Authors: Magano, Javier; Bock, Brandon; Brennan, John; Farrand, Douglas; Lovdahl, Michael; Maloney, Mark T.; Nadkarni, Durgesh; Oliver, Wendy K.; Pozzo, Mark J.; Teixeira, John J.; Wang, Jian; Rizzo, John; Tumelty, David; Organic Process Research & Development; (2014); 10.1021/op4002998
An optimized and scalable process to manufacture peptide–linker conjugate 1 is reported that avoids the chromatographic purification and lyophilization that are typically required for the isolation of this type of compound. An operationally simple protocol has been developed that couples the peptide to the linker in DMF followed by precipitation with MeCN. A scalable synthesis of the linker is also described which features the N-acylation of 2-azetidinone promoted by 1-propanephosphonic acid anhydride (T3P). The number of operations during the second step of the synthesis (nitrobenzene reduction to aniline) has been simplified by telescoping the aniline into the next step (reaction with diglycolic anhydride to form an acid), thus avoiding an additional isolation. Finally, two efficient activation methods for the acid have been developed by means of the corresponding pentafluorophenyl (PFP) and p-nitrophenyl (PNP) esters.