Chemistry of antibiotics Flashcards

1
Q

Beta lactam ring

A

Mimics d-ala-d-ala dipeptide in crosslinking

Ring is highly strained making it electrophilic

Forms a stable acyl-enzyme complex and removes nucleophile. This is irreversible inhibtion

High conc of antibiotic leads to less lysis called the ‘eagle phenomenon’

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2
Q

3 forms of resistance against b-lactams

A

Target modification- results in MRSA

Amidases- removes penicillin side chain

Beta lactamases

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3
Q

Beta-lactamase

A

Uses serine/cysteine residue to form acyl-enzyme complex which inactivates the drug

Evolved from PBP’s and B-lactamases are TEM 1 and 2

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4
Q

4 classes of b-lactamase

A

A-penicillinase (TEM 1/2)
B-metallo b lactamase
C-cephalosporins
D- extended spectrum b lactamases

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5
Q

New antibiotic discovery

A

Natural product screening

Manipulate biosynthetic pathways to make semisynthetic antibiotics-change penicillin branching

Engineering biosynthetic pathways using genetic techniques

6-aminopenicillanic acid used to make semi synthetic

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6
Q

Cephalosporins

A

Binds to pbp’s

Used when there is resistance to penicillin and made from penicillin n

Cephalexin preferred due to almost complete absorption despite lower antibacterial activity

Most cephalosproins given orally are cephalexin derivatives

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7
Q

overcoming b lactamase

A

modify drug

coadmin blocking antibiotic

suicide inhibitor- becomes a reactive species that inactivates b lactamase

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8
Q

Examples of irreversible b lactamase inhibitors

A

Sulbactam
6 b bromopenicillin
thienamycin
clavulanic acid (with amoxacillin it is co amoxiclav) does not work on class b,c,d

Not effective in vitro due to difficulty crossing biological membranes

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