Oxetanes in Drug Discovery Campaigns

Electrochemical Synthesis of C(sp3)-Rich Amines by Aminative Carbofunctionalization of Carbonyl Compounds

Alkylamines form the backbone of countless nitrogen-containing small molecules possessing desirable biological properties. Despite advances in amine synthesis through transition metal catalysis and photoredox chemistry, multicomponent reactions that leverage inexpensive materials to transform abundant chemical feedstocks into three-dimensional α-substituted alkylamines bearing complex substitution patterns remain scarce. Here, we report the design of a catalyst-free electroreductive manifold that merges amines, carbonyl compounds and carbon-based radical acceptors under ambient conditions without rigorous exclusion of air and moisture. Key to this aminative carbofunctionalization process is the chemoselective generation of nucleophilic α-amino radical intermediates that readily couple with electrophilic partners, providing straightforward access to architecturally intricate alkylamines and drug-like scaffolds which are inaccessible by conventional means.

Modular Access to Functionalized Oxetanes as Benzoyl Bioisosteres

Bioisosterism is a valuable principle exploited in drug discovery to fine-tune physicochemical properties of bioactive compounds. Functionalized 3-aryl oxetanes, as an important class of bioisosteres for benzoyl groups (highly prevalent structures in approved drugs), have been rarely utilized in agrochemicals and pharmaceuticals due to significant synthetic challenges. Here, we present a modular synthetic strategy based on the unexplored yet readily available reagents, oxetanyl trichloroacetimidates, inspired by Schmidt glycosylation, enabling easy access to a library of functionalized oxetanes. This operationally simple protocol leverages the vast existing libraries of aryl halides and various nucleophiles. The power and generality of this approach is demonstrated by late-stage functionalization of complex molecules, as well as the rapid synthesis of oxetane analogues of bioactive molecules and marketed drugs. Preliminary mechanistic study suggests that the oxygen atom in the oxetane ring plays a crucial role in stabilizing the carbocation intermediates.

Discovery of LHQ490 as a highly selective fibroblast growth factor receptor 2 (FGFR2) inhibitor

Fibroblast growth factor receptor 2 (FGFR2) represents an appealing therapeutic target for multiple cancers, yet no selective FGFR2 inhibitors have been approved for clinical use to date. Here, we report the discovery of a series of new selective, irreversible FGFR2 inhibitors. The representative compound LHQ490 potently inhibited FGFR2 kinase activity with an IC50 of 5.2 nM, and was >61-, >34-, and >293-fold selective against FGFR1, FGFR3, and FGFR4, respectively. LHQ490 also exhibited high selectivity in a panel of 416 kinases. Cell-based studies revealed that LHQ490 efficiently suppressed the proliferation of BaF3-FGFR2 cells with an IC50 value of 1.4 nM, and displayed >70- and >714-fold selectivity against BaF3-FGFR1 and the parental BaF3 cells, respectively. More importantly, LHQ490 potently suppressed the FGFR2 signaling pathways, selectively inhibited FGFR2-driven cancer cell proliferation, and induced apoptosis of FGFR2-driven cancer cells. Taken together, this study provides a potent and highly selective FGFR2 inhibitor for further development of FGFR2-targeted therapeutic agents.

Strengthening Molecular Glues: Design Strategies for Improving Thalidomide Analogs as Cereblon Effectors and Anticancer Agents

In the two decades since a novel thalidomide analog was last approved, many promising drug candidates have emerged with remarkable potency as targeted protein degraders. Likewise, the advent of PROTACs for suppressing 'undruggable' protein targets reinforces the need for new analogs with improved cereblon affinity, target selectivity and drug-like properties. However, thalidomide and its approved derivatives remain plagued by several shortcomings, such as structural instability and poor solubility. Herein, we present a review of strategies for mitigating these shortcomings and highlight contemporary drug discovery approaches that have generated novel thalidomide analogs with enhanced efficacy as cereblon effectors and/or anticancer agents.

Taming 3-Oxetanyllithium Using Continuous Flow Technology

The oxetane ring has evolved as a useful bioisostere for dimethyl and carbonyl groups for the improvement of physiochemical properties of drug candidates. Herein, we report the generation and utilization of highly unstable 3-oxetanyllithium as a hitherto unexplored nucleophile leveraging flash technology. A range of different electrophiles are suitable reaction partners in this protocol, and we demonstrate the utility of this protocol in late-stage pharmaceutical analogue synthesis.

