A Chiral Pool Strategy for the Synthesis of a SMARCA2 Degrading PROTAC

A scalable synthesis of the SMARCA2 degrading PROTAC 1 was developed. The linker fragment was derived from (S)-citronellol by oxidative cleavage and diastereoselective aryl Grignard addition to a derived N-tert-butanesulfinyl aldimine for generation of the chiral amine stereocenter and a one-pot borylation/Suzuki reaction for biaryl formation. The dipeptide fragment was prepared by T3P-mediated coupling of hydroxyproline benzyl ester and N-Boc tert-leucine followed by capping with 1-fluorocyclopropancarboxylic acid and ester hydrolysis. Unification of the linker with the SMARCA2 binding motif and dipeptide was achieved by sequential reductive amination and coupling. The synthesis did not require any preparative or chiral HPLC purifications and was used to prepare over 100 g of 1.