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Chemistry HL > Medicinal Chemistry > Flashcards

Medicinal Chemistry Flashcards

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1
Q

Drug

A

substance that affects bodily processes

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2
Q

What do drugs alter?

A
  • alters incoming sensory emotions
  • alters mood or emotions
  • alters physiological state, including consciousness, activity level or co-ordination
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3
Q

Therapeutic index for animals

A

the lethal dose of a drug for 50% of the population divided by the minimum effective dose for 50% of the population

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4
Q

Therapeutic index for humans

A

is the toxic dose for 50% of the population divided by the minimum effective dose for 50% of the population

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5
Q

Therapeutic window

A

the range of dosages between the minimum amount of the drug that produce the desired effect and a medically unacceptable adverse effect

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6
Q

Bioavailability

A

is the fraction of the administered dosage that reaches the target part of the human body

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7
Q

Type of parenteral drug administrations

A
  1. subcutaneous - beneath the skin, slow e.g. dental injections
  2. intra-muscular - into muscles, for use when immediate response is not required, e.g. vaccinations
  3. intravenous - directly into the blood stream, virtually instantaneous effect
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8
Q

Blood-brain barrier

A

the capillaries in the brain are denser and prevent diffusion
this is fortunate as many medications are unable to pass this barrier and hence do not affect the neurons

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9
Q

What does drug action depend on?

A

is determined by their ability to bind to a specific receptor in the body
this binding prevents or inhibits normal biological activity
the better the fit of the drug the greater the activity

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10
Q

Factors that influence a drugs bioavailability

A
  1. polarity - water solubility is important for circulation in the blood but lipid solubility helps in the passage of the drug through membranes during absorption
  2. administration - most effective way is intravenous injection, oral administration can lead to destruction in stomach acid
  3. functional groups - acid -base groups in particular, pKa and pKb values of these groups in the molecule will determine the charges carried on the drug at different pH values and therefore its reactivity and solubility parts on body
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11
Q

Steps in development of synthetic drugs

A
  • identification of the need
  • identification of the structure of the drug
  • the possible methods of synthesis
  • extraction and the yield
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12
Q

Side-effects

A

unwanted responses
no drug exerts a single effect
to achieve the main effect, the side-effects must be tolerated

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13
Q

Tolerance

A

over time with regular use, a user needs increasing amounts of a drug to achieve the original biological effect
this leads to a reduced therapeutic window

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14
Q

Dependence/addiction

A

occurs when a patient becomes dependent on the drug in order to feel normal and suffers from withdrawal symptom if the drug is not taken

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15
Q

Analgesics

A

drugs that relieve pain without causing a loss of consciousness
they function by intercepting the pain stimulus at the source, often by interfering with the production of substances (e.g. prostaglandins) that cause pain, swelling or fever
the type of analgesic used depends on the severity of the pain
mild analgesics are used for mild pain e.g. aspirin
strong analgesics are used for severe pain e.g. morphine

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16
Q

Synthesis of aspirin

A

salicylic acid is reacted with ethanoic acid anhydride (rather than ethanoic acid to produce a good yield) in the presence of an acid catalyst (H2SO4 or H2PO4)
aspirin (acetyl salicylic acid) + ethanoic acid is formed
this process is esterification (condensation reaction)
this product can be recrystallised (dissolving the impure crystals in hot ethanol, as this solution is cooled the solubility of aspirin decreases and it crystallises out of solution first ) from hot water to obtain pure aspirin

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17
Q

How can the purity of aspirin be tested?

A

melting point determination
pure aspirin has a melting point of 138-140 degrees celsius
salicylic acid has a melting point of 159 degrees celsius
a mixture would have a lower and less well-defined melting point

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18
Q

Bioavailability of aspirin

A

although aspirin is slightly polar due to the COOH group it is not very soluble in water
its bioavailability is increased by increasing its solubility in water
this involves reacting aspirin with an alkali such as NaOH so that it forms an ionic salt

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19
Q

How does aspirin work?

