cysteine in a different part of the protein. These bridges help to stabilize proteins, especially those secreted from cells. Some researchers use modified cysteines using S-acetomidomethyl (Acm) to block the formation of the disulfide bond but preserve the cysteine and the protein's original primary structure. Off-resin cyclization Off-resin cyclization is a solid-phase synthesis of key intermediates, followed by the key cyclization in solution phase, the final deprotection of any masked side chains is also carried out in solution phase. This has the disadvantages that the efficiencies of solid-phase synthesis are lost in the solution phase steps, that purification from by-products, reagents and unconverted material is required, and that undesired oligomers can be formed if macrocycle formation is involved. The use of pentafluorophenyl esters (FDPP, PFPOH) and BOP-Cl are useful for cyclising peptides. See also Oligonucleotide synthesis Clicked peptide polymer Bailey peptide synthesis References Further reading External links Chemical synthesis Peptides Peptide coupling reagents Biochemistry methods Biochemistry Amide synthesis reactions