Synthesis of Chamaecypanone C Analogues from <i>in Situ</i>-Generated Cyclopentadienones and Their Biological Evaluation

A rhodium-catalyzed dehydrogenation protocol for the conversion of 3,5-diarylcyclopentenones to the corresponding 2,4-diarylcyclopentadienones has been developed. With this protocol, analogues of the cytotoxic agent chamaecypanone C have been synthesized <i>via</i> Diels–Alder cycloaddition between the cyclopentadienones and <i>in situ</i>-generated <i>o</i>-quinols. Biological evaluation of these analogues revealed a compound with higher activity as a microtubule inhibitor and cytotoxic agent in comparison with the parent structure

Synthesis of Chamaecypanone C Analogues from <i>in Situ</i>-Generated Cyclopentadienones and Their Biological Evaluation

A rhodium-catalyzed dehydrogenation protocol for the conversion of 3,5-diarylcyclopentenones to the corresponding 2,4-diarylcyclopentadienones has been developed. With this protocol, analogues of the cytotoxic agent chamaecypanone C have been synthesized <i>via</i> Diels–Alder cycloaddition between the cyclopentadienones and <i>in situ</i>-generated <i>o</i>-quinols. Biological evaluation of these analogues revealed a compound with higher activity as a microtubule inhibitor and cytotoxic agent in comparison with the parent structure

Development of a Novel Class of Tubulin Inhibitor from Desmosdumotin B with a Hydroxylated Bicyclic B‑Ring

A series of newly synthesized hydroxylated analogues of triethyldesmosdumotin B (TEDB) with a bicyclic B-ring exhibited a significantly different mode of action for affecting microtubule dynamics and spindle formation but had the same antiproliferative activity spectrum, including activity against multidrug-resistant tumors. These analogues efficiently induced cell cycle arrest at prometaphase and caused formation of immature multipolar spindles. 6′-Hydroxyl TEDB-TB (<b>8</b>) disrupted bipolar spindle formation but had a negligible effect on interphase microtubules. On the basis of the predicted binding modes of the new compounds with tubulin dimer, compound <b>4</b> forms three hydrogen bonds (H-bonds) only with α-tubulin at the colchicine site; in contrast, <b>8</b> forms H-bonds with both α- and β-tubulin. We predict that, when a compound/ligand, such as <b>8</b>, forms H-bonds to both α- and β-tubulins, spindle formation is disrupted more than the dynamics of interphase microtubules. This result may reflect the well-known greater dynamicity of spindle microtubules as compared with interphase microtubules

Structure–Activity Relationship and in Vitro and in Vivo Evaluation of the Potent Cytotoxic Anti-microtubule Agent <i>N</i>‑(4-Methoxyphenyl)‑<i>N</i>,2,6-trimethyl-6,7-dihydro‑5<i>H</i>‑cyclopenta[<i>d</i>]pyrimidin-4-aminium Chloride and Its Analogues As Antitumor Agents

A series of 21 substituted cyclopenta­[<i>d</i>]­pyrimidines were synthesized as an extension of our discovery of the parent compound (±)-<b>1</b>·HCl as an anti-microtubule agent. The structure–activity relationship indicates that the <i>N</i>-methyl and a 4<i>N</i>-methoxy groups appear important for potent activity. In addition, the 6-substituent in the parent analogue is not necessary for activity. The most potent compound <b>30</b>·HCl was a one to two digit nanomolar inhibitor of most tumor cell proliferations and was up to 7-fold more potent than the parent compound (±)-<b>1</b>·HCl. In addition, <b>30</b>·HCl inhibited cancer cell proliferation regardless of Pgp or βIII-tubulin status, both of which are known to cause clinical resistance to several anti-tubulin agents. In vivo efficacy of <b>30</b>·HCl was demonstrated against a triple negative breast cancer xenograft mouse model. Compound <b>30</b>·HCl is water-soluble and easily synthesized and serves as a lead compound for further preclinical evaluation as an antitumor agent

Novel 3‑Substituted 7‑Phenylpyrrolo[3,2‑<i>f</i>]quinolin-9(6<i>H</i>)‑ones as Single Entities with Multitarget Antiproliferative Activity

A series of chemically modified 7-phenylpyrrolo­[3,2-<i>f</i>]­quinolinones was synthesized and evaluated as anticancer agents. Among them, the most cytotoxic (subnanomolar GI₅₀ values) amidic derivative <b>5f</b> was shown to act as an inhibitor of tubulin polymerization (IC₅₀, 0.99 μM) by binding to the colchicine site with high affinity. Moreover, <b>5f</b> induced cell cycle arrest in the G2/M phase of the cell cycle in a concentration dependent manner, followed by caspase-dependent apoptotic cell death. Compound <b>5f</b> also showed lower toxicity in nontumoral cells, suggesting selectivity toward cancer cells. Additional experiments revealed that <b>5f</b> inhibited the enzymatic activity of multiple kinases, including AURKA, FLT3, GSK3A, MAP3K, MEK, RSK2, RSK4, PLK4, ULK1, and JAK1. Computational studies showed that <b>5f</b> can be properly accommodated in the colchicine binding site of tubulin as well as in the ATP binding clefts of all examined kinases. Our data indicate that the excellent antiproliferative profile of <b>5f</b> may be derived from its interactions with multiple cellular targets

12,13-Aziridinyl Epothilones. Stereoselective Synthesis of Trisubstituted Olefinic Bonds from Methyl Ketones and Heteroaromatic Phosphonates and Design, Synthesis, and Biological Evaluation of Potent Antitumor Agents

