statins anti-cholesterol agents

STATINSSTATINSANTI-CHOLESTEROL AGENTSANTI-CHOLESTEROL AGENTS

Patrick: An IntroductionPatrick: An Introduction toto MedicinalMedicinal Chemistry 4eChemistry 4e

Case Study 1Case Study 1

1. Cholesterol1. Cholesterol

NotesNotes•Important in biosynthesis and cell membrane structureImportant in biosynthesis and cell membrane structure•Excess cholesterol leads to cardiovascular diseaseExcess cholesterol leads to cardiovascular disease•Fatty molecule transported round blood supply by low-density Fatty molecule transported round blood supply by low-density and high-density lipoproteins (LDLs and HDLs)and high-density lipoproteins (LDLs and HDLs)•LDLs carry cholesterol to cellsLDLs carry cholesterol to cells•HDLs carry cholesterol from cells to liverHDLs carry cholesterol from cells to liver•Mortality is associated with high levels of LDLs or low levels of Mortality is associated with high levels of LDLs or low levels of HDLsHDLs•Cholesterol can cause fatty plaques in arteries leading to a risk Cholesterol can cause fatty plaques in arteries leading to a risk of artherosclerosis, clot formation, stroke and heart attackof artherosclerosis, clot formation, stroke and heart attack

HO

H

H

H

2. Target for statins 2. Target for statins

NotesNotes•Inhibit biosynthetic pathway to cholesterolInhibit biosynthetic pathway to cholesterol•Prevent synthesis of cholesterol within cells but not from dietPrevent synthesis of cholesterol within cells but not from diet•Target the enzyme catalysing the rate limiting step in the Target the enzyme catalysing the rate limiting step in the biosynthetic pathwaybiosynthetic pathway

O CH3 O

OS

HO

+ CoASHCoA

CH3 O

OHO

HO

(S)-HMG-CoA (R)-Mevalonate

+ 2HHMG-CoA reductase

2NADPH 2NADP

Target enzymeTarget enzyme

3. Catalytic mechanism3. Catalytic mechanism

NotesNotes•Involves two hydride transfersInvolves two hydride transfers•Two molecules of cofactor required (NADPH)Two molecules of cofactor required (NADPH)

O

R S CoA

O

R S CoA

H

Mevaldyl-CoA

NADPH

NADP

+H

R H

Mevaldehyde

+ CoASH

NADPH + H OH

R H

HO

NADP


Substrate bindingSubstrate binding

H3N Lys-735

N

Lys-691

H HH

O

Ser-684

H

Asp-690

O O

ionic

H-bond

H-bond

H-bond

O CH3 O

OS

O

CoA

H

NotesNotes•Lys, His, Glu and Asp are involved in reaction mechanismLys, His, Glu and Asp are involved in reaction mechanism•Histidine acts as acid catalystHistidine acts as acid catalyst•Lysine stabilises negatively charged oxygen of mevaldyl-CoA and transition Lysine stabilises negatively charged oxygen of mevaldyl-CoA and transition state leading to itstate leading to it•Lowers activation energy for first stepLowers activation energy for first step


N

Lys-691

H HH

O

R S CoA

H-bond

H

(from NADPH)

Mevaldyl-CoA

O

R S CoAH

N

Lys-691

H HH

H-bond

IonicNHNH

His-866

Mevaldehyde

O

R H

N

Lys-691

H HH

H-bond

NHN

His-866

SH CoA

NotesNotes•Glutamic acid acts as an acid catalystGlutamic acid acts as an acid catalyst•Aspartate residue stabilises uncharged Glu-559 and charged Lys-691Aspartate residue stabilises uncharged Glu-559 and charged Lys-691


Glu-559

O ON

Lys-691

H HH

Asp-767O

OH

N

Lys-691

H HH

O

R H

H-bond

(from NADPH)

H

Mevalonate

OH

R H

N

Lys-691

H HH

H-bond

Glu-559

O O

H

O

R HH

H-bond

Ionic

N

Lys-691

H HH

Glu-559

O O

H

O

R HH

H-bond

Ionic

N

Lys-691

H HH

Glu-559

O O

H

4. Identification of a Lead Compound4. Identification of a Lead Compound

NotesNotes•Screening of compounds produced by microorganismsScreening of compounds produced by microorganisms•Microbes lacking HMGR might produce HMGR inhibitors to inhibit Microbes lacking HMGR might produce HMGR inhibitors to inhibit microbes having HMGR - chemical warfaremicrobes having HMGR - chemical warfare•Compactin (Mevastatin) isolated from Penicillium citrinumCompactin (Mevastatin) isolated from Penicillium citrinum•10,000 higher affinity for enzyme than substrate10,000 higher affinity for enzyme than substrate•Never reached the marketNever reached the market

