Boc (tert-Butyloxycarbonyl)
Definition
An acid-labile protecting group, and the basis of the older synthesis strategy that preceded Fmoc. Boc chemistry requires repeated acid treatment and a harsh final cleavage, which is why it survives mainly for sequences Fmoc handles badly.
Terms used in this definition
Other entries this definition refers to.
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Related Terms in Chemistry & Structure
Protecting Group
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.
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.