A

prevents the enzyme prostaglandin synthase being formed at the site of injury or pain
this enzyme is responsible for the synthesis of prostaglandins which produce fever and swelling and transmission of pain from the site of injury to the brain

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20
Q

Advantages of aspirin

A

pain relief
anti-inflammatory
anticoagulant (preventing blood clotting)
prophylactic (preventative for some bowl cancers)

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21
Q

Disadvantages of aspirin

A

can cause stomach upset due to acidic nature
has a synergistic effect with alcohol (meaning that it can cause increased bleeding and increased risk of ulcers)
some people have allergies
accidental poisoning in infants

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22
Q

Antibiotics

A

drugs that inhibit the growth, or kill microorganisms that cause infectious diseases
these drugs are selective; they only act against bacterial cells not human cells

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23
Q

Penicillans

A

are antibiotics produced by fungi

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24
Q

Structure of penicillan

A

considered as a dipeptide formed from two amino acids, cysteine and valine
the molecule contains a nucleus of a 5-membered ring attached to a four-membered ring containing a cyclic amide group, known as the beta-lactam ring
this consists of one nitrogen and three carbon atoms and is the part of the molecule which is responsible for its antibacterial properties

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25
Q

How do beta-lactam antibiotics work?

A

the bond angles of the ring are reduced to around 90 degrees despite that they have sp2 and sp3 hybridised orbitals (which seek bond angles of 120 and 109.5 degrees)
this puts a strain on the bonds, weakening them (ring strain) meaning that it breaks easily
the action of these antibiotics is to disrupt the formation of cell walls of bacteria by inhibiting the transpeptidase enzyme
as the drug approaches the enzyme, the high reactivity of the amide group in the ring causes it to bind irreversibly near the active site of the enzyme as the ring breaks
by inactivating this enzyme the cell wall construction is blocked (as it prevents polypeptide cross-links from forming)
without these links the cell wall is unable to support the bacterium and so bursts and dies

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26
Q

Antibiotic resistance

A

bacteria can become resistant as a result of mutation
resistant bacteria produce an enzyme penicillinase or beta-lactamase which can open penicillan’s for membered ring and render it inactive
by exposure to the antibiotic, as this wipes out the non-resistant strains it gives the resistant strains competitive advantage

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27
Q

Responses to antibiotic resistance

A
  • the synthesis of different forms of penicillan which are able to withstand the action of penicillinase. These include methicillin which has been replaced by oxacillin due to the spread of MR bacteria
    these still have the beta-lactam ring but have modified side chains which prevent the binding of the penicillinase enzyme and so protect the ring from cleavage before it finds the target
  • control and restriction of the use of antibiotics
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28
Q

Why does antibiotic resistance occur?

A
  • not completing a full course of antibiotics as exposure to small amounts of antibiotic allow naturally drug-resistant bacteria to survive, reproduce and spread
  • overuse
  • use in animal feeding stocks as healthy animals are given antibiotics to prevent disease but the antibiotics are passed through the meat and dairy therefore increasing the development of resistant bacteria
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29
Q

How do strong analgesics work?

A

they temporarily bind to opioid receptors in the brain which blocks the transmission of impulses between brain cells that signal pain
they interfere with the perception of pain without depressing the CNS
they may cause changed in behaviour or mood due to them affecting the brain
therefore they must enter the brain an pass through the blood-brain barrier (made primarily of lipids)
for a drug to pass through this they must be non-polar and lipid soluble

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30
Q

Morphine

A

used in the management of severe pain
can be habit forming and can lead to dependence so its use must be regulated by a medical professional
is the principle drug derived from opium
the two OH groups in morphine give it some polarity which limits its ability to cross the blood-brain barrier

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31
Q

Codeine

A

sometimes used in a preparation with a non-narcotic drug so is in the second stage of pain management
is found at low levels in opium but is more commonly prepared from morphine
it is therefore semi-synthetic
this reaction converts one of the -OH groups into the methyl ether so this process is methylation
this change makes codeine less polar so it can cross the blood-barrier better
however, this conversion causes a significant drop in the binding at opioid receptors and so codeine is weaker than morphine

32
Q

Opiates

A

natural narcotic analgesics that are derived from the opium poppy

33
Q

Diamorphine (heroin)

