Temsirolimus is a semisynthetic macrocyclic lactone prepared from rapamycin by selective acylation of the 42-hydroxy group with a protected bis(dihydromethyl)propionic acid, followed by deprotection. Like all tacrolimus analogues, temsirolimus binds to receptor protein, FKBP12. The complex then binds to mTOR preventing it from interacting with target proteins. Temsirolimus is extensively cited in the literature with over 700 citations.