Options (Choose One) - Medicinal chemistry

The Therapeutic Index ($TI$) measures a drug's relative safety. For humans, $TI = \frac{TD_{50}}{ED_{50}}$, where $TD_{50}$ is the toxic dose for $50\%$ of the population and $ED_{50}$ is the minimum effective dose for $50\%$ of the population.

Bioavailability is the fraction of the administered dosage that reaches the target part of the human body. Factors affecting it include method of administration, solubility (hydrophobicity/hydrophilicity), and functional groups.

Aspirin (acetylsalicylic acid) is synthesized by reacting salicylic acid with ethanoic anhydride: $C_7H_6O_3 + C_4H_6O_3 \rightarrow C_9H_8O_4 + C_2H_4O_2$. Recrystallization is used for purification.

Penicillins contain a beta-lactam ring (a four-membered ring including a nitrogen atom). It works by irreversibly inhibiting the transpeptidase enzyme, preventing bacterial cell wall synthesis.

Strong analgesics (opiates) like morphine, codeine, and diamorphine (heroin) work by binding to opioid receptors in the brain, blocking pain signals. Diamorphine is more potent than morphine as it is less polar, allowing it to cross the blood-brain barrier more easily.

Stomach pH regulation involves antacids like $Mg(OH)_2$ or $Al(OH)_3$ which neutralize excess $HCl$. $H_2$-receptor antagonists (e.g., ranitidine) and Proton Pump Inhibitors (e.g., omeprazole) reduce the production of stomach acid.

Antiviral drugs like Oseltamivir (Tamiflu) and Zanamivir (Relenza) work as neuraminidase inhibitors, preventing the virus from escaping the host cell to infect others.

Taxol is a chiral drug used in cancer treatment. Its synthesis requires a chiral auxiliary, which is a chiral molecule that binds to the starting material to force the reaction to follow a specific stereochemical path, producing only the desired enantiomer.

Nuclear Medicine uses radioisotopes. Technetium-$99m$ ($^{99m}Tc$) is commonly used in medical imaging due to its short half-life ($t_{1/2} \approx 6$ hours) and emission of low-energy gamma ($\gamma$) radiation.