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Biotransformation of drugs
PharmDr. Pavol Jeko
Center of Excellence PharmacyDepartment of Medicinal Chemistry
CADD Laboratory
Faculty of Pharmacy, Comenius University
Odbojarov 10, 832 32 Bratislava, Slovakia
Tel: + 421 250 117 221
e-mail: [email protected];[email protected]
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Drug metabolizms it is a biochemical modification or degradation of
drugs
drugs are partly eliminated unchanged or partiallyi r n f rm m li h n r
excreted as metabolites
drug metabolism is also of great importance in
medicinal chemistry because it influences (inqualitative, quantitative, and kinetic terms) thedeactivation, activation, detoxification, andtoxification of the vast majority of drugs
2
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OBJECTIVEOBJECTIVE::
conversion of lipophilic
compounds that are easier
eliminated
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XENOBIOTIXENOBIOTICSCS
substances that do not naturally occur in the body
(that enter the body ), are not necessary for thephysiological development and have no
drugs (health)
agrochemicals (agriculture) pesticides, herbicides, fertilizers
food additives
flavoring agents, coloring agents, preservatives, stabilizers
4
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Places of drug biotransformation liver: the majority of metabolic reactions
kidney: 2 phase guts: 2 phase
blood (ester hydrolysis)
lasma h drol sis of esters
within a cell:
endoplasmic reticulum (microsomes)
enzymes cytochrome P450 (CYP-450)
mitochondria
cell cytosol
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CONSEQUENCES
ofBIOTRANSFORMATION
bioinactivation:
usually products are less active or inactive
bioactivation:
in some cases, the metabolic process converts
non-active substance on its own active form(prodrug)
6
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TYPES OF BIOTRANSFORMATION
REACTIONS
drug metabolism takes place in two steps:
first phase - functionalization reactions the molecule introduces a new functional group, usually polar (-COOH,-OH,-NH2)
the polar group can serve as a reaction point for the second reaction phase
second phase - conjugation reactions includes the addition of endogenous molecules (glucuronic, sulphate) to the
metabolite of 1 phase
(prerequisite for conjugation reactions is the presence of a suitable chemical group(-COOH,-OH,-NH2)
results of both phases are metabolites more soluble in water ,
and thus easier elimininated
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Type of reaction The reaction pathway
Oxidation aromatic or aliphatic hydroxylationN- or S-oxidation
N-, O- or S-dealkylation
Reactions of 1 phase drug metabolism
Reduction Reduction NO2 group to hydroxylamine andamine
Reduction of the carbonyl to alcohol
Hydrolysis Ester on acid and alcoholAmid on acid and amine
Hydrazide on acid and substituted hydrazine
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Type of reaction Endogenous reagent or
substrate
Xenobiotic substrate
Glucuronidation Uridine-diphosphate of
glucuronic acid (UDPGT)
Carboxylic acid, alcohol,
phenol, amine
Sulfation 3-phosphoadenosine-5-
Alcohol, phenol, amine
Reaction of 2 phase drug metabolism
phosphosulfate (PAPS)Acetylation Acetyl-CoA Amine
Glutathione
conjugation
glutathione Epoxides, compounds
with chlorine atom
Metylation S-adenozylmethionine Phenols, amines, thiols
Aminoacid Glycine,glutamine Carboxylic acid
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1. OXIDATION1. OXIDATION incorporation of polar groups in the molecules of the drug or substitution
of one polar group by another for increase of the polarization
according to the character of reaction, metabolic oxidation is dividedinto several types:A. Oxidation of alkyl-compounds
B. Oxidation of alcohols aldeh des acids
C. Oxidative hydroxylations of aromatic compoundsD. Oxidative N and O dealkylation
E. Oxidation to Noxids
F. Oxidative deamination
G. Oxidation of sulfids to sulfoxids and sulfonesH. Oxidative desulfuration
I. Oxidative dehalogenation
J. Oxidative opening of the ring
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1. a) Oxidation of alkyl1. a) Oxidation of alkyl--compoundscompounds it is the most common type of oxidation on the side-alkyl chain (if
a compound has aliphatic, aromatic or heterocyclic character)
drugs containing aliphatic unbranched alkyls are
easily oxidized; oxidizing of alkyls decreases with ramifications of the
alkyl chain
oxidation usually begins on the last carbon through
the primary alcoholic group and proceed finally to acid
can take place on the penultimate carbon (beta-
oxidation), which are metabolised type of fatty acid compounds in the
body11
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oxidation of pentobarbital: metabolites with prim.
