19th Century Synthetic Organic Chemistry

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Questions and Answers

What was the primary goal of synthetic organic chemistry during the 19th century?

To identify the structures of active constituents in naturally derived medicinals and synthesize more effective agents.

Who conducted early studies on the relationship between chemical structure and biologic activity in 1869?

Crum-Brown and Fraser.

What specific chemical groups were shown to exhibit muscle relaxant activity?

Tertiary amine groups, when converted to quaternary ammonium compounds.

How did the understanding of molecular structures help in creating new drugs?

<p>It provided insights into the mechanistic action of components, allowing for the synthesis of more efficacious agents.</p> Signup and view all the answers

What was the significance of determining the molecular structures of complex mixtures?

<p>It was believed to enhance the understanding of how the components worked biologically.</p> Signup and view all the answers

What compound was identified as an analgesic in relation to molecular structure studies?

<p>Morphine.</p> Signup and view all the answers

What is N-Methylmorphine, and how is it related to the structure of morphine?

<p>N-Methylmorphine is a derivative of morphine that exhibits muscle relaxant properties.</p> Signup and view all the answers

What was the assumption made regarding the synthesis of new drugs based on molecular structure?

<p>Synthesis of drugs based on molecular structure was assumed to lead to more efficacious agents.</p> Signup and view all the answers

What happens to an acidic functional group when it loses a proton?

<p>It becomes negatively charged and is referred to as the 'ionized' form of the acid.</p> Signup and view all the answers

How does the ionized form of an acidic functional group enhance water solubility?

<p>It participates in ion-dipole interactions with water, increasing solubility.</p> Signup and view all the answers

What is the significance of understanding the relative acid–base strength of functional groups?

<p>It helps predict absorption, distribution, excretion, and potential drug incompatibilities.</p> Signup and view all the answers

In the context of ciprofloxacin, which functional group is significantly ionized at pH 1.0 to 3.5?

<p>The alkylamine functional group is significantly ionized.</p> Signup and view all the answers

What occurs when a basic functional group is converted to its conjugate acid?

<p>The basic functional group becomes ionized.</p> Signup and view all the answers

Why is an appreciation for the pKa value important in pharmacology?

<p>It describes the relative acid–base strength of functional groups, impacting drug behavior.</p> Signup and view all the answers

What defines a molecule as amphoteric?

<p>A molecule is described as amphoteric when it can act both as an acid and a base.</p> Signup and view all the answers

How does the structure of ciprofloxacin exemplify the concept of amphotericity?

<p>Ciprofloxacin contains functional groups that can donate or accept protons, demonstrating both acidic and basic properties.</p> Signup and view all the answers

What defines a Brönsted-Lowry acid?

<p>A Brönsted-Lowry acid is any substance that can yield a proton (H+).</p> Signup and view all the answers

How is a conjugate base formed according to Brönsted-Lowry theory?

<p>A conjugate base is formed when an acid donates a proton to a base.</p> Signup and view all the answers

In the equation CH3COOH + H2O ⇌ CH3COO− + H3O+, identify the acid and base.

<p>In this equation, CH3COOH (acetic acid) is the acid, and H2O (water) is the base.</p> Signup and view all the answers

What role does water play in the Brönsted-Lowry acid-base reactions presented?

<p>Water can act as a base by accepting a proton and forming hydronium ion (H3O+).</p> Signup and view all the answers

What type of functional groups in ciprofloxacin contribute to acidic and basic character?

<p>Ciprofloxacin contains carboxylic acid (acidic) and secondary/tertiary amines (basic).</p> Signup and view all the answers

What happens to a base in a reaction when it accepts a proton?

<p>When a base accepts a proton, it is converted into its conjugate acid.</p> Signup and view all the answers

Describe the condition under which ciprofloxacin behaves as both an acid and a base.

<p>Ciprofloxacin can act as both an acid and a base depending on the pH of the physiological environment.</p> Signup and view all the answers

What is the significance of functional groups in understanding the acid-base properties of molecules?

