First, it doesn’t inhibit TYK2’s catalytic (ATP) site like most kinase drugs. It binds the pseudokinase (regulatory) domain<\/strong>, which is far less conserved across the JAK family \u2014 the structural basis for its selectivity over JAK1\/2\/3 and its clean safety profile.<\/p>\n\n\n\n Second, and central to this whole story: it is a deuterated drug<\/strong>. One methyl group on the molecule is a trideuteromethyl (CD\u2083)<\/strong> rather than an ordinary CH\u2083. That single isotopic edit slows a specific metabolic dealkylation (the C\u2013D bond is harder to break than C\u2013H \u2014 the kinetic isotope effect), improving the drug’s metabolic profile. It also means the synthesis carries an unusual constraint: CD\u2083 is expensive<\/strong>, so the process must install it as late as possible and waste none of it.<\/p>\n\n\n\n This is the challenge the process chemists faced: take a discovery route that could make kilograms, and turn it into a route that safely, cheaply, and cleanly makes more than a metric ton<\/strong> \u2014 while respecting the economics of deuterium.<\/p>\n\n\n\n The commercial synthesis is convergent<\/strong>: two halves are built separately and then stitched together, with the precious CD\u2083 group added dead last.<\/p>\n\n\n\n Four steps in that sequence each hid a genuinely hard problem. They are what make this paper worth reading.<\/p>\n\n\n\n The aniline fragment carries a 1-methyl-1,2,4-triazole<\/strong>. The discovery route made it by methylating<\/em> a pre-formed triazole \u2014 and that reaction had poor regioselectivity<\/strong>, alkylating the wrong ring nitrogen a large fraction of the time and dragging down yield.<\/p>\n\n\n\n The process solution was to not methylate at all<\/strong>. Instead they built the methylated triazole de novo<\/em> from a nitrile<\/strong> \u2014 the cheap, chlorine-blocked benzonitrile 28<\/strong> \u2014 using N-methylformohydrazide<\/strong> and a strong base (potassium tert<\/em>-butoxide). This is a genuinely novel transformation: a direct nitrile-to-methyltriazole cyclocondensation<\/strong> that runs at low temperature and places the methyl group on the correct nitrogen by construction<\/em>, because the reagent already carries the atoms destined for the ring. Because the methyl is built in with defined connectivity, the regiochemistry problem simply disappears.<\/p>\n\n\n\n The useful lesson:<\/strong> when a late-stage selectivity problem is intractable, the best fix is often to redesign the bond-forming step so the selectivity is never in question \u2014 here, building the ring pre-methylated rather than methylating a ring.<\/p>\n\n\n\n A small, subtle, beautiful piece of process chemistry. The methyltriazole intermediate 27<\/strong> was isolated as a salt for handling. The obvious choice, the hydrochloride (27-01)<\/strong>, caused trouble two steps later: during the nitration<\/strong>, nitric acid oxidized the chloride counterion to an electrophilic chlorine species<\/strong>, which chlorinated the ring and produced a difficult-to-purge over-chlorinated impurity.<\/p>\n\n\n\n The fix was almost absurdly simple: switch the counterion<\/strong>. Isolating 27<\/strong> as the bisulfate salt (27-02)<\/strong> instead of the hydrochloride removed the chloride source entirely, and the nitration went from messy to >99% clean<\/strong>.<\/p>\n\n\n\n The useful lesson:<\/strong> the counterion you pick for an intermediate isn’t just a handling decision \u2014 it can carry a reactive atom into a downstream step. Trace impurities sometimes trace back to a “spectator” ion that turns out not to be a spectator.