János Éles

The route from problem to solution in multistep continuous flow synthesis of pharmaceutical compounds

Recent advances in the field of continuous flow chemistry allow the multistep preparation of complex molecules such as APIs (Active Pharmaceutical Ingredients) in a telescoped manner. Numerous examples of laboratory-scale applications are described, which are pointing towards novel manufacturing processes of pharmaceutical compounds, in accordance with recent regulatory, economical and quality guidances. The chemical and technical knowledge gained during these studies is considerable; nevertheless, connecting several individual chemical transformations and the attached analytics and purification holds hidden traps. In this review, we summarize innovative solutions for these challenges, in order to benefit chemists aiming to exploit flow chemistry systems for the synthesis of biologically active molecules.

Synthesis of vinca alkaloids and related compounds. Part 101: A new convergent synthetic pathway to build up the aspidospermane skeleton. Simple synthesis of 3-oxovincadifformine and 3-oxominovincine. Attempts to produce 15β-hydroxyvincadifformine

Abstract A molecule with an indole skeleton, containing a latent acrylic ester function—acting as a diene—was produced from Nb-trityl-2-(hydroxy-methyl)-tryptamine and reacted with esters containing an aldehyde or aldehyde-equivalent structural unit, yielding 3-oxo-16,17-dihydro-Δ20-secodin-17-ol type intermediates from which dehydration, followed by [4+2]cycloaddition, furnished 3-oxovincadifformine and 3-oxominovincine. We also wished to apply the method to produce 15β-hydroxyvincadifformine, however, the appearance of a dimeric product with indole skeleton was observed instead of the expected cycloaddition.

Continuous Synthesis and Purification by Coupling a Multistep Flow Reaction with Centrifugal Partition Chromatography

Abstract Continuous‐flow multistep synthesis is combined with quasi‐continuous final‐product purification to produce pure products from crude reaction mixtures. In the nucleophilic aromatic substitution of 2,4‐difluoronitrobenzene with morpholine followed by a heterogeneous catalytic hydrogenation, the desired monosubstituted product can be continuously separated from the co‐ and by‐products in a purity of over 99 % by coupling a flow reactor sequence to a multiple dual‐mode (MDM) centrifugal partition chromatography (CPC) device. This purification technique has many advantages over HPLC, such as higher resolution and no need for column replacement or silica recycling, and it does not suffer from irreversible adsorption.

Multistep Continuous-Flow Synthesis of Condensed Benzothiazoles

AbstractIn medicinal chemistry, the development of synthetic procedures for the access of new heterocyclic systems as potential scaffolds is elementary. Herein, we report our results on the formation of small drug-like heterocycles, utilizing flow chemistry. This approach enables the extension of the reaction parameter window, including high-pressure/high-temperature or hazardous chemistry. In our work, various novel condensed tricyclic benzothiazoles fused with furo- and thieno-rings were synthesized applying a multistep continuous-flow protocol. The process includes two ring closure steps and a nitro group reduction step. Batch and telescoped continuous-flow syntheses were also designed and performed.

Discovery of novel steroidal histamine H3 receptor antagonists/inverse agonists

Emerging from an HTS campaign, novel steroid-based histamine H3 receptor antagonists were identified and characterized. Structural moieties of the hit compounds were combined to improve binding affinities which resulted in compound 4 as lead molecule. During the lead optimization due to the versatile modifications of diamino steroid derivatives, several in vitro potent compounds with subnanomolar binding affinities to histamine H3 receptors were found. The unfavorable binding to rat muscarinic receptors was successfully reduced by tuning the basicity. Compound 20 showed significant in vivo activity in the rat dipsogenia model and could serve as a pharmacological tool in the future.