H-Abu-OH

H-Abu-OH
L-α-Aminobutyric acid (L-2-aminobutyric acid, L-Abu); (2S)-2-aminobutanoic acid

α-Aminobutyric acid is alanine with an ethyl side chain: one methylene longer, unbranched, and unreactive. Substituting it for cysteine or serine is a way of removing a thiol or a hydroxyl while leaving a side chain of comparable size. One demonstrated example: in the chemically synthesized HIV-1 protease whose crystal structure was solved at 2.8 Å, the cysteines had been replaced by L-α-amino-n-butyric acid and the protein was enzymatically active. What such a substitution does to folding and activity is sequence-dependent and has to be tested.

With a free α-amine and a free α-carboxyl this is a starting material and a solution-phase reagent rather than a stepwise SPPS building block: activating it would let it polymerize, so the α-amine is protected first. It is the starting material for the protected derivatives used on the resin, Fmoc-Abu-OH, Boc-Abu-OH and Z-Abu-OH, and for Abu dipeptides and other building blocks prepared in solution. The side chain is a plain ethyl group: it needs no protection at any stage, survives piperidine, TFA and the usual cleavage cocktails, and gives the residue no reactivity of its own.

Such substitutions are made to take a reactive side chain out of a sequence — a disulfide partner, a thiol conjugation site, a phosphorylation site — while keeping a side chain of similar size in its place. Whether the fold and the activity survive is tested in the sequence concerned.

Applications

• Preparation of Fmoc-, Boc- and Z-protected Abu building blocks
• Cysteine-to-Abu and serine-to-Abu substitutions, through those derivatives
• Solution-phase peptide synthesis and conjugation

Storage
Store at room temperature in a tightly closed container, protected from moisture.

References

1. Wlodawer A et al. Conserved Folding in Retroviral Proteases: Crystal Structure of Synthetic HIV-1 Protease. Science 1989, 245, 616–621. doi:10.1126/science.2548279

For research use only. Not for human or veterinary use.