<\/p>\n\n\n\n Converting the dihydroxypyridazine 8<\/strong> to the dichloride 18<\/strong> uses POCl\u2083<\/strong> \u2014 routine chemistry. The problem is the workup<\/em>. The standard way to destroy excess POCl\u2083 is a basic aqueous quench<\/strong>, but product 18<\/strong> is hydrolytically fragile (both C\u2013Cl bonds and the ester are labile), so the very conditions that neutralize the POCl\u2083 also chew up the product.<\/p>\n\n\n\n Worse, this failure was scale-dependent<\/strong>: controls that held hydrolysis to <1% in the lab gave ~3% on scale, because the quench mixture was biphasic<\/strong> \u2014 poor mixing and local hot-spots concentrated the damage where the phases met.<\/p>\n\n\n\n The solution was to engineer a homogeneous quench<\/strong>. By switching the reaction solvent to acetonitrile<\/strong> and raising the solvent loading (3 \u2192 5 L\/kg), the quenched mixture stayed single-phase \u2014 but only if water was added to the reaction, not the reaction to water<\/em> (order of addition mattered, because early on the water\/MeCN ratio would otherwise be too high and the mixture would split). Trimming the POCl\u2083 charge to just over stoichiometric (1.3 equiv per OH) cut the quench exotherm, and thermochemistry confirmed that even an uncontrolled quench (+29 \u00b0C adiabatic) wouldn’t run away.<\/p>\n\n\n\n The useful lesson:<\/strong> a workup can be the hardest part of a step. A quench that is fine in a flask can fail on scale for purely physical reasons \u2014 mixing, phase behavior, heat transfer \u2014 and the fix is often to make the system homogeneous so the chemistry stops depending on the stirring.<\/p>\n\n\n\n The penultimate step is a palladium-catalyzed C\u2013N coupling<\/strong> (Buchwald\u2013Hartwig type) that installs the cyclopropanecarboxamide onto the aryl chloride of intermediate 23<\/strong>. This one fought them at every turn.<\/p>\n\n\n\n The substrate 23<\/strong> is a zinc carboxylate salt<\/strong> with awkward solubility. Inorganic bases like K\u2083PO\u2084<\/strong> worked only if jet-milled to tiny particle size (surface area limited the rate) \u2014 impractical for commercial supply. Switching to K\u2082CO\u2083<\/strong> helped the impurity profile but, as a heterogeneous base, gave inconsistent rates on scale<\/strong> and agonizingly slow filtrations. A soluble organic base (DBU<\/strong>) dissolved everything and started fast \u2014 then stalled at ~50% conversion.<\/p>\n\n\n\n The breakthrough was a “dual-base” system: DBU plus<\/em> K\u2082CO\u2083<\/strong>. Together they dissolved the substrate and<\/em>drove the reaction to completion faster than either base alone \u2014 a real synergy. With the dual base locked in, they optimized to a cheap, stable Pd(OAc)\u2082 \/ Josiphos SL-J009<\/strong> catalyst system at low loading.<\/p>\n\n\n\n The useful lesson:<\/strong> base is not a passive spectator in Pd couplings. When one base gives solubility and another gives reactivity, a combination<\/strong> can beat either \u2014 and finding that combination unlocked a robust, scalable process.<\/p>\n\n\n\n The final step forms the CD\u2083 amide by coupling the penultimate acid 24<\/strong> with trideuteromethylamine<\/strong>(handled as its HCl salt). The coupling itself is easy \u2014 an unhindered amine on an unhindered acid; 95 of 96 conditions in the initial screen gave product. The hard part was choosing an activator<\/strong> that didn’t smuggle in impurities:<\/p>\n\n\n\n Even then, EDC brought its own family of side-products \u2014 the team ultimately identified and controlled seven<\/strong> EDC-related impurities (N-acylureas and their decomposition products, plus a dimethylamide from the urea byproduct). They were tamed by order of addition<\/strong> (to suppress premature decarboxylation of 24<\/strong>) and by tight control of the EDC charge<\/strong>, because product 1<\/strong> crystallizes as the reaction proceeds and a stalled charge can entrap unreacted 24<\/strong> in the growing crystals. This is why the process specifies an unusually precise 68 \u00b0C<\/strong> \u2014 hot enough to keep things dissolved and fast, controlled enough to avoid decarboxylation.