Bioengineering Lecture 9: Structure-Activity Relationship

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Questions and Answers

What effect does the addition of an alkyl chain to barbiturates have on their activity?

Will not affect their activity

completely abolishes their activity

Increases their activity (correct)

Decreases their activity

How does the length of a carbon chain affect the bioactivity of barbiturates?

Longer chains decrease bioactivity due to high lipophilicity

Only chains of exactly 6 carbons are effective

Longer chains increase bioactivity by enhancing lipophilicity (correct)

There is no effect based on chain length

What is the effect of an alkyl chain longer than 6 carbons on barbiturate activity?

Decreases activity due to bulky structure (correct)

Has no impact on activity whatsoever

Enhances water solubility

Increases bioactivity significantly

What role do OH groups in RNA play?

Aid in catalysis Signup and view all the answers

What happens when too many alkyl chains are added to a barbiturate compound?

They abolish activity due to loss of water solubility Signup and view all the answers

What is the main purpose of understanding the structure-activity relationship (SAR)?

To determine the relationship between chemical structure and biological activity Signup and view all the answers

Which group addition in aliphatic compounds typically reduces biological activity?

Hydroxyl group (-OH) Signup and view all the answers

What effect does unsaturation have on the toxicity of compounds?

Increases toxicity with each unsaturation Signup and view all the answers

How does the presence of the amino group (-NH3) affect the toxicity of a compound?

It increases the overall toxicity Signup and view all the answers

What is the result of alkylation or acetylation on amino groups?

Reduces the toxicity of the amino group Signup and view all the answers

Which compound is an example of reduced toxicity through acetylation?

Aniline Signup and view all the answers

What is indicated by the term 'pharmacophore' in the context of bioactivity?

A chemical structure responsible for biological effects Signup and view all the answers

What biological activity change arises from adding an -OH group to aromatic compounds?

Enhances physiological activities Signup and view all the answers

In organizing compounds by toxicity, what order would you expect if comparing amines?

Most toxic: -NH3, -N, -NH, NH2 Signup and view all the answers

How can existing drugs be repurposed for improvement in biological activity?

By modifying their chemical structures through SAR Signup and view all the answers

Study Notes

Structure-Activity Relationship (SAR)

SAR defines the connection between a molecule's chemical structure and its biological activity.
Introduced by Crum-Brown and Fraser in 1865.
Identifies pharmacophores, key chemical groups eliciting biological effects.
Modifying chemical structures can alter the effectiveness or potency of bioactive compounds, aiding drug discovery and repurposing.

Pharmacophores and Biological Effects

Hydroxyl group (-OH):
- Reduces biological activity in aliphatic compounds: Hexanal (more toxic) vs. Glucose.
- Propanol (more toxic) vs. Glycerol (less toxic).
Aromatic Compounds:
- Hydroxyl groups can increase activity, differentiating between antiseptic and non-antiseptic properties.
Toxicity:
- Generally increases with more unsaturation in compounds: Propanol (less toxic) vs. Allyl alcohol (poisonous).

Effects of Functional Groups

Amino Group (-NH2):
- Naturally toxic but can be modified through alkylation or acetylation to reduce toxicity.
Example of reduced toxicity: Acetanilide produced via acetylation of aniline.

Barbiturates as Sedative Medicines

Structure involves pyrimidine and variations with hydroxy and alkyl groups.
Increasing the length of the alkyl chain enhances bioactivity by improving lipophilicity.
However, chains longer than six carbons may decrease activity due to bulky structures.

Bioactivity of Barbiturates

Addition of alkyl chains generally increases barbiturate activity, while excessive chains reduce water solubility, hindering effectiveness.
Addition of phenyl groups significantly enhances lipophilicity and, consequently, bioactivity.

RNA and Catalytic Functions

Unlike DNA, RNAs also serve as information carriers and have catalytic properties.
The presence of hydroxyl groups in RNA structure is critical for its catalytic function.

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Description

This quiz covers Lecture 9 of the Bioengineering course (BBL1020), focusing on the structure-activity relationship (SAR). It explores how the chemical structure of a molecule correlates with its biological activity, building on foundational concepts introduced by Crum-Brown and Fraser in 1865.