 | Ahluwalia V.K. Chemistry of natural products: amino acids, peptides, proteins and enzymes / V.K.Ahluwalia, L.S.Kumar, S.Kumar. - Boca Raton: CRC Press/Ane Books India, 2006 (2007). - [8], 249 p.: ill. - Ind.: p.237-249. - ISBN 1-42005-917-3
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Preface ......................................................... v
CHAPTER 1: AMINO ACIDS
1.1 INTRODUCTION ............................................... 1
1.2 NOMENCLATURE OF AMINO ACIDS ................................ 2
1.2.1 Representation of Amino Acids ....................... 5
1.3 CLASSIFICATION OF AMINO ACIDS .............................. 7
1.3.1 Coded or Primary Protein Amino Acids ................ 7
1.3.1.1 Nonpolar or Apolar Amino Acids ............. 7
1.3.1.2 Neutral or Uncharged Polar Amino Acids ..... 9
1.3.1.3 Charged Polar Amino Acids ................. 10
1.3.2 Secondary and Tertiary Protein Amino Acids ......... 11
1.3.3 Non-Coded or Non-Protein Amino Acids ............... 13
1.3.4 Essential Amino Acids .............................. 14
1.4 STEREOCHEMICAL ASPECTS OF α- AMINO ACIDS .................. 15
1.4.1 Absolute Configuration of α-Amino Acids ............ 16
1.4.1.1 The RS Notation ............................ 17
1.4.2 Amino Acids with Two Chiral Centres ................ 18
1.5 PHYSICAL PROPERTIES OF α-AMINO ACIDS ...................... 20
1.5.1 General Physical Properties ........................ 20
1.5.2 Acid-Base Properties of Amino Acids ................ 21
1.5.2.1 Amino Acids with Non-Ionisable Side
Chains .................................... 22
1.5.2.2 Amino Acids with Ionisable Side Chains .... 25
1.5.3 Spectral Properties of α-Amino Acids ............... 28
1.5.3.1 Mass Spectrometry ......................... 28
1.5.3.2 Nuclear Magnetic Resonance (NMR)
Spectroscopy .............................. 29
1.5.3.3 UV Spectroscopy ........................... 31
1.5.3.4 IR Spectroscopy ........................... 31
1.5.3.4 Circular Dichroism (CD) ................... 32
1.6 CHEMICAL REACTIONS OF AMINO ACIDS ......................... 32
1.6.1 Reactions due to Amino Group ....................... 32
1.6.2 Reactions due to Carboxyl Group .................... 35
1.6.3 Reactions due to bom Amino and Carboxyl Groups ..... 36
1.7 INDUSTRIAL PREPARATION OF α- AMINO ACIDS .................. 39
1.8 CHEMICAL SYNTHESIS OF α-AMINO ACIDS ....................... 40
1.8.1 Enantiomeric Resolution of α-Amino Acids ............ 50
1.82 Asymmetric Synthesis of α-Amino Acids ............... 53
1.9 INDUSTRIAL APPLICATIONS OF α-AMINO ACIDS .................. 62
Exercises ................................................. 64
CHAPTER 2: PEPTIDES
2.1 INTRODUCTION .............................................. 67
2.2 STRUCTURE AND CLASSIFICATION OF PEPTIDES .................. 68
2.2.1 Structure of Peptide Bond .......................... 68
2.2.2 Classification of Peptides ......................... 71
2.3 NOMENCLATURE OF PEPTIDES .................................. 72
2.3.1 Representation of Peptides and Polypeptides ........ 73
2.4 PEPTIDE SYNTHESIS ......................................... 74
2.4.1 Protection of Amino Group .......................... 78
2.4.2 Protection of Carboxyl Group ....................... 86
2.4.3 Protection of Side Chains .......................... 87
2.4.4 Coupling Methods ................................... 88
2.5 SOLID PHASE PEPTIDE SYNTHESIS ............................. 95
2.5.1 Solid Phase Peptide Synthesis using t-Boc
Protection (Merrifield Approach) ................... 98
2.5.2 Solid Phase Peptide Synthesis using Fmoc
Protection (Sheppard's Approach) ................... 99
2.5.3 Limitations of Solid Phase Peptide Synthesis ...... 101
2.6 SOME BIOLOGICALLY IMPORTANT PEPTIDES ..................... 103
2.6.1 Oxytocin .......................................... 103
2.6.2 Glutathione ....................................... 105
2.6.2.1 Role of Glutathione in Disulphide Bond
Formation ................................ 106
