Chemistry for Pharmacy Students

General, Organic and Natural Product Chemistry
 
 
Standards Information Network (Verlag)
  • 2. Auflage
  • |
  • erschienen am 9. Juli 2019
  • |
  • 536 Seiten
 
E-Book | ePUB mit Adobe-DRM | Systemvoraussetzungen
978-1-119-39448-8 (ISBN)
 
Introduces the key areas of chemistry required for all pharmacy degree courses and focuses on the properties and actions of drug molecules

This new edition provides a clear and comprehensive overview of the various areas of general, organic, and natural products chemistry (in relation to drug molecules). Structured to enhance student understanding, it places great emphasis on the applications of key theoretical aspects of chemistry required by all pharmacy and pharmaceutical science students. This second edition particularly caters for the chemistry requirements in any 'Integrated Pharmacy Curricula', where science in general is meant to be taught 'not in isolation', but together with, and as a part of, other practice and clinical elements of the course.

Chemistry for Pharmacy Students: General, Organic and Natural Product Chemistry, 2nd Edition is divided into eight chapters. It opens with an overview of the general aspects of chemistry and their importance to modern life, with emphasis on medicinal applications. The text then moves on to discuss the concepts of atomic structure and bonding and the fundamentals of stereochemistry and their significance to pharmacy in relation to drug action and toxicity. Various aspects of organic functional groups, organic reactions, heterocyclic chemistry, nucleic acids and their pharmaceutical importance are then covered in subsequent chapters, with the final chapter dealing with drug discovery and development, and natural product chemistry.



Provides a student-friendly introduction to the main areas of chemistry required by pharmacy degree courses
Written at a level suitable for non-chemistry students in pharmacy, but also relevant to those in life sciences, food science, and the health sciences
Includes learning objectives at the beginning of each chapter
Focuses on the physical properties and actions of drug molecules

Chemistry for Pharmacy Students: General, Organic and Natural Product Chemistry, 2nd Edition is an essential book for pharmacy undergraduate students, and a helpful resource for those studying other subject areas within pharmaceutical sciences, biomedical sciences, cosmetic science, food sciences, and health and life sciences.
 

<b>Introduces the key areas of chemistry required for all pharmacy degree courses and focuses on the properties and actions of drug molecules</b>

This new edition provides a clear and comprehensive overview of the various areas of general, organic, and natural products chemistry (in relation to drug molecules). Structured to enhance student understanding, it places great emphasis on the applications of key theoretical aspects of chemistry required by all pharmacy and pharmaceutical science students. This second edition particularly caters for the chemistry requirements in any 'Integrated Pharmacy Curricula', where science in general is meant to be taught 'not in isolation', but together with, and as a part of, other practice and clinical elements of the course.

<i>Chemistry for Pharmacy Students: General, Organic and Natural Product Chemistry, 2nd Edition</i> is divided into eight chapters. It opens with an overview of the general aspects of chemistry and their importance to modern life, with emphasis on medicinal applications. The text then moves on to discuss the concepts of atomic structure and bonding and the fundamentals of stereochemistry and their significance to pharmacy in relation to drug action and toxicity. Various aspects of organic functional groups, organic reactions, heterocyclic chemistry, nucleic acids and their pharmaceutical importance are then covered in subsequent chapters, with the final chapter dealing with drug discovery and development, and natural product chemistry.

<ul><li>Provides a student-friendly introduction to the main areas of chemistry required by pharmacy degree courses</li><li>Written at a level suitable for non-chemistry students in pharmacy, but also relevant to those in life sciences, food science, and the health sciences</li><li>Includes learning objectives at the beginning of each chapter</li><li>Focuses on the physical properties and actions of drug molecules</li></ul>

<i>Chemistry for Pharmacy Students: General, Organic and Natural Product Chemistry, 2nd Edition</i> is an essential book for pharmacy undergraduate students, and a helpful resource for those studying other subject areas within pharmaceutical sciences, biomedical sciences, cosmetic science, food sciences, and health and life sciences.

