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Medicinal chemistry > Dugga 3 Antibiotics > Flashcards

Dugga 3 Antibiotics Flashcards

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1
Q

What are the five main targets if antibacterial agents?

A

Cell metabolism, the cell wall, the plasma membrane, protein synthesis, nucleic acid function

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2
Q

What do sulphonamides require to function?

A

Primary aromatic amine group and a secondary sulphonamide group for good activity

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3
Q

What is a common metabolic reaction of sulphonamides?

A

N-acetylation

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4
Q

What are sulphonamides used for?

A

Treating infections of urinary tract, gastrointestinal tract and mucous membranes. Also in eye lotion

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5
Q

Which structure is sulphonamides similar to?

A

PABA para amino benzoic acid which is necessary for bacteria to bind to an enzyme to synthesise dihydroteroate. They act as a competitive inhibitor

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6
Q

What are sulphonamides an example of? (Which class of antibiotic is it?)

A

Antimetabolite, antibacterial agent that act against cell metabolism

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7
Q

Give 3 examples of antimetabolites

A

Sulphonamides, trimethoprim, sulphones

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8
Q

Give examples of antibacterial agents that inhibit cell wall synthesis

A

Penicillin

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9
Q

What is the structure of penicillin? How does it react?

A

Bicycling with a beta lactam ring fused to a thiazolidone ring. The beta lactam ring reacts irreversibly with the transpeptidase enzyme that cross links the bacterial cell wall.

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10
Q

How can penicillin be made more resistant to acid conditions?

A

By incorporating an electron withdrawing group into the acyl side chain

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11
Q

How can penicillin be protected from beta lactamase enzymes?

A

By adding steric shields

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12
Q

What structure gives the penicillin broad spectrum activity?

A

The alpha hydrophilic group on the acyl side chain

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13
Q

What are prodrugs of penicillin useful for? Which structures are used?

A

Masking polar groups to imported the absorption from GI tract. Extended esters are used

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14
Q

What groups does penicillin contain?

A

A highly unstable bicyclic system of a strained four membered beta lactam ring fused to a five membered thiazolidine ring

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15
Q

What amino acids does the skeleton structure of penicillin suggest to be derived from?

A

Cysteine and valine

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16
Q

Benzylpenicillin (Penicillin G) cannot be taken orally, why?

A

It is broken down by stomach acids and must be injected

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17
Q

Benzylpenicillin is ineffective against which types of bacteria?

A

Gram negative and those that produce beta lactamase

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18
Q

What does penicillin target?

A

The enzyme transpeptidase, responsible for interlinking during cell wall synthesis

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19
Q

What is the bacteria cell wall made up of?

A

Peptidoglycan structure made up of NAM and NAG

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20
Q

Penicillin has a conformation similar to the transition state conformation of what moiety during crosslinking?

A

D-Ala-D-Ala

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21
Q

Do bacteria have both D and L amino acids?

A

Bacteria have racemase that can convert L amino acids into D amino acids

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22
Q

What is the most important way bacteria gain resistance to penicillin?

A

Beta lactamase enzymes

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23
Q

Most if not all Gram negative bacteria produce what that makes them more resistant to penicilin?

A

Beta lactamase enzymes

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24
Q

What was originally the only way to prepare different penicillins?

A

By varying fermentation conditions

25
Q

Which methods are used now to produce different penicillins?

A

Semi synthesis

26
Q

What is the SAR of penicillin?

A

The beta lactam ring is essential
Free carboxylic acid essential (usually ionised and penicillins administered as sodium salts)
Bicyclic system
6-acyl-amino side chain
Sulphur usual but not essential
Stereochemistry of the bicyclic ring with respect to the acylamino side chain important

27
Q

Why is penicillin G acid sensitive?

A

Ring strain
Highly reactive beta lactam carbonyl group
INfluence of the acyl side chain

28
Q

How can penicillin be made acid resistant?

A

Placing an electron withdrawing group in the side chain to draw electrons away from carbonyl oxygen and reduce the tendency to act as a nuclephile

Penicillin V has an electronegative O on the acyl side chain and can be given orally

29
Q

How are beta lactamase resistant penicillin made?