aliphatic hydroxyl or carboxyl group at the terminal methyl group
are produced; or the sec. alcoholic group on the penultimate carbon
atom of the alkyl is metabolised
NH
CH3
O
NH
CH3
O
NH CH
3
3
O
NH CH
3
3
O OH
NH
NH
O
CH3
C
H2
CH3O
O
OH
NH
NH
O
CH3
CH3O
O
OH
O
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1.1. b )b ) Oxidation alkohols, aldehydes, acidsOxidation alkohols, aldehydes, acids
aliphatic primary alkoholsaliphatic primary alkohols
light oxidation of alcohols (prim. drug) to aldehydes (COH, sec. metab.)
and to the acid (-COOH, final metab.)
ahk oxidcia cez aldehydy (COH) a na kyseliny (COOH)
tertiary alcohols are not so much metabolized
mainly are creating glucuronide conjugates
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alcohols
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1.1. c)c) OxidatOxidativeive hydroxylhydroxylationation ofof aromaticaromatic
compoundscompounds ((ringsrings))
phenolic substances are produced, the final metabolite is eliminated as
a conjugate with glucuronic acid or sulfuric acid, which is well soluble in water
14
phenolic substances are produced
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1.1. d)d) OxidativeOxidative NN andand OO dealkylationdealkylation
common reaction on ethers and alkylamino-drugs
etheric bond is quite strong, so simple aliphatic ethersare often excreted unchanged, the complex ethers are metabolised partially only
phenolic ethers are cleaved to the phenolic part and aldehyde.
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alcohols
alcohols
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drugs containing a tertiary or secondary amine (NH2) are
partially metabolized to secondary and primary amines, andaldehyde
it is assumed that N-metyl-derivates are dealkylatedthrough the N-oxides and N-hydroxymetyl-derivates by the
scheme:
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1.1. e)e) OxidationOxidation toto NNoxids (Noxids (Noxidation)oxidation)
drugs with tertiary amino-group
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alcohols
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1. f) Oxidative deamination drugs, which contains the primary aliphatic amines are metabolised by monoamineoxidase (MAO). These reactions vary according to the nature of the amine.
phenylethylamine-type drugs are oxidized to aldehyde and acid and ammonia:
substances like aryl-isopropylamine are oxidized to ketone
18alcohols
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1.1. g)g) OxidationOxidation ofof sulfides to sulfoxidssulfides to sulfoxids
andand sulfonessulfones
thioethers type drugs - this type of biotransformation is
common in the group of phenothiazines
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alcohols
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1.1. h)h) Oxidative desulfurizationOxidative desulfurization
some sulphur-compounds are oxidized by oxidative desulfurization,
the sulfur atom will be refund for oxygen atom in drug molecule (S O)
(some thiobarbiturates are oxidized to barbiturates)
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alcohols
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1. i) Oxidative dehalogenation
halogenated compounds are converted to acid
halothane is partially metabolised by the scheme
DDT
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alcohols
alcohols
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1. j) Oxidative opening of the ring
complete destruction of the drug molecule
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1.k) Oxidation of double bonds
alcohols
alcohols
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2. REDUCTION2. REDUCTION uncommon metabolic pathway
reduction takes place in liver microsomes, in the presence ofreductase
function groups: nitro and azo-groups, aldehydes, ketones,arsenic compounds
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2. a) Aromatic nitro2. a) Aromatic nitro--compoundscompounds are reduced (in the presence of nitro-reductase) to aromatic amines
(as intermediates can be nitroso- a hydroxylamines derivates)
amino-compounds are excreted as acetyl-derivates
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2. b)2. b) AzoAzo--compoundscompounds are reduced (in the presence of azo-reductase) to aromatic amines
(probably in the first step is produced hydrazo-benzene)
26alcohols
alcohols
alcohols
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2. c) Aldehydes and ketones2. c) Aldehydes and ketones aldehydes are reduced to primary alcohols
alcohols
ketones are partly eliminated unchanged
in some cases are reduced to secondary alcohols, and are excreted from the
body in the form of glucuronic acid conjugate
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cyclic ketones
alcohols
compounds which contains arsenic
alcohols
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3.3. HYDROLYHYDROLYSSIISS REACREACTTIIONSONS reactions, in which substances with a functional group is
broken down into simpler products
A. hydrolysis of esters
B. hydrolysis of amides
C. hydrolysis of anilides
D. hydrolysis of nitriles
E. hydrolysis of carbamates
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3. a) Hydrolysis of esters all esters are splited by esterase on the acid and alcohol part
hydrolysis of esters is realised in blood or in liver (depends on drug
character)
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alcohols
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3. b) Hydrolysis of anilides first is N-dealkylation, next step is hydrolysis of anilide bond
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alcohols
alcohols alcohols
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3. c) Hydrolysis of amides by amidase (in the liver).
