Download The lead compound

Chapter 12
Target disease
Priority for the Pharmaceutical Industry:
Can the profits from marketing a new drug outweigh the cost of developing and
testing that drug?
Questions to be addressed:
Is the disease widespread?
(e.g. cardiovascular disease, ulcers, malaria)
Does the disease affect the first world?
(e.g. cardiovascular disease, ulcers)
Are there drugs already on the market?
If so, what are their advantages and disadvantages (e.g. side effects)
Can one identify a market advantage for a new therapy?
Drug targets
A) Lipids
Cell membrane lipids
B) Proteins
Receptors
Enzymes
Carrier proteins
Structural proteins (tubulin)
C) Nucleic acids
DNA
RNA
D) Carbohydrates
Cell surface carbohydrates
Antigens and recognition molecules
Between species:
• Antibacterial, antifungal and antiviral agents
• Identify targets which are unique to the invading pathogen
• Identify targets which are shared but which are significantly different in
structure
Within the body:
• Selectivity between different enzymes, receptors etc.
• Selectivity between receptor types and subtypes
• Selectivity between isozymes
• Organ and tissue selectivity
Bioassays (test systems)
• Tests are required in order to find lead compounds and for drug optimisation
• Need to be quick, easy and relevant
• Tests can be in vivo or in vitro
• A combination of tests is often used in research programs
In vivo Tests
• Carried out on live animals or humans
• Measure an observed physiological effect
• Measure a drug’s ability to interact with its target and its ability to reach that
target
• Can identify possible side effects
• Rationalization may be difficult due to the number of factors involved
• Transgenic animals - genetically modified animals
• Drug potency - concentration of drug required to produce 50%
of the maximum possible effect
• Therapeutic ratio/index compares the dose level of a drug required to produce a
desired effect in 50% of the test sample (ED50) versus
the dose level that is lethal to 50% of the sample (LD50)
In vitro tests
• Tests not carried out on animals/humans
Target molecules (e.g. isolated enzymes or receptors)
Cells (e.g. cloned cells)
Tissues (e.g. muscle tissue)
Organs
Micro-organisms (for antibacterial agents)
• More suitable for routine testing
• Measure the interaction of a drug with the target but not the ability of the drug to
reach the target
• Results are easier to rationalize - less factors involved
• Does not demonstrate a physiological or clinical effect
• Does not identify possible side effects
• Does not identify effective prodrugs
Testing drugs
•High Throughput Screening
•NMR
•Enzyme Inhibition tests
•Identify competitive or non competitive inhibition
• Strength of inhibition measured as IC50
• IC50 = concentration of inhibitor required to reduce enzyme
activity by 50%
•Receptor tests
•Not easy to isolate membrane bound receptors
• Carried out on whole cells, tissue cultures, or isolated organs
• Affinity - strength with which compounds bind to a receptor
• Efficacy - measure of maximum biochemical effect resulting from
binding of a compound to a receptor.
• Potency - concentration of an agonist required to produce 50%
of the maximum possible effect.
The lead compound
• A compound demonstrating a property likely to be therapeutically useful
• The level of activity and target selectivity are not crucial
• Used as the starting point for drug design and development
• Found by design (molecular modelling or NMR) or by screening compounds
(natural or synthetic)
• Need to identify a suitable test in order to find a lead compound
• Active principle - a compound that is isolated from a natural extract and which
is principally responsible for the extract’s pharmacological activity. Often used
as a lead compound.
