Discovery and Development of Penicillin

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Discovery and Development of Penicillin

• The idea that moulds or fungi could be used to
  treat wounds extends back at least to Greek and
  Roman times and remained popular into the 20th
  century.
• In 1876, the physicist John Tyndall noted that
  Penicillium moulds killed some types of bacteria.
• In 1877, Pasteur noticed that some airborne
  organisms prevented the growth of anthrax
  bacteria, and realised that these facts may,
  perhaps, justify the greatest hope from the
  therapeutic point of view.
• Over the succeeding decades, several scientists
  observed the effect of Penicillium on bacteria,
  but none pursued this finding.
• The term antibiosis was coined by Jean-Paul
  Vuillemin in 1889 to describe the fight for
  survival between two living organisms. By 1928
  there were several hundred scientific papers on
  this subject.

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Discovery of penicillin

• Alexander Fleming, a Scottish doctor working in
  St Marys Hospital in London had a long-standing
  interest in antibacterial substances and was
  acutely aware of the need to discover much more
  effective agents.
• As a result of a highly improbable series of
  events in July 1928, he noticed that a colony of
  the mould Penicillium notatum was causing
  staphylococcus cells to undergo lysis (bursting)
  (see the actual culture plate below). Unlike
  others who had made similar observations, Fleming
  realised the potential of this phenomenon.

• He named the substance that killed the bacteria
  penicillin, and he demonstrated that it was
  highly effective against a range of pathogenic
  bacteria. However, he found that penicillin was
  quite unstable, and that it seemed unlikely to be
  useful in vivo. He was unable to make further
  progress.
• Others attempted to develop his work but were
  thwarted by the difficulty of isolating
  penicillin and by its instability.

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Development of penicillin

• In 1938 and 1939, Professor Howard Florey, an
  Australian physiologist who was Head of the
  School Pathology in Oxford, and Dr Ernst Chain, a
  German chemist in the same School surveyed the
  literature on antibiosis and decided to focus
  on Penicillium notatum in their efforts to find
  new antibacterial agents.
• As World War II began in Europe, Chain and Norman
  Heatley, an English biochemist, worked on the
  problems of (i) finding optimum conditions for
  the growth of the mould, and (ii) finding
  techniques for isolating the chemically sensitive
  active principle, penicillin.
• Despite the difficulties of working in wartime,
  they made great advances and by May 1940 they had
  enough crude penicillin to test it. On May
  25/26th they injected virulent streptococci into
  eight mice. Four of the mice were treated with
  penicillin, they other four were the control
  group. Within 12 hours the controls were all
  dead, the four who had been given penicillin
  survived. The Oxford group knew they were on the
  verge of a momentous development.
• That same morning, the evacuation of Dunkirk
  began Great Britains future had never looked so
  bleak.

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First tests of penicillin

• Heroic efforts by the Oxford group produced
  enough penicillin to test on patients in early
  1941. The first patient was terminally ill, but
  she did not suffer any adverse reaction
  penicillin was not toxic.
• The second patient was dying of septicaemia,
  after a scratch on his face became infected.
  Sulfonamides did not help, but penicillin brought
  about a dramatic improvement. Unfortunately, the
  course of treatment did not completely eradicate
  the pathogens, and when he suffered a relapse
  there was no more penicillin available and the 43
  year old patient died.

• The third patient was four-and-a-half-year-old
  Johnny Cox. Some measles spots on his left
  eyelid became infected and that led to formation
  of a blood clot in a vein behind his eye. When
  admitted to hospital the doctor predicted that
  he would be in his grave in three days.

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First tests of penicillin, contd.

• Johnny was put on an intravenous penicillin drip.
  He improved steadily and within a week he was
  talking and playing.
• A week later he suffered a major setback, and
  despite receiving more penicillin he died a few
  days later.
• However, an autopsy showed that the infection had
  nearly been cleared, and that Johnny had died as
  a result of a ruptured aneurysm in a weakened
  artery.

• The next two patients, a boy and a baby, were
  both cured.
• It was clear that penicillin was far more
  effective than any previous antibacterial drug
  a revolution in human health was about to begin.
• Full scale development of penicillin was achieved
  in the USA and by the end of WWII, it had already
  saved many thousands of lives.