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alcohols
alcohols
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3. d) Hydrolysis of nitriles on the acid (only with aromatic derivates)
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alcohols
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4. C4. CONJUGAONJUGATIONTION REACREACTIONSTIONS condensation reaction
metabolic reactions in which the drug, respectively its metabolite with hydroxyl
(OH), carboxyl (COOH) or amino (NH2) group in the body is conjugated with
hydrophilic - the body's own compound : glucuronic acid, sulphate, glycocoll,
, .
according to the nature body chemical component, we can divide conjugate
condensation reactions to conjugation:
A. glucuronic
B. sulfate
C. glycocollic
D. acetylation
E. methylation
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4. a)4. a) GlucuronicGlucuronic conjugationconjugation
glucuronic acid reacts with drugs containing hydroxyl (alcohols, phenols),
carboxylic, sulphydryl (SH) and partially amino group
glucuronic conjugation mechanism - a reaction occurs between the metaboliteand glucuronic acid in the active form
glucuronic acid reacts in the activated form as
uridine diphosphate glucuronic acid (UDP),
- binds to the drugs with the active semiacetyl hydroxyl group, it means
with hydroxyl group bound to the phosphoric acid
N
N
OO
OH
H
OH
OH
H
OH
HH
O
OHO
P O P O
O
OH
O
OH
OH OH
O OH
Kyselina uridn-difosfoglukurnov (UDP-glukurnov)uridine diphosphate glucuronic acid
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UDP reacts with the alcohol (with long aliphatic chains) or phenol and forms
ether-glucuronides
O
OH
H
OH
OH
H
OH
HH
O
OHO
R OH
O
OH
H
OH
OH
H
OH
HH
O
OHO
UDP
+
R
terglukuronid
examples:
menthol, borneol, camphor, paracetamol, morphine, estriol
ether-glucuronide
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UDPUDP reactsreacts withwith the aliphatic or aromatic carboxyl-groups and forms
ester-glucuronide
O
OH
H
OHOH
H
OH
HH
O
OHO
R COOHO
OH
H
OHOH
H
OH
H
H
O
OHO
O
R
Esterglukuroni
UDP +
examples:ester-glucuronide
benzoic acid, salicylic acid, acetylsalicylic acid
UDP forms with aromatic amines N-glucuronides
UDP forms with sulfhydryl groups S-glucuronides
UDP forms conjugates also with the body's own substances such as steroid
hormones
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4.b) Sulfate conjugation sulfate conjugation is conneted with
aliphatic and aromatic hydroxyl-group-
drugs (alcohols and phenols) andaromatic amine compounds, which
provide sulfamates
3-phosphoadenosine-
5-phosphosulfate
own process occurs n t e ver
it is few-steps process and sulphonation,
and agent in the final phase works
3 -phosphoadenosine-5-phosphosulfate
sulfate conjugation of the drug are
eliminated mainly phenolic nature such
as phenols, cresols, naphthols,
morphine, etc.
