistical parameters of R2=0.78, Q2=0.62, F=13.80 and R2(test) =0.99. CONCLUSION: Interpretation of reactivity-related descriptors such as HOMO-1 and LUMO energies and visual inspection of their maps of orbital electron density leads to a conclusion that the binding free energy of the entire binding process may be modulated by the kinetics of the hydrolyzing step of coumarins.

Design, synthesis, and biological activity of NCC149 derivatives as histone deacetylase 8-selective inhibitors.

We recently discovered N-hydroxy-3-[1-(phenylthio)methyl-1H-1,2,3-triazol-4-yl]benzamide (NCC149) as a potent and selective histone deacetylase 8 (HDAC8) inhibitor from a 151-member triazole compound library using a click chemistry approach. In this work, we present a series of NCC149 derivatives bearing various aromatic linkers that were designed and synthesized as HDAC8-selective inhibitors. A series of in vitro assays were used to evaluate the newly synthesized compounds, four of which showed HDAC8 inhibitory activity similar to that of NCC149, and one of which displayed HDAC8 selectivity superior to that of NCC149. In addition, these top four compounds induced the increase of acetylated cohesin (an HDAC8 substrate) in HeLa cells in a dose-dependent manner, indicating inhibition of HDAC8 in the cells. While none of these compounds enhanced the acetylation of H3K9 (a substrate of HDAC1 and 2), only one compound refrained from increasing α-tubulin acetylation, a substrate of HDAC6, indicating that this compound is more selective for HDAC8 than the other derivatives. Furthermore, this HDAC8-selective inhibitor suppressed the growth of T-cell lymphoma cells more potently than did NCC149. These findings are useful for the further development of HDAC8-selective inhibitors.

Tropolones as lead-like natural products: the development of potent and selective histone deacetylase inhibitors.

Natural products have long been recognized as a rich source of potent therapeutics but further development is often limited by high structural complexity and high molecular weight. In contrast, at the core of the thujaplicins is a lead-like tropolone scaffold characterized by relatively low molecular weight, ample sites for diversification, and metal-binding functionality poised for targeting a range of metalloenzyme drug targets. Here, we describe the development of this underutilized scaffold for the discovery of tropolone derivatives that function as isozyme-selective inhibitors of the validated anticancer drug target, histone deacetylase (HDAC). Several monosubstituted tropolones display remarkable levels of selectivity for HDAC2 and potently inhibit the growth of T-cell lymphocyte cell lines. The tropolones represent a new chemotype of isozyme-selective HDAC inhibitors.