Macrocyclic bisindolylmaleimides: Synthesis by inter- and intramolecular alkylation

Macrocyclic bisindolylmaleimides 1-4 have been identified as competitive reversible inhibitors of PKC beta(1) and beta(2) and are being advanced to the clinic for evaluation as a treatment of retinopathy associated with diabetic complications. Highly convergent and stereoselective syntheses of 1-4 have been developed. The key synthetic step involves intermolecular alkylation of symmetrical bisindolylmaleimide 9 with chiral bisalkylating agent 8c and is amenable to the preparation of multikilogram quantities of these compounds. The synthetic sequence to 1, the most active compound, proceeds in 11 steps and 26% overall yield (>98% ee) from (R)-1-chloro-2,3-propanediol. No chromatographic purifications are required throughout the process and the final product is isolated in >97% purity after crystallization from DMF/MeOH. Synthesis of 1-4 by intramolecular alkylation proved less efficient, requiring 1? steps and affording 1-4 in lower overall yields of 6.0-8.5%.