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The evolution from early medicinal chemistry to large-scale production of the chemical synthesis of Lilly D1 positive allosteric modulator mevidalen (LY3154207) and its hydroxybenzoate cocrystal is...

This editorial seeks to provide guidance to prospective OPR&D authors with respect to submissions involving continuous processing. Industrially relevant flow drivers are emphasized, along with incr...

Technology transfer of a small volume continuous (SVC) process and Current Good Manufacturing Practices (cGMP) manufacturing of merestinib are described. A hybrid batch-SVC campaign was completed at a contract manufacturing organization under cGMP. The decision process by which unit operations were selected for implementation in flow for the cGMP campaign is discussed. The hybrid process comprised a Suzuki–Miyaura cross-coupling reaction, a nitro-group hydrogenolysis, a continuous amide bond formation, and a continuous deprotection. A continuous crystallization using two mixed suspension, mixed product removal (MSMPR) crystallizers and a filtration with in situ dissolution were employed for purification between the two SVC steps. Impurity levels were monitored using both online process analytical technology (PAT) and offline measurements. The continuous processing steps operated uninterrupted for 18 days to yield the drug substance in solution at a throughput of 12.5 kg/day. Crystallization in batch mode ...

Development of a small volume continuous process that used a combination of batch and flow unit operations to manufacture the small molecule oncolytic candidate merestinib is described. Continuous processing was enabled following the identification and development of suitable chemical transformations and unit operations. Aspects of the nascent process control strategy were evaluated in the context of a 20 kg laboratory demonstration campaign, executed in walk-in fume hoods at a throughput of 5–10 kg of active pharmaceutical ingredient per day. The process comprised an automated Suzuki–Miyaura cross-coupling reaction, a nitro-group hydrogenolysis, a continuous amide bond formation, and a continuous deprotection. Three of the four steps were purified using mixed-suspension, mixed-product removal crystallizations. Process analytical technology enabled real-time or nearly real-time process diagnostics. Findings from the demonstration campaign informed a second process development cycle as well as decision mak...

A variety of high-pressure and low-pressure plug flow reactors (PFRs) are described in this chapter with manufacturing examples for each. Coiled tube PFRs and vertical pipes-in-series PFRs were used for two-phase gas–liquid reactions. A pulsating flow coiled tube PFR was used for gas–liquid reaction with solids precipitate. Superheated PFRs were used for reactions involving homogeneous solutions, heated above the boiling point of the solvent. Disposable coiled tube PFRs were used with highly potent compounds. Continuous stirred tank reactors (CSTRs) were needed for heterogeneous continuous processes. CSTRs, CSTRs-in-series, and intermittent flow CSTRs were used for reactions with long reaction times, positive order kinetics, and multiple reaction phases, either solid/liquid or liquid/liquid. This chapter also explains how to calculate the actual internal temperature profile along the length of a PFR, which is often not practical to measure.

A new synthesis of a key indazole-containing building block for the MET kinase inhibitor merestinib was designed and demonstrated. Crucial to the successful construction of the challenging indazole is an SNAr reaction, which forges the heterocyclic ring. Continuous processing was applied to two of the five steps: nitration of a benzaldehyde and high-temperature hydrolysis of an aniline to phenol. Compared to a highly developed historical route, the new route shows clear benefits in terms of product quality and potentially manufacturability and robustness.

For the manufacture of small molecule drugs, many pharmaceutical innovator companies have recently invested in continuous processing, which can offer significant technical and economic advantages over traditional batch methodology. This Expert Review will describe the reasons for this interest as well as many considerations and challenges that exist today concerning continuous manufacturing. Areas covered: Continuous processing is defined and many reasons for its adoption are described. The current state of continuous drug substance manufacturing within the pharmaceutical industry is summarized. Current key challenges to implementation of continuous manufacturing are highlighted, and an outlook provided regarding the prospects for continuous within the industry. Expert commentary: Continuous processing at Lilly has been a journey that started with the need for increased safety and capability. Over twelve years the original small, dedicated group has grown to more than 100 Lilly employees in discovery, development, quality, manufacturing, and regulatory designing in continuous drug substance processing. Recently we have focused on linked continuous unit operations for the purpose of all-at-once pharmaceutical manufacturing, but the technical and business drivers that existed in the very beginning for stand-alone continuous unit operations in hybrid processes have persisted, which merits investment in both approaches.

