Chapter 24: Q33P (page 1298)
Show how you would use the Strecker synthesis to make isoleucine. What stereochemistry would you expect in your synthetic product?
Short Answer

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Chapter 24: Q33P (page 1298)
Show how you would use the Strecker synthesis to make isoleucine. What stereochemistry would you expect in your synthetic product?

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Aspartame(Nutrasweet庐) is a remarkably sweet-tasting dipeptide ester. Complete hydrolysis of aspartame gives phenylalanine, aspartic acid, and methanol. Mild incubation with carboxypeptidase has no effect on aspartame. Treatment of aspartame with phenyl isothiocyanate, followed by mild hydrolysis, gives the phenylthiohydantoin of aspartic acid. Propose a structure for aspartame.
Draw the resonance forms of a protonated guanidino group and explain why arginine has such a strongly basic isoelectric point.
Peptides often have functional groups other than free amino groups at the N terminus and other than carboxyl groups at the C terminus.
(a) A tetrapeptide is hydrolyzed by heating with 6 M, and the hydrolysate is found to contain Ala, Phe, Val, and Glu. When the hydrolysate is neutralized, the odor of ammonia is detected. Explain where this ammonia might have been incorporated in the original peptide.
(b) The tripeptide thyrotropic hormone releasing factor(TRF) has the full name pyroglutamylhistidylprolinamide. The structure appears here. Explain the functional groups at the N terminus and at the C terminus.

(c)On acidic hydrolysis, an unknown pentapeptide gives glycine, alanine, valine, leucine and isoleucine. No odor of ammonia is detected when the hydrolysate is neutralized. Reaction with phenyl isothiocyanate followed by mild hydrolysis gives nophenylthiohydantoin derivative. Incubation with carboxypeptidase has no effect. Explain these findings.
Show how solid-phase peptide synthesis would be used to make Ile-Gly-Asn.
Draw the electrophoretic separation of Ala, Lys, and Asp at pH 9.7.
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