The synthesis and biological evaluation of a series of 12,13-aziridinyl epothilone B analogues is described. These compounds were accessed by a practical, general process that involved a 12,13-olefinic methyl ketone as a starting material obtained by ozonolytic cleavage of epothilone B followed by tungsten-induced deoxygenation of the epoxide moiety. The attachment of the aziridine structural motif was achieved by application of the Ess–Kürti–Falck aziridination, while the heterocyclic side chains were introduced via stereoselective phosphonate-based olefinations. In order to ensure high (<i>E</i>) selectivities for the latter reaction for electron-rich heterocycles, it became necessary to develop and apply an unprecedented modification of the venerable Horner–Wadsworth–Emmons reaction, employing 2-fluoroethoxyphosphonates that may prove to be of general value in organic synthesis. These studies resulted in the discovery of some of the most potent epothilones reported to date. Equipped with functional groups to accommodate modern drug delivery technologies, some of these compounds exhibited picomolar potencies that qualify them as payloads for antibody drug conjugates (ADCs), while a number of them revealed impressive activities against drug resistant human cancer cells, making them desirable for potential medical applications

12,13-Aziridinyl Epothilones. Stereoselective Synthesis of Trisubstituted Olefinic Bonds from Methyl Ketones and Heteroaromatic Phosphonates and Design, Synthesis, and Biological Evaluation of Potent Antitumor Agents

The synthesis and biological evaluation of a series of 12,13-aziridinyl epothilone B analogues is described. These compounds were accessed by a practical, general process that involved a 12,13-olefinic methyl ketone as a starting material obtained by ozonolytic cleavage of epothilone B followed by tungsten-induced deoxygenation of the epoxide moiety. The attachment of the aziridine structural motif was achieved by application of the Ess–Kürti–Falck aziridination, while the heterocyclic side chains were introduced via stereoselective phosphonate-based olefinations. In order to ensure high (<i>E</i>) selectivities for the latter reaction for electron-rich heterocycles, it became necessary to develop and apply an unprecedented modification of the venerable Horner–Wadsworth–Emmons reaction, employing 2-fluoroethoxyphosphonates that may prove to be of general value in organic synthesis. These studies resulted in the discovery of some of the most potent epothilones reported to date. Equipped with functional groups to accommodate modern drug delivery technologies, some of these compounds exhibited picomolar potencies that qualify them as payloads for antibody drug conjugates (ADCs), while a number of them revealed impressive activities against drug resistant human cancer cells, making them desirable for potential medical applications

Design, Synthesis, and Preclinical Evaluation of 4‑Substituted-5-methyl-furo[2,3‑<i>d</i>]pyrimidines as Microtubule Targeting Agents That Are Effective against Multidrug Resistant Cancer Cells

The design, synthesis, and biological evaluations of eight 4-substituted 5-methyl-furo­[2,3-<i>d</i>]­pyrimidines are reported. Synthesis involved <i>N</i>⁴-alkylation of <i>N</i>-aryl-5-methylfuro­[2,3-<i>d</i>]­pyrimidin-4-amines, obtained from Ullmann coupling of 4-amino-5-methylfuro­[2,3-<i>d</i>]­pyrimidine and appropriate aryl iodides. Compounds <b>3</b>, <b>4</b>, and <b>9</b> showed potent microtubule depolymerizing activities, while compounds <b>6</b>–<b>8</b> had slightly lower potency. Compounds <b>4</b>, <b>6</b>, <b>7</b>, and <b>9</b> inhibited tubulin assembly with IC₅₀ values comparable to that of combretastatin A-4 (CA-4). Compounds <b>3</b>, <b>4</b>, and <b>6</b>–<b>9</b> circumvented Pgp and βIII-tubulin mediated drug resistance, mechanisms that can limit the efficacy of paclitaxel, docetaxel, and the vinca alkaloids. In the NCI 60-cell line panel, compound <b>3</b> exhibited GI₅₀ values less than 10 nM in 47 of the cell lines. In an MDA-MB-435 xenograft model, compound <b>3</b> had statistically significant antitumor effects. The biological effects of <b>3</b> identify it as a novel, potent microtubule depolymerizing agent with antitumor activity

Steroidomimetic Tetrahydroisoquinolines for the Design of New Microtubule Disruptors

Structure–activity relationship translation offers an expeditious means for discovery of new active series. This approach was applied to discover tetrahydroisoquinoline (THIQ)-based steroidomimetic microtubule disruptors. The two A-ring elements of a three-point steroidal pharmacophore were incorporated into a THIQ-based A,B-ring mimic to which an H-bond acceptor was attached as the third motif. Optimization of the representative<b> 6c</b> through conformational biasing delivered a 10-fold gain in activity and a new series of microtubule disruptors (e.g., <b>9c</b>) with antiproliferative activity in the nanomolar range. The THIQ derivatives match, or surpass, the activities of the steroidal series and exhibit improved physicochemical properties

Discovery of Antitubulin Agents with Antiangiogenic Activity as Single Entities with Multitarget Chemotherapy Potential

Antiangiogenic agents (AA) are cytostatic, and their utility in cancer chemotherapy lies in their combination with cytotoxic chemotherapeutic agents. Clinical combinations of vascular endothelial growth factor receptor-2 (VEGFR2) inhibitors with antitubulin agents have been particularly successful. We have discovered a novel, potentially important analogue, that combines potent VEGFR2 inhibitory activity (comparable to that of sunitinib) with potent antitubulin activity (comparable to that of combretastatin A-4 (CA)) in a single molecule, with GI₅₀ values of 10^–7 M across the entire NCI 60 tumor cell panel. It potently inhibited tubulin assembly and circumvented the most clinically relevant tumor resistance mechanisms (P-glycoprotein and β-III tubulin expression) to antimicrotubule agents. The compound is freely water-soluble as its HCl salt and afforded excellent antitumor activity <i>in vivo</i>, superior to docetaxel, sunitinib, or Temozolomide, without any toxicity