Advances in drug potency and tailored therapeutics are promoting pharmaceutical manufacturing to transition from a traditional batch paradigm to more flexible continuous processing. Here we report the development of a multistep continuous-flow CGMP (current good manufacturing practices) process that produced 24 kilograms of prexasertib monolactate monohydrate suitable for use in human clinical trials. Eight continuous unit operations were conducted to produce the target at roughly 3 kilograms per day using small continuous reactors, extractors, evaporators, crystallizers, and filters in laboratory fume hoods. Success was enabled by advances in chemistry, engineering, analytical science, process modeling, and equipment design. Substantial technical and business drivers were identified, which merited the continuous process. The continuous process afforded improved performance and safety relative to batch processes and also improved containment of a highly potent compound.

An automated repeating batch approach has been developed for the rapid screening and scale up of a nitroaromatic to aniline catalytic hydrogenolysis. Advantages of this approach include the ability to scale up in small equipment using readily available powdered catalysts, rapid reaction kinetics due to high catalyst to substrate ratio, lower overall catalyst use, high throughput from a small reactor, and the ability to refresh the catalyst without manual intervention.

Adopting continuous manufacturing requires considerable upfront investment in technology and expertise to develop and execute robust processes. cGMP manufacturing control strategies for drug substance processes in particular are limited, with few real case studies available in the literature. Making the change from a traditional batch manufacturing paradigm to a new continuous paradigm can be highly disruptive. In this chapter, key enablers for running continuous processes including multi-step processes are presented. These enablers allow the process to run in a state of control such that the environmental, safety, quality and cost benefits associated with continuous processing may be realized. The enablers include the use of process analytical technology, a material tracking system, a diversion strategy and the incorporation of surge capacity. Examples from the field where these control strategy enablers were successfully used to produce drug substance API using continuous technology under cGMP conditions are also presented. In these case studies the environmental, safety and quality benefits realized are highlighted and the evolution of the technology from single step batch-continuous hybrid processes to multi-step fully continuous telescoped processes is described.

Efficient continuous Grignard and lithiation processes were developed to produce one of the key regulatory starting materials for the production of edivoxetine hydrochoride. For the Grignard process, organometallic reagent formation, Bouveault formylation, reduction, and workup steps were run in continuous stirred tank reactors (CSTRs). The lithiation utilized a hybrid approach where plug flow reactors (PFRs) were used for the metal halogen exchange and Bouveault formylation steps, while the reduction and workup steps were performed in CSTRs. Relative to traditional batch processing, both approaches offer significant advantages. Both processes were high-yielding and produced the product in high purity. The two main processes were directly compared from a number of perspectives including reagent and operational safety, fouling potential, process footprint, need for manual operation, and product yield and purity.

A visible light-mediated Smiles rearrangement providing the difluoroethanol motif has been shown to reliably operate on preparative scale up to 100 g of starting material. Mechanistic investigation has revealed the reaction proceeds predominantly via a radical chain process that in some instances can be initiated via visible light or thermal activation in the absence of a photocatalyst. The reaction was demonstrated in continuous flow, with visible light and thermal initiation using a thiophene substrate relevant to pharmaceutical development.

A single-step method and a two-step method for the synthesis of aminopyrazoles from isoxazoles are presented and compared. Based on in situ NMR monitoring, both processes proceed through a ketonitrile. In the single-step process, hydrazine serves to both open the isoxazole to the unisolated ketonitrile intermediate and form the aminopyrazole. The two-step process involves ring opening of the isoxazole by deprotonation with hydroxide to generate the ketonitrile followed by the addition of acetic acid and hydrazine to form the aminopyrazole.

A fully automated fill/empty reactor system for liquid–liquid biphasic Suzuki couplings is described. The system was capable of charging reactant and catalyst solutions to a heated vessel, heating reagent solutions by flow heat exchanger on the way into the reactor, allowing the reaction to occur, monitoring reaction completion, discharge of the product solution, and initiation of another cycle in a repeating fashion. A unique noncontact colorimetric method was used to monitor reaction completion. The reactor system exhibits many of the characteristics of a fully continuous reactor such as (1) high productivity from a small process footprint, (2) a large number of volume turnovers each day, (3) higher heat transfer area per unit volume compared to batch because the reactor is 50× smaller, and (4) rapid heat up and cool down of process streams enabled by heat exchangers. Downstream unit operations that are intended for eventual integrated end-to-end continuous production included a batch metal removal step...

