Peptide Synthesis Flashcards
What are natural peptides commonly used as?
- signalling molecules i.e. hormones, neurotransmitters
- substrates
What is a peptidomimetic?
A peptidomimetic is a small protein-like chain designed to mimic a peptide
Give examples of peptides & peptidomimetics in clinical use
- insulin
- interferons
Why is peptide synthesis important?
For drug manufacture and discovery
What are the 2 amino protecting groups?
- amides
- carbamates
How does N protection work?
- aims to make N non-nucleophilic
- removes lone pair availability
What is the most common N-protecting group?
carbamate
What depends on choice of carbamate?
functional group sensitivity in target molecule
Name the 3 types of sensitivity on target molecules
- acid sensitive (tBoc)
- reduction sensitive (Cbz)
- base sensitive (Fmoc)
What is the most common reagent used in tBoc protection?
Boc anhydride
What is used in tBoc de-protection?
TFA - trifluoroacetic acid
What is the source of Cbz protection?
benzyoxycarbonyl chloride
What 3 amino acids is Cbz protection unsuitable for?
Cys
Met
Lys
In Cbz proetction is R1=H, what is the product?
Cbz-Gly
How does Cbz de-protect?
Hydrogenation
In Fmoc protection why is succinimidyl ester often used?
Good leaving group
In Fmoc protection is R1=H, what is the product?
Fmoc-Gly
How does Fmoc de-protect?
With a mild base
Why does Fmoc not de-protect with a strong base?
Strong bases cause racemisation of amino acids - so we end up with a 1:1 mixture of D and L isomers
What happens when we end up with 1:1 D +L isomers?
We get peptides with non-natural stereoisomers that are usually inactive
Name a carboxyl protecting group
Esters
Methyl and ethyl esters hydrolyse with ______
hydroxide
tertiarybutyl hydrolyses with ___
TFA
Benzyl hydrolyses with ________
hydrogenate
Solid Phase Peptide Synthesis (SPPS) is a multistep solution synthesis that gives high/low overall product yields
low
What is SPPS performed on?
insoluble polymer bead
Describe the process of SPPS
- Add C-terminal amino acid to bead
- deprotect N-terminus
- add activated ester of 2nd amino acid
- deprotect N-terminus of dipeptide
- add activated ester of 3rd amino acid
- deprotect new N-terminus
- cleave peptide from resin
What are the advantages of SPPS?
- automation
- rapid reliable
- easy purification
- cheap
- many different applications
What are the reactive side chains?
- N-containing
- Carboxylate
- Alcohol
- Thiol
What is the orthogonal protection strategy of reactive side chains?
- can use same protecting groups considered but not the same group used to protect the end of the chain
If tBoc/Fmoc were used on the N-terminus why cant they be used on side chains?
Why is this bad?
it will de-protect at same time as N-terminus
- significant by-products
- harmful/inactive if administered
Peptide coupling is carried out using _______
carbodiimides
Why is Cbz rarely used as an N protecting agent of terminal amino acid?
requires hydrogenation
- incompatible with industrial scale + resin issues
Which reagent(s) would be most suitable for removing a Cbz-protecting group? A TFA B HF C DCC D H2 / Pd-C E Morpholine
D H2 / Pd-C
Which reagent(s) would be most suitable for coupling two amino acids together. A TFA B HF C DCC D H2 / Pd-C E Morpholine
C DCC
Which reagent(s) would be most suitable for removing a peptide from Merrifield resin? A TFA B HF C DCC D H2 / Pd-C E Morpholine
B HF