<p>Functional groups determine whether a molecule can donate or accept protons, influencing its acid-base behavior.</p> Signup and view all the answers

What is the pKa range for arylamines and what is their ionized form?

<p>The pKa range for arylamines is 9-11, and their ionized form is arylammonium.</p> Signup and view all the answers

Identify the pKa range for aromatic amines and their conjugate acid.

<p>The pKa range for aromatic amines is 5-6, and their conjugate acid is aromatic ammonium.</p> Signup and view all the answers

What is the ionized form of imines and their corresponding pKa?

<p>Imines have a pKa range of 3-4, and their ionized form is iminium.</p> Signup and view all the answers

What is the pKa range for alkylamines and what do they ionize to?

<p>Alkylamines have a pKa range of 10-11 and ionize to form alkylammonium.</p> Signup and view all the answers

Explain the relationship between amidine and its conjugate acid.

<p>Amidine has a pKa range of 10-11, and its conjugate acid is amidinium.</p> Signup and view all the answers

What is the pKa and the ionized form of guanidine?

<p>Guanidine has a pKa range of 12-13 and ionizes to form guanidinium.</p> Signup and view all the answers

Which is the strongest acid mentioned and how does it compare to OH−?

<p>The strongest acid mentioned is H3O+, which is stronger than OH−.</p> Signup and view all the answers

List the conjugate acid form of arylamine and its pKa range.

<p>The conjugate acid form of arylamine is arylammonium, with a pKa range of 9-11.</p> Signup and view all the answers

What is the relationship between pKa and the strength of an acid or base?

<p>The magnitude of the pKa value indicates the relative strength of an acid or base; lower pKa values correspond to stronger acids.</p> Signup and view all the answers

How can the Henderson-Hasselbalch equation be used to determine percent ionization at a specific pH?

<p>The Henderson-Hasselbalch equation relates pKa, pH, and the ratio of the concentrations of the acid and base forms to calculate percent ionization.</p> Signup and view all the answers

At a pH of 7.4, what can be predicted about the ionization of a compound with a pKa of 8.0?

<p>The compound will be predominantly in its ionized (base) form since the pH is lower than the pKa.</p> Signup and view all the answers

What percentage of amobarbital is ionized at a pH of 7.4 if its pKa is 8.0?

<p>At a pH of 7.4, 79.9% of amobarbital is in the acid form.</p> Signup and view all the answers

Why is it necessary to know the pKa value of functional groups when predicting ionization?

<p>Knowing the pKa values allows for the prediction of the ionization state of functional groups at a specific pH.</p> Signup and view all the answers

What does an increase in pH beyond the pKa value signify for an acid's ionization?

<p>An increase in pH beyond the pKa value generally signifies that the acid will become more ionized.</p> Signup and view all the answers

If a compound is found to have 4.98 units as the total concentration, what does this imply about the ratio of acid to base forms?

<p>This implies that the concentration of the acid form is 3.98 units and the base form is 1 unit.</p> Signup and view all the answers

What is the significance of the ratio of acidic to conjugate base forms in understanding chemical behavior in solution?

<p>This ratio helps determine the relative concentrations of different forms, impacting the compound’s solubility and reactivity.</p> Signup and view all the answers

Identify two functional groups present in Zyrtec and Tavist and explain their impact on the drug's ability to cross the blood-brain barrier.

<p>Zyrtec contains a carboxylic acid and an ether group, while Tavist has a hydroxyl group and an amine. The presence of the polar groups can limit their lipophilicity, affecting their ability to cross the blood-brain barrier.</p> Signup and view all the answers

Which of the two agents, Zyrtec or Tavist, is more water soluble and why?

<p>Zyrtec is more water soluble than Tavist due to the presence of a carboxylic acid group that can ionize and form hydrogen bonds with water.</p> Signup and view all the answers

How does the salt form of codeine phosphate compare to its free base form in terms of water solubility?

<p>The salt form of codeine phosphate is more water soluble than the free base form because it can ionize and interact more effectively with water.</p> Signup and view all the answers

Explain the consequence of mixing aqueous solutions of Zyrtec and Tavist in the same IV bag from an acid-base perspective.

