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Wahrend kontinuierliche chemische Prozesse in der akademischen Forschung und der Industrie untersucht werden, werden nach wie vor praktisch alle pharmazeutisch aktiven Wirkstoffe (APIs; active pharmaceutical ingredients) uber eine Abfolge einzelner Batchprozesse hergestellt. Methoden fur die divergente, mehrstufige kontinuierliche Produktion von niedermolekularen Verbindungen sind bislang nicht verfugbar. Wir beschreiben hier die Entwicklung eines chemischen Fertigungssystems bestehend aus austauschbaren Durchflussreaktionsmodulen, das einen grosen chemischen Strukturraum zuganglich macht. Die Steuerung des Gesamtprozesses auf drei Ebenen – durch die Wahl des Ausgangsmaterials, der Reagentien oder der Reihenfolge der Module – ermoglichte die Synthese von funf APIs als Vertreter dreier unterschiedlicher Strukturklassen (γ-Aminosauren, γ-Lactame, β-Aminosauren), einschlieslich der Bestseller-Medikamente Lyrica und Gabapentin, in guten Gesamtausbeuten (49–75 %).

Deracemisierung, also die Umwandlung eines Racemats in ein enantiomerenreines Produkt mit theoretisch 100 % Ausbeute und 100 % ee, stellt eine attraktive, aber auch anspruchsvolle Option fur die asymmetrische Synthese dar. Hier beschreiben wir ein neuartiges Konzept einer chemo-enzymatischen Deracemisierung mittels einer Kaskadenreaktion. Die Reaktionsfolge beinhaltet zwei enantioselektive Oxidationsschritte und einen nicht stereoselektiven Reduktionsschritt, durch welche zur gleichen Zeit eine Stereoinversion und eine kinetische Racematspaltung realisiert werden. Dieses Konzept wird anhand der Umwandlung von rac-Benzylisochinolinen in optisch reine (S)-Berbine vorgestellt. Die racemischen Substrate wurden in enantiomerenreine Produkte (ee>97 %) umgewandelt, wobei Umsatze von bis zu 98 % und Ausbeuten von bis zu 88 % erreicht wurden.

Biocatalytic approaches to the synthesis of optically pure chiral amines, starting from simple achiral building blocks, are highly desirable because such motifs are present in a wide variety of important natural products and pharmaceutical compounds. Herein, a novel one-pot ω-transaminase (TA)/monoamine oxidase (MAO-N) cascade process for the synthesis of chiral 2,5-disubstituted pyrrolidines is reported. The reactions proceeded with excellent enantio- and diastereoselectivity (>94 % ee; >98 % de) and can be performed on a preparative scale. This methodology exploits the complementary regio- and stereoselectivity displayed by both enzymes, which ensures that the stereogenic center established by the transaminase is not affected by the monoamine oxidase, and highlights the potential of this multienzyme cascade for the efficient synthesis of chiral building blocks. Mirror mirror on the wall: A ω-transaminase (ω-TA)/monoamine oxidase (MAO-N) cascade process for the asymmetric synthesis of chiral 2,5-disubstituted pyrrolidines is reported. The methodology exploits the complementary regio- and stereoselectivity displayed by both enzymes, which ensures that the stereogenic center established by the TA reaction is not affected by the MAO-N catalyzed step. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Chemo-enzymatic deracemisation was applied to obtain the (S)-enantiomer of 1-benzylisoquinolines from the racemate in high isolated yield (up to 85%) and excellent optical purity (ee > 97%). The one-pot deracemisation protocol encompassed enantioselective oxidation by a monoamine oxidase (MAO-N) and concomitant reduction of the resulting iminium species by ammonia-borane. The challenge was the oxidation at the sterically demanding chiral centre. Recently developed variants of MAO-N, featuring an enlarged active-site pocket, turned out to be suitable biocatalysts for these substrates. In contrast to previous MAO-N variants, which preferentially converted the (S)-enantiomer, the MAO-N variant D11 used in the present study was found to oxidise all tested benzylisoquinoline substrates with (R)-enantiopreference. The structural determinants of enantioselectivity were investigated by means of protein–ligand docking simulations. The applicability of the deracemisation system was demonstrated on preparative scale (150 mg) for three benzylisoquinoline alkaloids (natural as well as non-natural), including the hypotensive and antispasmodic agent (S)-reticuline.