The lead compound
A) The natural world
B) The synthetic world
C) The virtual world
Plantlife (flowers, trees, bushes)
Micro-organisms (bacteria, fungi)
Animal life (frogs, snakes, scorpions)
Biochemicals (Neurotransmitters, hormones)
Marine chemistry (corals, bacteria, fish etc)
Chemical synthesis (traditional)
Combinatorial synthesis
Computer aided drug design
Identification of the lead compound
A) Isolation and purification
solvent-solvent extraction
chromatography
crystallization
distillation
B) Structure determination
elemental analysis
molecular weight
mass spectrometry
IR spectroscopy
UV spectroscopy
NMR (1H, 13C, 2D) spectroscopy
X-ray crystallography
Lead compounds from the natural world
Plants
Lead compounds from the natural world
Morphine
Poppy capsule
Lead compounds from the natural world
•
OPIUM - Morphine
•
CINCHONA BARK - Quinine
•
YEW TREE - Taxol
Lead compounds from the natural world
Willow tree - salicylic acid
O
O
OH
OH
OH
Acetic
anhydride
O
CH3
Aspirin
O
Coca bush - cocaine
Me
N
CH3
CO2Me
H
N
O
CH3
C
H
O
Procaine
O
C
O
NH2
Lead compounds from the natural world
The beatons of pennycross
THE BEATONS OF PENNYCROSS
CURE for EPILEPSY
Add
a liberal
sprinkling
Flavour
with
essence
Heat
Simmer
a cauldron
for 20
of
minutes
water
Produce
one
juicy
spiders
of
dog
turd
until
then
warm
enjoy
to pedigree
the touch dog
Lead compounds from the natural world
Herbal remedies of old
Majority may have worked through a placebo effect
Lead compounds from the natural world
Rain forests
Lead compounds from the natural world
Coral and marine chemistry
CH3
OMe
S
N
CURACIN
CH3
H
H
Lead compounds from the natural world
Micro-organisms
Lead compounds from the natural world
Micro-organisms
R
OH
O
OH O
OH
H
N
O
S
O
NH2
•
•
•
•
•
H H
OH
Penicillin
H
Me
ClHO
NMe
Cephalosporins
Tetracyclines
NH
HN
HN
NH
Streptomycin
H N C NH
H
OH
HO
Chloramphenicol
H
N
CH3
CH3
O
CO2H
2
C
H
2
HO H
O2N
CH2OH
HN H
2
O
C
CHCl2
H
H
OH
H
O
O
CHO
H
Me
OH
H
O
O
HO
CH2OH
H MeHN
H
H
O
H
R C N
H H
S
OAc
N
O
CO2H
H
OH
H
Lead compounds from the natural world
O
Venoms and toxins
C OH
O
C
Teprotide
O
O
H2N CH C
N CH C
H
CH2
CH2
CH2
C O
OH
HN
N
O
O
C
N CH C
H
CH2
CH2
N
O
O
C
N CH C
H
CH2
N
O
H
N CH C
N
CH CH3
CH2
CH2
C O
CH3
NH2
O
CH2
C OH
NH
O
C NH
C
NH2
HS
N
CH3
Captopril
(anti-hypertensive)
Lead compounds from the natural world
Venoms and toxins
Lead compounds from the natural world
MeO
Venoms and toxins
N
HO
O
H3 C
H3 C
H
H
O
N
OH
OMe
Tubocurarine
(from curare)
CH 3
CH 3
Lead compounds from the natural world
MeO
Venoms and toxins
HO
O
H3 C
H3 C
H
CH 3
N
CH 3
H
O
N
OH
OMe
Tubocurarine
(from curare)
MeO
MeO
N
CH 3
O
O
C
C
O
OMe
OMe
(CH 2)5
O
OMe
H
N
MeO
OMe
Atracurium
(Neuromuscular blocker)
OMe
Lead compounds from the natural world
Endogenous compounds
Natural ligands for receptors
OH
HO
OH
H
N
Me
HO
H
N
Agonist
HO
HO
ADRENALINE
SALBUTAMOL
NH2
HO
NMe2
MeHN
N
H
5-HYDROXYTRYPTAMINE
O
Agonist
S
O
N
H
SUMATRIPTAN
Lead compounds from the natural world
Endogenous compounds
Natural ligands for receptors
OH
H
N
HO
O
OH
Antagonist
N
H
Me
HO
ADRENALINE
PROPRANOLOL
Me
NH2
HN
N
HISTAMINE
S
HN
N
CIMETIDINE
H
N
NHMe
CN
Antagonist
Lead compounds from the natural world
Endogenous compounds
Natural substrates for enzymes
Enkephalins
Enkephalinase inhibitors
