Matthew S. Winston

Herein we disclose a concise synthesis of inhaled soluble guanylate cyclase (isGC) stimulator Frespaciguat (MK-5475) that relies exclusively on complexity-increasing transformations from commodity chemicals. Key transformations include a solvent-free photochemical reaction that converts two gaseous reactants into a liquid product in high yield; a direct ester-to-amidine conversion using HMDS, water, and triflic acid; and a rare example of enantioselective methylation via copper-catalyzed asymmetric conjugate addition (ACA) to install a quaternary center using trimethylboroxine as a nucleophile. Given the general challenge of asymmetric methyl installation, we further demonstrate the utility of this methodology beyond the present setting and suggest its strategic value in synthetic planning where nonracemic, quaternary methyl-containing stereocenters are required.

Noncanonical amino acids (ncAAs) are valuable building blocks for therapeutic design. Prolines are particularly useful because their cyclic cores can limit the conformational flexibility of a larger molecular framework, allowing such scaffolds to be further tuned to enhance engagement with their biological targets. Herein, we describe a convergent approach to synthesizing noncanonical prolines from readily available starting materials mediated by a tryptophan synthase β-subunit (TrpB)-imine reductase (IRED) cascade. In the first step, the TrpB catalyzes C−C bond formation between a ketone substrate and an l-serine- or l-threonine (l-Thr)-derived amino acrylate intermediate. In the second step, the IRED reduces the resulting cyclic imine, in some cases simultaneously setting two stereocenters via a dynamic kinetic resolution. With this one-pot, sequential cascade, we demonstrate the synthesis of mono-, bi-, and tricyclic prolines bearing as many as four chiral centers, including three examples that contain a remote desymmetrized stereocenter and one example featuring an l-Thr-derived, fully functionalized pyrrolidine ring. Furthermore, we show that a d-proline is formed from l-amino acid starting materials, which has not been observed in closed-shell tryptophan synthase catalysis previously. This cascade is a scalable, operationally simple method to synthesize new prolines, and is poised to expand the development of therapeutics featuring structurally complex ncAAs.

Historically, many compelling therapeutic targets have been accessible only by injectable biologic drugs. Macrocyclic peptides, such as the proprotein convertase subtilisin/kexin type 9 inhibitor enlicitide for the treatment of atherosclerotic cardiovascular disease, are beginning to unlock these targets to orally administered therapies to enable broader patient access. We report the convergent biocatalytic assembly of enlicitide from simple building blocks enabled by a suite of engineered enzymes to catalyze selective peptide fragment formation, coupling, and macrocyclization in a protecting group–free manner. Together with efficient crystallizations that obviate the need for chromatography, this approach reduces the number of steps by greater than half compared with prior state-of-the-art methods, addressing long-standing synthetic challenges and offering a sustainable blueprint for the scalable development of complex peptide therapeutics.

The tumor microenvironment is characterized by conditions that frequently lead to immunosuppression, allowing tumors to escape immune surveillance and potentially contributing to resistance to immuno-oncology therapeutics. A potential strategy for combination therapy with checkpoint inhibitors is to target the A_2A and A_2B receptors with a dual antagonist that could rescue T cells from adenosine-mediated suppression. Herein, we describe efforts toward highly potent and selective A_2A/A_2B dual receptor antagonists with improved pharmacokinetic and solubility profiles compared to initial lead compounds. We discovered that a 1,3-cyclobutane linker between our triazoloquinazoline core and a pendant aryl substituent decorated with a tertiary carbinamine provided a desirable balance of potency and physicochemical properties. Our lead molecule 34 demonstrated an exceptional effective half-life across multiple species. Chemistry advances guided by high-throughput experimentation (HTE) facilitated efficient, late-stage access to complex derivatives in this series.

Noncanonical amino acids (ncAAs) are valuable building blocks for novel therapeutics. Prolines are particularly useful because their cyclic cores can limit the conformational flexibility of a larger molecular framework, allowing such scaffolds to be further tuned to enhance engagement with their biological targets. Herein, we describe a convergent approach to synthesizing noncanonical prolines from readily available starting materials mediated by a tryptophan synthase β-subunit (TrpB)-imine reductase (IRED) cascade. In the first step, the TrpB catalyzes ketone substrate activation and C–C bond formation with an L-serine- or L-threonine (L-Thr)-derived amino acrylate intermediate. In the second step, the IRED reduces the cyclic imine intermediate, in some cases simultaneously setting two stereocenters via a dynamic kinetic resolution. With this one-pot, sequential cascade, we demonstrate the synthesis of mono-, bi-, and tricyclic prolines bearing as many as four chiral centers, including three examples possessing a remote desymmetrized stereocenter and one example possessing an L-Thr-derived, fully functionalized pyrrolidine ring. Furthermore, we show that D-prolines are accessible from L-amino acid starting materials, which has not been observed in tryptophan synthase catalysis previously. This cascade is a scalable, operation-ally simple method to synthesize new prolines, and is poised to expand the development of novel therapeutics featuring structurally complex ncAAs.