O

OO

OHO

H

H Compactin (Mevastatin)Compactin (Mevastatin)ICIC5050 = 23 nM = 23 nM

5. Type I Statins5. Type I Statins

NotesNotes•Lovastatin isolated from Aspergillus terreusLovastatin isolated from Aspergillus terreus•First statin to be marketed (Merck; 1987)First statin to be marketed (Merck; 1987)•Revolutionised treatment of hypercholesterolaemiaRevolutionised treatment of hypercholesterolaemia•Simvastatin introduced in 1988 as semi-synthetic analogue of lovastatinSimvastatin introduced in 1988 as semi-synthetic analogue of lovastatin• Pravastatin derived from compactin by biological transformation (1991)Pravastatin derived from compactin by biological transformation (1991)

O

OOH

CO2HHO

H

H

HO

LovastatinLovastatinICIC5050 = 24 nM = 24 nM

O

OO

OHO

H

H

HO

OO

OHO

H

H

Me

SimvastatinSimvastatinICIC5050 = 24 nM = 24 nM

PravastatinPravastatinICIC5050 = 1900 nM = 1900 nM

R'

O

OH

CO2HHO

H

H

R''

O

R

Polar 'head'

Decalin ring

Hydrophobic moiety


NotesNotes•General structure of type I statins contains a polar head and a hydrophobic General structure of type I statins contains a polar head and a hydrophobic moiety including a decalin ringmoiety including a decalin ring•Lovastatin and simvastatin are prodrugs where lactone ring is hydrolysed to Lovastatin and simvastatin are prodrugs where lactone ring is hydrolysed to

give the polar headgive the polar head

R'

O

OH

CO2HHO

H

H

R''

O

R


Disadvantages of Type I statinsDisadvantages of Type I statins•Various side effectsVarious side effects•Difficult to synthesiseDifficult to synthesise•Large number of asymmetric centres Large number of asymmetric centres

**

****

*

** = asymmetric centres

Polar 'head'

Decalin ring

Hydrophobic moiety

6. Type II Statins6. Type II Statins

NotesNotes•Synthetic agentsSynthetic agents•Contain larger hydrophobic moiety with no asymmetric centresContain larger hydrophobic moiety with no asymmetric centres•Easier to synthesiseEasier to synthesise•Fluvostatin (1994), atorvastatin (1997), cerivastatin (1998), rosuvastatin Fluvostatin (1994), atorvastatin (1997), cerivastatin (1998), rosuvastatin

(2003(2003))

FluvastatinFluvastatinICIC5050 = 28 nM = 28 nM

AtorvastatinAtorvastatinICIC5050 = 8 nM = 8 nM

CerivastatinCerivastatinICIC5050 = 10 nM = 10 nM

OH

CO2HHO

N

F

H

N

OH

CO2HHO

H

F

O

NH

OH

CO2HHO

NOH3C

F

H

NotesNotes•Structures share a number of similar features (‘me too drugs’)Structures share a number of similar features (‘me too drugs’)•Rosuvastatin is the most potent - related to sulfonamide groupRosuvastatin is the most potent - related to sulfonamide group•Cerivastatin is the most hydrophobicCerivastatin is the most hydrophobic•Pravastatin and rosuvastatin are the least hydrophobicPravastatin and rosuvastatin are the least hydrophobic


RosuvastatinRosuvastatinICIC5050 = 5 nM = 5 nM

PitavastatinPitavastatinICIC5050 = 6.8 nM = 6.8 nM

OH

CO2HHO

N N

NS CH3

F

H3C

OO

H

OH

CO2HHO

H

N

F

NotesNotes•Statins with lower hydrophobic character target liver cells and Statins with lower hydrophobic character target liver cells and have lower side effects have lower side effects •Less hydrophobic statins do not cross cell membranes easilyLess hydrophobic statins do not cross cell membranes easily•Liver cells have transport proteins for statins whereas other Liver cells have transport proteins for statins whereas other cells do notcells do not•Majority of cholesterol synthesis takes place in liver cellsMajority of cholesterol synthesis takes place in liver cells•Side effects thought to be due to inhibition of HMGR in other Side effects thought to be due to inhibition of HMGR in other cells such as muscle cellscells such as muscle cells•Common side effect is myalgia (muscle pain)Common side effect is myalgia (muscle pain)•Rhabdomyolysis = severe muscle toxicity which can be fatalRhabdomyolysis = severe muscle toxicity which can be fatal•Cerivastatin withdrawn in 2001 due to rhabdomyolysis and 50 Cerivastatin withdrawn in 2001 due to rhabdomyolysis and 50 fatalatiesfatalaties