Peptides
Protease inhibitors
H CO2H
H2N
O
N
H H
N
N
H
O
L-Phe-L-Pro
O
O
H
N
H H
CONH2
SAQUINAVIR
H
N
OH
H
N
H
H
Lead compounds from the synthetic world
SYNTHETIC COMPOUNDS
Lead compounds from the synthetic world
O
H2N
N
N
S
O
NH2
NH2
PRONTOSIL
Lead compounds from the synthetic world
O
H2N
S
O
SULFANILAMIDE
NH2
Lead compounds from the synthetic world
ONO2
ONO2
ONO2
Lead compounds from the synthetic world
Rubber industry
CH3
S
H3C
N
C
S
S
C
S
H3C
Antabuse
N
CH3
4.4 Lead compounds from the synthetic world
Organic synthesis
4.4 Lead compounds from the synthetic world
Combinatorial synthesis
Automated synthetic machines
4.4 Lead compounds from the synthetic world
Combinatorial synthesis - peptide synthesis
AMINO ACID
RESIN
BEAD
AMINO ACIDS
X
PEPTIDE
4.4 Lead compounds from the synthetic world
Combinatorial synthesis - heterocyclic synthesis
RESIN
BEAD
N
N
Y
O
CHR1R2
4.4 Lead compounds from the synthetic world
Combinatorial synthesis - heterocyclic synthesis
N
N
RESIN
BEAD
R2
R3
O
H
4.4 Lead compounds from the synthetic world
Combinatorial synthesis - heterocyclic synthesis
N
N
RESIN
BEAD
R2
R3
O
R4
R5
EtO
O
4.4 Lead compounds from the synthetic world
Combinatorial synthesis - heterocyclic synthesis
N
N
RESIN
BEAD
R2
R3
N
R4
R5
HN
O
4.4 Lead compounds from the synthetic world
Combinatorial synthesis - heterocyclic synthesis
N
RESIN
BEAD
N
Y
R2
R3
N
R4
R5
HN
O
4.5 Lead compounds
- impact of the human genome project
The Past
Lead Compound
Targets
The Present and Future
Targets
Lead compounds
4.5 Lead compounds
- impact of the human genome project
4.5 Lead compounds
- impact of the human genome project
Lead compounds
- impact of the human genome project
4.5 Lead compounds
- impact of the human genome project
4.5 Lead compounds
- impact of the human genome project
4.6 Lead compounds - de novo design
4.6 Lead compounds - de novo design
X-RAY CRYSTALLOGRAPHY
4.6 Lead compounds - de novo design
PROTEIN STRUCTURE
4.6 Lead compounds - de novo design
Receptor
CH3
IONIC
BOND
+
H3N
-
Scaffold
Scaffold
Scaffold
Scaffold
Scaffold
CO2
VDW
BOND
O
HO
H-BOND
4.6 Lead compounds - de novo design
Thymidylate kinase inhibitors
N
H
H
N
N
N
S
O
O
O
Optimisation
O
N
N
S
N
H2N
O
Anticancer agent
O
Lead compound
4.7 Design of lead compounds using NMR spectrosc
NMR spectroscopy
4.7 Design of lead compounds using NMR spectrosc
Binding Site
Protein
4.7 Design of lead compounds using NMR spectrosc
Protein
No observable biological effect
4.7 Design of lead compounds using NMR spectrosc
CH3
CH CH
CH3
CH2
CH2
C
13C
CH
C
NMR
4.7 Design of lead compounds using NMR spectrosc
CH3
CH CH
CH3
CH2
CH2
C
13C
CH
C
NMR
4.7 Design of lead compounds using NMR spectrosc
Protein
Optimise
epitope
4.7 Design of lead compounds using NMR spectrosc
Protein
Optimise
epitope
Optimise
epitope
4.7 Design of lead compounds using NMR spectrosc
Link
Protein
Optimise
epitope
Optimise
epitope
4.7 Design of lead compounds using NMR spectrosc
LEAD COMPOUND
4.7 Design of lead compounds using NMR spectrosc
Design of a lead compound as an immunosuppressant
OH
O
OMe
N
O
O
O
MeO
HO
N
H
Epitope B
OMe
OMe
Epitope A
4.7 Design of lead compounds using NMR spectrosc
Design of a lead compound as an immunosuppressant
OH
O
OMe
N
O
O
O
MeO
HO
OMe
OMe
Lead compound
N
H