Toward a Scalable Synthesis and Process for EMA401, Part II: Development and Scale-Up of a Pyridine- and Piperidine-Free Knoevenagel–Doebner Condensation

Abstract

During route scouting for EMA401 (1), an angiotensin II type 2 antagonist, we identified the synthesis of key amino acid intermediate 2 via its cinnamic acid derivative 3 as a streamlined option. In general, cinnamic acids can be synthesized from the corresponding aldehydes by a Knoevenagel−Doebner condensation in pyridine with piperidine as an organocatalyst. We aimed to replace both of these reagents and found novel conditions involving toluene as the solvent and morpholine as the organocatalyst. Scale-up of the process allowed the production of 25 kg of cinnamic acid 3 that was of the quality required for process development of the subsequent phenylalanine ammonia lyase-catalyzed step. The modified conditions were found to be widely applicable to alternative aldehydes and thus are of relevance to practitioners of chemical scale-up.

Toward a Scalable Synthesis and Process for EMA401, Part I: Late Stage Process Development, Route Scouting, and ICH M7 Assessment

“…Due to the issues observed in the isolation of ketoacid 28 , we turned our attention to an alternative biocatalytic system and identified the phenylalanine ammonia lyase (PAL) catalyzed synthesis of amino acid 2 as a very attractive alternative in terms of safety, ecology, and economy. These findings are disclosed in parts II and III of this publication series. , …”

“…These findings are disclosed in parts II and III of this publication series. 20,21 Investigations on the Theoretical Impurity Bis-(chloromethyl) ether. Bis(chloromethyl) ether (BCME; CAS #542-888-1) is a highly toxic compound and known mutagen, classified as an ICH M7 class 1 impurity.…”

Toward a Scalable Synthesis and Process for EMA401, Part III: Using an Engineered Phenylalanine Ammonia Lyase Enzyme to Synthesize a Non-natural Phenylalanine Derivative

“…A streamlined manufacturing process afforded the substrate, cinnamic acid 2 , with a morpholine content of around 4–5 mol % . Use tests and screenings showed that morpholine in 2 was not critical and that up to 10 mol % morpholine did not have an impact on the conversion (Table S5).…”

“…For the preparation of amino acid 3 via the chemocatalytic route, aldehyde 5 was treated with Horner–Wadsworth–Emmons reagent 6 to obtain enamide 7 , which was subjected to asymmetric hydrogenation conditions to afford amide 8 , followed by functional group interconversion to give carbamate 9 and finally deprotection to yield amino acid 3 . The synthetic approach using the biocatalytic route described in this publication requires only two stages to obtain the key intermediate 3 starting from 5 , which was reacted to give cinnamic acid 2 followed by PAL-catalyzed hydroamination to furnish amino acid 3 …”

“…The synthetic approach using the biocatalytic route described in this publication requires only two stages to obtain the key intermediate 3 starting from 5, which was reacted to give cinnamic acid 2 followed by PALcatalyzed hydroamination to furnish amino acid 3. 2 The key step of the biocatalytic route, the hydroamination to obtain amino acid 3, is catalyzed by a phenylalanine ammonia lyase (PAL, EC 4.3.1.24), an enzyme class that has attracted a lot of attention during the past decade in the academic and industrial communities. 3,4 The advantages of the biocatalytic route are obvious: It is three steps shorter than the chemocatalytic route, uses readily available reagents, avoids the use of heavy metals, and is environmentally more sustainable.…”