Boc Chemistry

Boc chemistry is the original solid-phase peptide synthesis strategy, in which the alpha-amino group of each incoming residue is masked by a tert-butyloxycarbonyl group removed with trifluoroacetic acid at the start of every cycle. Side chains carry benzyl-type protection, stable to that acid and removable only under much stronger acid. Both release from the resin and side-chain deprotection therefore require anhydrous hydrogen fluoride in dedicated fluoropolymer apparatus. The scheme is graduated rather than orthogonal: everything is acid-labile, separated by degree.

This is the chemistry Bruce Merrifield introduced in the early 1960s and for which he received the Nobel Prize in Chemistry in 1984. It survives because the repeated acid steps protonate the growing chain and break up the interchain hydrogen bonding that makes hydrophobic sequences stall in base-mediated schemes. Long syntheses, aggregating sequences, and the preparation of peptide thioesters for native chemical ligation are where it still wins.

Choosing this route means accepting a serious hazard and a capital cost in exchange for reaching sequences the alternative fails on. It also inverts which modifications survive: acid-sensitive groups do not tolerate hydrogen fluoride, while base-sensitive motifs, including the aspartimide-prone ones, pass through untouched. The choice is made per sequence, before the first residue is loaded.

The misreading on product listings is treating the named strategy as a quality grade. It certifies a route, nothing more. Both routes produce deletion sequences, epimers and incompletely deprotected species, and neither says whether the crude was ever purified. Hydrogen fluoride cleavage also leaves a different residual and counterion profile, so the route changes what to look for, not how much to trust it.