A

produced from morphine by an esterification reaction in which both -OH groups are converted into ethanoate (ester) groups by a reaction with ethanoic acid or ethanoic anhydride
this reduces the polarity significantly making diamorphine much more lipid soluble so is much more able to cross the blood-brain barrier leading to it being the fastest acting (also meaning it has greater side-effects)

34
Q

Side effects of strong analgesics

A
  • constipation
  • suppression of cough reflex
  • constriction of the pupil in the eye
  • narcotic effects
  • weight gain/loss
  • loss of libido
  • theft/prostitution to fund habit
35
Q

Narcotic effects and addiction

A

in the short term heroin induces a feeling of euphoria
but relatively quickly heroin users start to show dependence so they cannot function properly without the drug and suffer from withdrawal symptoms therefore to experience the same feelings of euphoria higher doses need to be taken
heroin is normally dealt on an illegal market and can bring about social problems and crime
helping heroin addicts is difficult and sometimes the alternate analgesic methadone is administered

36
Q

Conditions caused by excess stomach acid and solutions to these conditions

A

acid indigestion
heartburn
ulceration

dyspepsia - feelings of pain and discomfort in the upper abdomen
treatments include:
- antacids to instantly neutralise the acid
- H2 receptor anatagonists which block the histamine - H2 interaction
- proton pumps inhibitors which inhibit the production of stomach acid

37
Q

Antacids

A

are weak bases which neutralise excess acid such as metal oxides, hydroxides, carbonates or hydrogen carbonates
metal hydroxides: calcium hydroxide, magnesium hydroxide and aluminium hydroxide. These neutralise acid with the formation of a salt and water
magnesium salts tend to be faster acting but aluminium compounds dissolve more slowly meaning that they are longer lasting
Mg salts act as a laxative and Al salts cause constipation

metal carbonates/metal hydrogen carbonates: sodium carbonate and sodium hydrogen carbonate. These neutralise HCl with formation of salt, water and carbon dioxide
the gas formed can cause bloating
to reduce this antifoaming agents are added
some antacids also contain alginates which float to the top of the raft to act as a barrier

38
Q

H2-receptor antagonists - Ranitidine (zantac)

A

when the stomach wall is stimulated by the presence of food and distension, histamine is released
in the stomach it stimulates the secretion of stomach acid by interacting at receptors known as H2 (not hydrogen gas) which are in the parietal cells in the gastric glands
this histamine interaction initiates a sequence of events leading to the release in acid
blocking the histamine-H2 receptor interaction reduces the amount of acid produced
drugs that do this and which compete with histamine for binding are known as H2-receptor antagonists
ranitidine (Zantac) is an example of this

39
Q

Proton pump inhibitors

A

in the last step of gastric acid secretion, the parietal cells in the gastric glands pump protons across their membranes and into the lumen
for each H+ pumped into the lumen one K+ ion is pumped into the opposite direction so there is no charge build up (this is active transport)
the enzyme used in this process is H+/K+ ATPase or simply a gastric proton pump
drugs which inhibit the proton pump will directly prevent the release of acid
e.g. Prilosec and esomeprazole (nexium)

40
Q

Viruses

A

contain only a protein and nucleic acid (either RNA or DNA)
have no cellular structure and are only capable of reproducing inside another living cell
therefore, they are not classified as living organisms and are more difficult to target with drugs than bacteria as they live inside host cells
they also reproduce very quickly and are often spread throughout the organism by the time that symptoms appear
they mutate quickly => changes their susceptibility to drugs

41
Q

Flu - hemagglutinin (H)

A

is a glycoprotein that enables the viral particle to “dock” with the host cell before it enters

42
Q

Flu - neuraminidase (N)

A

is an enzyme that catalyses a cleavage reaction which allows new viral particles to escape from the host cell and spread infection
it binds to its reactant sialic acid
good target for drug design
drug inhibitors such as oseltamivir and zanamivir have a similar structure to that of sialic acid

43
Q

AIDS

A

acquired immune deficiency syndrome caused by human immunodeficiency virus (HIV)
HIV primarily affects white blood cells
it is difficult to fight because:
- the virus destroys helper T cells, the very cells in the immune system that should be defending the body against the virus
- the virus mutates very rapidly
- the virus often lies dormant within host cells

progress has been made in the development of specific antiretroviral drugs. Although these do not cure the virus they give lasting supression.