2nd Revised edition
  • Englisch
  • USA
John Wiley & Sons Inc
  • Für Beruf und Forschung
  • Überarbeitete Ausgabe
  • Reflowable
  • 39,13 MB
978-1-119-39448-8 (9781119394488)

weitere Ausgaben werden ermittelt
Lutfun Nahar, BSc (Hons), PhD, MRSC, FHEA, is an Honorary Lecturer, and actively involved in research at the Faculty of Science at Liverpool John Moores University, UK. She has published well over 350 peer-reviewed scientific papers, invited reviews, abstracts, books, and book chapters in the areas of Synthetic Organic Medicinal and Natural Products Chemistry. She is the Managing Editor of the Wiley journal, Phytochemical Analysis. Her scientific profile has been published in every edition of the Marquis "Who's Who in the World" since 2009, and "Who's Who in Science and Engineering" since 2010.

Satyajit Sarker BPharm (Hons), MPharm, PhD, FHEA, is a Professor of Pharmacy, and the Director of School of Pharmacy and Biomolecular Sciences at Liverpool John Moores University, UK. He is the President of the Phytochemical Society of Europe, and the Editor-in-Chief of the Wiley journal, Phytochemical Analysis. He has over 520 publications to his credit. His scientific profile has been published in every edition of the Marquis "Who's Who in the World" since 2010.

<b>Lutfun Nahar, BSc (Hons), PhD, MRSC, FHEA,</b> is an Honorary Lecturer, and actively involved in research at the Faculty of Science at Liverpool John Moores University, UK. She has published well over 350 peer-reviewed scientific papers, invited reviews, abstracts, books, and book chapters in the areas of Synthetic Organic Medicinal and Natural Products Chemistry. She is the Managing Editor of the Wiley journal, <i>Phytochemical Analysis</i>. Her scientific profile has been published in every edition of the Marquis "Who's Who in the World" since 2009, and "Who's Who in Science and Engineering" since 2010.

<b>Satyajit Sarker BPharm (Hons), MPharm, PhD, FHEA,</b> is a Professor of Pharmacy, and the Director of School of Pharmacy and Biomolecular Sciences at Liverpool John Moores University, UK. He is the President of the Phytochemical Society of Europe, and the Editor-in-Chief of the Wiley journal, <i>Phytochemical Analysis</i>. He has over 520 publications to his credit. His scientific profile has been published in every edition of the Marquis "Who's Who in the World" since 2010.

