Convert the following Fischer Projection of L-Proline into a bondline structure.

Draw the structure of the phenylthiohydantoin derivatives of

(c) lysine.

Sometimes chemists need the unnatural D enantiomer of an amino acid, often as part of a drug or an insecticide. Most L-amino acids are isolated from proteins, but the D-amino acids are rarely found in natural proteins. D-amino acids can be synthesized from the corresponding L-amino acids. The following synthetic scheme is one of the possible methods.

(a) Draw the structures of intermediates 1 and 2 in this scheme.

(b) How do we know that the product is entirely the unnatural D configuration?

Suggest how you would separate the free L-amino acid from its acylated D enantiomer in Figure 24-5.

Provide the Fischer Projection representation of D-Aspartic Acid. Indicate if the chiral center is R or S.

An opioid pentapeptide has the following structure: Tyr-Cys-Gly-Phe-Cys

a. Draw the structure of the pentapeptide including all the side chains.

b. Write its structure following mild oxidation.

Metabolism of arginine produces urea and the rare amino acid ornithine. Ornithine has an isoelectric point close to 10. Propose a structure for ornithine.

Suggest a method for the synthesis of the unnatural D enantiomer of alanine from the readily available L enantiomer of lactic acid.

Draw the structure of the phenylthiohydantoin derivatives of

(a) alanine.