44
Q

How do antiretroviral drugs work?

A

they target and disrupt the following different stages in the HIV life cycle:
- binding and fusion of the virus to the receptor on the CD4 cell membrane
- reverse transcription of viral RNA to DNA in the host cell
- integration of viral DNA into the host chromosome
- release of new viral particles by budding from the host cell surface

45
Q

High level waste (HLW)

A

is waste that gives off large amounts of ionizing radiation for a long time
disposal is complex because the products of decay are often radioactive themselves and continue to emit radiation
usually it is stored under water in reinforced cooling ponds for 5 to 10 years and then transferred to dry storage in shielded structures

46
Q

Low level waste (LLW)

A

is waste that gives off small amounts of ionizing radiation for a short time
disposal usually involves first interim storage in sealed containers that are safe, secure and environmentally sound, the radioactivity typically decays in hours or days and the waste can then be disposed of normally

47
Q

Green chemistry

A

seeks to reduce the footprint of chemical manufacturing processes while improving product and environmental safety

48
Q

Solvent waste

A

drug synthesis is often complex and involves multiple steps hence organic solvents are often used
these may be toxic and are often left over at the end of synthesis
disposal of solvents often involves incineration which can release toxins into the environment
chlorinated compounds, ethers and many aromatic compounds are considered problematic
principles of green chemistry:
use of safer solvents and avoid use of auxiliaries when possible as well as to prevent waste

49
Q

Antibiotic waste

A

improper drug disposal can lead to antibiotic resistance
expired, unused antibiotics are frequently discarded by households and medical profession which can lead to contamination of the ground and drinking water supplies

50
Q

Obtaining the Tamiflu precursor

A

oseltamivir (tamiflu) is an antiviral that lessens the spread of virus within the body by preventing the release of new viral particles from their host cells
the drug has attracted attention as it is the only orally administered antiviral that may be effective in cases of the H5N1 flu
the key precursor for the synthesis of Tamiflu is shikimic acid
this is found in low concentrations in many plants but Chinese star anise the the favoured source but the lengthy process of extracting it only results in low yields
there have been active efforts in discovering alternate sources for the shikimic acid some of which use green chemistry:
- production of shikimimate from fermentation reactions of genetically engineered bacteria
- the harvesting of shikimate from the needles of several varieties of pine trees. Even though yields are quite low, the needles represent a plentiful source.

51
Q

Chiral molecules

A

have two mirror image forms, known as enantiomers
although the two enantiomers have identical chemical properties they can react differently with the enzymes and receptors in the body

52
Q

Biological synthesis - enantiomers

A

biological synthesis within cells produce only one enantiomeric form
so when a drug is harvested from a natural source such as morphine from opium seed, only a single enantiomer is obtained

53
Q

Chiral auxiliaries

A

are optically active substances that are temporarily incorporated into an organic synthesis so that it can be carried out asymmetrically with the selective formation of a single enantiomer

54
Q

Synthetic synthesis - enantiomers

A

when drugs are produced by synthetic processes they yield mixtures of enantiomers known as racemate
drug companies have to find out the physiological properties of each enantiomer before determining whether the drug can be marketed in the racemic mixture or as a single enantiomer

55
Q

Taxol

A

is a drug commonly used to treat several different forms of cancer (breast + ovarian mainly)
naturally occurs in yew trees (using bark caused controversy about the environmental impact) but is now commonly synthetically produced

56
Q

Synthesis of taxol

A

taxol is very chiral with 11 chiral centres
this means it can exist in a large range of enantiomers which may have different effects on the body (which may be harmful)
only one enantiomer has the desired effect - isolating this is possible but difficult and produces a lot of waste
therefore the single enantiomer can be produced using asymmetric synthesis (using chiral auxiliary)
this binds to the reactant and blocks the reaction site through steric hindrance ensuring that the next step in the reaction can only take place from one side
once the specific enantiomer of the new product has been set the auxiliary can be taken off and recycled
this only produces a low yield though
a more efficient process uses the extraction of the compound which is related to Taxol from the needles and leaves of yew trees from Europe and Himalayans (this causes less damage to tree)
this related compound is chemically modified to form taxol (semi-synthetic process)

57
Q

How can enantiomers be identified?