The photocatalytic preparation of aminoalkylated heteroarenes from haloalkylamides via a 1,4-aryl migration from nitrogen to carbon, conceptually analogous to a radical Smiles rearrangement, is reported. This method enables the substitution of amino groups in heteroaromatic compounds with aminoalkyl motifs under mild, iridium(III)-mediated photoredox conditions. It provides rapid access to thienoazepinone, a pharmacophore present in multiple drug candidates for potential treatment of different conditions, including inflammation and psychotic disorders.

A visible-light-mediated radical Smiles rearrangement has been developed to address the challenging synthesis of the gem-difluoro group present in an opioid receptor-like 1 (ORL-1) antagonist that is currently in development for the treatment of depression and/or obesity. This method enables the direct and efficient introduction of the difluoroethanol motif into a range of aryl and heteroaryl systems, representing a new disconnection for the synthesis of this versatile moiety. When applied to the target compound, the photochemical step could be conducted on 15 g scale using industrially relevant [Ru(bpy)3Cl2] catalyst loadings of 0.01 mol %. This transformation is part of an overall five-step route to the antagonist that compares favorably to the current synthetic sequence and demonstrates, in this specific case, a clear strategic benefit of photocatalysis.

Knowledge of the kinetic behavior of catalysts under synthetically relevant conditions is vital for the efficient use of compounds that mediate important transformations regardless of their composition or driving force. In particular, these data are of great importance to add perspective to the growing number of applications of photoactive transition metal complexes. Here we present kinetic, synthetic, and spectroscopic evidence of the mechanistic behavior of fac-Ir(ppy)3 in a visible light-mediated radical addition to 3-methylindole, demonstrating the instability of fac-Ir(ppy)3 under these conditions. During the reaction, rapid in situ functionalization of the photocatalyst occurs, eventually leading to deactivation. These findings demonstrate a conceivable deactivation process for catalytic single electron reactions in the presence of radicophilic ligands. Attempts to inhibit photocatalyst deactivation through structural modification provide further insight into catalyst selection for a given system of interest.

The design, development, and implementation of a pilot-scale continuous Schotten–Baumann amide bond formation and reactive crystallization to afford LY2886721 is described. The material met all API quality attributes and was comparable to material produced by a defined batch process. The scalability of the reaction and crystallization processes was confirmed during the development process. The pilot-scale equipment set was contained in a walk-in fume hood and operated at a production rate of 3 kg/day in a 72 h continuous run. Significant technical and business drivers for running the process in continuous flow mode were proposed and examined during development. The continuous process provided for lab hood commercialization and provided for minimal material at risk in the process. The demonstration also confirmed the risk inherent to operation of a tubular reactor under supersaturated conditions, and fouling occurred in the plug flow reactor. Fouling also occurred in the crystallizer. Recognizing these def...

An intramolecular thermal cyclization protocol was developed in a flow reactor to take advantage of the high pressures and temperatures that are easily obtained in small scale autoclave reactors that have been modified to handle slurries. This reactor was equipped with a fill/empty pumping system to enable easy and nearly complete transfer of slurries. The reaction conditions were designed to take advantage of the insolubility of the product in order to separate it from residual starting material by filtration after short reaction times. Recycling of the filtrate maximized the yield and throughput while minimizing decomposition. Recycles were accomplished using a strip to dryness protocol that was easily performed in a rotary evaporator. This new equipment set was designed with lab-hood manufacturing in mind, a minimized footprint, and the system was completely automated for charging, emptying, rinsing, and reacting. Additional efforts for quick screening and alternate modes of addition were also investig...

We report a detailed investigation into the application of visible light-mediated photocatalysis to a challenging bond construction in a complex pharmaceutical target. The optimized reaction allowed the direct coupling of N-methylmorpholine with an unfunctionalized pyridazine in good yield and selectivity, and with high purity of the product isolated via crystallization. The reaction also facilitated the expedient synthesis of a range of analogues via the use of other commercially available N-methyl substituted tertiary amines, and therefore it represents an attractive tool for medicinal chemistry. Furthermore, a number of other interesting photoredox reactions were discovered during the course of this investigation, such as a formal methylation reaction via C–N bond cleavage, functionalization of C–H bonds alpha to amides, and a visible light-mediated iminium ion reduction.

The development of an alternative synthetic route to a functionalized imidazopyridazine which strategically streamlines the synthesis and avoids a number of problematic reagents is described. Key to the success of this alternative route is the use of two C–H functionalization reactions: a Pd-catalyzed direct benzylation reaction to functionalize a C–H bond with a substituted benzyl group and a V-catalyzed NMO addition reaction to install a benzylic morpholine moiety.

