Endothelin antagonist ABT

Development of a Catalytic, A mmetric Michael Addition in the Synthesis of Endothelin Antagonist ABT-546... 

Wittenberger SJ, McLaughlin MA. Preparation of endothelin antagonist ABT-627. Tetrahedron Lett. 1999 40 7175-7178. 

The development of a highly enantioselective catalytic asymmetric conjugate addition of 1,3-dicarbonyl compounds to nitroalkenes is described, as is its use in the synthesis of the selective endothelin A antagonist ABT-546. Employing 4 mol% of a bis(oxazoline)-Mg(OTf)2 complex with 5.5 mol% of an amine co-catalyst, the product nitroketone is obtained in 88% ee, with good yields. Particularly important to the reaction is the water content. While water is necessary during the generation of the catalyst, the water must then be removed in order to maximize selectivity and reactivity. The scope of the reaction has been extended to other ketoester and malonate nucleophiles, as well as other nitroolefins. 

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