Anthony G. M. Barrett

Heavier Alkaline Earth Catalysts for the Intermolecular Hydroamination of Vinylarenes, Dienes, and Alkynes

The heavier group 2 complexes [M{N(SiMe(3))(2)}(2)](2)(1, M = Ca; 2, M = Sr) and [M{CH(SiMe(3))(2)}(2)(THF)(2)] (3, M = Ca; 4, M = Sr) are shown to be effective precatalysts for the intermolecular hydroamination of vinyl arenes and dienes under mild conditions. Initial studies revealed that the amide precatalysts, 1 and 2, while compromised in terms of absolute activity by a tendency toward transaminative behavior, offer greater stability toward polymerization/oligomerization side reactions. In every case the strontium species, 2 and 4, were found to outperform their calcium congeners. Reactions of piperidine with para-substituted styrenes are indicative of rate-determining alkene insertion in the catalytic cycle while the ease of addition of secondary cyclic amines was found to be dependent on ring size and reasoned to be a consequence of varying amine nucleophilicity. Hydroamination of conjugated dienes yielded isomeric products via η(3)-allyl intermediates and their relative distributions were explained through stereoelectronic considerations. The ability to carry out the hydroamination of internal alkynes was found to be dramatically dependent upon the identity of the alkyne substituents while reactions employing terminal alkynes resulted in the precipitation of insoluble and unreactive group 2 acetylides. The rate law for styrene hydroamination with piperidine catalyzed by [Sr{N(SiMe(3))(2)}(2)](2) was deduced to be first order in [amine] and [alkene] and second order in [catalyst], while large kinetic isotope effects and group 2 element-dependent ΔS(++) values implicated the formation of an amine-assisted rate-determining alkene insertion transition state in which there is a considerable entropic advantage associated with use of the larger strontium center.

A Novel Pyrazolo[1,5-a]pyrimidine Is a Potent Inhibitor of Cyclin-Dependent Protein Kinases 1, 2, and 9, Which Demonstrates Antitumor Effects in Human Tumor Xenografts Following Oral Administration

Cyclin-dependent protein kinases (CDKs) are central to the appropriate regulation of cell proliferation, apoptosis, and gene expression. Abnormalities in CDK activity and regulation are common features of cancer, making CDK family members attractive targets for the development of anticancer drugs. Here, we report the identification of a pyrazolo[1,5-a]pyrimidine derived compound, 4k (BS-194), as a selective and potent CDK inhibitor, which inhibits CDK2, CDK1, CDK5, CDK7, and CDK9 (IC₅₀= 3, 30, 30, 250, and 90 nmol/L, respectively). Cell-based studies showed inhibition of the phosphorylation of CDK substrates, Rb and the RNA polymerase II C-terminal domain, down-regulation of cyclins A, E, and D1, and cell cycle block in the S and G₂/M phases. Consistent with these findings, 4k demonstrated potent antiproliferative activity in 60 cancer cell lines tested (mean GI₅₀= 280 nmol/L). Pharmacokinetic studies showed that 4k is orally bioavailable, with an elimination half-life of 178 min following oral dosing in mice. When administered at a concentration of 25 mg/kg orally, 4k inhibited human tumor xenografts and suppressed CDK substrate phosphorylation. These findings identify 4k as a novel, potent CDK selective inhibitor with potential for oral delivery in cancer patients.

Cascade polyketide and polyene cyclizations: biomimetic total synthesis of hongoquercin B.

The total synthesis of hongoquercin B was carried out in 9 steps from trans,trans-farnesyl acetate using a palladium catalyzed decarboxylative π-farnesyl rearrangement of a diketo-dioxinone ester, aromatization and cationic diene-epoxide cyclization as key steps. This cascade tetracyclization simplifies the synthesis of terpenoid resorcylate natural products.

Heavier alkaline earth catalyzed ene-yne cyclizations: Atom-efficient access to tetrahydroisoquinoline frameworks

Tetrahydroisoquinoline frameworks may be accessed with 100% atom efficiency through the alkaline earth catalyzed addition of primary amines to ene-yne substrates through a sequence of intermolecular alkene and intramolecular alkyne hydroamination steps.

1,7-Diazaspiro[5.5]undecane - A Neglected Heterocycle.

A convenient and simple three step synthesis of 1,7-diazaspiro[5.5]undecane via Claisen condensation and acid catalyzed decarboxylation and spirocyclization of N-Boc-δ-valerolactam is described. Reactions of this spiroaminal with electrophiles including alkyl halides, alkane dihalides, acid chlorides, and sulfonyl chlorides gave either spirocyclic adducts or tetrahydropyridine derivatives. Additionally, the parent heterocycle is a novel bidentate ligand and formed complexes with ruthenium(II) and copper(II).