(Phenoxyimine)nickel-Catalyzed C(sp2)-C(sp3) Suzuki-Miyaura Cross-Coupling: Evidence for a Recovering Radical Chain Mechanism

Phenoxyimine (FI)-nickel(II)(2-tolyl)(DMAP) compounds were synthesized and evaluated as precatalysts for the C(sp2)-C(sp3) Suzuki-Miyaura cross coupling of (hetero)arylboronic acids with alkyl bromides. With 5 mol % of the optimal (MeOMeFI)Ni(Aryl)(DMAP) precatalyst, the scope of the cross-coupling reaction was established and included a variety of (hetero)arylboronic acids and alkyl bromides (>50 examples, 33-97% yield). A β-hydride elimination-reductive elimination sequence from reaction with potassium isopropoxide base, yielding a potassium (FI)nickel(0)ate, was identified as a catalyst activation pathway that is responsible for halogen atom abstraction from the alkyl bromide. A combination of NMR and EPR spectroscopies identified (FI)nickel(II)-aryl complexes as the resting state during catalysis with no evidence for long-lived organic radical or odd-electron nickel intermediates. These data establish that the radical chain is short-lived and undergoes facile termination and also support a "recovering radical chain" process whereby the (FI)nickel(II)-aryl compound continually (re)initiates the radical chain. Kinetic studies established that the rate of C(sp2)-C(sp3) product formation was proportional to the concentration of the (FI)nickel(II)-aryl resting state that captures the alkyl radical for chain propagation. The proposed mechanism involves two key and concurrently operating catalytic cycles; the first involving a nickel(I/II/III) radical propagation cycle consisting of radical capture at (FI)nickel(II)-aryl, C(sp2)-C(sp3) reductive elimination, bromine atom abstraction from C(sp3)-Br, and transmetalation; and the second involving an off-cycle catalyst recovery process by slow (FI)nickel(II)-aryl → (FI)nickel(0)ate conversion for nickel(I) regeneration.

Multicomponent Synthesis of α-Branched Amines via a Zinc-Mediated Carbonyl Alkylative Amination Reaction

Methods for the synthesis of α-branched alkylamines are important due to their ubiquity in biologically active molecules. Despite the development of many methods for amine preparation, C(sp3)-rich nitrogen-containing compounds continue to pose challenges for synthesis. While carbonyl reductive amination (CRA) between ketones and alkylamines is the cornerstone method for α-branched alkylamine synthesis, it is sometimes limited by the sterically demanding condensation step between dialkyl ketones and amines and the more restricted availability of ketones compared to aldehydes. We recently reported a "higher-order" variant of this transformation, carbonyl alkylative amination (CAA), which utilized a halogen atom transfer (XAT)-mediated radical mechanism, enabling the streamlined synthesis of complex α-branched alkylamines. Despite the efficacy of this visible-light-driven approach, it displayed scalability issues, and competitive reductive amination was a problem for certain substrate classes, limiting applicability. Here, we report a change in the reaction regime that expands the CAA platform through the realization of an extremely broad zinc-mediated CAA reaction. This new strategy enabled elimination of competitive CRA, simplified purification, and improved reaction scope. Furthermore, this new reaction harnessed carboxylic acid derivatives as alkyl donors and facilitated the synthesis of α-trialkyl tertiary amines, which cannot be accessed via CRA. This Zn-mediated CAA reaction can be carried out at a variety of scales, from a 10 μmol setup in microtiter plates enabling high-throughput experimentation, to the gram-scale synthesis of medicinally-relevant compounds. We believe that this transformation enables robust, efficient, and economical access to α-branched alkylamines and provides a viable alternative to the current benchmark methods.

Direct Bioisostere Replacement Enabled by Metallaphotoredox Deoxydifluoromethylation

The replacement of a functional group with its corresponding bioisostere is a widely employed tactic during drug discovery campaigns that allows medicinal chemists to improve the ADME properties of candidates while maintaining potency. However, the incorporation of bioisosteres typically requires lengthy de novo resynthesis of potential candidates, which represents a bottleneck in their broader evaluation. An alternative would be to directly convert a functional group into its corresponding bioisostere at a late stage. Herein, we report the realization of this approach through the conversion of aliphatic alcohols into the corresponding difluoromethylated analogues via the merger of benzoxazolium-mediated deoxygenation and copper-mediated C(sp3)-CF2H bond formation. The utility of this method is showcased in a variety of complex alcohols and drug compounds.