Application of Transition-Metal Catalysis, Biocatalysis, and Flow Chemistry as State-of-the-Art Technologies in the Synthesis of LCZ696.

LCZ696 is a novel treatment for patients suffering from heart failure that combines the two active pharmaceutical ingredients sacubitril and valsartan in a single chemical compound. While valsartan is an established drug substance, a new manufacturing process suitable for large-scale commercial production had to be developed for sacubitril. The use of chemocatalysis, biocatalysis, and flow chemistry as state-of-the-art technologies allowed to efficiently build up the structure of sacubitril and achieve the defined performance targets.

Fouling of Flow Reactors in Organolithium Mediated Transformations: Experience on Scale-up and Proposed Solution.

Continuous processing has been demonstrated to be a superior approach when applied to fast and energetic chemical transformations. Indeed, whereas classical batch or semi-batch methods require cryogenic conditions and slow addition rates of reactive species, flow technologies enable rapid mixing of synthetic partners in a highly controlled environment. As a result, low yielding and dangerous processes in batch can be performed at scale in a cost competitive and safer continuous manner. Despite the advantages of higher quality and safety, the perennial problems of solids build-up and pipe fouling threaten the robustness and reliability of flow processes. In this contribution, a new methodology to prevent reactor fouling is reported and discussed. The implementation of this methodology has been decisive in solving fouling issues encountered during the piloting of an organolithium based flow process.

Glucuronidation of bile acids under flow conditions: design of experiments and Koenigs-Knorr reaction optimization.

An efficient method for the C3-glucuronidation of bile acids is developed under flow conditions. A modular mesoreactor assisted flow set-up was combined with statistical design of experiments to speed up the optimization of the Koenigs-Knorr reaction in terms of yield, regioselectivity, costs, as well as technical and practical standpoints. Using the optimal conditions, selective glucuronidation of naturally occurring bile acids was successfully achieved offering a new, valuable route to C3-glucuronidated bile acids useful for biological, diagnostic and PK/ADMET investigations.

Continuous flow synthesis and scale-up of glycine- and taurine-conjugated bile salts.

A multi-gram scale protocol for the N-acyl amidation of bile acids with glycine and taurine has been successfully developed under continuous flow processing conditions. Selecting ursodeoxycholic acid (UDCA) as the model compound and N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) as the condensing agent, a modular mesoreactor assisted flow set-up was employed to significantly speed up the optimization of the reaction conditions and the flow scale-up synthesis. The results in terms of yield, in line purification, analysis, and implemented flow set-up for the reaction optimization and large scale production are reported and discussed.

Development of 3α,7α-dihydroxy-6α-ethyl-24-nor-5ß-cholan-23-sulfate sodium salt (INT-767): Process optimization, synthesis and characterization of metabolites.

Herein we report our synthetic efforts in supporting the development of the bile alcohol sulfate INT-767, a FXR/TGR5 dual agonist with remarkable therapeutic potential for liver disorders. We describe the process development to a final route for large scale preparation and analogues synthesis. Key sequences include Grignard addition, a one-pot two-step shortening-reduction of the carboxylic side chain, and the final sulfation reaction. The necessity for additional steps such as the protection/deprotection of hydroxyl groups at the steroidal body was also evaluated for step-economy and formation of side-products. Critical bottlenecks such as the side chain degradation have been tackled using flow technology before scaling-up individual steps. The final synthetic route may be successfully employed to produce the amount of INT-767 required to support late-stage clinical development of the compound. Furthermore, potential metabolites have been synthesized, characterized and evaluated for their ability to modulate FXR and TGR5 receptors providing key reference standards for future drug investigations, as well as offering further insights into the structure-activity relationships of this class of compounds.

Exploring the synthetic versatility of the Lewis acid induced decomposition reaction of α-diazo-ß-hydroxy esters. The case of ethyl diazo(3-hydroxy-2-oxo-2,3-dihydro-1H-indol-3-yl)acetate.

Ethyl diazo(3-hydroxy-2-oxo-2,3-dihydro-1H-indol-3-yl)acetate was prepared by aldol-type condensation of ethyl diazoacetate with isatin. A systematic and mechanistic study on the Lewis acid induced decomposition reaction of this valuable diazo precursor was carried out with the aim to gain new insights into the mechanistic aspects of the reaction as well as to further understand the factors and experimental conditions which affect the relative product distribution. The reaction, which may proceed via cationic and noncationic mechanisms, was found to be significantly influenced by the reaction environment determined by the characteristics of the Lewis acid employed, by the ability of the Lewis acid to form a complex with the alcohol functionality of the α-diazo-ß-hydroxy ester, and by the polarity and nucleophilicity of the solvent used.

