DESIGN OF A NOVEL ANXIOLYTIC DESIGN OF A NOVEL ANXIOLYTIC AND ANTIDEPRESSANT AGENTAND ANTIDEPRESSANT AGENT
Target - Serotonin Receptor Target - Serotonin Receptor Target - Serotonin Receptor Target - Serotonin Receptor Notes• Important receptor in central nervous system
• 7 types (5-HT1 - 5HT7) and 14 subtypes
• G-Protein-coupled receptors (except 5-HT3)
• Three subtypes of 5-HT2 receptor (5-HT2A 5-HT2B 5-HT2C)
• 5-HT2C receptor thought to be involved in anxiety
• mCPP is an agonist with some selectivity for 5-HT2C receptor
• mCPP causes anxiety in human and animal studies
• Antagonist with selectivity for 5-HT2C receptor may be useful in treating anxiety
HN N
Cl
meta-Chlorophenylpiperazine (mCPP)
Notes• Serotonin is a neurotransmitter• Abnormal levels of serotonin are related to various disorders
(e.g. anxiety, depression, migraine)• Indole ring system is present
Natural Ligand Natural Ligand Natural Ligand Natural Ligand
N
H
NH2
HO
Serotonin(5-Hydroxytryptamine)
Aims of Drug Design Aims of Drug Design Aims of Drug Design Aims of Drug Design • Selectivity for 5-HT2C receptor
• Selectivity over 5-HT2A is more important than over 5-HT2B
5-HT2B predominates in peripheral nervous system
5-HT2A and 5-HT2C receptors predominate in CNS• Resistance to drug metabolism• No effect on metabolic enzymes (drug-drug interactions)• Aqueous solubility• Non-sedating• No interaction with alcohol• Fast onset of action• High response rate • No withdrawal effects
Testing Procedures Testing Procedures Testing Procedures Testing Procedures In vitro tests
• Radioligand binding studies on 5-HT2A, 5-HT2B and 5-HT2C receptor subtypes
• Tests for activity against cytochrome P450 enzymes
In vivo testsAbility to block hypoactivity in rats caused by mCPP
Modelling studiesDrug design carried out on model binding sites
Lead Compound Lead Compound Lead Compound Lead Compound
• Produced by Lilly Pharmaceuticals• Serotonin antagonist• Insoluble in water
N
Me
CH2CH3
Me
HN
HN
O
CF3
UreaUrea
IndoleIndole
AromaticAromatic
From Lead Compound to SB 200646From Lead Compound to SB 200646From Lead Compound to SB 200646From Lead Compound to SB 200646
Notes• Substituents removed from indole ring (simplification)• Pyridine ring introduced (ring variation)• Pyridine ring more polar - increases water solubility• Urea link at optimum positions for both ring systems
• First selective 5-HT2B/2C antagonist
• 50-fold selectivity over 5-HT2A receptor
• Modest in vitro activity • Some oral activity in vivo
N
Me
CH2CH3
Me
HN
HN
O
CF3
3 5
N
Me
HN
HN
ON
SB 200646SB 200646PyridinePyridine
3 5
N
Me
HN
HN
ON
SB 200646SB 200646
Metabolically labile
From SB 200646 to SB 206553From SB 200646 to SB 206553From SB 200646 to SB 206553From SB 200646 to SB 206553
Notes• Rigidification limits number of possible conformations• Rigidify structure such that active conformation still allowed• Increased chance of active conformation being present• 10-fold increase of in vitro affinity
• 160-fold selectivity over 5-HT2A receptor
• 4-fold increase of in vivo activity
Tricyclic ring Tricyclic ring systemsystem
3 5
N
Me
HN
HN
ON
SB 200646 SB 206553
N
N
CH3
OHN
N
Rigidification
Extra ring
Conformation of SB 206553Overall structure is roughly planar
From SB 200646 to SB 206553From SB 200646 to SB 206553From SB 200646 to SB 206553From SB 200646 to SB 206553
7. From SB 200646 to SB 2065537. From SB 200646 to SB 2065537. From SB 200646 to SB 2065537. From SB 200646 to SB 206553Metabolism of SB 206553Metabolism of SB 206553
N
N
CH3
OHN
N
Metabolically labile
N
N
H
OHN
N
N-Demethylation
Metabolite is active but non-selective
Variation permitted
Analogues of SB 206553Analogues of SB 206553Analogues of SB 206553Analogues of SB 206553
N
HN
N
O
N
Me
Substitution bad
Substitution bad
Notes• Methyl group replacable with Et, Pr or iPr
• Slightly increased selectivity for 5-HT2C over 5-HT2A
• Hydrophobic pocket available for N-alkyl group
• Slightly bigger for 5-HT2C receptor
