Download Sedative-Hypnotic Drugs

Sedative‐Hypnotic Drugs
NEPHAR 305
Pharmaceutical Chemistry I
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Assist.Prof.Dr. Banu Keşanlı
Sedative-Hypnotic Drugs
¾ Chemical substances used to reduce tension and anxiety and
induce calm (sedative effect) or to induce sleep and drowsiness
(hypnotic effect).
¾ Most such drugs exert a quieting or calming effect at low doses and
a sleep-inducing effect in larger doses.
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Examples of Sedative-Hypnotic Drugs
Barbiturates e.g. Methohexitone, Phenobarbital, Pentabarbital
Thiopentone,Thiamylal
Benzodiazepines e.g. Diazepam (Valium), Midazolam (Versed),
Clonazepam (Klonopin) Nitrazepam (Ormodon) Flunitrazepam
(Rohypnol)
Glutethimide : Piperidinediones
Meprobamate : Propanediol carbamates
Alcohols : Ethanol, Chloral hydrate, Paraldehyde
Buspirone : Azaspirodecanedione
Zolpidem : Imidazopyridine
Zaleplon
: Pyrazolopyrimidine
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Barbiturates
– Derivatives of barbituric acid
– Hypnotic/anxiolytic effect discovered in the early 20th century (Veronal®, 1903)
– Until the 60s the largest group of hypnotics (more hypnotic than anxiolytic)
– Act by both enhancing GABA responses and mimicking GABA (open Cl-channels
in the absence of GABA) => increased inhibition of the CNS (also block
glutamate receptors)
– High risk of dependence (severe withdrawal symptoms)
– Strong depressant activity on the CNS => anesthesia
– At higher doses respiratory and cardiovascular depression =>
very little use today as hypnotics (only for epilepsy and anesthesia)
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Barbiturates
Different barbiturates vary mostly in their duration of action
• Phenobarbital
– Long-acting: used for anticonvulsive therapy
5-ethyl-5-phenylbarbituric acid
• Thiopental
– Very short acting (very lipophilic => redistributed from the brain into the
fat tissue)
⇒CNS concentration falls below effective levels:
used for i.v. anesthesia
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General Synthesis Method for Barbiturates
9 Substituted malonic acid esters undergo condensation with urea or thiourea
in the presence of a base to give the desired barbiturates
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R
1
R
2
R
COOC2H5
HN
+
C
COOC2H5
1
C X
H2N
NaOC2H5
R
R3
O
1
N
XNa
2
R
N
H+
R
R3
O
N
X
2
R
NH
O
O
X: O Barbitürik
asit türevi
X : O, barbituric acid
derivatives
X: S acid
Tiyobarbitürik
asit türevi
X : S, thiobarbituric
derivatives
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Structure-Activity Relationship of Barbiturates
The keto and enol tautomeric forms of barbituric acid with the sites of substitution
in the hypnotically active barbiturates identified as 1, 2, and 5.
Substitution at carbon 5
* Hypnotic activity is introduced
9 Branched chain --> greater hypnotic activity than straight chain
9 Phenol group (like phenobarbital) --> Greater anticonvulsant activity
9 Presence of hydrophilic groups such as –OH, -SH, -NH2, -COOH, -SO2
decreases lipophilicity so decreases activity
Secobarbital
phenobarbital
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Structure-Activity Relationship of Barbiturates
Carbon 2
* No substitution (oxygen) - oxybarbiturates (ex. pentobarbital and secobarbital)
* Substitution with sulfur - thiobarbiturates (ex. thiopental and thiamylal)
* Sulfuration at carbon 2 increases lipid solubility
9 Greater hypnotic potency
9 More rapid onset, but shorter duration of action e.g. thiopental has faster onset
and shorter duration than pentobarbital
Nitrogen 1
* Addition of a methyl group to nitrogen (e.g. methohexital)
9 Short duration of action
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Hypnotics / Sedatives: Benzodiazepines
¾ Benzodiazepines have sedative, hypnotic, anti-anxiety, anticonvulsant,
and muscle relaxant properties.
¾ They are the most widely used anxiolytic drugs used to treat anxiety,
insomnia ,and a range of other conditions.
¾ Benzodiazepines have largely replaced barbiturates and meprobamate
in the treatment of anxiety, because they are safer (less side effects and
dependence) and more effective
¾ At low doses are useful sedatives and high doses produce a hypnotic effect
¾ Absorption and distribution: The benzodiazepines are lipophilic, and
they are rapidly and completely absorbed after oral administration and
distribute throughout the body.