Preface to the second edition xv

Preface to the first edition xvii

<b>Chapter 1: Introduction 1</b>

1.1 Role of Chemistry in Modern Life 1

1.2 Solutions and Concentrations 4

1.3 Suspension, Colloid and Emulsion 6

1.4 Electrolytes, Nonelectrolytes and Zwitterions 7

1.5 Osmosis and Tonicity 8

1.6 Physical Properties of Drug Molecules 10

1.6.1 Physical State 10

1.6.2 Melting Point and Boiling Point 10

1.6.3 Polarity and Solubility 11

1.7 Acid-Base Properties and pH 13

1.7.1 Acid-Base Definitions 14

1.7.2 Electronegativity and Acidity 18

1.7.3 Acid-Base Properties of Organic Functional Groups 19

1.7.4 pH, pOH and p<i>K</i><sub>a</sub> Values 22

1.7.5 Acid-Base Titration: Neutralization 30

1.8 Buffer and its Use 32

1.8.1 Common Ion Effects and Buffer Capacity 34

<b>Chapter 2: Atomic Structure and Bonding 37</b>

2.1 Atoms, Elements and Compounds 37

2.2 Atomic Structure: Orbitals and Electronic Configurations 39

2.3 Chemical Bonding Theories: Formation of Chemical Bonds 43

2.3.1 Lewis Structures 43

2.3.2 Resonance and Resonance Structures 47

2.3.3 Electronegativity and Chemical Bonding 48

2.3.4 Various Types of Chemical Bonding 49

2.4 Bond Polarity and Intermolecular Forces 54

2.4.1 Dipole-Dipole Interactions 54

2.4.2 van der Waals Forces 55

2.4.3 Hydrogen Bonding 56

2.5 Hydrophilicity and Lipophilicity 57

2.6 Significance of Chemical Bonding in Drug-Receptor Interactions 60

2.7 Significance of Chemical Bonding in Protein-Protein Interactions 63

2.8 Significance of Chemical Bonding in Protein-DNA Interactions 63

<b>Chapter 3: Stereochemistry 65</b>

3.1 Stereochemistry: Definition 66

3.2 Isomerism 66

3.2.1 Constitutional Isomers 66

3.2.2 Stereoisomers 67

3.3 Stereoisomerism of Molecules with More than One Stereocentre 82

3.3.1 Diastereomers and Meso Structures 82

3.3.2 Cyclic Compounds 84

3.3.3 Geometrical Isomers of Alkenes and Cyclic Compounds 85

3.4 Significance of Stereoisomerism in Determining Drug Action and Toxicity 88

3.5 Synthesis of Chiral Molecules 91

3.5.1 Racemic Forms 91

3.5.2 Enantioselective Synthesis 92

3.6 Separation of Stereoisomers: Resolution of Racemic Mixtures 93

3.7 Compounds with Stereocentres Other than Carbon 94

3.8 Chiral Compounds that Do Not Have Four Different Groups 94

<b>Chapter 4: Organic Functional Groups 97</b>

4.1 Organic Functional Groups: Definition and Structural Features 97

4.2 Hydrocarbons 100

4.3 Alkanes, Cycloalkanes and Their Derivatives 100

4.3.1 Alkanes 100

4.3.2 Cycloalkanes 108

4.3.3 Alkyl Halides 111

4.3.4 Alcohols 119

4.3.5 Ethers 125

4.3.6 Thiols 129

4.3.7 Thioethers 131

4.3.8 Amines 134

4.4 Carbonyl Compounds 140

4.4.1 Aldehydes and Ketones 140

4.4.2 Carboxylic acids 148

4.4.3 Acid Chlorides 154

4.4.4 Acid Anhydrides 155

4.4.5 Esters 157

4.4.6 Amides 160

4.4.7 Nitriles 163

4.5 Alkenes and their Derivatives 164

4.5.1 Nomenclature of Alkenes 165

4.5.2 Physical Properties of Alkenes 166

4.5.3 Structure of Alkenes 167

4.5.4 Industrial uses of Alkenes 167

4.5.5 Preparations of Alkenes 168

4.5.6 Reactivity and Stability of Alkenes 168

4.5.7 Reactions of Alkenes 169

4.6 Alkynes and their Derivatives 169

4.6.1 Nomenclature of Alkynes 170

4.6.2 Structure of Alkynes 170

4.6.3 Acidity of Terminal Alkynes 171

4.6.4 Heavy Metal Acetylides: Test for Terminal Alkynes 171

4.6.5 Industrial Uses of Alkynes 172

4.6.6 Preparations of Alkynes 172

4.6.7 Reactions of Alkynes 172

4.6.8 Reactions of Metal Alkynides 174

4.7 Aromatic Compounds and their Derivatives 174

4.7.1 History 175

4.7.2 Definition: Hueckel's Rule 175

4.7.3 General Properties of Aromatic Compounds 175

4.7.4 Classification of Aromatic Compounds 176

4.7.5 Pharmaceutical importance of Aromatic Compounds: Some Examples 177

4.7.6 Structure of Benzene: Kekule Structure of Benzene 179