The application of flow microreactors to the preparation of a family of casein kinase I inhibitors.

In this article we demonstrate how a combination of enabling technologies such as flow synthesis, solid-supported reagents and scavenging resins utilised under fully automated software control can assist in typical medicinal chemistry programmes. In particular automated continuous flow methods have greatly assisted in the optimisation of reaction conditions and facilitated scale up operations involving hazardous chemical materials. Overall a collection of twenty diverse analogues of a casein kinase I inhibitor has been synthesised by changing three principle binding vectors.

BF(3).Et(2)O-induced decomposition of ethyl 2-diazo-3-hydroxy-3,3-diarylpropanoates in acetonitrile: a novel approach to 2,3-diaryl beta-enamino ester derivatives.

The BF(3).Et(2)O-induced decomposition of ethyl 2-diazo-3-hydroxy-3,3-diarylpropanoates, prepared by the addition of a series of benzophenones to ethyl diazo(lithio)acetate, is reported and studied. By using acetonitrile as a solvent, the corresponding N-acyl beta-enamino ester derivatives are obtained in good yields and with a diverse regioselectivity as the result of 1,2-aryl migration in the vinyl cation intermediates. The factors that govern the migratory aptitude as well as the mechanistic aspects of the reaction are discussed.

A multistep flow process for the synthesis of highly functionalized benzoxazoles.

An efficient and scalable transformation of 3-halo-N-acyl anilines to the corresponding benzoxazoles within a continuous flow reactor is reported. This transformation proceeds via base-mediated deprotonation, ortho-lithiation, and intramolecular cyclization to provide unstable lithiated benzoxazole moieties. The subsequent in-line electrophilic quench results in the formation of substituted benzoxazoles in high yield and quality. Continuous flow technology allowed for accurate temperature control and immediate in-line quench while minimizing the hold-up time for the unstable lithiated intermediates thereby minimizing associated byproduct formation.

HPLC/ELSD analysis of amidated bile acids: an effective and rapid way to assist continuous flow chemistry processes.

The employment of the flow N-acyl amidation of natural bile acids (BAs) required the in-line connection with suitable analytical tools enabling the determination of reaction yields as well as of the purity grade of the synthesized glyco- and tauro-conjugated derivatives. In this framework, a unique HPLC method was successfully established and validated for ursodeoxycholic (UDCA), chenodeoxycholic (CDCA), deoxycholic (DCA) and cholic (CA) acids, as well as the corresponding glyco- and tauro-conjugated forms. Because of the shared absence of relevant chromophoric moieties in the sample structure, an evaporative light scattering detector (ELSD) was profitably utilized for the analysis of such steroidal species. For each of the investigated compounds, all the runs were contemporarily carried out on the acidic free and the two relative conjugated variants. The different ELSD response of the free and the corresponding conjugated BAs, imposed to build-up separate calibration curves. In all the cases, very good precision (RSD% values ranging from 1.04 to 6.40% in the long-period) and accuracy (Recovery% values ranging from 96.03 to 111.14% in the long-period) values along with appreciably low LOD and LOQ values (the former being within the range 1-27 ng mL(-1) and the latter within the range 2-44 ng mL(-1)) turned out.

Avicholic Acid: A Lead Compound from Birds on the Route to Potent TGR5 Modulators.

Grounding on our former 3D QSAR studies, a knowledge-based screen of natural bile acids from diverse animal species has led to the identification of avicholic acid as a selective but weak TGR5 agonist. Chemical modifications of this compound resulted in the disclosure of 6α-ethyl-16-epi-avicholic acid that shows enhanced potency at TGR5 and FXR receptors. The synthesis, biological appraisals, and structure-activity relationships of this series of compounds are herein described. Moreover, a thorough physicochemical characterization of 6α-ethyl-16-epi-avicholic acid as compared to naturally occurring bile acids is reported and discussed.

On the way to selective PARP-2 inhibitors. Design, synthesis, and preliminary evaluation of a series of isoquinolinone derivatives.

PARP-1 and PARP-2 are members of the family of poly(ADP-ribose)polymerases, which are involved in the maintenance of genomic integrity under conditions of genotoxic stimuli. The different roles of the two isoforms under pathophysiological conditions have not yet been fully clarified, and this is partially due to the lack of selective inhibitors. We report herein the synthesis and preliminary pharmacological evaluation of a large series of isoquinolinone derivatives as PARP-1/PARP-2 inhibitors. Among them, we identified the 5-benzoyloxyisoquinolin-1(2 H)-one derivative as the most selective PARP-2 inhibitor reported so far, with a PARP-2/PARP-1 selectivity index greater than 60.