A

Steric shield, adding a bulky group on the side chain (but not too bulky so the penicillin couldn’t bind target)
Nafcillin and Temocilin (reserve troops)

30
Q

What are broad spectrum penicillins?

A

Having activity against both gram positive and negative bacteria

31
Q

What is used as first line of defense against infection?

A

Ampicillin and amoxicillin

32
Q

Mention three types of broad spectrum penicillins

A

Ueridopenicillin, aminopenicillin and carboxypenicillin

33
Q

Mention another type of antibiotic than penicilin

A

Cephalosporin, it has a similar bicyclic system with a four membered ring and then a six membered ring

34
Q

What advantages do first generation cephalosporins have over penicillin?

A

Greater stability to acid conditions (stomach) and resistance towards beta lactamases and effective against both gram negative and positive, but lower activity

35
Q

How can semi-synthetic cephalosporins be prepared?

A

From 7-ACA (aminocephalosporanic acid)

36
Q

How is 7-ACA obtained?

A

From hydrolysis of cephalosporins

37
Q

What type of cephalosporins have increased potency?

A

Oximinocephalosporins

38
Q

What other beta lactam antibiotics exist?

A

Carbapenems, monobactams

39
Q

What are beta lactamase inhibitors and what are they used for?

A

Given together with antibiotics such as penicillin, they inhibit the beta lactamase enzymes so that the penicillin will work

40
Q

Mention two beta lactamase inhibitors

A

Avibactam and Clavulanic acid

41
Q

Mention other classes of antibacterial agents that act on the biosynthesis of the cell wall, besides penicillin and cephalosporins

A

Vanomycin, D-cycloserine and bacitracin

42
Q

How does vancomycin work?

A

It is a glycopeptide that binds to the building blocks for cell wall synthesis preventing incorporation of the blocks into the cell wall

43
Q

What antibacterial agents are the last resort against drug resistant bacterial strains?

A

Glycopeptides such as vancomycin

44
Q

How does valinomycin and gramicidin work against bacteria?

A

They are ion-conducting antibiotics (ionophores) and allow uncontrolled movement of ions across the call membrane

45
Q

Are cyclic lipopeptides a new class of antibiotics?

A

Yes

46
Q

Do valinomycin and gramicidin A show selective toxicity for bacterial cells over mammalian cells?

A

No and therefore useless as systemic therapeutic agents

47
Q

How do antibacterial agents that impair protein synthesis show selectivity for bacterial cells over mammalian?

A

Because bacterial cells have a 70S bacterial ribosome consisting of 30S subunit and 50S subunit. Mammals have 80S consisting of 60S and 40S.

48
Q

Give an example of an antibacterial agent working in disrupting protein synthesis

A

Streptomycin (aminoglycoside), tetracyclines, chloramphenicol, macrolides, lincosamides, streptogramins, oxazolidinones, pleuromutilins

49
Q

Why has widespread resistance to tetracyclines occured?

A

Because they have been used in farming to promote growth of newborn animals

50
Q

Give an example of an antibacterial agents that act on nucleic acid transcription and replication

A

Quinolones and fluoroquinolones
Aminoacridines
Rifamycins
Nitroimidazoles and nitrofurantoin

51
Q

How do quinolones work?

A

They inhibit topoisomerase enzymes which means replication and transcription is inhibited

52
Q

How do aminoacridines work?

A

They intercalate with bacterial DNA and hinder replication and transcription

53
Q

How do rifamycins work?

A

They inhibit the enzyme RNA polymerase and prevent RNA synthesis which prevents protein synthesis

54
Q

What are nitoimidazoles used for?

A

Infections caused by protozoa and anaerobic bacteria

55
Q

How is drug resistance transfered by genetic transfer?

A

Transduction or conjugation

56
Q

How does transduction work?

A

Plasmids transfered by bacteriophages with gene for resistance

57
Q

Are some bacterial strains quicker to gain resistance than others?

A

Yes

58
Q
A

Medicinal chemistry (10 decks)

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