2.6.2.2 Role of Glutathione as an Antioxidant .... 107
2.6.3 Insulin ........................................... 108
2.6.3.1 Structure Determination of Insulin ........ 108
2.6.3 Bradykinin ........................................ 109
2.6.4 Gramicidin ........................................ 110
Exercises ................................................ 112
CHAPTER 3: PROTEINS
3.1 INTRODUCTION ............................................. 113
3.2 CLASSIFICATION OF PROTEINS ............................... 114
3.2.1 Classification on the Basis of Shape and
Structure ......................................... 114
3.2.2 Classification on the Basis of Products of
Hydrolysis ........................................ 116
3.2.3 Classification on the Basis of Biological
Functions ......................................... 121
3.3 PROPERTIES OFPROTEINS .................................... 122
3.3.1 Molecular Weight .................................. 122
3.3.2 Amphoteric Nature ................................. 123
3.3.3 Solubility ........................................ 124
3.3.4 Precipitation ..................................... 125
3.3.5 Denaturation ...................................... 126
3.3.6 Colour Reactions .................................. 126
3.4 STRUCTURAL ORGANISATION OF PROTEINS ...................... 131
3.4.1 Covalent or Primary Structure of Proteins ......... 131
3.4.1.1 Amino Acid Composition of Proteins ....... 131
3.4.1.2 Amino Acid Sequence of Polypeptides ...... 134
3.4.2 Conformational Aspects of Proteins: Higher Order
Structures ........................................ 147
3.4.2.1 Secondary Structure of Proteins .......... 147
3.4.2.2 Tertiary Structure of Proteins ........... 157
3.4.2.3 Quaternary Structure of Proteins ......... 158
Exercises ................................................ 160
CHAPTER 4: ENZYMES
4.1 INTRODUCTION ............................................. 163
4.2 NOMENCLATURE AND CLASSIFICATION OF ENZYMES ............... 164
4.2.1 Systematic and Recommended Names .................. 165
4.2.2 Classification Numbers and Code Names ............. 165
4.3 CHARACTERISTICS OF ENZYMES ............................... 173
4.3.1 Catalytic Power ................................... 173
4.3.2 Enzyme Specificity ................................ 173
4.3.3 Enzyme Regulation ................................. 175
4.4 MECHANISM OF ENZYME ACTION ............................... 176
4.5 FACTORS AFFECTING ENZYME ACTION .......................... 179
4.6 CHYMOTRYPSIN: AN ENZYME IN ACTION ........................ 182
4.6.1 Structure of Chymotrypsin ......................... 182
4.6.2 Important Amino Acid Residues of Chymoteypsin ..... 184
4.6.3 Mechanism of Action ............................... 186
4.7 COFACTORS (or COENZYMES) ................................. 190
4.7.1 Nicotinamide Adenine Dinucleotide (NAD+) and
Nicotinamide Adenine Dinucleotide Phosphate
(NADP+) ........................................... 192
4.7.2 UDP-Glucose ....................................... 195
4.7.3 Flavin Mononucleotide (FMN) and Ravin Adenine
Dinucleotide (FAD) ................................ 197
4.7.4 Thiamine Pyrophosphate (TPP) ...................... 200
4.7.5 CoCarboxylase ..................................... 202
4.7.6 Pyridoxal-5-Phosphate ............................. 205
4.8 ENZYMES IN ORGANIC SYNTHESIS ............................. 210
4.8.1 Enzymatic Oxidations .............................. 212
4.8.2 Enzymatic Hydroxylation ........................... 214
4.8.3 Enzymatic Hydrolysis .............................. 214
4.8.4 Enzymatic Reductions .............................. 215
4.8.5 Enzymatic Isomerisations .......................... 217
4.6.4 Pharmaceutical Applications of Enzymes ............ 217
Exercises ................................................ 219
Glossary ...................................................... 221
Index ......................................................... 237
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