Glecaprevir
was identified as a potent HCV NS3/4A protease inhibitor,
and an enabling synthesis was required to support the preclinical
evaluation and subsequent Phase I clinical trials. The enabling route
to glecaprevir was established through further development of the
medicinal chemistry route. The key steps in the synthesis involved
a ring-closing metathesis (RCM) reaction to form the 18-membered macrocycle
and a challenging fluorination step to form a key amino acid. The
enabling route was successfully used to produce 41 kg of glecaprevir,
sufficient to support the preclinical evaluation and early clinical
development.
[reaction: see text] A [3 + 2] cycloaddition reaction between alkynyldimethylsilyl ethers and aryl and alkyl nitrile oxides to produce isoxazolylsilanols has been developed. The cross-coupling reactions of these heterocyclic silanols with a variety of aryl iodides affords 3,4,5-trisubstituted isoxazoles. This sequential process allows for rapid variation of substituents at the 3, 4, and 5 positions of the isoxazole.
The cross-coupling of geometrically defined (E)- and (Z)-alkenyl- and styrylsilanolates with a wide variety of aromatic and heteroaromatic chlorides has been achieved. Under catalysis by bulky, biphenyl-derived phosphines and allylpalladium chloride, the (preformed, stable) potassium salts of di-, tri- and tetrasubstituted alkenyldimethylsilanols undergo high yielding and highly stereospecific coupling to aryl chlorides in THF or dioxane. A variety of functional groups are compatible with these reaction conditions including nitro, ester, ketone, and nitrile. Both (E)- and (Z)-alkenylsilanolates coupled with nearly identical rate and efficiency.
[reaction: see text] A mild and general palladium-catalyzed insertion of 1,2-diethoxy-1,1,2,2-tetramethyldisilane into a variety of aryl bromides affords the aryldimethylsilyl ethers in high yields. Hydrolysis of the ethers under pH-optimized conditions results in the exclusive formation of the desired aryldimethylsilanols.
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