Textbook Question
(a) The isoelectric point (pI) of phenylalanine is pH 5.5. Draw the structure of the major form of phenylalanine at pH values of 1, 5.5, and 11.
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Ch. 24 - Amino Acids, Peptides, and Proteins
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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Table of contents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
Chapter 24, Problem 19c
Draw the structure of the phenylthiohydantoin derivatives of
(c) lysine.
Verified step by step guidance1
Understand the context: Phenylthiohydantoin (PTH) derivatives are formed during Edman degradation, a method used to sequence amino acids in peptides. The process involves reacting the amino group of an amino acid with phenyl isothiocyanate (PITC) to form a PTH derivative.
Identify the structure of lysine: Lysine is an amino acid with the structure H₂N-(CH₂)₄-CH(NH₂)-COOH. It has two amino groups: one on the α-carbon (α-amino group) and one on the side chain (ε-amino group).
Determine which amino group reacts: In the context of forming a PTH derivative, the α-amino group reacts with phenyl isothiocyanate (PITC) to form the PTH derivative. The ε-amino group on the side chain remains unreacted.
Draw the reaction: The α-amino group of lysine reacts with PITC to form a cyclic structure. The reaction involves the nucleophilic attack of the α-amino group on the carbon of the isothiocyanate group (-N=C=S) in PITC, followed by cyclization to form the PTH derivative.
Complete the structure: The final structure of the PTH derivative of lysine will include the phenylthiohydantoin ring attached to the α-carbon of lysine, with the side chain (CH₂)₄-NH₂ intact. Ensure the stereochemistry at the α-carbon is preserved if specified.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Phenylthiohydantoin (PTH) Derivatives
Phenylthiohydantoin derivatives are compounds formed by the reaction of phenylthiohydantoin with amino acids. This reaction typically involves the formation of a stable derivative that can be used for amino acid analysis, particularly in sequencing. The PTH group allows for the identification of the amino acid by chromatographic methods.
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Ammonia Derivatives
Amino Acid Structure
Amino acids are organic compounds that serve as the building blocks of proteins. Each amino acid consists of a central carbon atom bonded to an amino group, a carboxyl group, a hydrogen atom, and a variable side chain (R group). The side chain determines the specific properties and identity of the amino acid, such as lysine, which has a positively charged side chain at physiological pH.
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11:14Charged Amino Acids
Lysine
Lysine is an essential amino acid characterized by its aliphatic side chain containing an amino group, making it positively charged at physiological pH. It plays a crucial role in protein synthesis and is involved in various biological processes, including enzyme function and hormone production. Understanding lysine's structure is vital for drawing its PTH derivative accurately.
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Draw the structure of the phenylthiohydantoin derivatives of
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The isoelectric point of glutamic acid is pH 3.2. Draw the structures of the major forms of glutamic acid at pH values of 1, 3.2, 7, and 11. Explain why the side-chain carboxylic acid is a weaker acid than the acid group next to the α-carbon atom.
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