Download [2] N 1 - Millennium Organization

Lecture 7 & 8
Medicinal Chemistry 1
PC 509
Prof. Dr/ Ghaneya Sayed Hassan
[email protected]
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Antibacterial Sulfonamides
Discovery:
In 1932: Gerhard Domagk studied the antimicrobial effect of
Prontosil Dye "brilliant red Dye" it was found to be active ≠
Streptococcal infection in mice [in vivo] but inactive on bacterial culture
[in vitro].
In 1935: Jacques Tréfouël discovered the conversion
of inactive prontosil dye -in vivo- into active Sulfanilamide
"Lead compound or Prototype". This finding was confirmed
by isolating free sulfonamide from blood & urine of patients
treated with Prontosil.
H2N
N
NH2
2
N
Prontosil Dye
SO2
NH2
In vivo
Reduction
H2N
NH2
NH2
+
H2N
SO2
Sulfanilamide
NH2
N.B: Side effects & resistance to sulfonamides limit its use today;
Penicillins were excellent alternatives for sulfonamides.
Antibacterial Sulfonamides denote
3 different cases:
[1] Anilinesubstituted
sulfonamide
[2] Prodrugs giving active
sulfonamide
[3] Non-aniline
sulfonamides
O
OH
H2N
SO2
NH
R
O
HN
N
Sulfanilamides
3
S
N
N
O
Sulfasalazine
OH
SO2
NH2
H2N
. CH3-COOH
Mafenide acetate
All sulfanilamides are sulfonamides,
but not all sulfonamides are sulfanilamides
Mechanism of action:
(1) Sulfanilamides are active BACTERIOSTATIC.
(2) Many bacteria are impermeable to folic acid, so they rely on their
ability to synthesize folate from PABA “p-Amino Benzoic Acid”,
Petridine & Glutamate against MAMMALS who can't synthesize folic
acid, so obtained from diet & so not affected by sulfanilamides
[selective chemotherapy].
(3) Because of their structural similarity to PABA, sulfonamides act as
competitive inhibitor with this substrate for the enzyme
dihydropteroate synthetase. Thus  synthesis of folic
acid  thymidine, purine synthesis   synthesis of DNA  
multiplication & growth of m.o.
COOH
H2N
4
PABA
H2N
SO2NH2
Sulfanilamide
Biosynthesis of folate co-enzymes:
Sulpha drugs
OH
N
N
H2N
N
CH PPi
H2N
N
H
CH2 NH
C
O
DHF reductase
NH
H2 N
H2 N
N
N
H
N
CH2 NH
COOH
N
HO
Dihydropteroic acid
N
H
CH2 NH
O
H2N
HO
O
O
C
NH
O
HO
N
N
H
Tetrahydrofolate [THF]
[Folate coenzyme]
N
N
Trimethoprim
OH
HO
O
H
N
Dihydropteroate synthetase
H2N
PABA
Dihydropteridine
Pyrophosphate
OH
COOH
OH
Glutamic acid
Dihydrofolate [DHF]
O
O
HO
HO
By using sulfonamides
OH
N
N
H2N
OH
N
N
H
Dihydropteridine
Pyrophosphate
5
CH OPP
H2N
SO2NH2
N
N
Dihydropteroate synthetase
H2N
N
CH2 NH
SO2NH2
N
H
STOP REACTION
This mechanism is supported by:
1- PABA added to culture media antagonizes effect of
sulfonamides.
2- Man can't form folic acid  so his cells are immune to
sulfonamides.
3- M.O. which can utilize performed folic acid is less
sulfonamides susceptible.
Resistance of m.o. to sulfonamide drugs is by:
(1) The bacterial cell wall becomes more permeable
to folic acid.
(2) The m.o. learns to utilize preformed folic acid.
(3) The organism develop alternate pathway for
synthesis of folic acid.
(4)  PAPA synthesis by m.o. to overcome inhibition
of dihydropteroate synthetase.
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Adverse effects of sulfonamides therapy:
(1) Gastrointestinal distress.