4.7.7 Nomenclature of Benzene Derivatives 183

4.7.8 Electrophilic Substitution of Benzene 184

4.7.9 Alkylbenzene: Toluene 190

4.7.10 Phenols 192

4.7.11 Aromatic Amines: Aniline 199

4.7.12 Polycyclic Benzenoids 207

4.8 Importance of Functional Groups in Determining Drug Actions and Toxicity 209

4.8.1 Structure-Activity Relationships of Sulpha Drugs 210

4.8.2 Structure-Activity Relationships of Penicillins 211

4.8.3 Paracetamol Toxicity 213

4.9 Importance of Functional Groups in Determining Stability of Drugs 213

<b>Chapter 5: Organic Reactions 215</b>

5.1 Types of Organic Reactions Occur with Functional Groups 215

5.2 Reaction Mechanisms and Types of Arrow in Chemical Reactions 216

5.3 Free Radical Reactions: Chain Reactions 217

5.3.1 Free Radical Chain Reaction of Alkanes 217

5.3.2 Relative Stabilities of Carbocations, Carbanions, Radicals and Carbenes 219

5.3.3 Allylic Bromination 221

5.3.4 Radical Inhibitors 222

5.4 Addition Reactions 223

5.4.1 Electrophilic Additions to Alkenes and Alkynes 223

5.4.2 Symmetrical and Unsymmetrical Addition to Alkenes and Alkynes 226

5.4.3 Nucleophilic Addition to Aldehydes and Ketones 240

5.5 Elimination Reactions: 1,2-Elimination or ?-Elimination 254

5.5.1 E1 Reaction or First Order Elimination 255

5.5.2 E2 Reaction or Second Order Elimination 256

5.5.3 Dehydration of Alcohols 257

5.5.4 Dehydration of Diols: Pinacol Rearrangement 259

5.5.5 Base-Catalysed Dehydrohalogenation of Alkyl Halides 260

5.6 Substitution Reactions 265

5.6.1 Nucleophilic Substitutions 266

5.6.2 Nucleophilic Substitutions of Alkyl Halides 273

5.6.3 Nucleophilic Substitutions of Alcohols 276

5.6.4 Nucleophilic Substitutions of Ethers and Epoxides 282

5.6.5 Nucleophilic Acyl Substitutions of Carboxylic Acid Derivatives 286

5.6.6 Substitution Versus Elimination 293

5.7 Electrophilic Substitutions 294

5.7.1 Electrophilic Substitution of Benzene 294

5.8 Hydrolysis 300

5.8.1 Hydrolysis of Carboxylic Acid Derivatives 300

5.9 Oxidation-Reduction Reactions 305

5.9.1 Oxidizing and Reducing Agents 305

5.9.2 Oxidation of Alkenes 305

5.9.3 Oxidation of Alkynes 307

5.9.4 Hydroxylation of Alkenes 307

5.9.5 Oxidative Cleavage of <i>syn</i>-Diols 308

5.9.6 Ozonolysis of Alkenes 308

5.9.7 Ozonolysis of Alkynes 309

5.9.8 Oxidation of Alcohols 309

5.9.9 Oxidation of Aldehydes and Ketones 311

5.9.10 Baeyer-Villiger Oxidation of Aldehydes or Ketones 312

5.9.11 Reduction of Alkyl Halides 312

5.9.12 Reduction of Organometallics 312

5.9.13 Reduction of Alcohols via Tosylates 313

5.9.14 Reduction of Aldehydes and Ketones 313

5.9.15 Clemmensen Reduction 315

5.9.16 Wolff-Kishner Reduction 316

5.9.17 Reduction of Acid Chlorides 316

5.9.18 Reduction of Esters 317

5.9.19 Hydride Reduction of Carboxylic Acids 318

5.9.20 Reduction of Oximes or Imine Derivatives 318

5.9.21 Reduction of Amides, Azides and Nitriles 319

5.9.22 Reductive Amination of Aldehydes and Ketones 320

5.10 Pericyclic Reactions 320

5.10.1 Diels-Alder Reaction 320

5.10.2 Essential Structural Features for Dienes and Dienophiles 321

5.10.3 Stereochemistry of the Diels-Alder Reaction 322

5.10.4 Sigmatropic Rearrangements 323

5.10.5 Hydrogen Shift 323

5.10.6 Alkyl Shift: Cope Rearrangement 324

5.10.7 Claisen Rearrangement 324

<b>Chapter 6: Heterocyclic Compounds 327</b>

6.1 Heterocyclic Compounds and their Derivatives 327

6.1.1 Medicinal Importance of Heterocyclic Compounds 328

6.1.2 Nomenclature of Heterocyclic Compounds 329

6.1.3 Physical Properties of Heterocyclic Compounds 331

6.2 Pyrrole, Furan and Thiophene: Unsaturated Heterocycles 332

6.2.1 Physical Properties of Pyrrole, Furan and Thiophene 333

6.2.2 Preparations of Pyrrole, Furan and Thiophene 333

6.2.3 Reactions of Pyrrole, Furan and Thiophene 335

6.3 Pyridine 339

6.3.1 Physical Properties of Pyridine 339

