Chemoselective Electrosynthesis Using Rapid Alternating Polarity

Challenges in the selective manipulation of functional groups (chemoselectivity) in organic synthesis have historically been overcome either by using reagents/catalysts that tunably interact with a substrate or through modification to shield undesired sites of reactivity (protecting groups). Although electrochemistry offers precise redox control to achieve unique chemoselectivity, this approach often becomes challenging in the presence of multiple redox-active functionalities. Historically, electrosynthesis has been performed almost solely by using direct current (DC). In contrast, applying alternating current (AC) has been known to change reaction outcomes considerably on an analytical scale but has rarely been strategically exploited for use in complex preparative organic synthesis. Here we show how a square waveform employed to deliver electric current-rapid alternating polarity (rAP)-enables control over reaction outcomes in the chemoselective reduction of carbonyl compounds, one of the most widely used reaction manifolds. The reactivity observed cannot be recapitulated using DC electrolysis or chemical reagents. The synthetic value brought by this new method for controlling chemoselectivity is vividly demonstrated in the context of classical reactivity problems such as chiral auxiliary removal and cutting-edge medicinal chemistry topics such as the synthesis of PROTACs.

Abstract 2696: Genetic and pharmacologic evaluation of the ubiquitin ligase CBL-B as a small-molecule, tumor immunotherapy target

E3 ubiquitin ligases play critical roles in directing cellular protein fate by controlling the specificity of ubiquitin conjugation to substrate proteins and targeting them for cellular relocalization or degradation by the ubiquitin proteasome system. The E3 ubiquitin ligase CBL-B is expressed in immune cell lineages and negatively regulates activity of the T-cell receptor (TCR) by imposing a requirement for a costimulatory signal to mount a productive immune response upon TCR engagement. Mice deficient in Cbl-b, and more specifically in the RING Zn-finger ligase domain of Cbl-b, demonstrate a tumor rejection phenotype mediated by CD8+ T cells (Paolino et al., JI, 2011). We have reproduced these results and demonstrate that Cbl-b deficient mice show enhanced anti-tumor activity. In addition, we show that CD4+ and CD8+ T cells from mice deficient in Cbl-b have 5 to 10-fold enhanced secretion of IL-2 and IFN γ when stimulated ex vivo. These data provide a genetic rationale for the development of a small molecule inhibitor of CBL-B ligase activity for use in patients with tumor-mediated immune suppression of effector T cells.

We have identified a series of small molecule inhibitors of CBL-B activity with biochemical potency at low nanomolar concentrations. CBL-B inhibitors increased cytokine secretion in vitro at low nanomolar concentrations, as measured by IL-2 and IFN γ secretion, in primary human and mouse T cells stimulated with CD3/CD28 or CD3 alone. The compounds also stimulated proliferation and elevated levels of the T cell surface activation markers CD25 and CD69. CBL-B inhibitors enhanced an antigen recall response in human PBMCs ex vivo, as measured by approximately 5-fold higher secretion of GM-CSF, TNF-α and RANTES, and demonstrated effects in an ex vivo model of exhausted T cell function.

Oral dosing of an optimized CBL-B inhibitor enhanced anti-CD3 stimulated T cell activation in mouse CD4+ and CD8+ T cells, demonstrating a dose proportional pharmacodynamic effect. Oral administration over 28 days in the syngeneic CT-26 tumor model was well tolerated and resulted in single agent tumor growth inhibition.

These data support the continued advancement of small molecule oral CBL-B inhibitors for future development in immuno-oncology.

Citation Format: Jennifa Gosling, Ryan Rountree, Asad Taherbhoy, Chenbo Wang, Thomas Cummins, Frederick Cohen, Hiroko Tanaka, Dahlia Weiss, Mario Cardozo, Christopher Karim, May Tan, Joseph Juan, Austin Tenn-McClellan, Szerenke Kiss von Soly, Julie Sheung, Kathleen Boyle, Ketki Dhamnaskar, Katherine Kurylo, Jilliane Bruffey, Jennifer McKinnell, Dane Karr, Andria Christianson, Anne-Renee Van Der Vuurst de Vries, Pallavur Sivakumar, Mark Gallop, Paul A. Barsanti, Anjanabha Saha, Neil F. Bence, Christoph W. Zapf. Genetic and pharmacologic evaluation of the ubiquitin ligase CBL-B as a small-molecule, tumor immunotherapy target [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2696.

Aminopyrazole Carboxamide Bruton's Tyrosine Kinase Inhibitors. Irreversible to Reversible Covalent Reactive Group Tuning

Potent covalent inhibitors of Bruton's tyrosine kinase (BTK) based on an aminopyrazole carboxamide scaffold have been identified. Compared to acrylamide-based covalent reactive groups leading to irreversible protein adducts, cyanamide-based reversible-covalent inhibitors provided the highest combined BTK potency and EGFR selectivity. The cyanamide covalent mechanism with BTK was confirmed through enzyme kinetic, NMR, MS, and X-ray crystallographic studies. The lead cyanamide-based inhibitors demonstrated excellent kinome selectivity and rat pharmacokinetic properties.