(2) Hemolytic anemia.
(3) Hepatitis.
(4) Stevens-Johnson Syndrome [sever skin eruption].
(5) Crystalluria.
General synthesis of Sulfa drugs:
For protection
of amino gp
O
NH C CH3
ClSO3H
[Chlorosulphonic acid]
NH C
7
CH3
RNH2
- H2O
Acetanilide
O
O
NH C
CH3
NH2
Hydrolysis
- HCl
SO2 Cl
SO2 NH R
SO2 NH R
Structure Activity Relationship [SAR]:
N.B: As structure become more close to PABA  more active.
The 2 functional gps must be
para that other positional
isomers [m- or o-] are inactive.
Other substitution on benzene ring
inactive
Other aromatic ring: decrease activity
Free NH2 gp is ESSENTIAL for activity:
4
1
SO2
Substitution of benzene ring with
5-membered ring cause inactivation.
[due to different spacing between
the two functional gps]
[1] If substituted by another gp
[as alkyl or alkoxy]
inactive
But, if substituted by a gp that will be converted
to NH2 gp in vivo [as NO2,NO, N=N, NHCOR, NHOH]
active
NH2
NH2
[2] Acylation of N-4 with Dicarboxylic acid as succinic
or phthalic acid, give slufonamide NOT absorbed
from small intestine BUT hydrolyzed in large intestine
into free sulfonamide [Local Intestinal action]
If di-substituted [ -SO2NR2]
If mono-substituted
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Inactive
activity
Main characters of Sulfonamides:
[1] They are weak organic acids  due to SO2NH2 group [by loss of
proton & stabilization of –ve charge by resonance], & this determine
pka of the drug.
O
Ar
S
NH2
O
O
- H+
Ar
O
S
NH
Ar
S
NH
O
O
N.B: acidity  by attachment of e-withdrawing group to N1
[2] Metabolism:
By N4-acetylation  sulfanilamides excreted as it’s N4-acetate and
glucuronide [both two metabolites are inactive]
N4-acetate is less water soluble than parent drug   tendency of
crystalluria
O
NH2
NH
C
CH3
[less water soluble than parent drug so,
make crystalluria]
N-acetyl transferase
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SO2 NH
R
SO2 NH
R
Crystalluria:
Those sulfanilamides and their acetyl derivatives are sparingly soluble
in water & excreted almost in urine precipitation in kidney 
crystalluria.
According to the following equation:
pka drug = pH urine + log
Unionized form of the drug
Ionized form of the drug
(1) If pH of urine = pka of drug  ionized/unionized = 1
(2) If pka of drug > pH of urine  unionized/ionized >1 
 solubility
(3) If pka of drug < pH of urine  unionized/ionized <1 
 solubility
(4) pH of urine is about 6 & pka of sulfanilamide “prototype’
is 10.4  drug present in urine in unionized form  
solubility
 crystalluria.
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Question: if pka of sulfisoxazole is 5, determine its risk of crystalluria.
5 = 7 + log
log Unionized = -2
Ionized
Unionized
Ionized
1
Unionized
=
Ionized
100
So, it’s present mainly in ionized form  more soluble
  risk of crystaluria.
N.B. Sulfanilamides drugs are AMPHOTERIC in nature [with acidic &
basic characters]
NH
NH2
2
unionized form
-
OH
ionized form
+
H
SO2 NH R
SO2 N R
So, in when we make urine alkaline  we  solubility
[ ionized form]
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To solve problem of crystalluria:
(1) Drinking large amount of water 
 urine flow by  rate of glumerular filtration.
(2) Combination therapy [triple therapy]: using mixed
sulphonamides [3 sulpha drugs: Sulfadiazine + Sulfamerazine +
Sulfamethazine]  only 1/3 of the amount of each drug is used
giving the same bacterial action but each one is present in amount
less that its solubility product  no precipitation.
(3)  pH of urine by alkalinization [using NaHCO3]
(4)  pka of drug by N1-substitution with electronwithdrawing group [as heterocycle or acyl group]
4
NH2
1
SO2NHR
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Assay:
[1] Methods depends on primary aromatic amino group [ N4 ]:
Diazotization and diazocoupling.
