Insights into Factors Affecting Ethylene-Vinyl Acetate Copolymer Crystallinity in Islatravir Implant.

Islatravir, a highly potent nucleoside reverse transcriptase translocation inhibitor (NRTTI) for the treatment of HIV, has great potential to be formulated as ethylene-vinyl acetate (EVA) copolymer-based implants via hot melt extrusion. The crystallinity of EVA determines its physical and rheological properties and may impact the drug-eluting implant performance. Herein, we describe the systematic analysis of factors affecting the EVA crystallinity in islatravir implants. Differential scanning calorimetry (DSC) on EVA and solid-state NMR revealed drug loading promoted EVA crystallization, whereas BaSO4 loading had negligible impact on EVA crystallinity. The sterilization through γ-irradiation appeared to significantly impact the EVA crystallinity and surface characteristics of the implants. Furthermore, DSC analysis of thin implant slices prepared with an ultramicrotome indicated that the surface layer of the implant was more crystalline than the core. These findings provide critical insights into factors affecting the crystallinity, mechanical properties, and physicochemical properties of the EVA polymer matrix of extruded islatravir implants.

Cocrystal Synthesis through Crystal Structure Prediction.

Crystal structure prediction (CSP) is an invaluable tool in the pharmaceutical industry because it allows to predict all the possible crystalline solid forms of small-molecule active pharmaceutical ingredients. We have used a CSP-based cocrystal prediction method to rank ten potential cocrystal coformers by the energy of the cocrystallization reaction with an antiviral drug candidate, MK-8876, and a triol process intermediate, 2-ethynylglyclerol. For MK-8876, the CSP-based cocrystal prediction was performed retrospectively and successfully predicted the maleic acid cocrystal as the most likely cocrystal to be observed. The triol is known to form two different cocrystals with 1,4-diazabicyclo[2.2.2]octane (DABCO), but a larger solid form landscape was desired. CSP-based cocrystal screening predicted the triol-DABCO cocrystal as rank one, while a triol-l-proline cocrystal was predicted as rank two. Computational finite-temperature corrections enabled determination of relative crystallization propensities of the triol-DABCO cocrystals with different stoichiometries and prediction of the triol-l-proline polymorphs in the free-energy landscape. The triol-l-proline cocrystal was obtained during subsequent targeted cocrystallization experiments and was found to exhibit an improved melting point and deliquescence behavior over the triol-free acid, which could be considered as an alternative solid form in the synthesis of islatravir.

Scalable Asymmetric Synthesis of MK-8998, a T-Type Calcium Channel Antagonist.

Two scalable and efficient synthetic routes for the synthesis of a T-type calcium channel antagonist MK-8998 were developed from a simple pyridine building block. The key step to set the stereochemistry relied on either chiral rhodium catalyst-mediated asymmetric hydrogenation of an enamide or transamination of an arylketone that provided the corresponding product in high enantioselectivity and high yield.

Palladium-Catalyzed Carbon Isotope Exchange on Aliphatic and Benzoic Acid Chlorides.

An operationally simple protocol for a palladium-catalyzed 13CO and 14CO exchange with activated aliphatic and benzoic carbonyls is presented. Several 13C and 14C building blocks, natural product derivatives, and pharmaceuticals have been prepared to showcase the method for late-stage carbon isotope incorporation and its functional group compatibility.

Practical synthesis of a potent bradykinin B(1) antagonist via enantioselective hydrogenation of a pyridyl N-acyl enamide.

A practical and efficient synthesis of bradykinin B(1) antagonist 1 is described. A convergent strategy was utilized which involved synthesis of three fragments: 3, 6, and 7. Cross coupling of fragments 6 and 7 followed by amidation with 3 enabled efficient synthesis of 1 in 19 steps total, a 35% overall yield from commercially available pyridine 10. The key to the success of the synthesis was the development of a fluorodenitration step to install the fluorine in pyridine 7 and a catalytic enantioselective hydrogenation of N-acyl enamide 9 to set the stereochemistry.

An efficient catalyst for Pd-catalyzed carbonylation of aryl arenesulfonates.

Aryl carboxylic esters were synthesized by Pd-catalyzed carbonylation of aryl p-fluorobenzenesulfonates or -tosylates. A unique Josiphos ligand was discovered through high-throughput catalyst screening, which was the key for the successful carbonylation of various substrates. This catalyst is effective and works well for both electron-rich and electron-poor aryl arenesulfonates. Isolated yields of up to 90% were obtained for aryl p-fluorobenzenesulfonates and -tosylates. [reaction: see text]

Asymmetric hydrogenation of N-sulfonylated-alpha-dehydroamino acids: toward the synthesis of an anthrax lethal factor inhibitor.

A novel and highly enantioselective Ru-catalyzed hydrogenation of N-sulfonylated-alpha-dehydroamino acids has been discovered and demonstrated in the synthesis of an anthrax lethal factor inhibitor (LFI). Herein, this methodology is used to prepare N-sulfonylated amino acids in up to 98% ee. This unprecedented hydrogenation uses a chiral Ru catalyst rather than Rh as typical for acylated dehydroamino acids and esters, and this work reports the first asymmetric hydrogenation of a tetrasubstituted dehydroamino acid derivative using a Ru catalyst. [reaction: see text]

A [2 + 2] cycloaddition route to dimethylaminomethylene vinamidinium salts.

[reaction: see text] Trifluoropropanoic acid reacts with 1 equiv of POCl3 in DMF to generate the trifluoromethyl enamine (7). At this stage, two reaction manifolds are available. The expected reaction with additional POCl3 generates the 2-trifluoromethyl vinamidinium salt (3c). However, thermally driven loss of fluoride generates an iminium ion, which sets the stage for a [2 + 2] cycloaddition to ultimately generate the dimethylaminomethylene vinamidinium salt (1).

Synthesis of a tertiary carbinamide via a novel Rh-catalyzed asymmetric hydrogenation.

Asymmetric hydrogenation of allylic dimethylcarbinamide 2 with 1 mol % of cationic Rh(I)-Josiphos complex in THF under 500 psi of H2 generated the corresponding tertiary carbinamide 1 in 98.5% assay yield and a 94:6 enantiomeric ratio. Upon crystallization, the product was isolated in 91% isolated yield and 95:5 enantiomeric ratio.

Unlocking the potential of asymmetric hydrogenation at Merck.

This Account outlines the efforts of Merck scientists toward implementing asymmetric hydrogenation as a core competency within Merck Research Laboratories. Several key factors are discussed including (i) a focus on efficient chemical synthesis, (ii) implementation of high throughput screening (HTS) techniques, (iii) demonstration of robustness on scale, and (iv) diligence to ensure freedom of operation and catalyst supply for manufacturing. Several examples of the development of efficient asymmetric hydrogenation processes are described.