Agent MadHatter - 16-8-2009 at 13:57
Hey guys, your favorite college student is back with another question.
I did some of my own reactions, really fun stuff!
I was looking into making some proteins or something alittle smaller like peptides and I had a few questions.
If I react a carboxyl with an amine, using a peptide bonding agent such as BOP or HBTU, would I need heat to help the reaction? I haven't decided what
peptide I'd make, or what amine/carboxyl i'd use, but it sounds like a fun thing to make!
So would I need heat? And I know that hydrolysis of the finished reaction would break the peptide bond, so if I used say, BOP as a bonding agent,
would adding water remove the bonding agent leaving the peptide (the carboxyl and amine molecules) alone?
I don't know much about bonding agents, still just looking for fun reactions.
Thanks.
[Edited on 16-8-2009 by Agent MadHatter]
JohnWW - 16-8-2009 at 18:31
The bonds between amino-acid (usually alpha-amino-acids) units in peptides and proteins are amide linkages, -C-C(=O)-NH-C- . Hydrolysis is achieved by
use of a strong mineral acid (including HCl, on ingestion).
These linkages also occur in nylons, in which either (usually) 1,6-dicarboxylic acids and 1,6-diamines are heated together (about 280ºC which favors
this instead of ionic amine carboxylic acid salts), or else cyclic lactams (usually 6-carbon cyclic amides) are made to undergo ring-opening and
mutual polymerization.
Agent MadHatter - 16-8-2009 at 18:39
So to break the bond formed by using a coupling agent I'd need to use a strong acid?
Also would I need to reflux the reaction for the coupling agent to actually work?
chemoleo - 17-8-2009 at 15:50
Standard peptide coupling reactions using HATU, HBTU, PyBOB etc work at RT, usually coupling times are betw 30- 60 min. THere are microwave
synthesisers however, which operate at 80 deg C.
What you need is the activator (see the three above)
DIPEA (Activator base, it is diisopropylethylamine, although there are good substitutes)
and the two amino acids.
All functional side chains on the amino acids need to be protected, becuase side reactions occur otherwise with them.
So to safely couple two un-protected amino acids without obtaining a mix of peptides, you can only use alanine, glycine, valine, isoleucine, leucine,
phenylalanine (they are all hydrophobic (presenting possible solubility issues if you were interested to study the peptide in aq. solution) and the
sidechains are aliphatic/aromatic and have no functional groups).
The reason why reactions are done in solid phase (=linked to a resin) is so that coupling reagents/base/reaction products etc can be washed off.
If you do synthesis in solution, then you'd probably have to HPLC the product jsut for that. But any peptide synth. is usually followed by HPLC
purification.
Have a look on the net, there are many many comprehensive sites on how pept. synth works, the chemistry behind it etc. Novabiochem is a good one to
start at.
Agent MadHatter - 17-8-2009 at 17:34
Well I remember reading the reason behind using a pep. coupler and it said that mixing the two chemicals together won't have any reaction. So I
wouldn't need the activator would I?