[2] Methods depend on acidity of sulfonamide group [ -SO2NH-R]
[a] Non-aqueous titration
[b] Argentometric method [Back titration]
H2N
SO2 N
R+
AgNO3
H2 N
Na
SO2 N
+ NaNO3
R
Ag
[3] Bromometric method
- Add known excess of standard Br2 solution in HCl 
bromination of sulphonamides.
- Excess Br2 determined by adding KI  I2  titrated ≠ standard
NH2
NH2
Na2S2O3
Br
Br
e.g. Sulfadiazine
+3 HBr
+3 Br
2
N
13
SO2 NH
N
SO2 NH
N
Br
N
Classification of antibacterial sulfonamides
Systemic Sulfonamides
[Oral / Absorbable]
Topical Sulfonamides
[Skin / Eye]
Intestinal Sulfonamides
[Oral / Non-absorbable]
[i] Systemic Sulfonamides
- Used in treatment of systemic infections.
- Classified according to rate of excretion [t1/2] into:
SHORT ACTING
MEDIUM ACTING
LONG ACTING
Taken every 6 hrs
Taken every 8-12
hrs
Taken every 24 hrs
t1/2 < 10 hrs
t1/2 = 10-24 hrs
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With slow
excretion rate
Systemic Sulfonamides classified into:
N1- Heteroatomic
derivative
N1-acyl Derivative
Pyrimidine Derivatives
Pyridazine Derivatives
Isoxazole Derivatives
Thiadiazole Derivatives
[1] N1-Acyl Derivatives
Sulfacetamide
Synthesis:
selective and reductive deacylation
Acetic Anhydride
NH2
NH CO CH3
(CH3CO)2 O
NH2
Zn/ NaOH
Sulfacetamide
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SO2 NH2
SO2 NH CO CH3
SO2 NH CO CH3
Sulfacetamide
Sodium
NH2
Water soluble, its solution with pka 5.4
Na
SO2 N CO CH3
Sodium salt of N-[(4aminophenyl) sulfonyl]
acetamide
OR
16[N1-acetyl sulfanilamide]
 Its Na salt is less alkaline than
Na salts of other sulfonamides  nonirritant to mucous membrane  used
as eye drops till 10 % concentration.
 Can be used for urinary tract
infection [why?]  it's highly soluble
with t1/2 = 7 hrs [rapid excretion]
[2] N1-Heteroatomic Derivatives
[i] Pyrimidine Derivative
Short Acting
Sulfamethazine
NH2
CH3
N
SO 2 NH
N
CH3
N1(
4,6-dimethyl- 2pyrimidinyl ) Sulphanilamide
17
t1/2 = 7 hrs / pka = 7.2
More water soluble >
sulfadiazine &
sulfamerazine in acidic urine
[pH=5.5], but lower activity
in vitro & in vivo.
Used in combination
sulfa [Tri-sulfapyrimidine
therapy]
Moderate Acting
Sulfadiazine
N1(2- pyrimidinyl )
Sulfanilamide
t1/2 = 17 hrs / pka = 6.3
Broad spectrum, the drug of choice
in UTI.
NaHCO3 is co-given [why?]
Uses:
1.Na salt as 5 % solution: In
Meningitis.
2.Ag salt: topically in burns.
Sulfamerazine
Long Acting
NH2
N
SO 2 NH
N
NH2
CH3
N
SO 2 NH
N
N1(4-methyl-2- pyrimidinyl )
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Sulfanilamide
t1/2 = 27 hrs / pka = 6.99
Similar properties to sulfadiazine,
but:
1.With more water solubility.
2.More absorbable.
3.Less excretion rate.
4.Higher blood level can be obtained
with a similar dose.