<p>Mixing Zyrtec and Tavist may lead to a potential acid-base reaction, altering the pH, which can affect the solubility and stability of both drugs.</p> Signup and view all the answers

What is the role of hydrogen bonding in the absorption of Patanol into ocular membranes?

<p>Hydrogen bonding allows Patanol to interact with the dipole-rich membranes surrounding the eye, facilitating its absorption.</p> Signup and view all the answers

Discuss the structural properties that contribute to the water solubility of the hydrochloride salt form of Patanol.

<p>The hydrochloride salt form of Patanol increases its water solubility due to the positive charge from the protonated amine, promoting ion-dipole interactions with water.</p> Signup and view all the answers

What functional group modification would enhance the hydrogen bonding capability of an eye drop formulation like Patanol?

<p>Introducing additional hydroxyl groups or amine groups would enhance the hydrogen bonding capability of the formulation.</p> Signup and view all the answers

Based on their structural characterization, predict whether Zyrtec or Tavist would more likely cause drowsiness. Provide a rationale.

<p>Zyrtec is more likely to cause drowsiness due to its ability to cross the blood-brain barrier more readily than Tavist, attributed to its structural properties.</p> Signup and view all the answers

Flashcards

Revolution in Synthetic Organic Chemistry

The process of identifying the structures of active ingredients in natural medicines and creating synthetic versions of these medications with hopefully better effects.

Structure-Activity Relationship (SAR)

The study of the relationship between the chemical structure of a molecule and its biological effects on living organisms.

Functional Group

A group of atoms within a molecule that has a specific function or characteristic.

Tertiary Amine

A nitrogen-containing compound with three alkyl groups attached to the nitrogen atom.

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Quaternary Ammonium Compound

A nitrogen-containing compound with four alkyl groups attached to the nitrogen atom.

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Muscle Relaxant

A compound that relaxes muscles, often by interfering with nerve signals.

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Biologic Activity

The ability of a molecule to bind to a specific biological target, such as a protein or enzyme, and elicit a biological response.

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Analgesic

A compound known to relieve pain.

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Brønsted-Lowry Acid

Any substance capable of donating a proton (H+).

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Brønsted-Lowry Base

Any substance capable of accepting a proton (H+).

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Conjugate Base

The species formed when an acid loses a proton.

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Conjugate Acid

The species formed when a base gains a proton.

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Amphoteric Molecule

A molecule containing multiple functional groups with acid-base properties, capable of acting as both an acid and a base depending on the pH.

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pH Dependence of Acid-Base Properties

The ability of a molecule to act as an acid or a base depends on the pH of the environment.

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Acid-Base Strength

The relative strength of an acid or base can be determined by its ability to donate or gain protons respectively.

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pKa

The pH at which a molecule or ion is 50% protonated and 50% deprotonated.

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Strongest Base

In a solution, the strongest base will be the species that is most likely to accept a proton (H+).

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Strongest Acid

In a solution, the strongest acid will be the species that is most likely to donate a proton (H+).

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What is a Functional Group?

A group of atoms within a molecule that has a specific function or characteristic. Examples include amines, amides, ketones, and carboxylic acids.

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What is a Tertiary Amine?

These are nitrogen-containing compounds with three alkyl groups attached to the nitrogen atom.

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What is a Quaternary Ammonium Compound?

These are nitrogen-containing compounds with four alkyl groups attached to the nitrogen atom.

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What is a Muscle Relaxant?

These are compounds that relax muscles, often by interfering with nerve signals. They can be used to treat muscle spasms, spasticity, and other conditions.

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What is Biologic Activity?

This refers to the ability of a molecule to bind to a specific biological target, such as a protein or enzyme, and elicit a biological response.

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What is an Analgesic?

These are compounds known to relieve pain.

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Acidic Functional Group

The ability of a molecule to donate a proton (H+) to a solution, making the solution more acidic.

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Ionized Acid

A negatively charged form of an acidic functional group when it loses a proton.