by sulfate conjugation are
eliminated some of the body's own
substances such as hormones
(estrone, Androsteron)
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4.c)4.c) GlycocollicGlycocollic condenzationcondenzation
by this way are predominantly metabolised aromatic acid as conjugation ingredients except
glycocoll (glycine) also apply to amino acids (cysteine, ornithine, glutamine)
reaction: acid reacts with glycocoll or amino acids in the active form, it means binding to
coenzyme A (CoA):
ROH
O
RS
O
NH2
O
OH
R NH
O
OH
O
CoA-SH
N-acyl-glykokol
CoA +
+ CoA-SH
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4.d) Acetylation closely related to the glycocollic conjugation, as acetylation agent is
acetylcoenzyme A, which reacts with the amino group of the drug
reaction occurs in the liver and kidneys
acetylation is important conjugation reaction, especially for drugs with
a prim. amino group (histamine, p-aminobenzoic acid, sulfonamides)
40
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4.e) Methylation this conjugation reaction is unique in humans (common reaction in animals)
common reaction with primary and secondary amines, unique at drugs with hydroxyl or
sulphydryl group
donor of the methyl group is activated S-adenosyl methionine:
most common meth lation is reaction with
catecholamines (adrenaline, noradrenaline),histamine, nicotinic acid )
N-methylation pyridin derivates morphine, codeine, barbiturates
S-methylation mercaptopurine, dimercaptopropanol 41
PRODRUGPRODRUG
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PRODRUGPRODRUG
inactiveinactive prodrugprodrug formform isis metabolisedmetabolised inin organismorganism
onon thethe activeactive drugdrug formform
42
St t iSt t i ff d l td l t
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StrategiesStrategies forfor developmentdevelopment
ofof prodrugprodrug formform improvementimprovement ofof solubilitysolubility oror betterbetter preparationpreparation
ofof drugdrug formform improvementimprovement ofof per osper os absorptionabsorption andand distributiondistribution
stability orstability or prolongationprolongation ofof drugdrug releaserelease
better tolerance by patients
protectiong group must be stable against stomach acidand enzymes, but after absorption should be sufficiently
labile, for release of aktive drug form (metabolite)
43
Metabolizms of selected drugs
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Metabolizms of selected drugs
OCOCH3
COOH
OH
COOH
eliminated without changes (2 22%)
OH
CONHCH2COOH
conjugation
with glycine
Acetyl-
salicyl
acid
Salicyl acid45-91%
OH
COOH
OH
Gentisic acid 2-4%esters and ether
glucuronids
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NHCOCH3
OHOH
NOH COCH3
NHCOCH3
Paracetamol
Acetaminophen
ox.
paracetamol cysteineintermediate
glutathion cleavage
O-glucuronide 60%
O-sulphate 30%
p-aminophenol
(nephrotoxic)
NHCOCH3
OH
NHCOCH3
S peptidy
OH
S C
H2
C COOH
NH2
OH
NHCOCH3
S CH
2
CH
COOH
NHCOCH3
N-acetyl-benzoquinone-imine
hepatic peptides
hepatotoxic metabolite
paracetamol
mercapturate
O
OH OH
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OHOH
OH
CH CH
2OH
NH2
OMe
OH
OH
OH
CH
OH
OH
CH2OH
OHOH
OH
OMe
COMT
COMTMAO
in the periphery
in CNS
CH CH2OH
NH2
OH
CH CH
2OH
NHCH3
OH
OH
CH CH
2OH
NHCH3
OMe
CH
OH
CHO CH
OHCOOH CH
OHCOOH
Noradrenaline
(Norepinephrine)
COMT
Adrenaline(Epinephrine)
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TheThe endend
nono drugdrug isis metabolisedmetabolised onlyonly byby oneone pathwaypathway,, butbut therethere areare
moremore ofof thisthis pathwayspathways atat thethe samesame timetime
so,so, forfor thethe drugdrug metabolimsmetabolims,, therethere areare nono generalgeneral rulesrules
e.g. sulphonamides are metabolised side by side with oxidative hydroxylation and next
ste is sul hate con u ation, next reaction is acet lation, the mutual relationshi of
metabolites may vary according to the total amount of drug metabolized
e.g. small amount of phenole-derivate is eliminated by conjugation with sulphate, but
when there is an excess of phenole-derivates in the body, there is the higher part of its
conjugate with glucuronic acid
47
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