7. Statins - Mechanism of action 7. Statins - Mechanism of action

NotesNotes•Competitive inhibitors of HMGRCompetitive inhibitors of HMGR•Polar head group mimics the natural substrate (HMG-SCoA)Polar head group mimics the natural substrate (HMG-SCoA)•Same binding interactions for polar head group as natural Same binding interactions for polar head group as natural substratesubstrate•Hydrophobic moiety forms additional binding interactionsHydrophobic moiety forms additional binding interactions•Binds more strongly than natural substrate, but does not Binds more strongly than natural substrate, but does not undergo reaction - no leaving groupundergo reaction - no leaving group

Hydrophobic group

OH

CO2

HO

H

H

Statins

O CH3 O

OS

HO

CoA

HMG-SCoASCoA

CO2

HOCH3

O=

Hydrophobic group

OH

CO2

HO

H

H

Statins

SCoA

CO2

HOCH3

OH

Mevaldyl CoA

H

7. Statins - Mechanism of action 7. Statins - Mechanism of action

NotesNotes•Statins are closer mimics of the first reaction intermediate Statins are closer mimics of the first reaction intermediate mevaldyl CoA than the substratemevaldyl CoA than the substrate•Statins likely to bear a resemblance to the transition state for Statins likely to bear a resemblance to the transition state for the first stage of the reaction mechanismthe first stage of the reaction mechanism•Can be viewed as transition-state analogues Can be viewed as transition-state analogues

8. Statins - Binding interactions8. Statins - Binding interactions

NotesNotes•Polar head group binds in similar manner to substratePolar head group binds in similar manner to substrate•Hydrophobic moiety does not bind to the pocket for SCoAHydrophobic moiety does not bind to the pocket for SCoA•Enzyme is flexible and alters shape to accommodate statinsEnzyme is flexible and alters shape to accommodate statins•Hydrophobic pocket is created to bind the hydrophobic moietyHydrophobic pocket is created to bind the hydrophobic moiety

N

HO

HO2COH

H

F

O

HN

LeuValAla

HN

NH2

HN

OH

Ser-565

Arg-590

H-bond

1-dipole bond

vdw


Methylethyl substituent of Type II statins binds to same region Methylethyl substituent of Type II statins binds to same region as decalin ring of type I statinsas decalin ring of type I statins

methylethylmethylethylsubstituentsubstituent

N

HO

HO2COH

H

F

O

HN

LeuValAla

HN

NH2

HN

OH

Ser-565

Arg-590

H-bond

1-dipole bond

vdw


•Arg-590 forms important polar interaction with fluorophenyl Arg-590 forms important polar interaction with fluorophenyl substituentsubstituent•Planar guanidium group is also stacked over the phenyl ringPlanar guanidium group is also stacked over the phenyl ring

fluorophenylfluorophenylsubstituentsubstituent

N

HO

HO2COH

H

F

O

HN

LeuValAla

HN

NH2

HN

OH

Ser-565

Arg-590

H-bond

1-dipole bond

vdw

amide groupamide group


•Amide group forms an additional hydrogen bonding interaction Amide group forms an additional hydrogen bonding interaction with Ser-565with Ser-565•Additional interaction not formed with other statins other than Additional interaction not formed with other statins other than rosuvastatin rosuvastatin

N

HO

HO2COH

H

F

O

HN

LeuValAla

HN

NH2

HN

OH

Ser-565

Arg-590

H-bond

1-dipole bond

vdw

LeuValAla

HN

NH2

HN

OH

Ser-565

Arg-590

sulfone groupsulfone group


NotesNotes•Rosuvastatin forms additional H-bonding interactions Rosuvastatin forms additional H-bonding interactions •Sulfone oxygen forms a hydrogen bonding interaction with Ser 565Sulfone oxygen forms a hydrogen bonding interaction with Ser 565•Sulfone group also interacts uniquely with Arg-568Sulfone group also interacts uniquely with Arg-568•Explains why rosuvastatin is most potent statinExplains why rosuvastatin is most potent statin•Sulfone group important for binding as well as selectivitySulfone group important for binding as well as selectivity

HO

HO2COH

NN

NSH3C

F

CH3

OO

H

vdw

1-dipole bond

H-bond

9. Other mechanisms of action for statins9. Other mechanisms of action for statins

NotesNotes•Statins inhibit HMGR in liver cellsStatins inhibit HMGR in liver cells•Lowers the levels of cholesterol in liver cellsLowers the levels of cholesterol in liver cells•Causes an increase in the synthesis of hepatic LDL receptorsCauses an increase in the synthesis of hepatic LDL receptors•Increases the number of LDL receptors in the cell membrane of Increases the number of LDL receptors in the cell membrane of liver cellsliver cells•Increases the amount of LDL-cholesterol cleared from the Increases the amount of LDL-cholesterol cleared from the plasmaplasma•Crucial to the effectiveness of statinsCrucial to the effectiveness of statins

statins anti-cholesterol agents

Documents