Synthesis of Quinoline and Dihydroquinoline Embelin Derivatives as Cardioprotective Agents.

A set of new dihydroquinoline embelin derivatives was obtained from the reaction of the natural benzoquinone embelin (1) with anilines and aromatic aldehydes in the presence of AgOTf. The synthesis of these compounds involves the formation of a Knoevenagel adduct, followed by nucleophilic addition of aniline and subsequent electrocyclic ring closure. The scope of the reaction regarding the aldehydes and anilines was determined. Quinoline derivatives were also obtained from the corresponding dihydroquinolines under oxidation with DDQ. The cardioprotective activity of the synthesized compounds was screened using a doxorubicin-induced cardiotoxicity model in H9c2 cardiomyocytes. Some structure-activity relationships were outlined, and the best activities were achieved with quinoline-embelin derivatives having a 4-nitrophenyl group attached at the pyridine ring. The obtained results indicated that embelin derivatives 4i, 6a, 6d, 6k, and 6m could have potential as cardioprotective agents, as they attenuated a DOX-induced cardiotoxicity effect acting on oxidative stress and apoptosis.

Kinetically guided radical-based synthesis of C(sp3)-C(sp3) linkages on DNA.

DNA-encoded libraries (DEL)-based discovery platforms have recently been widely adopted in the pharmaceutical industry, mainly due to their powerful diversity and incredible number of molecules. In the two decades since their disclosure, great strides have been made to expand the toolbox of reaction modes that are compatible with the idiosyncratic aqueous, dilute, and DNA-sensitive parameters of this system. However, construction of highly important C(sp3)-C(sp3) linkages on DNA through cross-coupling remains unexplored. In this article, we describe a systematic approach to translating standard organic reactions to a DEL setting through the tactical combination of kinetic analysis and empirical screening with information captured from data mining. To exemplify this model, implementation of the Giese addition to forge high value C-C bonds on DNA was studied, which represents a radical-based synthesis in DEL.

Mechanistic insights into the activation of ester prodrugs of 666-15.

cAMP-response element binding protein (CREB) is an oncogenic transcription factor implicated in many different types of cancer. We previously reported the discovery of 666-15 as a potent inhibitor of CREB-mediated gene transcription. In an effort to improve the aqueous solubility of 666-15, amino ester prodrugs 1 and 4 were designed and synthesized. Detailed chemical and biological studies of 1 and 4 revealed that a small portion of the prodrugs were converted into 666-15 through intermediate 3 instead of a long-range O,N-acyl transfer reaction that was initially proposed. These results provide unique insights into the activation of these ester prodrugs.

Design, synthesis and biological evaluation of new embelin derivatives as CK2 inhibitors.

A new series of furan embelin derivatives was synthesized and characterized as ATP-competitive CK2 inhibitors. The new compounds were efficiently synthesized using a multicomponent approach from embelin (1), aldehydes and isonitriles through a Knoevenagel condensation/Michael addition/heterocyclization. Several compounds with inhibitory activities in the low micromolar or even submicromolar were identified. The most active derivative was compound 4l (2-(tert-butylamino)-3-(furan-3-yl)-5-hydroxy-6-undecylbenzofuran-4,7-dione) with an IC50 value of 0.63 µM. It turned out to be an ATP competitive CK2 inhibitor with a Ki value determined to be 0.48 µM. Docking studies allowed the identification of key ligand-CK2 interactions, which could help to further optimize this family of compounds as CK2 inhibitors.

Efficient Multicomponent Synthesis of Diverse Antibacterial Embelin-Privileged Structure Conjugates.

A library of embelin derivatives has been synthesized through a multicomponent reaction from embelin (1), aldehydes and privileged structures such as 4-hydroxycoumarin, 4-hydroxy-2H-pyran-2-one and 2-naphthol, in the presence of InCl3 as catalyst. This multicomponent reaction implies Knoevenagel condensation, Michael addition, intramolecular cyclization and dehydration. Many of the synthesized compounds were active and selective against Gram-positive bacteria, including one important multiresistant Staphylococcus aureus clinical isolate. It was found how the conjugation of diverse privileged substructure with embelin led to adducts having enhanced antibacterial activities.

5-Ethynylarylnaphthalimides as antitumor agents: Synthesis and biological evaluation.

A set of 5-ethynylarylnaphthalimides was synthesized by Sonogashira cross-coupling reactions and evaluated for antiproliferative and antitopoisomerase II in vitro activities. Furthermore docking studies of these molecules as DNA-intercalators were carried out and the in vivo DNA-damaging activity was also determined with the model organism Saccharomyces cerevisiae. From the obtained results three naphthalimides 6, 13 and 14 showed strong topoisomerase II inhibitory activity. These three molecules also presented good docking scores as DNA-intercalators using a self-complementary oligodeoxynucleotide d(ATGCAT)2 as a model, and compounds 13 and 14 were among the most cytotoxic in the in vivo DNA-damaging activity.

Microwave-Assisted Organocatalytic Intramolecular Knoevenagel/Hetero Diels-Alder Reaction with O-(Arylpropynyloxy)-Salicylaldehydes: Synthesis of Polycyclic Embelin Derivatives.

A highly efficient and regioselective approach to new polycyclic embelin derivatives through a domino Knoevenagel condensation/intramolecular hetero Diels-Alder reaction using O-(arylpropynyloxy)-salicylaldehydes in the presence of ethylenediamine diacetate (EDDA) is reported. This organocatalyzed protocol is compatible toward a wide range of aryl-substituted alkynyl ethers with electron-donating and electron-withdrawing groups. When other active methylene compounds were subjected to this domino reaction the corresponding adducts were obtained in high yield.

