The synthesis of a polypeptide containing lysine requires...

Name: Problem 13, Chapter 24: Organic Chemistry
Uploaded: 2020-10-15T08:15:07-08:00
Duration: 6 min 5 s
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Description: The synthesis of a polypeptide containing lysine requires the protection of both amino groups. (a) Show how you might do this in a synthesis of the dipeptide KI using the benzyloxycarbonyl group as a protecting group. (b) The benzyloxycarbonyl group can also be used to protect the guanidino group, (FIGURE CANNOT COPY) of arginine. Show a synthesis of the dipeptide RA.

The synthesis of a polypeptide containing lysine requires the protection of both amino groups. (a) Show how you might do this in a synthesis of the dipeptide KI using the benzyloxycarbonyl group as a protecting group. (b) The benzyloxycarbonyl group can also be used to protect the guanidino group, (FIGURE CANNOT COPY) of arginine. Show a synthesis of the dipeptide RA.

Key Concepts

Protecting Groups in Organic Synthesis

Protecting groups are chemical modifications used to temporarily mask a reactive functional group, allowing selective reactions at other sites in complex molecules. In peptide synthesis, they prevent undesired side reactions by blocking groups that might interfere with coupling reactions, ensuring that only the intended bonds form during the stepwise assembly of the polypeptide chain.

Benzyloxycarbonyl (Cbz) Protecting Group

The benzyloxycarbonyl (Cbz or Z) group is a common protecting group for amino functionalities, particularly in peptide synthesis. It forms stable carbamates when attached to an amine, protecting it from reacting during peptide bond formation, and is typically removed by catalytic hydrogenation or other specific deprotection conditions.

Peptide Bond Formation

Peptide bond formation is the key reaction in synthesizing polypeptides, involving the coupling of the amino group of one amino acid to the carboxyl group of another. This process is typically facilitated by coupling reagents and requires the temporary protection of other reactive groups to ensure that each bond is formed in a controlled and selective manner.

Side Chain Protection in Amino Acids

Amino acids with multiple reactive groups, such as lysine and arginine, require selective protection of their side chains in addition to the main chain groups to ensure controlled reactivity during synthesis. This strategy allows specific bond formation and avoids undesirable cross-reactions, which is critical when synthesizing complex peptides.

Transcript

00:01 Question is asking us to come up with a method in which we use benzyloxycarbonone group as a protectant group while forming our dipeptide chain or our dipeptide of lysine and isolucine.

00:21 So first we're starting off with lysine.

00:25 We're going to combine it with benzyl chloroformate and we'll form the benzyl oxycarbonil group.

00:34 So now our first amino acid is protected and that was lysine.

00:38 Next, we're going to take the step of adding hydrobomic acid, hbr, as well as ascetic acid, to remove the protectant group, which is the benzyloxycarboneal.

01:17 And then we end up forming co2.

01:24 We've gotten our benzene ring with the bromine, and now we have an isolated lysine structure.

01:34 But now we're going to add an additional, we're going to add an additional amino acid, which is our isolucine to the structure.

01:48 So we will be removing this part and connect or forming our dipeptide bond.

01:58 So isolucine and the side chain of isolucine isolucine is kind of tricky.

02:36 So trying to position in a certain way.

02:44 I don't know if that looks any better, but this is supposed to be isolucine.

02:48 So we do now have our dipeptide bond, and we protect it lysine long enough to get it to react.

02:58 And now what we're going to do is we're actually going to add another amount of the first reactant, which was benzylchloroformate.

03:11 And we're doing that so that then we're actually going to add two equivalents of it so that then we end up protecting both ends of this newly formed dipeptide bond.

03:26 The next question is asking us to show the synthesis of ra.

03:34 So r a, r is tyrosine, and a is alanine...

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