The tetrahydro-β-carboline (THBC) ring system is an important structural motif found in a large number of bioactive alkaloid natural products. Herein we report a broadly applicable method for the synthesis of enantiomerically pure β-carbolines via a deracemization procedure employing the D9 and D11 variants of monoamine oxidase from Aspergillus niger (MAO-N) in combination with a nonselective chemical reducing agent. Biotransformations were performed on a preparative scale, leading to the synthesis of optically enriched products in excellent enantiomeric excess (e.e.; up to 99%) and isolated yield (up to 93%). Interestingly, a switch in enantioselectivity associated with the MAO-N variants is observed as the nature of the C-1 substituent of the THBC is varied. Molecular modeling provided an explanation for this observation and highlighted key active site residues which were modified, resulting in an increase in (R)-selectivity associated with the enzyme. These results provide insight into the factors whic...

Enzymatic catalysis and homogeneous catalysis offer complementary means to address synthetic challenges, both in chemistry and in biology. Despite its attractiveness, the implementation of concurrent cascade reactions that combine an organometallic catalyst with an enzyme has proven challenging because of the mutual inactivation of both catalysts. To address this, we show that incorporation of a d(6)-piano stool complex within a host protein affords an artificial transfer hydrogenase (ATHase) that is fully compatible with and complementary to natural enzymes, thus enabling efficient concurrent tandem catalysis. To illustrate the generality of the approach, the ATHase was combined with various NADH-, FAD- and haem-dependent enzymes, resulting in orthogonal redox cascades. Up to three enzymes were integrated in the cascade and combined with the ATHase with a view to achieving (i) a double stereoselective amine deracemization, (ii) a horseradish peroxidase-coupled readout of the transfer hydrogenase activity towards its genetic optimization, (iii) the formation of L-pipecolic acid from L-lysine and (iv) regeneration of NADH to promote a monooxygenase-catalysed oxyfunctionalization reaction.

While continuous chemical processes have attracted both academic and industrial interest, virtually all active pharmaceutical ingredients (APIs) are still produced by using multiple distinct batch processes. To date, methods for the divergent multistep continuous production of customizable small molecules are not available. A chemical assembly system was developed, in which flow-reaction modules are linked together in an interchangeable fashion to give access to a wide breadth of chemical space. Control at three different levels— choice of starting material, reagent, or order of reaction modules—enables the synthesis of five APIs that represent three different structural classes (g-amino acids, g-lactams, b- amino acids), including the blockbuster drugs Lyrica and Gabapentin, in good overall yields (49-75 %).

The chemoselective reductive cyclization of diones of type (I) in the presence of transaminase ATA113 is presented.

The development of cost-effective and sustainable catalytic methods for the production of enantiomerically pure chiral amines is a key challenge facing the pharmaceutical and fine chemical industries. This challenge is highlighted by the estimate that 40-45% of drug candidates contain a chiral amine, fueling a demand for broadly applicable synthetic methods that deliver target structures in high yield and enantiomeric excess. Herein we describe the development and application of a "toolbox" of monoamine oxidase variants from Aspergillus niger (MAO-N) which display remarkable substrate scope and tolerance for sterically demanding motifs, including a new variant, which exhibits high activity and enantioselectivity toward substrates containing the aminodiphenylmethane (benzhydrylamine) template. By combining rational structure-guided engineering with high-throughput screening, it has been possible to expand the substrate scope of MAO-N to accommodate amine substrates containing bulky aryl substituents. These engineered MAO-N biocatalysts have been applied in deracemization reactions for the efficient asymmetric synthesis of the generic active pharmaceutical ingredients Solifenacin and Levocetirizine as well as the natural products (R)-coniine, (R)-eleagnine, and (R)-leptaflorine. We also report a novel MAO-N mediated asymmetric oxidative Pictet-Spengler approach to the synthesis of (R)-harmicine.

A very short and cost-effective synthesis of the commercial drug paliperidone has been achieved starting from its parent compound risperidone, through a thoroughly optimized oxidation with air under basic conditions.