Telaprevir 2 (VX-950), an inhibitor of the hepatitis C virus (HCV(a)) NS3-4A protease, is in phase 3 clinical trials. One of the major metabolites of 2 is its P1-(R)-diastereoisomer, 3 (VRT-394), containing an inversion at the chiral center next to the alpha-ketoamide on exchange of a proton with solvent. Compound 3 is approximately 30-fold less active against HCV protease. In an attempt to suppress the epimerization of 2 without losing activity against the HCV protease, the proton at that chiral site was replaced with deuterium (d). The compound 1 (d-telaprevir) is as efficacious as 2 in in vitro inhibition of protease activity and viral replication (replicon) assays. The kinetics of in vitro stability of 1 and 2 in buffered pH solutions and plasma samples, including human plasma, suggest that 1 is significantly more stable than 2. Oral administration (10 mg/kg) in rats resulted in a approximately 13% increase of AUC for 1.

A novel Pd-catalyzed coupling of Cbz-protected proline amide with 4-bromo-5-ethoxyfuran-2(5H)-one was developed for the synthesis of the P1-P2 unit (5) of VX-765. The process afforded quantitative coupling in the presence of water, providing a 1:1 mixture of 5 and its ethoxy epimer epi-5. Compound 5 was isolated as a single diastereomer via fractional crystallization, which was stereoselectively converted to 17 via hydrogenation, and subsequently transformed to VX-765. Nine examples of the Pd coupling are presented with yields ranging from 76-98%.

A stereoselective process for the manufacture of bicyclopyrrolidine 7 to 2 has been developed. The process utilizes a stereoselective lithiation/carboxylation sequence. The achiral diamine ligand DPBP induces excellent diastereocontrol, and resolution with ( S )-THNA provides the corresponding salt of 8 in high er and dr. Subsequent processing of 8 gives 2 as the oxalate salt in an overall yield of 27% from 7 (based on total molar charge of 7). Compound 2 was obtained with high chemical and chiral purities. The process was successfully demonstrated on >100 kg scale.

A process for the manufacture of merimepodib (VX-497), an inosine monophosphate dehydrogenase (IMPDH) inhibitor, has been developed and efficiently scaled to produce clinical supply. The process comprises five steps, incorporating simple and robust chemistry that ultimately yielded 96.5 kg with a purity of 100% (by HPLC analysis) and 99.7% w/w assay. Highlights of the process are the effective use of production-scale phosgene, manipulation of Schotten−Baumann reaction conditions to give a low pH procedure that avoids a critical impurity, and the use of online tools to better identify parameters of the API purification.