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Flow synthesis of Fluoxetine

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Scheme 1: Flow synthesis of fluoxetine (46).

PIC CREDIT, The synthesis of active pharmaceutical ingredients (APIs) using continuous flow chemistry,  Marcus Baumann and Ian R. Baxendale, Beilstein J. Org. Chem. 2015, 11, 1194–1219.,doi:10.3762/bjoc.11.134

One of the early published examples of industry-based research on multi-step flow synthesis of a pharmaceutical was reported in 2011 by scientists from Eli Lilly/UK and detailed the synthesis of fluoxetine 46, the API of Prozac[1]. In this account each step was performed and optimised individually in flow, with analysis and purification being accomplished off-line. The synthesis commences with the reduction of the advanced intermediate ketone 47 using a solution of pre-chilled borane–THF complex (48) to yield alcohol 49 (Scheme 1).

Conversion of the pendant chloride into iodide 51 was attempted via Finckelstein conditions, however, even when utilising phase-transfer conditions in order to maintain a homogeneous flow regime the outcome was not satisfactory giving only low conversions. Alternatively direct amination of chloride 49 utilising high temperature flow conditions (140 °C) allowed the direct preparation of amine 50 in excellent yield.

Flow processing using a short residence time (10 min) at the elevated temperature allowed for a good throughput; in addition, the handling of the volatile methylamine within the confines of the flow reactor simplifies the practical aspects of the transformation, however, extra precautions were required in order to address and remove any leftover methylamine that would pose a significant hazard during scaling up.

The final arylation of 50 was intended to be performed as a SNAr reaction, however, insufficient deprotonation of the alcohol 50 under flow conditions (NaHMDS or BEMP instead of using a suspension of NaH as used in batch) required a modification to the planned approach. To this end a Mitsunobu protocol based on the orchestrated mixing of four reagent streams (50, 54 and reagents 52 and 53) was developed and successfully applied to deliver fluoxetine (46) in high yield.

Overall, this study is a good example detailing the intricacies faced when translating an initial batch synthesis into a sequence of flow steps for which several adaptations regarding choice of reagents and reaction conditions are mandatory in order to succeed.

Marcus

Dr Marcus Baumann
Postdoc

Marcus Baumann studied chemistry at the Philipps-University Marburg/Germany, from where he graduated in 2007. His studies involved a 6 month period as an Erasmus student at the Innovative Technology Centre at the University of Cambridge, UK (with Prof. Steven V. Ley and Dr Ian R. Baxendale), where he developed a new flow-based oxazole synthesis. He soon returned to Cambridge to pursue his doctoral studies with Prof. Steven V. Ley where he developed flow processes for Curtius rearrangements, different fluorination reactions as well as important heterocycle syntheses. Upon completion of his PhD in 2010 Marcus was awarded a Feodor Lynen Postdoctoral Fellowship (Alexander von Humboldt Foundation, Germany) allowing him to join the group of Prof. Larry E. Overman at UC Irvine, USA (2011-2013). During his time in California his research focused on the synthesis of naturally occurring terpenes as well as analogues of ETP-alkaloids. The latter project generated potent and selective histone methyltransferase inhibitors and opened routes towards new probes for epigenetic diseases which are currently under further investigation. In early 2013 Marcus returned to the UK and took up a postdoctoral position with Prof. Ian R. Baxendale at the University of Durham, where his interests concentrate on the development of flow and batch based strategies towards valuable compounds en route for regenerative medicines.

Prof. Ian R. Baxendale

Personal web page

Professor in the Department of Chemistry
Telephone: +44 (0) 191 33 42185

(email at i.r.baxendale@durham.ac.uk)

Research Interests

My general areas of interest are: Organic synthesis (natural products, heterocyclic and medicinal chemistry), Organometallic chemistry, Catalyst design and application, Meso flow chemistry, Microfluidics, Microwave assisted synthesis, Solid supported reagents and scavengers, and facilitated reaction optimisation using Robotics and Automation.

My primary research direction is the synthesis of biologically potent molecules which encompasses the design, development and integration of new processing techniques for their preparation and solving challenges associated with the syntheses of new pharmaceutical and agrochemical compounds. In our work we utilise the latest synthesis tools and enabling technologies such as microwave reactors, solid supported reagents and scavengers, enzymes, membrane reactors and flow chemistry platforms to facilitate the bond making sequence and expedite the purification procedure. A central aspect of our investigations is our pioneering work on flow chemical synthesis and microreactor technology as a means of improving the speed, efficiency, and safety of various chemical transformations. As a part of these studies we are attempting to devise new chemical reactions that are not inherently feasible or would be problematic under standard laboratory conditions. It is our further challenge to enhance the automation associated with these reactor devices to impart a certain level of intelligence to their function so that repetitive wasteful actions currently performed by chemists can be delegated to a machine; for example, reagent screening or reaction optimisation. We use these technologies as tools to enhance our synthetic capabilities but strongly believe in not becoming slaves to any methodology or equipment.