¾ The benzodiazepines are excreted in the urine as glucuronides or
oxidized metabolites.
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Benzodiazepines
9 Derivatives of Benzodiazepine
9 Valium (diazepam) in 1962
9 Characteristic seven-membered ring fused to aromatic ring
9 Used to treat anxieties of all kinds (phobias, preoperative anxiety, myocardial
infarction (prevent cardiac stress due to anxiety…)
Mechanism of Action of Benzodiazepines
Benzodiazepines work by enhancing the effect of the neurotransmitter
gamma-aminobutyric acid (GABA) - which is responsible for reducing the activity
of neurons that cause stress and anxiety.
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The Core Structure of Benzodiazepines
¾ Heterocyclic ring system which is a fusion between benzene and diazepine ring
system.
¾ This heterocycle has two nitrogen atoms, five carbon atoms and maximum
possible number of cumulative double bonds.
¾ “Benzo” prefix benzene ring fused onto the diazepin ring
¾ "R" labels denote common locations of side chains, which give different
benzodiazepines their unique properties.
Left: The 1,4-benzodiazepine ring system.
Right: 5-phenyl-1H-benzo[e][1,4]diazepin-2(3H)-one forms the skeleton of
many of the most common benzodiazepine pharmaceuticals, such as
diazepam (7-chloro-1-methyl substituted).
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Diazepam (valium)
7- Chloro-1,3-dihydro-1-methyl-5-phenyl-1,4benzodiazepin-2-one
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What are the different types of benzodiazepines?
There are many different benzodiazepines and they all have differences in potency,
speed at which they are metabolized, and "half-life" (time required for the quantity
of the drug in the bloodstream to decrease to half its value), and therapeutic use.
¾ Different benzodiazepines vary mostly in their duration of action
¾ A substituent in the 7 position, such as a halogen or a nitro group, is required
for sedative-hypnotic activity
Clonazepam
Diazepam
Lorazepam
Flunitrazepam
Clonazepam Naming: 5-(2-chlorophenyl)-7-nitro-1,3-dihydro-1,4-benzodiazepin-2-one
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General Synthesis Method for Benzodiazepines
Reaction of 2-aminobenzophenone derivatives and chloroacetyl chloride, followed
by reaction with ammonia gives 1,3-dihydro-2H-1,4-benzodiazepin-2-on
derivatives.
Alkylation will then gives 1-substituted-1,3-dihydro-2H-1,4-benzodiazepin-2-on
derivatives
NH3
R1
C
O R4
NH C CH Cl
R4
ClCOCHCl
O
R1
R5
N
R1
NH3
R5
R2
R2 X
C O
O
R4
N H
R5
H
N
R1
O
R4 Clonazepam
Klonazepam
Nitrazepam
Nitrazepam
H
N
Lorazepam
Nordazepam
Lorazepam
R5 Nordazepam
Oksazepam
Oxazepam
Diazepam
Flunitrazepam
Diazepam
Flurazepam
Flunitrazepam
Halazepam
Flurazepam
Nimetazepam
Pinazepam
Pinazepam
Pirazepam
Prazepam
Temezepam
Lormetazepam
Lormetazepam
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Diazepam (Valium Synthesis)
H
N
CH3
Ac2 O
(1)
Cl
4-Chloro-Nmethylaniline
NaOH, H2 O
(3)
O
O
N
CH3
O
PhCCl, AlCl3
(2)
Cl
Cl
CH3
N
H
O
Cl
Cl
Cl
(4)
CH3
O
CH3
O
N
O
O
Cl
(B)
Cl
NH3
(5)
(A)
CH3
O
N
CH3
O
N
Cl
N
O
NH2
(6)
Cl
N
Diazepam
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Synthesis of Diazepam
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Metabolism of Diazepam
N-desmethyldiazepam
conjugates
conjugates
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Metabolism of Clonazepam
H
N
Redüksiyon
reduction
O
reduction
Redüksiyon
OH
O 2N
H
N
N
Cl
7-Asetamidoklonazepam
3-Hidroksiklonazep
am
3-Hydroxyclonazepam
Glükuronit
ve&
sülfat
Glucuronic
sulfate
konjügatları
conjugation
Hidroksilasyon
hydroxylation
H
N
O
acetylation
Asetilasyon
OH
H 2N
N
Cl
7-acetaminoclonazepam
hydroxylation
Hidroksilasyon
Hidroksilasyon
hydroxylation
O
CH 3CONH
7-aminoclonazepam
Clonazepam
H
N
acetylation
Asetilasyon
7-Aminoklonazepam
Klonazepam
H
N
O
N
Cl
H 2N
N
Cl
O 2N
H
N
O
N
Cl
3-Hidroksi-7-aminoklonazepam
3-Hydroxy-7-aminoclonazepam
Glükuronit ve
sülfat
Glucuronic
& sulfate
konjügatları
conjugation
O
OH
CH 3CONH
N
Cl
3-Hidroksi-7-asetamidoklonazepam
3-Hydroxy-7-acetaminoclonazepam
Glükuronit&ve
sülfat
Glucuronic
sulfate
konjügatları
conjugation
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Structure Activity Relationship of Benzodiazepines
¾
¾
¾
In ring A an electron withdrawing group such as Cl, Br, NO2, or CN at
position 7 increases activity
A small group like methyl group attached to the nitrogen atom in position
1 in ring B has optimal activity. However, substituents at position 1 that
are metabolically related are still clinically useful e.g. Flurazepam.