Discovery of Clinical Candidate 1-{[(2S,3S,4S)-3-Ethyl-4-fluoro-5-oxopyrrolidin-2-yl]methoxy}-7-methoxyisoquinoline-6-carboxamide (PF-06650833), a Potent, Selective Inhibitor of Interleukin-1 Receptor Associated Kinase 4 (IRAK4), by Fragment-Based Drug Design

Through fragment-based drug design focused on engaging the active site of IRAK4 and leveraging three-dimensional topology in a ligand-efficient manner, a micromolar hit identified from a screen of a Pfizer fragment library was optimized to afford IRAK4 inhibitors with nanomolar potency in cellular assays. The medicinal chemistry effort featured the judicious placement of lipophilicity, informed by co-crystal structures with IRAK4 and optimization of ADME properties to deliver clinical candidate PF-06650833 (compound 40). This compound displays a 5-unit increase in lipophilic efficiency from the fragment hit, excellent kinase selectivity, and pharmacokinetic properties suitable for oral administration.

Discovery of a stable macrocyclic o-aminobenzamide Hsp90 inhibitor which significantly decreases tumor volume in a mouse xenograft model

An extension of our previously reported series of macrocyclic ortho-aminobenzamide Hsp90 inhibitors is reported. Addition of a second methyl group to the tether provided analogs that show increased potency in binding as well as cell-proliferation assays and, more importantly, are stable toward microsomes. We wish to disclose the discovery of a macrocycle which showed impressive biomarker activity 24-h post dosing and which demonstrated prolonged exposure in tumors. When studied in a lung cancer xenograft model, the compound demonstrated significant tumor size reduction.

Design and SAR of macrocyclic Hsp90 inhibitors with increased metabolic stability and potent cell-proliferation activity

A novel series of macrocyclic ortho-aminobenzamide Hsp90 inhibitors is reported. A basic nitrogen within the tether linking the aniline nitrogen atom to a tetrahydroindolone moiety allowed access to compounds with good physical properties. Important structure-activity relationship information was obtained from this series which led to the discovery of a soluble and stable compound which is potent in an Hsp90 binding and cell-proliferation assay.

Utilizing the intramolecular Fukuyama–Mitsunobu reaction for a flexible synthesis of novel heterocyclic scaffolds for peptidomimetic drug design

We report the synthesis of the novel scaffolds pyrazino[1,2-b]isoquinoline and pyrrolo[1,2-a]pyrazine displaying the somatostatin pharmacophores. Both classes of compounds contain a pyrazine heterocycle, which can be prepared in a straightforward manner utilizing an intramolecular Fukuyama-Mitsunobu reaction. As both the families derive from amino acids, they can be accessed in high optical purity.

Synthesis of 2-Amino-4-pyrimidinones from Resin-Bound Guanidines Prepared Using Bis(allyloxycarbonyl)-Protected Triflylguanidine

We have synthesized novel heterocyclic compounds from resin-bound guanidines. For this purpose, an amine immobilized on a solid support was acylated with protected amino acids. Following the deprotection, the liberated amines were guanidinylated utilizing a new member of the family of diurethane-protected triflyl guanidine reagents, N,N'-bis(allyloxycarbonyl)-N' '-triflylguanidine. The deprotected guanidines were subsequently regioselectively cyclized with beta-keto esters yielding novel compounds containing heterocyclic structures in high purities.

A Novel Traceless Resin-Bound Guanidinylating Reagent for Secondary Amines To Prepare N,N-Disubstituted Guanidines

[reaction: see text]. We report the development of a solid support-linked guanidinylating reagent. This reagent consists of a urethane-protected triflyl guanidine attached to the resin via a carbamate linker. It allows for rapid synthesis of guanidines from a variety of amines. It provides access to N-alkyl/aryl- or N,N-dialkylguanidines under mild conditions. Cleavage with 50% TFA produces target molecules in high yields and purity. The ability to guanidinylate secondary amines is a significant feature of this guanidinylating reagent.

Solid-phase synthesis of pyridones and pyridopyrazines as peptidomimetic scaffolds

[formula: see text] We report the syntheses of peptidomimetic opioids containing the core structure N-alkyl-2-alkyl-2,3-dihydro-4-pyridone. By employing imines bound on a solid support and the Danishefsky diene, this [4 + 2] cyclocondensation reaction facilitates the synthesis of novel complex heterocycles. The central reaction is carried out under mild conditions and employs readily available building blocks. In this study we demonstrate the suitability of N-alkyl-2-alkyl-2,3-dihydro-4-pyridones as a central scaffold for peptidomimetics and establish the scope of this [4 + 2] cyclocondensation reaction with imino acids on a solid phase. We also combine the synthesis of diketopiperazines with the [4 + 2] cyclocondensation reaction to form a 9,9a-dihydro-2H-pyrido-[1,2a]- pyrazine-3,8(1,4-dialkyl)dione, a bicyclic molecule containing a pyridopyrazine core structure.