For those interested in our research and wishing to find out more we invite you to visit our website at: http://www.dur.ac.uk/i.r.baxendale/

 

  1. Ahmed-Omer, B.; Sanderson, A. J. Org. Biomol. Chem. 2011, 9, 3854–3862. doi:10.1039/C0OB00906G
    Paper

    Preparation of fluoxetine by multiple flow processing steps

    *Corresponding authors
    aEli Lilly and Co. Ltd., Lilly Research Centre, Erl Wood Manor, Windlesham, Surrey, UK
    Org. Biomol. Chem., 2011,9, 3854-3862

    DOI: 10.1039/C0OB00906G

    http://pubs.rsc.org/en/Content/ArticleLanding/2011/OB/c0ob00906g#!divAbstract

Microflow technology is established as a modern and fashionable tool in synthetic organic chemistry, bringing great improvement and potential, on account of a series of advantages over flask methods. The study presented here focuses on the application of flow chemistry process in performing an efficient multiple step syntheses of (±)-fluoxetine as an alternative to conventional synthetic methods, and one of the few examples of total synthesis accomplished by flow technique.

Graphical abstract: Preparation of fluoxetine by multiple flow processing steps

1 The general method set-up of flow process used for the synthesis of (±)- fluoxetine.

Scheme 1 Synthesis of (±)-fluoxetine in flow: (i) BH3·THF, r.t., 5 min (77%); (ii) NaI, toluene: water, 100 °C, 20 min (43%); (iii); MeNH2 (aq), …

//////////Flow synthesis, fluoxetine


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DR ANTHONY CRASTO

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DR ANTHONY MELVIN CRASTO Ph.D

DR ANTHONY MELVIN CRASTO Ph.D

DR ANTHONY MELVIN CRASTO, Born in Mumbai in 1964 and graduated from Mumbai University, Completed his Ph.D from ICT, 1991,Matunga, Mumbai, India, in Organic Chemistry, The thesis topic was Synthesis of Novel Pyrethroid Analogues, Currently he is working with GLENMARK PHARMACEUTICALS LTD, Research Centre as Principal Scientist, Process Research (bulk actives) at Mahape, Navi Mumbai, India. Total Industry exp 29 plus yrs, Prior to joining Glenmark, he has worked with major multinationals like Hoechst Marion Roussel, now Sanofi, Searle India Ltd, now RPG lifesciences, etc. He has worked with notable scientists like Dr K Nagarajan, Dr Ralph Stapel, Prof S Seshadri etc, He did custom synthesis for major multinationals in his career like BASF, Novartis, Sanofi, etc., He has worked in Discovery, Natural products, Bulk drugs, Generics, Intermediates, Fine chemicals, Neutraceuticals, GMP, Scaleups, etc, he is now helping millions, has 9 million plus hits on Google on all Organic chemistry websites. His friends call him worlddrugtracker. His New Drug Approvals, Green Chemistry International, All about drugs, Eurekamoments, Organic spectroscopy international, etc in organic chemistry are some most read blogs He has hands on experience in initiation and developing novel routes for drug molecules and implementation them on commercial scale over a 29 year tenure till date Aug 2016, Around 30 plus products in his career. He has good knowledge of IPM, GMP, Regulatory aspects, he has several International patents published worldwide . He has good proficiency in Technology transfer, Spectroscopy, Stereochemistry, Synthesis, Polymorphism etc., He suffered a paralytic stroke/ Acute Transverse mylitis in Dec 2007 and is 90 %Paralysed, He is bound to a wheelchair, this seems to have injected feul in him to help chemists all around the world, he is more active than before and is pushing boundaries, He has 9 million plus hits on Google, 2.5 lakh plus connections on all networking sites, 25 Lakh plus views on dozen plus blogs, He makes himself available to all, contact him on +91 9323115463, email amcrasto@gmail.com, Twitter, @amcrasto , He lives and will die for his family, 90% paralysis cannot kill his soul., Notably he has 13 lakh plus views on New Drug Approvals Blog in 212 countries......https://newdrugapprovals.wordpress.com/ , He appreciates the help he gets from one and all, Friends, Family, Glenmark, Readers, Wellwishers, Doctors, Drug authorities, His Contacts, Physiotherapist, etc

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