Transaminases are choice biocatalysts for the synthesis of chiral primary amines, including amino acids bearing contiguous stereocenters. In this study, we employ lysine as a "smart" amine donor in transaminase-catalyzed dynamic kinetic resolution reactions to access β-branched noncanonical arylalanines. Our mechanistic investigation demonstrates that, upon transamination, the lysine-derived ketone byproduct readily cyclizes to a six-membered imine, driving the equilibrium in the desired direction and thus alleviating the need to load superstoichiometric quantities of the amine donor or deploy a multienzyme cascade. Lysine also shows good overall compatibility with a panel of wild-type transaminases, a promising hint of its application as a smart donor more broadly. Indeed, by this approach, we furnished a broad scope of β-branched arylalanines, including some bearing hitherto intractable cyclopropyl and isopropyl substituents, with high yields and excellent selectivities.

Transaminases are choice biocatalysts for the synthesis of chiral primary amines, including amino acids bearing contiguous stereocenters. In this study, we employ lysine as a “smart” amine donor in transaminase-catalyzed dynamic kinetic resolution reactions to access β-branched noncanonical arylalanines. Our mechanistic investigation demonstrates that, upon transamination, the lysine-derived ketone byproduct readily cyclizes to a six-membered imine, driving the equilibrium in the desired direction and thus alleviating the need to load superstoichiometric quantities of the amine donor or deploy a multi-enzyme cascade. Lysine also shows good overall compatibility with a panel of wild-type transaminases, a promising hint of its application as a smart donor more broadly. Indeed, with this discovery in hand, we furnished a broad scope of β-branched arylalanines, including some bearing hitherto intractable cyclopropyl and isopropyl substituents, with high yields and excellent selectivities.

Biocatalytic oxidations are an emerging technology for selective C−H bond activation. While promising for a range of selective oxidations, practical use of enzymes catalyzing aerobic hydroxylation is presently limited by their substrate scope and stability under industrially relevant conditions. Here, we report the engineering and practical application of a non‐heme iron and α‐ketoglutarate‐dependent dioxygenase for the direct stereo‐ and regio‐selective hydroxylation of a non‐native fluoroindanone en route to the oncology treatment belzutifan, replacing a five‐step chemical synthesis with a direct enantioselective hydroxylation. Mechanistic studies indicated that formation of the desired product was limited by enzyme stability and product overoxidation, with these properties subsequently improved by directed evolution, yielding a biocatalyst capable of >15,000 total turnovers. Highlighting the industrial utility of this biocatalyst, the high‐yielding, green, and efficient oxidation was demonstrated at kilogram scale for the synthesis of belzutifan.

Biocatalytic oxidations are an emerging technology for selective C−H bond activation. While promising for a range of selective oxidations, practical use of enzymes catalyzing aerobic hydroxylation is presently limited by their substrate scope and stability under industrially relevant conditions. Here, we report the engineering and practical application of a non‐heme iron and α‐ketoglutarate‐dependent dioxygenase for the direct stereo‐ and regio‐selective hydroxylation of a non‐native fluoroindanone en route to the oncology treatment belzutifan, replacing a five‐step chemical synthesis with a direct enantioselective hydroxylation. Mechanistic studies indicated that formation of the desired product was limited by enzyme stability and product overoxidation, with these properties subsequently improved by directed evolution, yielding a biocatalyst capable of >15,000 total turnovers. Highlighting the industrial utility of this biocatalyst, the high‐yielding, green, and efficient oxidation was demonstrated at kilogram scale for the synthesis of belzutifan.

The chemical structure of excipients molecularly mixed in an amorphous solid dispersion (ASD) has a significant impact on properties of the ASD including dissolution behavior, physical stability, and bioavailability. Polymers used in ASDs require a balance between hydrophobic and hydrophilic functionalities to ensure rapid dissolution of the amorphous dispersion as well as sustained supersaturation of the drug in solution. This work demonstrates the use of postpolymerization functionalization of poly(vinylpyridine) excipients to elucidate the impact of polymer properties on the dissolution behavior of amorphous dispersions containing posaconazole. It was found that N-oxidation of pyridine functionalities increased the solubility of poly(vinylpyridine) derivatives in neutral aqueous conditions and allowed for nanoparticle formation which supplied posaconazole into solution at concentrations exceeding those achieved by more conventional excipients such as hydroxypropyl methylcellulose acetate succinate (HPMCAS) or Eudragit E PO. By leveraging these functional modifications of the parent poly(vinylpyridine) excipient to increase polymer hydrophilicity and minimize the effect of polymer on pH, a new polymeric excipient was optimized for rapid dissolution and supersaturation maintenance for a model compound.