Peptide Synthesis

Question 1

What are natural peptides commonly used as?

Answer 1

• signalling molecules i.e. hormones, neurotransmitters

- substrates

Question 2

What is a peptidomimetic?

Answer 2

A peptidomimetic is a small protein-like chain designed to mimic a peptide

Question 3

Give examples of peptides & peptidomimetics in clinical use

Answer 3

• insulin

- interferons

Question 4

Why is peptide synthesis important?

Answer 4

For drug manufacture and discovery

Question 5

What are the 2 amino protecting groups?

Answer 5

• amides

- carbamates

Question 6

How does N protection work?

Answer 6

• aims to make N non-nucleophilic

- removes lone pair availability

Question 7

What is the most common N-protecting group?

Answer 7

carbamate

Question 8

What depends on choice of carbamate?

Answer 8

functional group sensitivity in target molecule

Question 9

Name the 3 types of sensitivity on target molecules

Answer 9

• acid sensitive (tBoc)
• reduction sensitive (Cbz)
• base sensitive (Fmoc)

Question 10

What is the most common reagent used in tBoc protection?

Answer 10

Boc anhydride

Question 11

What is used in tBoc de-protection?

Answer 11

TFA - trifluoroacetic acid

Question 12

What is the source of Cbz protection?

Answer 12

benzyoxycarbonyl chloride

Question 13

What 3 amino acids is Cbz protection unsuitable for?

Answer 13

Cys
Met
Lys

Question 14

In Cbz proetction is R1=H, what is the product?

Answer 14

Cbz-Gly

Question 15

How does Cbz de-protect?

Answer 15

Hydrogenation

Question 16

In Fmoc protection why is succinimidyl ester often used?

Answer 16

Good leaving group

Question 17

In Fmoc protection is R1=H, what is the product?

Answer 17

Fmoc-Gly

Question 18

How does Fmoc de-protect?

Answer 18

With a mild base

Question 19

Why does Fmoc not de-protect with a strong base?

Answer 19

Strong bases cause racemisation of amino acids - so we end up with a 1:1 mixture of D and L isomers

Question 20

What happens when we end up with 1:1 D +L isomers?

Answer 20

We get peptides with non-natural stereoisomers that are usually inactive

Question 21

Name a carboxyl protecting group

Answer 21

Esters

Question 22

Methyl and ethyl esters hydrolyse with ______

Answer 22

hydroxide

Question 23

tertiarybutyl hydrolyses with ___

Answer 23

TFA

Question 24

Benzyl hydrolyses with ________

Answer 24

hydrogenate

Question 25

Solid Phase Peptide Synthesis (SPPS) is a multistep solution synthesis that gives high/low overall product yields

Answer 25

low

Question 26

What is SPPS performed on?

Answer 26

insoluble polymer bead

Question 27

Describe the process of SPPS

Answer 27

- 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

Question 28

What are the advantages of SPPS?

Answer 28

- automation - rapid reliable - easy purification - cheap - many different applications

Question 29

What are the reactive side chains?

Answer 29

- N-containing - Carboxylate - Alcohol - Thiol

Question 30

What is the orthogonal protection strategy of reactive side chains?

Answer 30

- can use same protecting groups considered but not the same group used to protect the end of the chain

Question 31

If tBoc/Fmoc were used on the N-terminus why cant they be used on side chains? Why is this bad?

Answer 31

it will de-protect at same time as N-terminus - significant by-products - harmful/inactive if administered

Question 32

Peptide coupling is carried out using _______

Answer 32

carbodiimides

Question 33

Why is Cbz rarely used as an N protecting agent of terminal amino acid?

Answer 33

requires hydrogenation - incompatible with industrial scale + resin issues

Question 34

``` 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 ```

Answer 34

D H2 / Pd-C

Question 35

``` 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 ```

Answer 35

C DCC

Question 36

``` 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 ```

Answer 36

B HF