Continuous processing enables the use of non-standard reaction conditions such as high temperatures and pressures while in the liquid phase. This expands the chemist's toolbox and can enable previously unthinkable chemistry to proceed with ease. For a series of amphoteric amino acid derivatives, we have demonstrated the ability to hydrolyze the tert-butyl ester functionality in protic solvent systems. Using a continuous plug flow reactor at 120-240°C and 15-40min reaction times, no pH modification or additional reagents are needed to achieve the desired transformation. The method was then expanded to encompass a variety of more challenging substrates to test selectivity and racemization potential. The acid products were generally isolated as crystalline solids by simple solvent exchange after the deprotection reaction in good to high yield and purity.

The direct trifluoromethylation of (hetero)arenes is a process of high importance to the pharmaceutical industry. Many reagents exist for this purpose and have found widespread use in discovery efforts; however, the step-intensive preparation of these reagents and their corresponding cost have resulted in minimal use of these methods in large-scale applications. For the ready transition of direct trifluoromethylation methodologies to large-scale application, the further development of processes utilizing inexpensive CF3 sources available on a metric ton scale is highly desirable. We report the use of pyridine N-oxide derivatives in concert with trifluoroacetic anhydride to promote a high-yielding and scalable trifluoromethylation reaction. Key mechanistic insights include the observation of electron donor-acceptor complexes in solution as well as a high dependence on photon flux. These observations have culminated in the application of this chemistry on a kilogram scale, demonstrating the utility of this reagent combination for preparative applications.

A photolytic Smiles rearrangement of sulfonic acid esters (I) to produce difluoroalkyl substituted arenes and hetarenes is described.

Our efforts in constructing the ABD-ring of phomactin A through an intramolecular oxa-[3+3] annulation strategy is described. This struggle entailed finding a practical and efficient preparation of annulation precursor, and a realization of the unexpected competing regioisomeric pathway. The success entailed accessing the A-ring through Diels–Alder cycloaddition of Rawal’s diene. Furthermore, the discovery that the regioisomers from the annulation existed as atropisomers with respect to the D-ring olefin and that they could be equilibrated to the desired ABD-tricycle, allowing large quantities of tricycle to be accessed.

The route selection and process research and development of a practical synthesis for JAK2 inhibitor LY2784544 is described. The first-generation synthesis route, similar to that used in discovery for derivatization of a benzylic amine moiety, was 14 overall steps and possessed several steps that required extensive development for large-scale production. Route selection considerations led to a modified synthesis that utilized a novel vanadium-catalyzed carbon–carbon bond-forming arylation reaction for incorporation of the key benzylic morpholine moiety. A protecting group used to mask an amino pyrazole unit was modified from PMB to tert-butyl, resulting in a dramatic reduction in the overall length of the route. These two major changes resulted in an eight-step synthesis, which was six steps shorter than the first-generation synthesis. In the pilot plant, the new synthesis was scaled to produce >100 kg of LY2784544 in high yield and purity under GMP conditions. The overall development including the vanadi...

A route for the synthesis of ( S , S )-7-amino-5-methyl-5 H -dibenzo[ b , d ]azepin-6(7 H )-one hydrochloride is disclosed. The synthesis includes a Friedel–Crafts alkylation to form the seven-membered ring and a highly efficient classical resolution. Additional studies on the enantiopure material showed the amine to be highly resistant to racemization, which led us to investigate the unexpected stability. We propose that the inherent axial chirality contained in the dibenzazepinone works to produce an interesting chirality transfer mechanism, which accounts for the observed robustness of the stereocenter. This previously unrecognized stereochemical element exists within this specific class of molecules, and they should be drawn in a manner which displays the axial chirality.

As the largest secondary metabolite to be discovered as of yet, the polyether marine neurotoxin maitotoxin constitutes a major structural and synthetic challenge. After its originally proposed structure ( 1) had been questioned on the basis of biosynthetic considerations, we provided computational and experimental support for structure 1. In an effort to provide stronger experimental evidence of the molecular architecture of maitotoxin, its GHIJKLMNO ring system 3 was synthesized. The (13)C NMR chemical shifts of synthetic 3 matched closely those corresponding to the same domain of the natural product providing strong evidence for the correctness of the originally proposed structure of maitotoxin ( 1).