A

using a polarimeter
this instrument measures the rotation of plane polarised light by the optically active compound using an analyser

58
Q

Side effects of radiation

A

side effects can vary from person to person
external radiotherapy tends to cause more side effects than localised targeted radiotherapy
- hair loss
- nausea
- tiredness
- skin disorders
- loss of appetite
- damage to DNA in surrounding healthy cells
- sterility
note: MRI uses low energy radio waves so is safe

59
Q

What is ionizing radiation?

A

radioactivity is known as ionising radiation as it has enough energy to interact with an atom and cause the removal of electrons so the atom becomes ionised

60
Q

Half life

A

time taken for the mass of a reactant to decrease to half of its original value
it is a first order reaction
rate = k[N]

61
Q

Use of technetium -99m in diagnostic nuclear medicine

A

mostly used to moniter kidney function
this is a metastable iostope
has a half life of 6 hours (its biological half life is 1 day)
it emits gamma radiation which can be detected by conventional x-ray equipment
the decay product of Tc-99m is Tc-99 which emits beta radiation (which has a much lower rate of energy release compared to gamma - and has a longer half life)
hence due to this and the fact that it does not remain in the body long the benefits outweigh the risks

62
Q

PET (positron emission tomography)

A

type of scanner that gives 3D images of tracer concentration in the body
the radionuclide contains a positron-emitting tracer and is injected into the patients body where it accumulates in the target tissue
positrons are emitted from the tracer and these combine immediately with electrons, releasing energy as gamma rays
detection of gamma rays by camera enables their origin to be precisely determined
a common tracer is F-8 (which is bonded to glucose - the uptake of glucose between healthy and cancer cells is different hence this difference is visible on the scan)

63
Q

MRI (magnetic resonance imaging)

A

is an application of nuclear magnetic resonance (NMR) spectroscopy and so uses the fact that hydrogen atoms have a magnetic movement due to their odd number of protons
in the presence of a powerful magnet, radio waves are used to generate an electronic signal that can be decoded to produce 2D or 3D images
MRI is useful in the diagnosis of living tissue because hydrogen atoms are present in water
it does not use ionising radiation and is considered relatively non-invasive
they are widely used in cancer detection, diagnosis of soft tissue injuries and in monitoring degenerative diseases

64
Q

Targeted Alpha Therapy (TAT)

A

is used to direct radiation directly at cancerous cells, in particular to prevent micrometastatic cancerous cells forming secondary cancers in other parts of the body
alpha particles used release a large amount of ionising radiation directly at the specific tumour but they do much less damage to the surrounding area than beta emitters
lead-212 is an alpha emitter used for TAT
it has a half life of 10.6 hours
it initially decomposes by beta emission to give bismuth-212 which then rapidly decomposes by alpha emission to give Ti-208

65
Q

Boron neutron capture therapy (BNCT)

A

used on brain tumours
B-10 (non-radioactive isotope) is injected
the boron is taken up by cancer cells
the patient is irradiated with a beam of neutrons which convert the boron into an isotope of lithium and the emission of a high energy alpha particle
the alpha particle acts directly on the tumour without damaging surrounding area

65
Q

Lutetium-177 and Yttrium-90

A

Lutetium-177 is both a beta and gamma emitter
it has a half life of 6.64 days
it is bonded to carrier molecules such as DOTE-TATE which attach to receptors on specific tumours such as endocrine and thyroid tumours
this delivers radiation directly to tumour
the low energy gamma photons are used for targeting visualisation by external imaging
the beta particles, which only travel short distances in tissue destroy the cancer cells in the target site