A clickable photoaffinity probe of betulinic acid identifies tropomyosin as a target.

Target identification of bioactive compounds is important for understanding their mechanisms of action and provides critical insights into their therapeutic utility. While it remains a challenge, unbiased chemoproteomics strategy using clickable photoaffinity probes is a useful and validated approach for target identification. One major limitation of this approach is the efficient synthesis of appropriately substituted clickable photoaffinity probes. Herein, we describe an efficient and consistent method to prepare such probes. We further employed this method to prepare a highly stereo-congested probe based on naturally occurring triterpenoid betulinic acid. With this photoaffinity probe, we identified tropomyosin as a novel target for betulinic acid that can account for the unique biological phenotype on cellular cytoskeleton induced by betulinic acid.

PROTACs to address the challenges facing small molecule inhibitors.

Small molecule inhibitors of proteins represent important medicines and critical chemical tools to investigate the biology of the target proteins. Advances in various -omics technologies have fueled the pace of discovery of disease-relevant proteins. Translating these discoveries into human benefits requires us to develop specific chemicals to inhibit the proteins. However, traditional small molecule inhibitors binding to orthosteric or allosteric sites face significant challenges. These challenges include drug selectivity, therapy resistance as well as drugging undruggable proteins and multi-domain proteins. To address these challenges, PROteolysis TArgeting Chimera (PROTAC) has been proposed. PROTACs are heterobifunctional molecules containing a binding ligand for a protein of interest and E3 ligase-recruiting ligand that are connected through a chemical linker. Binding of a PROTAC to its target protein will bring a E3 ligase in close proximity to initiate polyubiquitination of the target protein ensuing its proteasome-mediated degradation. Unlike small molecule inhibitors, PROTACs achieve target protein degradation in its entirety in a catalytical fashion. In this review, we analyze recent advances in PROTAC design to discuss how PROTACs can address the challenges facing small molecule inhibitors to potentially deliver next-generation medicines and chemical tools with high selectivity and efficacy. We also offer our perspectives on the future promise and potential limitations facing PROTACs. Investigations to overcome these limitations of PROTACs will further help realize the promise of PROTACs for human benefits.

Modular Synthesis and Antiproliferative Activity of New Dihydro-1H-pyrazolo[1,3-b]pyridine Embelin Derivatives.

A set of new dihydro-1H-pyrazolo[1,3-b]pyridine and pyrazolo[1,3-b]pyridine embelin derivatives was synthesized through a multicomponent reaction from natural embelin, 3-substituted-5-aminopyrazoles and aldehydes. The synthesized compounds were evaluated against three hematologic tumor cell lines, HEL (acute erythroid leukemia), K-562 (chronic myeloid leukemia) and HL-60 (acute myeloid leukemia), and five breast cancer cell lines (SKBR3, MCF-7, MDA-MB-231, BT-549, HS-578T). The primate non-malignant kidney Vero cell line was used as the control of cytotoxicity. From the obtained results, some structure-activity relationships were outlined. Furthermore, in silico prediction of physicochemical properties and ADME parameters were determined for the derivatives with the best antiproliferative values.

JKST6, a novel multikinase modulator of the BCR-ABL1/STAT5 signaling pathway that potentiates direct BCR-ABL1 inhibition and overcomes imatinib resistance in chronic myelogenous leukemia.

Chronic myelogenous leukemia (CML) is a hematological malignancy that highly depends on the BCR-ABL1/STAT5 signaling pathway for cell survival. First-line treatments for CML consist of tyrosine kinase inhibitors that efficiently target BCR-ABL1 activity. However, drug resistance and intolerance are still therapeutic limitations in Ph+ cells. Therefore, the development of new anti-CML drugs that exhibit alternative mechanisms to overcome these limitations is a desirable goal. In this work, the antitumoral activity of JKST6, a naphthoquinone-pyrone hybrid, was assessed in imatinib-sensitive and imatinib-resistant human CML cells. Live-cell imaging analysis revealed JKST6 potent antiproliferative activity in 2D and 3D CML cultures. JKST6 provoked cell increase in the subG1 phase along with a reduction in the G0/G1 phase and altered the expression of key proteins involved in the control of mitosis and DNA damage. Rapid increases in Annexin V staining and activation/cleavage of caspases 8, 9 and 3 were observed after JKST6 treatment in CML cells. Of interest, JKST6 inhibited BCR-ABL1/STAT5 signaling through oncokinase downregulation that was preceded by rapid polyubiquitination. In addition, JKST6 caused a transient increase in JNK and AKT phosphorylation, whereas the phosphorylation of P38-MAPK and Src was reduced. Combinatory treatment unveiled synergistic effects between imatinib and JKST6. Notably, JKST6 maintained its antitumor efficacy in BCR-ABL1-T315I-positive cells and CML cells that overexpress BCR-ABL and even restored imatinib efficacy after a short exposure time. These findings, together with the observed low toxicity of JKST6, reveal a novel multikinase modulator that might overcome the limitations of BCR-ABL1 inhibitors in CML therapy.

A new family of densely functionalized fused-benzoquinones as potent human protein kinase CK2 inhibitors.

A new series of 2-amino-4-phenyl-6-hydroxy-7-alkyl-pyranobenzoquinones was synthesized as ATP-competitive CK2 inhibitors. They were readily synthesized through a three-component Knoevenagel condensation-Michael addition-heterocyclization reaction from aldehydes, malononitrile, and 3-alkyl-2,5-dihydroxybenzoquinones. Some of the synthesized compounds presented interesting inhibitory activity with IC50 values in the submicromolar range. A structure-activity relationship study was carried out and the mode of binding was analysed by docking studies and supported by ATP competition assays.