6.3.2 Preparations of Pyridine 340

6.3.3 Reactions of Pyridine 340

6.4 Oxazole, Imidazole and Thiazole 342

6.4.1 Physical Properties of Oxazole, Imidazole and Thiazole 343

6.4.2 Preparations of Oxazole, Imidazole and Thiazole 344

6.4.3 Reactions of Oxazole, Imidazole and Thiazole 345

6.5 Isoxazole, Pyrazole and Isothiazole 346

6.5.1 Physical Properties of Isoxazole, Pyrazole and Isothiazole 348

6.5.2 Preparations of Isoxazole, Pyrazole and Isothiazole 348

6.5.3 Reactions of Isoxazole, Pyrazole and Isothiazole 348

6.6 Pyrimidine 349

6.6.1 Physical Properties of Pyrimidine 350

6.6.2 Preparations of Pyrimidine 350

6.6.3 Reactions of Pyrimidine 351

6.7 Purine 352

6.7.1 Physical Properties of Purine 353

6.7.2 Preparations of Purine 353

6.7.3 Reactions of Purine 353

6.8 Quinoline and Isoquinoline 354

6.8.1 Physical Properties of Quinoline and Isoquinoline 354

6.8.2 Preparations of Quinoline and Isoquinoline 355

6.8.3 Reactions of Quinoline and Isoquinoline 357

6.9 Indole 358

6.9.1 Physical Properties of Indole 359

6.9.2 Preparations of Indole 359

6.9.3 Reactions of Indole 360

6.9.4 Test for Indole 361

<b>Chapter 7: Nucleic Acids 363</b>

7.1 Nucleic Acids 363

7.1.1 Synthesis of Nucleosides and Nucleotides 365

7.1.2 Structure of Nucleic Acids 366

7.1.3 Nucleic Acids and Heredity 370

7.1.4 DNA Fingerprinting 373

7.2 Amino Acids and Peptides 373

7.2.1 Fundamental Structural Features of an Amino acid 376

7.2.2 Essential Amino Acids 376

7.2.3 Glucogenic and Ketogenic Amino Acids 377

7.2.4 Amino Acids in Human Body 377

7.2.5 Acid-Base Properties of Amino Acids 378

7.2.6 Isoelectric Points of Amino Acids and Peptides 378

<b>Chapter 8: Natural Product Chemistry 381</b>

8.1 Introduction to Natural Products 381

8.1.1 Natural Products 381

8.1.2 Natural Products in Medicine 382

8.1.3 Drug Discovery and Natural Products 385

8.2 Alkaloids 390

8.2.1 Properties of Alkaloids 391

8.2.2 Classification of Alkaloids 391

8.2.3 Tests for Alkaloids 410

8.3 Carbohydrates 410

8.3.1 Classification of Carbohydrates 411

8.3.2 Stereochemistry of Sugars 414

8.3.3 Cyclic Structures of Monosaccharides 415

8.3.4 Acetal and Ketal Formation in Sugars 416

8.3.5 Oxidation, Reduction, Esterification and Etherification of Monosaccharides 417

8.3.6 Pharmaceutical Uses of Monosaccharides 420

8.3.7 Disaccharides 420

8.3.8 Polysaccharides 423

8.3.9 Miscellaneous Carbohydrates 426

8.3.10 Cell Surface Carbohydrates and Blood Groupings 428

8.4 Glycosides 429

8.4.1 Biosynthesis of Glycosides 430

8.4.2 Classification 430

8.4.3 Test for Hydrocyanic Acid (HCN) 432

8.4.4 Pharmaceutical Uses and Toxicity 432

8.4.5 Anthracene/Anthraquinone Glycosides 433

8.4.6 Isoprenoid Glycosides 436

8.4.7 Iridoid and Secoiridoid Glycosides 440

8.5 Terpenoids 442

8.5.1 Classification 442

8.5.2 Biosynthesis of Terpenoids 443

8.5.3 Monoterpenes 445

8.5.4 Sesquiterpenes 446

8.5.5 Diterpenes 455

8.5.6 Triterpenes 461

8.5.7 Tetraterpenes 465

8.6 Steroids 466

8.6.1 Structures of Steroids 467

8.6.2 Stereochemistry of Steroids 468

8.6.3 Physical Properties of Steroids 468

8.6.4 Types of Steroid 469

8.6.5 Biosynthesis of Steroids 471

8.6.6 Synthetic Steroids 472

8.6.7 Functions of Steroids 473

8.7 Phenolics 476

8.7.1 Phenylpropanoids 477

8.7.2 Coumarins 478

8.7.3 Flavonoids and Isoflavonoids 481

8.7.4 Lignans 486

8.7.5 Tannins 489

Index 493

Chapter 1
Introduction


Learning Objectives


After completing this chapter, students should be able to

  1. describe the role of chemistry in modern life;
  2. define some of the physical properties of drugs, for example, melting point, boiling point, polarity, solubility and acid-base properties;
  3. explain the terms pH, pK a, buffer and neutralization.

1.1 ROLE OF CHEMISTRY IN MODERN LIFE


