Chapter 4 — Case Study 1: Reading a Drug Label — The Vocabulary in Practice

How the functional-group vocabulary of this chapter shows up on the drug label of a prescription bottle.

1. The problem

Pick up any prescription medication from a pharmacy. Turn the bottle over. You will see several names: a brand name (the trademarked marketing name — Lipitor, Zoloft, Advil), a generic name (the official medical name — atorvastatin, sertraline, ibuprofen), and an IUPAC chemical name usually in small print. The three names tell you three different things, at three different levels of chemistry.

This case study walks through the different naming systems using five common medications as examples, showing how the vocabulary of Chapter 4 maps onto real drugs.

2. Five drugs, five naming systems

Acetaminophen (Tylenol)

• Brand name: Tylenol (US), Panadol (international).
• Generic name (US): Acetaminophen. (International: paracetamol.)
• Chemical name: N-(4-hydroxyphenyl)acetamide.

The chemical name is a complete recipe. The parent compound is acetamide ($CH_3-C(=O)-NH_2$). Its nitrogen bears a 4-hydroxyphenyl substituent — a phenyl ring with a hydroxyl at the para (4-) position. You can draw the structure from the name alone.

Functional groups: amide, phenol, aromatic ring. That is the whole molecule.

Ibuprofen (Advil, Motrin)

• Brand name: Advil, Motrin, Nurofen.
• Generic name: Ibuprofen.
• Chemical name: (2RS)-2-[4-(2-methylpropyl)phenyl]propanoic acid.

The chemical name again gives you everything. Parent compound is propanoic acid ($CH_3CH_2COOH$). Position 2 bears a substituent: a phenyl ring at position 4 of which is the 2-methylpropyl (i.e., isobutyl) group. The 2RS prefix tells you the molecule is a racemate: the chiral center at position 2 exists as both enantiomers.

Functional groups: carboxylic acid, aromatic ring, branched alkyl. No heteroatom beyond the carboxylate oxygens.

Sertraline (Zoloft)

• Brand name: Zoloft.
• Generic name: Sertraline.
• Chemical name: (1S,4S)-4-(3,4-dichlorophenyl)-N-methyl-1,2,3,4-tetrahydronaphthalen-1-amine.

Now the complexity ramps up. Parent compound is a tetrahydronaphthalenamine (a partially reduced naphthalene — two fused six-membered rings, one aromatic, with an amine substituent at position 1). At position 4 sits a dichlorophenyl group. The amine is N-methylated (N is the nitrogen of the amine, methylated with a single methyl group).

Functional groups: secondary amine (NHCH₃), aromatic ring (two of them), alkyl, two aryl chlorines.

Notice: the chemical name now requires knowing what "tetrahydronaphthalenamine" is — ring-system nomenclature, which is more than this book covers. Appendix H handles ring-system nomenclature. For now, recognize that even complicated drug names follow systematic rules.

Atorvastatin (Lipitor)

• Brand name: Lipitor.
• Generic name: Atorvastatin.
• Chemical name: (3R,5R)-7-[2-(4-fluorophenyl)-3-phenyl-4-(phenylcarbamoyl)-5-(propan-2-yl)-1H-pyrrol-1-yl]-3,5-dihydroxyheptanoic acid.

This is the chemical name of one of the best-selling drugs ever made. It has twelve words and four distinct stereocenter designators. Reading it requires knowing about pyrroles (five-membered aromatic N-heterocycle), carbamoyl groups (an amide written in substituent form), and standard alkyl substituent names.

Functional groups: carboxylic acid, two hydroxyls, one amide (written as phenylcarbamoyl), pyrrole (aromatic heterocycle), three phenyl rings (one with a para-fluorine), an isopropyl. Roughly ten functional groups in one molecule.

Sildenafil (Viagra)

• Brand name: Viagra.
• Generic name: Sildenafil.
• Chemical name: 5-[2-ethoxy-5-(4-methylpiperazin-1-yl)sulfonyl-phenyl]-1-methyl-3-propyl-6H-pyrazolo[4,3-d]pyrimidin-7-one.

Another long name. It reveals: the molecule is a pyrazolopyrimidinone (a fused bicyclic heterocycle with multiple nitrogens), bearing a substituted phenyl group that itself carries an ether (ethoxy), a sulfonyl, and a piperazine (a six-membered ring with two nitrogens). Plus methyl, propyl, and the core carbonyl.

Functional groups: ketone, aromatic heterocycles (two), piperazine (aliphatic heterocycle), sulfonyl (R-SO₂-R'), ether, amines. Many groups in a small molecule.

3. The pattern

Every one of these drugs, regardless of its complexity, has a chemical name that follows IUPAC rules. You can — with enough practice and Appendix H — read the name and draw the structure.

The level of detail varies. Some chemical names fit in ten characters; some run to forty words. The rule is the same: parent compound, substituents with locants, stereochemistry indicators.

More importantly, every drug can be analyzed functionally-group-by-functionally-group. Its physical properties (solubility, melting point, lipophilicity) are determined by the functional groups. Its chemical reactivity (stability in acid, susceptibility to hydrolysis, metabolism by liver enzymes) is determined by the functional groups. Its pharmacological activity (binding to the target, affinity, specificity) is determined, in large part, by the geometry and electronic properties of the functional groups.

The vocabulary of Chapter 4 is, in a real sense, the vocabulary of medicinal chemistry.

4. Why common names persist

Look at the five drug-name pairs above. In each case, the generic name is short, pronounceable, and memorable. The chemical name is precise but verbose.

The generic name is what the pharmacist dispenses. The chemical name is what appears on the patent, in the USP monograph, in the scientific paper that first published the synthesis. Different purposes, different names.

Most everyday chemical work uses either common names (aspirin, acetic acid, glycerol, caffeine) or semi-systematic names (ibuprofen, atorvastatin). The fully systematic IUPAC names are reserved for the situations where precision matters. A medicinal chemist talking to a colleague says "the Lipitor analog" or "the 4-fluorophenyl-substituted version," not the full IUPAC. A patent attorney writes the IUPAC name because any ambiguity could cost millions of dollars.

Learn the functional-group vocabulary well enough that common names are transparent to you ("ethyl acetate is an ester, so it probably has a fruity smell and is a common solvent") and IUPAC names are readable (you can reconstruct the structure in your head from the name). That is the working skill.

5. Looking ahead

Chapter 5 begins using the functional-group vocabulary you have just learned. Alkane nomenclature appears in every conformational analysis. Alcohols appear in thermodynamic discussions. Carbonyls introduce the first reaction energetics.

Chapter 6 uses functional-group vocabulary spectroscopically: a $C=O$ has a characteristic IR absorption around 1700 cm⁻¹; an $N-H$ stretches around 3350 cm⁻¹; an aromatic ring has characteristic bands near 1600 and 1500 cm⁻¹. Identifying functional groups by their IR signatures is half of what spectroscopy is.

Every chapter of Part II and beyond will assume the Chapter 4 vocabulary. If the functional-group table is not yet memorized, now is the time. It is the kind of memorization that pays back disproportionately for the rest of the book.

Further reading. International Union of Pure and Applied Chemistry (2013). Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names. Royal Society of Chemistry. The official rule book; available online. Hawley's Condensed Chemical Dictionary (current edition, Wiley). Look up any drug or chemical by common name to find its IUPAC name and vice versa.