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Dont forget
Ernst Chain 1906-1979 Nobel Prize 1945
Norman Heatley 1911-2004
Howard Florey 1898-1968 Nobel Prize 1945
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2. Structure Reactivity

• What is the chemical structure of the drug that
  started the antibiotic era? The structure was
  unexpected and was finally determined by X-ray
  crystallography.
• The active compound obtained from Penicillium
  notatum was called penicillin G. The key feature
  of this structure is a b-lactam ring an amide
  contained within a four-membered ring. Other
  features are
• A fused five membered ring containing sulfur
• A carboxylic acid group attached to the
  five-membered ring
• An acylamino side chain attached to the b-lactam.

Before we can understand how penicillin works, we
need to take a closer look at the structures of
organic compounds.
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2.1 Shapes of molecules, VSEPR

• The first aspect that we need to consider is the
  shapes of molecules. The geometrical arrangement
  of bonds around the atoms determines the shape of
  molecules
• For the elements in the second row of the
  periodic table, e.g. carbon, nitrogen and oxygen,
  the bond angles are determined by one factor
  repulsion between pairs of electrons.
• Valence Shell Electron Pair Repulsion (VSEPR)
  theory predicts that the pairs of valence shell
  electrons around an atom will be arranged as far
  apart as possible so as to minimise electronic
  repulsions between them.
• Bonding pairs and lone pairs will both cause
  repulsions, so the shape will depend on the total
  number of pairs of electrons.
• However, the two pairs of a double bond or the
  three pairs of a triple bond are all in the same
  region of space so they count as only one pair.

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VSEPR in action
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VSEPR in action
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Shapes of organic molecules tetrahedral carbon

• When carbon has four single bonds, it has a
  tetrahedral shape the four bonding pairs point
  to the corners of a tetrahedron, because thats
  the furthest apart they can get. Ethane is a
  simple example. Each carbon atom is at the
  centre of a (virtual) tetrahedron, with the four
  atoms to which it is bonded occupying the corners
  of the tetrahedron, and all the bond angles are
  approximately 109. Remember that ordinary
  bonds ( ) are in the plane of the paper,
  wedged bonds ( ) are projecting out of the
  paper and dashed bonds ( ) are projecting
  behind the plane.

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Shapes of organic molecules trigonal carbon

• When carbon atoms have one double bond (and 2
  single bonds), they are trigonal, i.e. the carbon
  and the three atoms to which it is attached are
  all in the same plane, and the bond angles are
  approximately 120. This is because two of the
  bonding pairs form one double bond and so are
  aligned with each other. Thus there are
  effectively three pairs of electron that get as
  far apart as possible.
• Ethene (ethylene), acetone (CH3COCH3) and benzene
  are examples

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2.2 Shapes of molecules chiral centres and
chirality

• A tetrahedral carbon that has four different
  groups attached to it, is termed a chiral centre.
  Penicillin G contains three chiral centres (in
  red below).
• There are two different ways of arranging four
  groups around a tetrahedral carbon. This gives
  rise to two different structures, that are
  stereoisomers, isomers that differ only in the
  arrangement of atoms in space
• The particular 3D orientation of atoms around a
  chiral centre is called its configuration.
• Most (but not all) molecules that contain chiral
  centres are chiral, i.e. they are not
  superimposable on their mirror images.
  Penicillin G is a chiral molecule.

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Chirality, contd.

• There are two possible structures for chiral
  molecules, that differ only in the
  three-dimensional orientation of the atoms in
  space. The two possible mirror-image forms are
  called enantiomers.
• Many biomolecules, e.g. amino acids and sugars,
  are chiral. They, like penicillin G, occur in
  enantiomerically pure form in living organisms,
  i.e. only one enantiomer is formed in
  biosynthesis.
• Enantiomers often have different biological
  activity, e.g. often only one enantiomeric form
  of a chiral drug will have the desired
  therapeutic activity, because only that one will
  fit the target biomolecule which is itself
  chiral. This is analogous to a hand fitting into
  a glove.

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Shape of Penicillin

• For simplicity, lets look at the shape of
  6-aminopenicillanic acid, a derivative lacking
  the side chain. Note the tetrahedral and
  trigonal carbons, the pyramidal nitrogen and the
  angular sulfur. Note also the butterfly shape
  of the fused ring system.

Tetrahedral
Angular
Pyramidal
Trigonal