Analogues of SB 206553Analogues of SB 206553Analogues of SB 206553Analogues of SB 206553
• No methyl group• Loss of
selectivity
•Retains Me group •More stable to metabolism•Good in vitro affinity and selectivity•Poor oral activity •Poorly absorbed from gut or rapidly metabolized•Administered by IV injection
Ring variation strategyRing variation strategy
Pyrrole
N
HN
N
O
N
MeSB206553
No methyl group
ThipoheneN
S
OHN
N
FuranN O
Me
OHN
N
3D QSAR studies of SB 206553 and 3D QSAR studies of SB 206553 and analoguesanalogues 3D QSAR studies of SB 206553 and 3D QSAR studies of SB 206553 and analoguesanalogues
Notes• Structures overlaid using urea group• Dark and light blue = areas accessed by compounds having 5-
HT2C activity
• Light blue = disallowed area for 5-HT2A activity
• Light blue area = region of N-methyl group of SB 206553
Molecular modelling studies of SB Molecular modelling studies of SB 206553 and analogues206553 and analoguesMolecular modelling studies of SB Molecular modelling studies of SB 206553 and analogues206553 and analogues
Notes• Model receptor binding site created• SB 206553 docked into binding site• Carbonyl oxygen of urea group is crucial for activity• Positioned to form hydrogen bond to Ser-312
- Ser-312 present in 5-HT2 receptors but not 5-HT1 receptors
- binding to Ser-312 thought to be important for selectivity for 5-HT2 receptors over 5-HT1 receptors
• Carbonyl oxygen interacts with Ser-312 and Ser-315• Aromatic rings positioned into hydrophobic pockets
Molecular modelling studies of SB Molecular modelling studies of SB 206553 and analogues206553 and analoguesMolecular modelling studies of SB Molecular modelling studies of SB 206553 and analogues206553 and analogues
N
N
Me
ONH
N
Molecular modelling studies of SB Molecular modelling studies of SB 206553 and analogues206553 and analogues Molecular modelling studies of SB Molecular modelling studies of SB 206553 and analogues206553 and analogues
O
HO
H
Ser- 138Ser- 141
Phe-223
Trp-324
Phe-327
Phe-328
Phe-220
Phe-224
Val-212
Val-608
Hydrophobic pocket
Hydrophobic pocket
N
N
Me
OHN
N
Molecular modelling studies of SB Molecular modelling studies of SB 206553 and analogues206553 and analoguesMolecular modelling studies of SB Molecular modelling studies of SB 206553 and analogues206553 and analogues
Notes•Val-608 and Val-212 are present in the hydrophobic pocket occupied by the N-methyl group
•Bulkier leucine groups are present in the model binding site for the 5-HT2A receptor
•Hydrophobic pocket is smaller for the 5-HT2A receptor
•More difficult for N-methyl group of SB 206553 to fit the 5-HT2A receptor
•May account for selectivity of SB 206553
From SB 206553 to SB 221284From SB 206553 to SB 221284 From SB 206553 to SB 221284From SB 206553 to SB 221284
Aim•To replace the metabolically labile N-methyl group with a metabolically stable group•The new group must bind to the hydrophobic pocket for selectivity
SB 206553
N
N
CH3
OHN
N
N
X
Y6
5
OHN
N
Indolines
Notes•Indole ring is removed - simplification•Indoline structures are synthesized with varying substituents •Substituent X needs to bind to the hydrophobic pocket•Electron-withdrawing substituent at position 6 is preferred •Thioether or ether at position 5 is beneficial
From SB 206553 to SB 221284From SB 206553 to SB 221284From SB 206553 to SB 221284From SB 206553 to SB 221284
Notes•Best balance of affinity vs selectivity•Potent inhibitor of 5-HT2B and 5-HT2C receptors•Good selectivity over 5-HT2A receptor•Inhibits cytochrome P450 enzymes•Pyridine N is responsible for inhibiting cyt P450 enzymes •Selectivity increases for SEt, SnPr or OiPr, but affinity falls
Inhibits cytochrome
P450 enzymes
N
SMe
CF3
OHN
N
SB221284
Fits hydrophobic pocket
Metabolically stable
N
SMe
CF3
OHN
N
SB221284
Electron-withdrawing
Fits hydrophobic pocket
Metabolically stable
N
SMe
CF3
OHN
N
SB221284
Notes
• SB 221284 is docked into the model binding site for the 5-HT2C receptor