<\/p>\n\n\n\n The useful lesson:<\/strong> for the API-forming step, reagent reproducibility<\/em> can matter more than peak yield. A slightly lower-yielding reagent with zero lot-to-lot surprises is worth more at commercial scale than a high-yielding one whose impurity level you can’t predict.<\/p>\n\n\n\n The redesigned route wasn’t just cleaner chemistry \u2014 it scored well on sustainability, hitting several of the 12 Principles of Green Chemistry:<\/p>\n\n\n\n The result was a process scaled repeatedly to >80\u2013100 kg per batch<\/strong>, ultimately delivering more than a metric ton<\/strong> of deucravacitinib for clinical and commercial supply.<\/p>\n\n\n\n Process chemistry rarely makes headlines, but this is where a molecule becomes a medicine<\/em> \u2014 manufacturable, affordable, and safe at scale. Deucravacitinib is a textbook example of the craft.<\/p>\n\n\n\n How a team at Bristol Myers Squibb turned a workable discovery route into a metric-ton commercial process for Sotyktu \u2014 the first-in-class TYK2 inhibitor \u2014 solving four hard chemistry problems along the way. Based on Treitler et al., Org. Process Res. Dev. 2022, 26, 1202\u20131222.<\/em><\/p>\n","protected":false},"excerpt":{"rendered":" Why this molecule is special Deucravacitinib (BMS-986165, brand name Sotyktu) is a first-in-class, oral TYK2 inhibitor approved for plaque psoriasis and being pursued across a range of autoimmune diseases \u2014 psoriatic arthritis, lupus, inflammatory bowel disease. It is unusual on two…<\/p>\n","protected":false},"author":1,"featured_media":125,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-123","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-blog"],"_links":{"self":[{"href":"https:\/\/astinovabiolabs.com\/blog\/wp-json\/wp\/v2\/posts\/123","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/astinovabiolabs.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/astinovabiolabs.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/astinovabiolabs.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/astinovabiolabs.com\/blog\/wp-json\/wp\/v2\/comments?post=123"}],"version-history":[{"count":1,"href":"https:\/\/astinovabiolabs.com\/blog\/wp-json\/wp\/v2\/posts\/123\/revisions"}],"predecessor-version":[{"id":126,"href":"https:\/\/astinovabiolabs.com\/blog\/wp-json\/wp\/v2\/posts\/123\/revisions\/126"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/astinovabiolabs.com\/blog\/wp-json\/wp\/v2\/media\/125"}],"wp:attachment":[{"href":"https:\/\/astinovabiolabs.com\/blog\/wp-json\/wp\/v2\/media?parent=123"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/astinovabiolabs.com\/blog\/wp-json\/wp\/v2\/categories?post=123"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/astinovabiolabs.com\/blog\/wp-json\/wp\/v2\/tags?post=123"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}The route at a glance<\/h2>\n\n\n\n
![\"\"](\"https:\/\/astinovabiolabs.com\/blog\/wp-content\/uploads\/2026\/08\/image-8-1024x594.png\")
<\/figure>\n\n\n\n\n
Challenge 1 \u2014 Building the methyltriazole with the right<\/em> regiochemistry<\/h2>\n\n\n\n
Challenge 2 \u2014 A counterion that quietly controls an impurity<\/h2>\n\n\n\n
Challenge 3 \u2014 Quenching POCl\u2083 on a substrate that hates water<\/h2>\n\n\n\n
Challenge 4 \u2014 The “dual-base” palladium C\u2013N coupling<\/h2>\n\n\n\n
\n\n\n\nThe endgame: installing CD\u2083 cleanly, and taming seven<\/em> impurities<\/h2>\n\n\n\n
\n
\n\n\n\nThe payoff: green, safe, and a metric ton<\/h2>\n\n\n\n
\n
\n\n\n\nTakeaways for the bench and the plant<\/h2>\n\n\n\n
\n