Chemistry is the science of the composition, structure, properties and reactions of matters, especially of atomic and molecular systems.

Life itself is full of chemistry, that is, life is the reflection of a series of continuous biochemical processes. Right from the composition of the cell to the whole organism, the presence of chemistry is conspicuous. Human beings are physically constructed of chemicals, live in a plethora of chemicals and are dependent on chemicals for their quality of modern life. All living organisms are composed of numerous organic substances. Evolution of life begins from one single organic compound called a nucleotide. Nucleotides join together to form the building blocks of life. Our identities, heredities and continuation of generations, all are governed by chemistry.

In our everyday life, whatever we see, use or consume have been the gifts of research in chemistry for thousands of years. In fact, chemistry is applied everywhere in modern life. From the colour of our clothes to the shapes of our PCs, all are possible due to chemistry. It has played a major role in pharmaceutical advances, forensic science and modern agriculture. Diseases and their remedies have also been a part of human lives. Chemistry plays an important role in understanding diseases and their remedies; that is, drugs.

Medicines or drugs that we take for the treatment of various ailments are chemicals, either organic or inorganic molecules. However, most drugs are organic molecules. These molecules are either obtained from natural sources or synthesized in chemistry laboratories. Some important drug molecules are discussed here.

Aspirin, an organic molecule, is chemically known as acetyl salicylic acid and is an analgesic (relieves pain), antipyretic (reduces fever) and anti-inflammatory (reduces swelling) drug. Studies suggest that aspirin can also reduce the risk of heart attack. It is probably the most popular and widely used analgesic drug because of its structural simplicity and low cost. Salicin is the precursor of aspirin. It is found in the willow tree bark, whose medicinal properties have been known since 1763. Aspirin was developed and synthesized in order to avoid the irritation in the stomach caused by salicylic acid, which is also a powerful analgesic, derived from salicin. In fact, salicin is hydrolysed in the gastrointestinal tract to produce D-glucose and salicyl alcohol (see Section 8.4). Salicyl alcohol, on absorption, is oxidized to salicylic acid and other salicylates. However, aspirin can easily be synthesized from phenol using the Kolbe reaction (see Section 4.7.10.6).

Paracetamol (acetaminophen), an N-acylated aromatic amine having an acyl group (R─CO─) substituted on nitrogen, is an important over-the-counter headache remedy. It is a mild analgesic and antipyretic medicine. The synthesis of paracetamol involves the reaction of p-aminophenol and acetic anhydride (see Section 4.7.10.6).

L-Dopa (L-3,4-dihydroxyphenylalanine), an amino acid, is a precursor of the neurotransmitters dopamine, norepinephrine (noradrenaline) and epinephrine (adrenaline), collectively known as catecholamines, and found in humans as well as in some animals and plants. It has long been used as a treatment for Parkinson's disease and other neurological disorders. L-Dopa was first isolated from the seedlings of Vicia faba (broad bean) by Marcus Guggenheim in 1913, and later it was synthesized in the lab for pharmaceutical uses.

Morphine is a naturally occurring opiate analgesic found in opium and is a strong pain reliever, classified as a narcotic analgesic (habit-forming) (see Section 8.2.2.5). Opium is the dried latex obtained from the immature poppy (Papaver somniferum) seeds. Morphine is widely used in clinical pain management, especially for pain associated with terminal cancers and post-surgery pain.

