Protecting Group
Definition
A chemical group fitted to a reactive site so it stays out of the way while a reaction happens elsewhere, then removed. Peptide synthesis is largely the management of these: every amino acid side chain that could react has one.
In more detail
An amino acid has more than one reactive site, and a synthesis that let them all react would produce a mixture of branched products rather than one chain. Protecting groups are fitted to the sites that must stay out of the way and removed when they are needed.
Two kinds are at work at once. The temporary group on the alpha-amino end comes off at every cycle to let the next residue couple. Side-chain groups stay on throughout and come off together at final cleavage. Choosing groups that are removed by different chemistry is called orthogonal protection, and it is what makes selective work such as deliberate disulfide pairing possible.
Terms used in this definition
Other entries this definition refers to.
Where this term comes up
Entries whose definition mentions Protecting Group.
What this means for research sourcing
Structure and identity terms are what a certificate of analysis is written in. Every Volta compound ships with its sequence, molecular weight and measured purity, so these terms map directly onto the specification on the product page.
Related Terms in Chemistry & Structure
Side-Chain Protection
Protecting groups on amino acid side chains, as distinct from the one on the alpha-amino group removed at every cycle. Side-chain groups stay on throughout the synthesis and come off together at final cleavage.
Orthogonal Protection
Using protecting groups removed by different chemistry, so one can be taken off while others stay on. It is what makes selective modification possible, including branched and cyclic structures.
Deprotection
Removing a protecting group to expose the site underneath. In Fmoc synthesis it names the piperidine step that frees the amino group for the next coupling, repeated once per residue.
Cleavage
Releasing the finished chain from the resin, usually with trifluoroacetic acid, which also strips most side-chain protection in the same step. Scavengers are included to catch the reactive fragments this generates.
Capping
Permanently blocking any chain that failed to couple, so it cannot react in later cycles. It converts a deletion impurity that would be hard to separate into a short truncated one that is easier to remove.
Coupling Reagent
The activator that turns a carboxylic acid into a form reactive enough to form an amide bond with the next amino group. Coupling efficiency compounds over a synthesis, so a small per-step loss becomes a large one over a long sequence.
Carbodiimide
A class of coupling reagent including DIC and EDC, usually paired with an additive to suppress side reactions. They are inexpensive and widely used, and the by-product they form differs in how easily it washes away.
HOBt (Hydroxybenzotriazole)
A coupling additive that forms a more selective active ester, raising yield and suppressing racemisation. Its shipping restrictions as a dry solid are part of why alternatives such as Oxyma came into use.