66
Q

Side effects of radiotherapy

A
  • the ionizing effects of radiation cause changes in the DNA of healthy as well as cancerous cells (particularly those that divide frequently)
  • fatigue
  • nausea
  • hair loss
  • sterility
  • skin reaction
67
Q

Recrystallisation

A

can be used to separate solutes from solutions and the purity of the crystals formed can be determined by its melting point

68
Q

Distillation

A

a solvent can be separated from a solution by a simple distillation
e.g. ethanol (b.p 78) from water (bp 100)

69
Q

Fractional distillation

A

when there is a mixture of liquids fractional distillation can be used
this involves the application of Raoult’s Law
the vapour pressure is the pressure exerted by a vapour in equilibrium with its liquid at a given temperature in a closed system
Raoult’s Law states that “for an ideal solution the total vapour pressure is equal to the vapour pressure of each component multiplied by its mole fraction”
For a solution containing components A and B, the total P is given by:
Ptotal=PaXa + PbXb (where X are the mole fractions)
when the mixture boils (Ptotal = Patmosphere) the vapour will be richer in the more volatile component
by repeating this process in a fractionation column each subsequent boiling followed by condensation will eventually end up with the more volatile component being condensed in the pure form

70
Q

Solvent extraction

A

exploits the fact that a solute may be much more soluble in one solvent compared to another
it uses two immiscible solvents in which the required solute has very different solubilities
the distribution of the solute between the two solvents is an equilibrium and this equilibrium is called the partition coefficient
the key to this is that more of a solute can be extracted if several extractions with smaller quantities are used successively rather than using all the extracting solvent in one extraction

71
Q

Chromatography

A

can be sed to separate different components in a mixture
it can be used both qualitatively and quantitatively
there are several different techniques but all of them contain a fixed stationary phase and a mobile phase that moves
in simple paper or thin-layer chromatography the retention factor (Rf value) is equal to the distance moved by the component compared to the distance moved the the solvent front
Rf=dcomponent/dsolvent
the Rf values can then be compared with a known pure sample of the component

72
Q

Gas chromatography-mass spectrometry (GC-MS)

A

is used to separate and identify mixtures of volatile substance that do not decompose at or near their boiling points
the mobile carrier gas is inert
the sample passes through a stationary phase and heated
the different components have different retention times according to their boiling points and polarity
as they elute they pass through a MS and are matched against known spectral data stored on the computer
more volatile components are eluted more quickly and so have shorter retention times

73
Q

Steroid detection

A

steroids are lipids with a structure of four fused rings
anabolic steroids (usually synthesised from testosterone) can be used as performance enhancing drugs
the most common method of detection of steroids is GC-MS
- GC separates the chemical mixture into pure chemicals
-MC identities and quantifies the components

74
Q

General idea of breathalysers

A

as ethanol is a volatile compound it forms an equilibrium in the lungs between the blood and gas which is released in exhaled breath
Kc has a fixed value at particular temperatures so measurement of ethanol in breath can be used to assess the blood alcohol concentrations
the concentration of the alcohol in exhaled air is directly related to the conc. of the alcohol in blood

75
Q

Roadside breathalysers

A

use redox chem
ethanol is oxidised to ethanal and ethanoic acid by the oxidising agent potassium dichromate (K2Cr2O7)
during this reaction chromate (VI) is reduced to chromate (III) which causes a colour change from orange to green
the extent of the colour change can be measured using a photocell and so can determine ethanol conc.

76
Q

Fuel cell inoximeters

A

uses electrochemical processes in a fuel cell to measure ethanol conc.
the fuel cell contains two Pt electrodes with a porous acid electrolyte between
exhaled air is passed over the cell and any ethanol present is oxidised to ethanoic acid at the anode
C2H5OH + H2O -> CH3COOH + 4H+ +4e-
protons and e- released from this reaction pass to the cathode where they reduce oxygen to water
O2 + 4H+ + 4e- -> 2H2O
overall reaction is:
C2H5OH + O2 -> CH3COOH + H2O
the electric current produced by the reaction is measured by a computer and the larger the current the greater conc. of ethanol in breath

Chemistry HL (18 decks)

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