Penicillin V (phenoxymethylpenicillin), an analogue of the naturally occurring penicillin G (see Section 7.3.2), is a semisynthetic narrow-spectrum antibiotic useful for the treatment of bacterial infections. Penicillin V is quite stable even in high humidity and strong acidic medium (e.g. gastric juice). However, it is not active against beta-lactamase-producing bacteria. As we progress through various chapters of this book, we will come across a series of other examples of drug molecules and their properties.

In order to have proper understanding and knowledge about these drugs and their behaviour, there is no other alternative but to learn chemistry. Everywhere, from discovery to development, from production and storage to administration, and from desired actions to adverse effects of drugs, chemistry is directly involved.

In the drug discovery stage, suitable sources of potential drug molecules are explored. Sources of drug molecules can be natural, such as a narcotic analgesic, morphine, from P. somniferum (poppy plant), synthetic, such as a popular analgesic and antipyretic, paracetamol, and semisynthetic, such as penicillin V. Whatever the source is, chemistry is involved in all processes in the discovery phase. For example, if a drug molecule has to be purified from a natural source, for example, plant, the processes like extraction, isolation and identification are used, and all these processes involve chemistry (see Section 8.1.3.1).

Similarly, in the drug development steps, especially in pre-formulation and formulation studies, the structures and the physical properties (e.g. solubility and pH), of the drug molecules are exploited. Chemistry, particularly physical properties of drugs, is also important to determine storage conditions. Drugs having an ester functionality, for example, aspirin, could be quite unstable in the presence of moisture and should be kept in a dry and cool place. The chemistry of drug molecules dictates the choice of the appropriate route of administration. Efficient delivery of drug molecules to the target sites requires manipulation of various chemical properties and processes; for example, microencapsulation, nanoparticle-aided delivery and so on. When administered, the action of a drug inside our body depends on its binding to the appropriate receptor and its subsequent metabolic processes, all of which involve complex enzyme-driven biochemical reactions.

All drugs are chemicals, and pharmacy is a subject that deals with the study of various aspects of drugs. Therefore, it is needless to say that to become a good pharmacist the knowledge of the chemistry of drugs is essential. Before moving on to the other chapters, let us try to understand some of the fundamental chemical concepts in relation to the physical properties of drug molecules (see Section 1.6).

1.2 SOLUTIONS AND CONCENTRATIONS


A solution is a mixture where a solute is uniformly distributed within a solvent. A solute is the substance that is present in smaller quantities and a solvent usually the component that is present in greater quantity. Simply, a solution is a special type of homogenous mixture composed of two or more substances. For example, sugar (solute) is added to water (solvent) to prepare sugar solution. Similarly, saline (solution) is a mixture of sodium chloride (NaCl) (solute) and water (solvent). Solutions are extremely important in life as most chemical reactions, either in laboratories or in living organisms, take place in solutions.

Ideally, solutions are transparent and light can pass through the solutions. If the solute absorbs visible light, the solution will have a colour. We are familiar with liquid solutions, but a solution can also be in any state, such as solid, liquid or gas. For example, air is a solution of oxygen, nitrogen and a variety of other gases all in the gas state; steel is also a solid-state solution of carbon and iron. Solutes may be crystalline solids, such as sugars and salts that dissolve readily into solutions, or colloids, such as large protein molecules, which do not readily dissolve into solutions (see Section 1.3).

In Chemistry, especially in relation to drug molecules, their dosing, therapeutic efficacy, adverse reactions and toxicity, we often come across with the term concentration, which can simply be defined as the amount of solute per unit of solvent. Concentration is always the ratio of solute to solvent and it can be expressed in many ways. The most common method of expressing the concentration is based on the amount of solute in a fixed amount of solution where the quantities can be expressed in weight (w/w), in volume (v/v) or both (w/v). For example, a solution containing 10?g of NaCl and 90?g of water is a 10% (w/w) aqueous solution of NaCl.

Weight measure (w/w) is often used to express concentration and is commonly known as percent concentration (parts per 100), as shown in the previous example of 10% NaCl aqueous solution. It is the ratio of one part of solute to one hundred parts of...

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