• Pyridine and indoline rings are positioned in hydrophobic pockets
• Hydrogen bonding interactions take place with serine residues
• S-Methyl group fits the hydrophobic pocket
• CF3 group orientates the thiomethyl group into the correct conformation
• CF3 acts as a conformational blocker
Modelling Studies on SB 221284Modelling Studies on SB 221284Modelling Studies on SB 221284Modelling Studies on SB 221284
Modelling Studies on SB 221284Modelling Studies on SB 221284Modelling Studies on SB 221284Modelling Studies on SB 221284
O
HO
H
Ser- 138Ser- 141
Phe-223
Trp-324
Phe-327
Phe-328
Phe-220
Phe-224
Val-212
Val-608N
S
CF3
OHN
N
Me
Hydrophobic pocket
Hydrophobic pocket
N
S
CF3
OHN
N
Me
NoteVacant areas are available in the hydrophobic pocket accommodating the pyridine ring
3D-QSAR Studies on SB 2212843D-QSAR Studies on SB 2212843D-QSAR Studies on SB 2212843D-QSAR Studies on SB 221284Notes
• 55 Analogues are synthesized• Analogues are docked into the model receptor • Receptor-ligand complex is minimized• Ligands are removed and subjected to CoMFA analysis• Predicted affinity versus actual affinity demonstrates a good
relationship 9.00
8.50
8.00
7.50
7.00
6.50
6.006.00 6.50 7.00 7.50 8.00 8.50 9.00
Actual pKi
Pre
dic
ted
p
K i
3D-QSAR Studies on SB 2212843D-QSAR Studies on SB 2212843D-QSAR Studies on SB 2212843D-QSAR Studies on SB 221284
Notes
• Steric fields are more important than electrostatic fields• Dark blue represents beneficial areas• Light blue represents detrimental areas• Large number of detrimental areas round the indoline ring• Suggests a tight binding pocket• Little scope for modification
Electronrich
Notes• Aromatic ring is best placed at position 5• Increased binding interactions with hydrophobic pocket • Slightly increased affinity and selectivity• Aromatic ring acts as a steric shield for pyridine • 100-fold decrease in cytochrome P450 inhibition• Level of cytP450 enzyme inhibition is still unacceptable • Low oral activity• Electron-rich aromatic ring is possibly susceptible to
metabolism
N
SMe
CF3
SB 221284
OHN
N
Inhibits cytochrome
P450 enzymes
From SB 221284 to SB 228357From SB 221284 to SB 228357From SB 221284 to SB 228357From SB 221284 to SB 228357
I
N
OMe
CF3
OHN
N
5
Structure II• Pyridine ring is more polar leading to increased water
solubility• 10-fold increase in affinity due to additional binding
interactions
• Lower selectivity between 5-HT2C and 5-HT2A receptors
Structure III• Selectivity is recovered by adding a methyl substituent
• Slightly increased affinity for the 5-HT2C receptor
• Moderate oral activity• Slight drop in cytochrome P450 inhibition
I
N
OMe
CF3
OHN
N
5
Electronrich
Vary ring and rigidification
II R=HIII R=Me
4'
N
OMe
CF3
OHN
N
N
R
5
From SB 221284 to SB 228357From SB 221284 to SB 228357 From SB 221284 to SB 228357From SB 221284 to SB 228357
Steric clash
Notes• Methyl group acts as a conformational blocker• Forces rings to be orthogonal
• Orthogonal rings favored by 5-HT2C receptor but not 5-HT2A receptor
From SB 221284 to SB 228357From SB 221284 to SB 228357From SB 221284 to SB 228357From SB 221284 to SB 228357
N
OMe
CF3
OHN
N
N
Me H
N
HN
N
O
CF3
OMe
NCH3 H
OrthogonalringsStructure III
Notes• Pyridine nitrogen is responsible for inhibiting cytochrome
P450 enzymes• Pyridine is replaced by an aromatic ring (ring variation)• Poor water solubility• Water solubility is improved by a pyridine substituent (R)• Substituent is best at position 3 (variation of substituents)
From SB 221284 to SB 228357From SB 221284 to SB 228357From SB 221284 to SB 228357From SB 221284 to SB 228357
Ring variation
R 3
IV
4
N
OMe
CF3
OHN
N
OMe
CF3
OHN
N
N
Me H
Structure III
4’
5
V
N
OMe
CF3
OHN
N
Me
From SB 221284 to SB 228357From SB 221284 to SB 228357From SB 221284 to SB 228357From SB 221284 to SB 228357
Ring variation
N
OMe
CF3
OHN
N
N
Me H
Structure III
4’
5
Notes• Pyridine nitrogen is responsible for inhibiting cytochrome