Sequential Ketene Generation from Dioxane-4,6-dione-keto-dioxinones for the Synthesis of Terpenoid Resorcylates

Trapping of the ketene generated from the thermolysis of 2-methyl-2-phenyl-1,3-dioxane-4,6-dione-keto-dioxinone at 50 °C with primary, secondary, or tertiary alcohols gave the corresponding dioxinone β-keto-esters in good yield under neutral conditions. These intermediates were converted by palladium(0)-catalyzed decarboxylative allyl migration and aromatization into the corresponding β-resorcylates. These transformations were applied to the syntheses of the natural products (±)-cannabiorcichromenic and (±)-daurichromenic acid.

Iodoaromatization reactions of enyne-dioxinones: syntheses of 4H-1,3-benzodioxin-4-ones, masked pentasubstituted arenes.

Sequential reaction of a keto-dioxinone with dimethylformamide dimethyl acetal and a range of magnesium acetylides gave the corresponding enyne-dioxinones as mixtures of E and Z isomers (E > Z). Subsequent reaction with iodine monochloride resulted in cycloaromatization, presumably via an iodovinyl cation, giving a range of 4H-1,3-benzodioxin-4-ones.

ICEC0942, an Orally Bioavailable Selective Inhibitor of CDK7 for Cancer Treatment

Recent reports indicate that some cancer types are especially sensitive to transcription inhibition, suggesting that targeting the transcriptional machinery provides new approaches to cancer treatment. Cyclin-dependent kinase (CDK)7 is necessary for transcription, and acts by phosphorylating the C-terminal domain (CTD) of RNA polymerase II (PolII) to enable transcription initiation. CDK7 additionally regulates the activities of a number of transcription factors, including estrogen receptor (ER)-α. Here we describe a new, orally bioavailable CDK7 inhibitor, ICEC0942. It selectively inhibits CDK7, with an IC50 of 40 nmol/L; IC50 values for CDK1, CDK2, CDK5, and CDK9 were 45-, 15-, 230-, and 30-fold higher. In vitro studies show that a wide range of cancer types are sensitive to CDK7 inhibition with GI50 values ranging between 0.2 and 0.3 μmol/L. In xenografts of both breast and colorectal cancers, the drug has substantial antitumor effects. In addition, combination therapy with tamoxifen showed complete growth arrest of ER-positive tumor xenografts. Our findings reveal that CDK7 inhibition provides a new approach, especially for ER-positive breast cancer and identify ICEC0942 as a prototype drug with potential utility as a single agent or in combination with hormone therapies for breast cancer. ICEC0942 may also be effective in other cancers that display characteristics of transcription factor addiction, such as acute leukaemia and small-cell lung cancer. Mol Cancer Ther; 17(6); 1156–66. ©2018 AACR.

Synthesis and Reactions of Benzannulated Spiroaminals: Tetrahydrospirobiquinolines

An efficient two-step synthesis of symmetrical and unsymmetrical tetrahydrospirobiquinolines from o-azidobenzaldehydes is reported. A novel series of tetrahydrospirobiquinolines was prepared by sequential double-aldol condensation with acetone, cyclopentanone, and cyclohexanone to form the corresponding o,o′-diazido-dibenzylidene-acetone, -cyclopentanone, and -cyclohexanone derivatives, respectively, and hydrogenation–spirocyclization. The spirodiamines were further derivatized by electrophilic aromatic bromination, Suzuki coupling, and N-alkylation, all of which proceeded with preservation of the spirocyclic core.

Discovery of the Antitumor Effects of a Porphyrazine Diol (Pz 285) in MDA-MB-231 Breast Tumor Xenograft Models in Mice

A series of porphyrazines (Pzs) with chiral bis-acetal moieties in the β-pyrrole positions ((2R,3R)-2,3-dimethyl-2,3-dimethoxy-1,4-diox-2-ene) have been synthesized and screened as antitumor agents in MDA-MB-231 breast tumor cells in vitro. The lead Pz 285 was further tested in a mouse tumor xenograft model with Td-tomato-luc2 fluorescent breast tumor cells (MDA-MB-231 LM24 Her2+) that are highly metastatic to the lungs. Pz 285 shows marked antitumor effects in vivo, with treated mice exhibiting longer median survival that we attribute to smaller primary tumor regrowth after resection and less occurrence of metastasis when compared to vehicle control groups. Pz 285 is further compared to the clinically approved chemotherapeutic doxorubicin (Dox). This report lays the groundwork for development of an understudied class of compounds for classical chemotherapy.