John McMurry, Professor Emeritus

Aromatic: Phe, Tyr, Trp, His; sulfur-containing: Cys, Met; alcohols: Ser, Thr; hydrocarbon side chains: Ala, Ile, Leu, Val, Phe

Problem 26-2

The sulfur atom in the −CH₂SH group of cysteine makes the side chain higher in ranking than the −CO₂H group.

Problem 26-3

Three structures of threonine. One structure is a Fischer projection of L-threonine. The other two structures represent the diastereomers of L-threonine. The configuration of each carbon atom is mentioned.

Problem 26-4

Net positive at pH = 5.3; net negative at pH = 7.3

Problem 26-5

(a)

Start with 3-phenylpropanoic acid: 1. Br₂, PBr₃; 2. NH₃

(b)

Start with 3-methylbutanoic acid: 1. Br₂, PBr₃; 2. NH₃

Problem 26-6

(a)

(b)

The structure of an imidazole, with an N-H group at C 1, nitrogen at C 3, and a bromomethyl group at C 5.

(c)

The structure of an indole comprises a benzene ring fused to a cyclopentene, with an N-H group at C 1, and a bromomethyl group at C 3.

(d)

Problem 26-7

Ethene with H (up) and isopropyl on left, and carboxyl (up) and N with acetyl on right reacts with hydrogen and rhodium catalyst, then aqueous hydroxide, forming (2S)-2-amino-4-methylpentanoic acid.

Problem 26-8

Val-Tyr-Gly (VYG), Tyr-Gly-Val (YGV), Gly-Val-Tyr (GVY), Val-Gly-Tyr (VGY), Tyr-Val-Gly (YVG), Gly-Tyr-Val (GYV)

Trypsin: Asp-Arg + Val-Tyr-Ile-His-Pro-Phe

Chymotrypsin: Asp-Arg-Val-Tyr + Ile-His-Pro-Phe

Problem 26-13

Methionine

Problem 26-14

A P T H derivative containing an acetic acid residue formed from the Edman degradation of the N-terminal residue of a peptide.

Problem 26-15

(a)

Arg-Pro-Leu-Gly-Ile-Val

(b)

Val-Met-Trp-Asp-Val-Leu (VMWNVL)

Problem 26-16

This is a typical nucleophilic acyl substitution reaction, with the amine of the amino acid as the nucleophile and tert-butyl carbonate as the leaving group. The tert-butyl carbonate then loses CO₂ and gives tert-butoxide, which is protonated.

Problem 26-17

(1) Protect the amino group of leucine.

(2) Protect the carboxylic acid group of alanine.

(3) Couple the protected amino acids with DCC.

(4) Remove the leucine protecting group.

(5) Remove the alanine protecting group.

Problem 26-18

(a)

Lyase

(b)

Hydrolase

(c)

Oxidoreductase

Chapter 26