P450 enzymes• Pyridine is replaced by an aromatic ring (ring variation)• Poor water solubility• Water solubility is improved by a pyridine substituent (R)• Substituent is best at position 3 (variation of substituents)
• Improved selectivity
• Higher 5-HT2C affinity
• Potent oral activity• Still inhibits cytochrome P450
enzymes
From SB 221284 to SB 228357From SB 221284 to SB 228357From SB 221284 to SB 228357From SB 221284 to SB 228357
V
N
OMe
CF3
OHN
N
Me
Ring variation
N
OMe
CF3
OHN
N
N
Me H
Structure III
4’
5
Notes• Methyl substituent moved to the ortho position• Acts as a conformational blocker • Aromatic and pyridine rings cannot be co-planar
• Increased selectivity for the 5-HT2C over the 5-HT2A receptor
• Short duration of action • Electron-rich aromatic ring is susceptible to metabolism
From SB 221284 to SB 228357From SB 221284 to SB 228357From SB 221284 to SB 228357From SB 221284 to SB 228357
V
N
OMe
CF3
OHN
N
Me
3
Electron rich
Vary substituents
N
OMe
CF3
OHN
N
H
Me
Structure VI
Notes• Analogues made with electron-withdrawing substituents on
the aromatic ring• Substitution at 2 and 6 is bad - ring is twisted out of plane
with the urea group• Substitution at positions 4 and 5 is acceptable
From SB 221284 to SB 228357From SB 221284 to SB 228357From SB 221284 to SB 228357From SB 221284 to SB 228357
Electron rich
N
OMe
CF3
OHN
N
H
Me
Structure VI
Bad
Bad
2
6
4
5 N
OMe
CF3
OHN
N
R
Structure VIIIStructure VIII
• Increased duration of action (6 hours)
• Modeling studies suggest extra space available in hydrophobic pocket
• Further extension possible
From SB 221284 to SB 228357From SB 221284 to SB 228357From SB 221284 to SB 228357From SB 221284 to SB 228357
Electron rich
N
OMe
CF3
OHN
N
H
Me
Structure VI
N
OMe
CF3
OHN
N
F
SB 228357
Notes• Substitution pattern is altered to para• Linker oxygen atom is inserted • Pushes pyridine further into the hydrophobic pocket• Poor oral activity due possibly to reduced solubility
From SB 228357 to SB 243213From SB 228357 to SB 243213From SB 228357 to SB 243213From SB 228357 to SB 243213
N
OMe
CF3
OHN
N
F
SB 228357
N
OMe
CF3
OHN
ON
Structure IXLinker
Original pyridine restored to increase water solubility
15. From SB 228357 to SB 24321315. From SB 228357 to SB 24321315. From SB 228357 to SB 24321315. From SB 228357 to SB 243213
N
OMe
CF3
OHN
N
F
SB 228357
N
OMe
CF3
OHN
ON
Structure IXLinker
N
OMe
CF3
OHN
NO
N
Structure X
From SB 228357 to SB 243213From SB 228357 to SB 243213 From SB 228357 to SB 243213From SB 228357 to SB 243213
N
OMe
CF3
OHN
N
F
SB 228357
N
OMe
CF3
OHN
ON
Structure IXLinker
N
OMe
CF3
OHN
NO
N
Structure X
N
OMe
CF3
OHN
NO
N
Me Structure XI
Notes• ortho Methyl group acts as a conformational blocker• Increases torsion angle between the pyridine rings
• Increased selectivity and affinity for 5-HT2C receptor
• 80-fold selectivity over 5-HT2B receptor
• Low cyctochrome P450 activity• Good in vivo activity
From SB 228357 to SB 243213From SB 228357 to SB 243213From SB 228357 to SB 243213From SB 228357 to SB 243213
N
OMe
CF3
OHN
NO
N
Me Structure XI
Notes• Methoxy group is replaced with a methyl group• Less liable to metabolism• Good profile of affinity, activity and selectivity• Negligible cytochrome P450 activity• Better aqueous solubility than SB 228357• Entered phase I clinical trials as a non-sedating
antidepressant / anxiolytic
From SB 228357 to SB 243213From SB 228357 to SB 243213From SB 228357 to SB 243213From SB 228357 to SB 243213
N
OMe
CF3
OHN
NO
N
Me Structure XI
N
Me
CF3
OHN
NO
N
Me SB 243213
Modelling studies for SB 243213Modelling studies for SB 243213
Pyridine ring substituent well inserted into hydrophobic pocket
From SB 228357 to SB 243213From SB 228357 to SB 243213From SB 228357 to SB 243213From SB 228357 to SB 243213
O
HO
H
Ser- 138Ser- 141
Phe-223
Trp-324
Phe-327
Phe-328
Phe-220
Phe-224
Val-212
Val-608N
Me
CF3
OHN
NO
N
Me
Binding interactions for SB 243213Binding interactions for SB 243213
From SB 228357 to SB 243213From SB 228357 to SB 243213From SB 228357 to SB 243213From SB 228357 to SB 243213