TOPIC: 24. Proteins / Peptides

SUBTOPIC: 241. Polypeptides

1. Aspartame, a nonnutritive sweetener marketed under the name of Nutrasweet is the methyl ester of a simple dipeptide H-Asp-Phe-OCH₃.

(a) Draw the complete structure of aspartame as it exists at pH = 1. For Asp: R = CH₂COOH; For Phe: R = CH₂Ph.

(b) The isoelectric point of aspartame is 5.9. Draw the principal structure present in aqueous solution at this pH.

(c) Draw the principal form present at physiological pH = 7.6.

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2. (a) Draw the structure of a cyclic dipeptide which hydrolyzes to give two naturally occurring amino acids. Show the stereogenic centers in 3-D.

(b) Draw the structure of one of the amino acids as it would exist in solution at pH 10.

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