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Fiduxosin (1) has been under development at Abbott Laboratories for the treatment of benign prostatic hyperplasia. A convergent strategy required methodologies for preparation of an enantiomerically pure 3,4-cis-disubstituted pyrrolidine and a 2,3,5-trisubstituted thienopyrazine in a regiospecific manner. A [3+2] cycloaddition of an enantiopure azomethine ylide followed by a diastereoselective crystallization was employed to prepare the benzopyranopyrrolidine in high diastereomeric and enantiomeric purity. Conditions for reduction of an O-aryl lactone susceptible to epimerization were developed, and cyclization of the alcohol/phenol to the ether was accomplished in high yield. The thienopyrazine was prepared by condensation of methyl thioglycolate and a regiospecifically prepared 2-bromo-3-cyano-5-phenylpyrazine. Conditions for effective halogen substitutive deamination to prepare regiospecific trisubstituted pyrazines will be described.

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Dasabuvir (1) is an HCV polymerase inhibitor which has been developed as a part of a three-component direct-acting antiviral combination therapy. During the course of the development of the synthetic route, two novel coupling reactions were developed. First, the copper-catalyzed coupling of uracil with aryl iodides, employing picolinamide 16 as the ligand, was discovered. Later, the palladium-catalyzed sulfonamidation of aryl nonaflate 33 was developed, promoted by electron-rich palladium complexes, including the novel phosphine ligand, VincePhos (50). This made possible a convergent, highly efficient synthesis of dasabuvir that significantly reduced the mutagenic impurity burden of the process.