MEDCHEM E CHEM BIO LECTURE 2 Penicillin

• Penicillin


  The first antibiotic, discovered by chance in 1928 by Fleming
• Penicillin discovery


  1. Fleming studying Staphilococci

  2. Culture got contaminated by a mould

  3. Noticed bacteria not growing around mould

  4. Realised mould was producing a substance inhibiting bacterial growth

  5. Grew pure culture of Penicillium notatum mould

  6. Coined the term "penicillin"
• Pasteur, 1854: 'In the fields of observation chance favors only the prepared mind'
• Penicillin structure


  Elucidated in the 1940s by Dorothy Crowfoot Hodgkin using X-ray crystallography
• Penicillin synthesis


  1. Chemist John Sheehan completed the first total synthesis in the 1950s

  2. Methods not efficient for mass production

  3. Enabled synthesis of designed penicillins with superior activity
• Penicillin


  • β-lactam ring is essential for antibiotic activity
  • Structure is not planar, implications for reactivity
  • Resonance not possible in some parts due to non-planar structure

  
• Penicillin production


  • Based on culturing of the Penicillium mould
  • Understanding of Penicillium chrysogenum metabolic pathways essential for optimised industrial production
• Penicillin as a secondary metabolite


  Fungus will not produce antibiotics while growing, but will produce when growth is inhibited by stress
• Factors that inhibit Penicillin production 


  1. Synthesis pathway: α-ketoglutarate + AcCoA -> homocitrate -> L-α-aminoadipic acid -> L-Lysine + penicillin

  2. By-product L-Lysine inhibits homocitrate production (negative feedback) which is a precursor of penicillin
• Fed-batch culture is a technique for the penicillin cells growth


  Produce nutrient stress throughout the fermentation process the critical nutrient is added at intervals so that it is always in short supply, forcing the micro-organism to continually produce the antibiotic
• Factors monitored and controlled in penicillin production: carbon sources (: glucose inhibits penicillin, whereas lactose does not), pH level, nitrogen level, Lysine level, Phosphate level, and oxygen availability.
• Penicillin extraction


  1. Liquid medium pumped out, filtered and concentrated after 6-8 days

  2. Basic antibiotic precipitated as crystals

  3. May be modified by micro-organisms or chemically before formulation
• Isolate


  A single strain (pure culture) of organism from a particular source
• Screening programme


  Many experiments, testing lots of strains to see if they work or not
• Penicillin structure


  • Strained β-lactam ring
  • Carboxylic acid
  • Fused 4- and 5-membered ring systems
  • Amide side-chain
  • Cis-stereochemistry
• 1. APA


  • Acquired through enzymatic hydrolysis of Penicillin G or Penicillin V, or through organic synthesis
  • Allows synthesis of many semisynthetic penicillin derivatives
• Prodrugs


  Ester prodrugs like pivampicillin developed to improve bioavailability of parent drug
• Penicillin V

  Natural penicillin antibiotic administered orally, more resistant to inactivation by gastric acid
• Ampicillin


  Broad spectrum semi-synthetic antibiotic that can be administered orally, acid resistant

  
• β-lactamases (penicillinase)


  Enzymes produced by some bacteria that provide antibiotic resistance by breaking the β-lactam ring structure trough hydrolysis. Solution: Development of antibiotica that are b-lactamase resistant, Steric hindrance at a certain position in a molecule may slow down or prevent reactions at that position, due to the presence of the bulky surrounding groups.
• Flucloxacillin


  Development of β-lactamase resistant antibiotics, with bulky side chains that prevent enzyme access to the lactam ring
• Penicillin molecules

  • Molecule b) is more resistant to hydrolysis by β-lactamase due to the bulky side chain that sterically hinders enzyme access
• How might mutations be encouraged?


  Mainly: RADIATIONS, we mutate the DNA, se colpisci con radiazioni il dna diventa mutato. But also with more stress
• What is meant by a screening programme?


  Many experiments, testing lots of strains to see if they work or not. So: collect from different part and analisys
• What is meant by an isolate?


  a single strain (pure culture) of organism from a particular source
• Why is the liquid stirred?


  to dissolve oxygen, mix contents (even distribution of nutrients, mould, waseat)
• For what purpose is air pumped in?


  oxygen dissolves so aerobic respiration occurs, leading to efficient growth
• Why must the air be sterile?


  so that no bacteria or other microorganisms get in
• Why is the temperature monitored?


  to prevent overheating - inefficient / kills Penicillium
• How is the temperature controlled?


  by pumping cold water into jacket /varying throughput - carries away heat
• How is the temperature controlled?

  by pumping cold water into jacket /varying throughput - carries away heat
• Why is the pH monitored?


  to prevent buildup of excess acid (e.g.), leading to adverse pH. ( ther is a optimal Ph for the mould to growt, and to not distroid the penicillin)
• How is the pH controlled?


  additions of base / acid. (ph to high or low the substances can become acidic.)
• What is the diagram beside showing?


  (the antibiotic production starts only at a certain point, when i havestressed enogh my mould.)
• The production process still relies on fungal fermentation based on biological principles, although modern strains are much more productive than the early strains. This has been achieved through screening programmes involving isolates from different sources, and treatment to encourage mutations.
• Penicillin redesign Problems:


  Antibiotic resistance, sensitivity to acid, limited breath of activity
• the b-lactam ring is very stretched, is subject to hydrolysis, gives reactivity to the molecule, which is unstable and reactive.
• the cell wall is continuosly riformed by enzymes
• total synthesis= from strach.


  semisinthesys= start from a precursor
• The b-lactam ring is unstable and extremely reactive, It can react with water under acidic conditions, causing the opening of the ring.