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Basic Functional Group

The ability of a molecule to accept a proton (H+) from a solution, making the solution more basic.

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Ionized Base

A positively charged form of a basic functional group when it gains a proton.

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Water Solubility

The ability of a compound to interact with water molecules through hydrogen bonding.

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Blood-brain barrier

A biological barrier that prevents many molecules from passing from the bloodstream into the brain.

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Lipophilicity

The ability of a drug to pass through lipid membranes, such as cell membranes.

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Salt formation

The process of transforming a drug containing a basic amine group into its salt form by adding an acid.

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Drug affinity

The ability of a drug to bind to a specific target in the body, such as a receptor or enzyme.

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Drug efficacy

The ability of a drug to elicit a biological response, such as reducing inflammation.

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Percent Ionization

The ratio of the protonated (acidic) and deprotonated (basic) forms of a molecule.

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Henderson-Hasselbalch Equation

A mathematical equation that relates the pKa of a molecule, the pH of its surroundings, and the ratio of its acidic and basic forms.

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pKa and Ionization

A molecule with a pKa value of 8.0 will be 50% ionized at a pH of 8.0, and the ionization will increase as the pH increases.

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Acid-Base Ratio

The concentration of a molecule in its acidic form divided by the concentration of the molecule in its base form.

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Ionization

The process of a molecule gaining or losing a proton (H+).

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Acidity and Basicity

The ability of a molecule to donate or accept a proton (H+).

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Study Notes

Drug Design and Relationship of Functional Groups to Pharmacologic Activity

  • Medicinal chemistry is an interdisciplinary science that blends organic chemistry, biochemistry, computational chemistry, pharmacology, pharmacognosy, molecular biology, and physical chemistry. It focuses on the identification, design, synthesis, and development of new drugs for humans and animals.
  • It studies how chemical structure influences biological activity, including the mechanism of action and the physicochemical properties that affect drug absorption, distribution, metabolism, toxicity, and elimination (pharmacokinetics) and the drug's effects on the body (pharmacodynamics).
  • Structure-activity relationships (SARs) are crucial for drug design. Researchers systematically manipulate molecular structures to determine how changes affect biological activity.
  • Functional groups play a significant role in drug design, influencing a molecule's overall physicochemical properties and biological activity.
  • Understanding acid-base properties is fundamental to medicinal chemistry. Acid-base properties influence drug absorption, excretion, and interactions with other drugs in solution.

Relationship Between Molecular Structure and Biological Activity

  • Early studies by Crum-Brown and Fraser (1869) demonstrated the connection between chemical structure and biologic activity. They observed that molecules with quaternary ammonium groups often exhibited muscle relaxant activity.
  • The concept of "one chemical group giving one biological action" was later disproven by the discovery of acetylcholine, a compound with multiple biologic actions.
  • Ehrlich's concept of receptor theory, modifying earlier suggestions, was crucial to understanding a drug's action on a host organism. Ehrlich theorized that specific chemical groups on cell surfaces ("side-chains") bind with drugs similarly to how dyes bind cells leading to selective toxicity toward specific diseases.
  • This theory emphasized the importance of understanding how a drug's structure interacts with its target—a principle central to medicinal chemistry.
  • Compounds' structure can determine whether it will be an agonist or antagonist to a specific receptor or enzyme.

Physicochemical Properties of Drugs

  • Drugs are mostly dissolved in water within the human body.
  • Understanding acid-base behaviours of compounds is crucial in medicinal chemistry, with the Brønsted-Lowry theory commonly used to explain acid and base behaviour. A drug's acid-base properties influence its absorption, excretion, and interactions with other drugs.
  • The water solubility of a drug directly affects its administration route, absorption, distribution, and excretion. Hydrogen bond formation and ionization of functional groups influence a molecule's water solubility.
  • Calculation of percent ionization using the Henderson-Hasselbalch equation is a necessary method for elucidating which form of the drug will be present in a given pH. This is critical information in predicting distribution, absorption, and excretion.

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