The large number of reagents that have been developed for the synthesis of trifluoromethylated compounds is a testament to the importance of the CF3 group as well as the associated synthetic challenge. Current state-of-the-art reagents for appending the CF3 functionality directly are highly effective; however, their use on preparative scale has minimal precedent because they require multistep synthesis for their preparation, and/or are prohibitively expensive for large-scale application. For a scalable trifluoromethylation methodology, trifluoroacetic acid and its anhydride represent an attractive solution in terms of cost and availability; however, because of the exceedingly high oxidation potential of trifluoroacetate, previous endeavours to use this material as a CF3 source have required the use of highly forcing conditions. Here we report a strategy for the use of trifluoroacetic anhydride for a scalable and operationally simple trifluoromethylation reaction using pyridine N-oxide and photoredox catalysis to affect a facile decarboxylation to the CF3 radical., Trifluoromethylation is a key transformation, particularly for pharmaceuticals, but many reagents are expensive and difficult to scale up. Here, the authors show that trifluoroacetic anhydride can act as a CF3 source, allowing the radical reactions to be easily and inexpensively carried out at scale.

Key step in the preparation of title compound (Ib) is the direct photochemical aminomethylation of building block (II).

The naturally occurring but scarce marine neurotoxins azaspiracids-1, -2, and -3 have been synthesized from five key building blocks by a convergent strategy that involved dithiane and Stille coupling reactions. The ABCD fragments were constructed through a cascade reaction involving deprotection/self-assembly of the precursors, while the FGHI fragment was forged by a neodymium triflate-induced cyclization. The final ring closure (ring G) was achieved, after the union of all fragments, through an iodoetherification reaction followed by reductive removal of the facilitating iodine residue. These improved, second-generation routes confirm the absolute structures and render all three azaspiracids readily available for biological studies.

The 39 steps: The recently proposed revised structures of azaspiracid-2 and -3 (see picture), the two most potent members of the azaspiracid family, have been confirmed through the total syntheses of the two compounds. These 39-step syntheses represent a major improvement over the first-generation synthesis of azaspiracid-1 (50 steps).

The ABD-ring of phomactin A was synthesized using an intramolecular formal oxa-[3 + 3] cycloaddion of an alpha,beta-unsaturated iminium salt tethered to a 1,3-diketone. This represents the first time that the 12-membered ring has been formed simultaneously with the 1-oxadecalin and should afford a facile route to the challenging structure of phomactin A. [reaction: see text]

The title (1H-pyrrol-2-yl)pyridines, C(9)H(8)N(2), substituted at the ortho, meta, and para positions of the pyridine ring all have hydrogen-bonded arrangements with geometrically similar, nearly linear, N(pyrrole)-H...N(pyridine) hydrogen bonds of average length. The graph sets for the ortho, meta, and three para polymorphs are R(2)(2)(10), C(6), C(7), C(7), and R(4)(4)(28), respectively.

Endeavors including an unexpected retro-aldol–aldol process that proved to be critical for our eventual total synthesis of arisugacin A are described here.

Tert-Butylhydrazine hydrochloride 3-Aminocrotonitrile tert-Butyl-3-methyl-1H-pyrazol-5-amine 2-Chloropyridine Pd(dba)2 4,5-Bis(diphenylphosphino) 9,9-dimethylxanthene Tetra-n-butylammonium bromide Trifluoroacetic acid Keywords: Pyrazole protection; Single-step preparation; Triethylamine; Ethanol; Amination; Safety; Waste disposal

[reaction: see text]We describe here an inherent problem in direct epoxidation of the endocyclic olefin in 2H-pyrans fused to 2-pyrones. Such difficulties led to the development of highly stereoselective trans- and cis-dihydroxylations of these olefinic systems in both 2H-pyrans and dihydropyridines fused to a 2-pyrones or a 2-cyclohexenone. Protocols for the removal of the activated allylic hydroxyl group are also reported.

[reaction: see text] A Lewis acid-catalyzed formal cycloaddition of alpha,beta-unsaturated aldehydes with 6-methyl-4-hydroxy-2-pyrone, 1,3-diketones, and vinylogous silyl esters is described here.

Our efforts in constructing the ABD-ring of phomactin A through an intramolecular oxa-[3 + 3] annulation strategy is described. This struggle entailed finding a practical and efficient preparation of annulation precursor, and a realization of the unexpected competing regioisomeric pathway. The success entailed accessing the A-ring through Diels-Alder cycloaddition of Rawal’s diene. Furthermore, the discovery that the regioisomers from the annulation existed as atropisomers with respect to the D-ring olefin and that they could be equilibrated to the desired ABD-tricycle, allowing large quantities of tricycle to be accessed.