Replacement of the carbonyl function with two hydrogens in position 2
gives medazepam, less effective than diazepam.
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Structure Activity Relationship of Benzodiazepines
¾ Introduction of a carbonyl function in the 3 position
increases the duration of action and also favours formation
of water soluble salts.
¾ A phenyl substituent at 5 position increases activity. If this phenyl group has
electronegative substituents such as Cl or F at the ortho and di ortho positions
activity is improved.
¾ Saturation of the 4,5- double bond reduces potency, as does a shift of the
unsaturation into the 3,4-position.
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Chloral Hydrate
Chloral hydrate, (trichloroacetaldehyde monohydrate) a sedative, is used in the
short-term treatment of insomnia and to relieve anxiety and induce sleep before surgery.
CH3 CH2 OH
Cl2
Cl3C CH2 OH
oxidation
Oks.
OH
Cl3C CHO
H2O
Cl3C CH
OH
2,2,2-trichloroethane-1,1-diol
Metabolism: Chloral hydrate is converted to the active metabolite,
trichloroethanol, in the body.
OH
Cl3C
Cl3C
CH
OH
CHO
oxidation
Redüksiyon
reduction
Oksidasyon
Cl3C CH 2 OH
Trikloroetanol
trichloroethanol
Cl3C COOH
Trikloroasetik asit
trichloroacetic acid
Konjügasyon
conjugation
COOH
Cl3C
CH 2
O O
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HO
OH
OH
Buspirone
Buspirone is useful in the treatment of generalized anxiety disorder and
has an efficacy comparable to that of the benzodiazepines.
8-[4-(4-pyrimidin-2-ylpiperazin-1-yl)butyl]-8-azaspiro[4.5]decane-7,9-dione
Synthesis: begins with N-alkylation 1-(2-pyrimidyl)piperazine with 4-chlorobutyronitrile
followed by hydrogenation nitrile over Raney nickel catalyst. The primary amine
product of the previous step is reacted with the spirocyclic acid anhydride in order
to yield buspirone.
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Meprobamate
Meprobamate (Miltown, Equanil, Meprospan) is a carbamate derivative which
is used as an sedative drug.
2-methyl-2-propyl-1,3-propandiol dicarbamate
Synthesis: by the reaction of 2-methylvaleraldehyde with two molecules of
formaldehyde and the subsequent transformation of the resulting
2-methyl-2-propylpropan-1,3-diol into the dicarbamate via successive
reactions with phosgene and ammonia
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Other Nonbenzodiazepine Sedatives
The hypnotic zolpidem (Ambien, Stilnox) is not a
benzodiazepine in structure, but it acts on a subset
of the benzodiazepine receptor family
Zaleplon (Sonata, Starnoc and Andante) is very similar
to zolpidem in its hypnotic actions,
but it causes fewer residual effects functions compared to
zolpidem or the benzodiazepines.
Eszopiclone (Lunesta) is an oral nonbenzodiazepine
hypnotic and is also used for treating insomnia.
Ethanol has anxiolytic and sedative effects,
but its toxic potential outweighs its benefits.
CH3CH2OH
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