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Chapter 32: Problem 742

Show how each of the following substances can be synthesized starting with the individual amino acids. (a) glycylalanylcysteine (b) \(\mathrm{HO}_{2} \mathrm{C}\left(\mathrm{CH}_{2}\right)_{2} \mathrm{CH}\left(\mathrm{NH}_{2}\right) \mathrm{CONHCH}_{2} \mathrm{CO}_{2} \mathrm{H}\) (c) glutamine from glutamic acid

Short Answer

Expert verified
(a) To synthesize glycylalanylcysteine, start with individual amino acids glycine, alanine, and cysteine. Form a peptide bond between glycine and alanine to create glycylalanine, and then form another peptide bond between glycylalanine and cysteine to obtain glycylalanylcysteine. (b) The compound is a dipeptide formed by glycine and β-alanine. To synthesize it, form a peptide bond between glycine and β-alanine, resulting in Glycyl-β-alanine. (c) To synthesize glutamine from glutamic acid, treat glutamic acid with an amidating agent such as ammonia or carbodiimide, converting the carboxyl group in the side chain into an amide group to obtain glutamine.

Step by step solution

01

Starting materials

We need to begin with the individual amino acids: - Glycine: \(\mathrm{NH}_{2}\mathrm{CH}_{2}\mathrm{COOH}\) - Alanine: \(\mathrm{NH}_{2}\mathrm{CH}(\mathrm{CH}_{3})\mathrm{COOH}\) - Cysteine: \(\mathrm{NH}_{2}\mathrm{CH}(\mathrm{CH}_{2}\mathrm{SH})\mathrm{COOH}\)
02

Peptide bond formation between glycine and alanine

Form a peptide bond between the amine group of glycine and the carboxyl group of alanine, releasing a water molecule in the process: Glycine + Alanine -> Glycylalanine + \(\mathrm{H}_{2}\mathrm{O}\)
03

Peptide bond formation between glycylalanine and cysteine

Form another peptide bond between the amine group of glycylalanine and the carboxyl group of cysteine, releasing a water molecule in the process: Glycylalanine + Cysteine -> Glycylalanylcysteine + \(\mathrm{H}_{2}\mathrm{O}\) (b) Synthesize the given compound:
04

Identify the compound and its amino acids

The given formula can be rewritten as: \(\mathrm{NH}_{2}\mathrm{CH}(\mathrm{COOH})\mathrm{CH}_{2}\mathrm{CH}_{2}\mathrm{CO}\mathrm{NH}\mathrm{CH}_{2}\mathrm{COOH}\), which corresponds to a dipeptide formed by glycine and β-alanine. The individual amino acids are: - Glycine: \(\mathrm{NH}_{2}\mathrm{CH}_{2}\mathrm{COOH}\) - β-Alanine: \(\mathrm{NH}_{2}\mathrm{CH}_{2}\mathrm{CH}_{2}\mathrm{COOH}\)
05

Peptide bond formation between glycine and β-alanine

Form a peptide bond between the amine group of glycine and the carboxyl group of β-alanine, releasing a water molecule in the process: Glycine + β-Alanine -> Glycyl-β-alanine + \(\mathrm{H}_{2}\mathrm{O}\) (c) Synthesize glutamine from glutamic acid:
06

Identify structural differences

Glutamic acid: \(\mathrm{NH}_{2}\mathrm{CH}(\mathrm{CH}_{2}\mathrm{CH}_{2}\mathrm{COOH})\mathrm{COOH}\) Glutamine: \(\mathrm{NH}_{2}\mathrm{CH}(\mathrm{CH}_{2}\mathrm{CH}_{2}\mathrm{CONH}_{2})\mathrm{COOH}\) The structural difference between them is an amide group (\(\mathrm{NH}_{2}\)) instead of a carboxyl group (\(\mathrm{COOH}\)) in the side chain.
07

Amide formation

Treat glutamic acid with an amidating agent, such as ammonia or carbodiimide, to convert the carboxyl group into an amide group: Glutamic acid + \(\mathrm{NH}_{3}\) / Carbodiimide -> Glutamine

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Most popular questions from this chapter

The proteolytic enzyme, papain, differs from \(\alpha\) -chymdtrypsin in having cysteine or a labile derivative thereof as part of its active site. The enzyme is deactivated by substances that form complexes with, or react with, -SH groups and the activity is restored by reactions expected to regenerate an -SH group. Work out a schematic mechanism for cleavage of a peptide chain with papain which is in agreement with the idea that, while papain may not normally contain a free \(\mathrm{SH}\) group, it reacts readily with mercuric ion to give compounds of the type RSHgX. One of the most interesting features of papain is that more than 100 of its total of 185 amino acid residues may be removed with the aid of an aminopeptidase to give a fragment with considerable enzymic activity.

It is thought that the first amino acids were synthesized from formaldehyde, hydrogen cyanide, ammonia and water in the primitive atmosphere. A possible synthesis involves a series of nucleophilic attacks and proton transfers. Propose a mechanism for the synthesis of glycine using the above mentioned compounds.

Write a mechanism for the reaction of glycine with N- carboethoxyphthalimide involving a sequence of carbony1 addition, ring opening, ring closure and elimination. Would you expect a similar reaction with L-phenylalanine to yield the \(L\), the \(D\), or the D,L-product?

Hemoglobin, the protein responsible for carrying oxygen from the lungs to the body tissues, contains \(0.355\) per cent iron. Hydrolysis of \(100 \mathrm{~g}\) of hemoglobin gives \(1.48 \mathrm{~g}\) of tryptphan; calculate the minimum molecular weight of hemoglobin which is consistent with these results.

The complete structure of Gramicidin \(\mathrm{S}\), a polypeptide with antibiotic properties, has been worked out as follows: (a) Analysis of the hydrolysis products gave an empirical formula of Leu, Orn, Phe, Pro, Val. (Ornithine, Orn, is a rare amino acid of formula \(\left.{ }^{+} \mathrm{H}_{3} \mathrm{NCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}\left(\mathrm{NH}_{2}\right) \mathrm{COO}^{-} .\right)\) It is interesting that the phenylalanine has the unusual D-configuration. Measurement of the molecular weight gave an approximate value of \(1300 .\) On this basis, what is the molecular formula of Gramicidin \(\mathrm{S} ?\) (b) Analysis for the C-terminal residue was negative; analysis for the N-terminal residue using DNFB yielded only DNP-NHCH \(_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}\left(\mathrm{N}^{+} \mathrm{H}_{3}\right) \mathrm{COO}^{-}\). What structural feature must the peptide chain possess? (c) Partial hydrolysis of Gramicidin \(\mathrm{S}\) gave the following di- and tripeptides: Leu.Phe Phe.Pro Phe.Pro.Val Val.Orn.Leu \(\begin{array}{lll}\text { Orn.Leu } & \text { Val.Orn } & \text { Pro. Val.Orn }\end{array}\) What is the structure of Gramicidin \(\mathrm{S} ?\)
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