The Formal Total Synthesis of FR252921 - An Immunosuppressant

The formal total synthesis of FR252921 is described. The key steps include the preparation of three fragments starting from 1,4‐butanediol, (R)‐malic acid, and prenol, respectively, followed by two consecutive peptide couplings of the three fragments. Other key steps involve an allene‐type rearrangement or enyne isomerization to install the triene moiety, a Seebach methylation, a Julia olefination to construct the trisubstituted diene unit, and an enzymatic resolution strategy to generate the C‐18 stereocenter. The formal total synthesis of FR252921 is described. The key steps include the preparation of three fragments starting from 1,4‐butanediol, (R)‐malic acid, and prenol, respectively, followed by two consecutive peptide couplings of the three fragments.