We are capable of using solid-phase Fmoc chemistry and Boc chemistry. For complex peptide synthesis, we also use solution phase peptide synthesis. Chemically synthesized peptides occur by coupling the carboxyl group of the incoming amino acid to the N-terminus of the growing peptide chain. Because amino acids have multiple reactive groups, to facilitate peptide formation with minimal side reactions, amino acids with special protecting groups will be used to avoid side reactions that can reduce the length and prevent nonspecific side reaction during synthesis. These side chain protection groups are normally the benzyl (Bzl) or tert-butyl (tBu) group. The specific protecting groups used during peptide synthesis vary depending on the peptide sequence and the type of N-terminal protection used. These side protecting groups are also known as "permanent" protecting groups, because they can withstand the multiple cycles of chemical treatment during each synthesis cycle. They can only be removed selectively using special chemical treatment after peptide synthesis is complete.
N-termini of amino acids are also protected by groups that are "temporary" block with protecting groups, because they can be easily removed to allow peptide bond formation. Two common N-terminal protecting groups are tert-butoxycarbonyl (Boc) and 9-fluorenylmethoxycarbonyl (Fmoc), and each group has distinct characteristics that determine their use. Boc requires a moderately strong acid such as trifluoracetic acid (TFA) to be removed from the newly added amino acid, while Fmoc is a base-labile protecting group that is removed with a mild base such as piperidine.
Because multiple protecting groups are normally used in peptide synthesis, it is evident that these groups must be compatible to allow deprotection of distinct protecting groups while not affecting other protecting groups. Protecting schemes are therefore established to match protecting groups so that deprotection of one protecting group does not affect the binding of the other groups. Because N-terminal deprotection occurs continuously during peptide synthesis, protecting schemes have been established in which the different types of side chain protecting groups (Bzl or tBu) are matched to either Boc or Fmoc, respectively, for optimized deprotection.
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Visit our Peptide Synthesis Chemistry page in the technical library for more information.