Long Acting
Sulfameter
NH2
N
SO 2 NH
OCH3
N
N1(5-methoxy
-2- pyrimidinyl )
Sulphanilamide
Sulfadimethoxine
NH2
OCH3
SO 2 NH
N
N
OCH3
19
N1(2,6-dimethoxy-4- pyrimidinyl)
Sulphanilamide
 Long duration of action due
to presence of OCH3  
plasma protein binding  
excretion rate.
 As a result of  excretion 
may cause hypersensitivity
upon accumulation.
 T1/2 of Sulfameter is 37-48
hrs & for Sulfadimethoxine is
40 hrs.
[ii] Pyridazine Derivative
Sulfamethoxypyridazine
NH2
NH2
SO2 NH
O
N
CH3
N
N1(6-methoxy-3-pyridazinyl)
Sulphanilamide
t1/2 = 37 hrs  long acting
[why?] , due to presence of
methoxy group.
With bitter taste.
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Sulfamethoxypyridazine acetyl
SO2 N
CO
O
N
CH3
N
CH3
N1-acetyl-N1(6-methoxy-3-pyridazinyl)
Sulphanilamide
 PRODRUG for
sulfamethoxypyridazine   bitter
taste  used for pediatrics.
 Inactive in vitro  activated by
deacetylation in intestine.
[iii] Isoxazole Derivative
Sulfamethoxazole
NH2
N1(5-methyl-3-isoxazolyl) Sulphanilamide
CH3
SO2 NH
N
O
● t1/2 = 11 hrs  short acting.
● Not rapidly absorbed as sulfisoxazole 
its peak blood level is only about 50 %.
Sulfaisoxazole
NH2
H3C
SO2 NH
O
N1(3,4-dimethyl-5-isoxazolyl) Sulphanilamide
● t1/2 = 6 hrs  short acting.
● Rapidly absorbed.
CH3 ● Highly water soluble  no need for using
alkalinizing agent with it.
N
● With bitter taste.
pka
of sulfisoxazole is 5
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[iv] Thiadiazole Derivative
Sulfaimethizole
N
N
H2N
SO2 NH
Sulfaethidole
S
N
CH3
H2N
SO2 NH
N
S
C2H5
N1(5-methyl-1,3,4-thiadiazol-2-yl)
Sulphanilamide
IUPAC name: 4-amino-N-(5-methyl1,3,4-thiadiazol-2-yl)benzenesulfonamide
● t1/2 = 2 hrs  short acting.
● Highly soluble used in UTI.
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N1(5-ethyl-1,3,4-thiadiazol-2-yl)
Sulphanilamide
● Moderate duration.
● Has the lowest degree of
acetylation of sulfonamides
[2] Topical Sulfonamides
Sulfadiazine Silver
[Silvadene®, Dermazine]
NH2
N
SO2 N
Ag
N
Applied in water-miscible cream
[Dermazine]  active topically ≠
Pseudomonas species  used in burn
therapy [that Pseudomonas is responsible
for failure of therapy].
Slightly soluble, Not penetrate cell wall but
act on external cell structures.
Prepared by mixing equimolar amount of
AgNO3 & Na sulfadiazine [both dissolved in
water].
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Sulfacetamide (Klaron®, Ovace®)
Sulfacetamide 10% topical lotion, is approved for the
treatment of acne and seborrheic dermatitis.
(e.g., seborrheic dermatitis, seborrhea sicca [dandruff]); also indicated
for the treatment of secondary bacterial infections of the skin due to
organisms susceptible to sulfonamides
NH2
SO 2 NH
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CO
CH3
Mafenide acetate (Sulfamylon)
O
H2N
H2C
S
O
NH
O
C
CH3
O
4-(Aminomethyl)benzenesulfonamide
• Not true sulfanilamide compound
•Not inhibited by PABA [its M.O.A. involves different mechanism than
true sulfonamides].
• Effective ≠ Clostridium welchii in topical use for infected wounds.
• Not effective orally.
• Used alone or with antibiotics in treatment of slow healing infected
wounds.
• If used in large quantities  metabolic acidosis. So, a series of new
organic salts was prepared.
• The acetate derivative in ointment base is the most efficient.
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[3] Non-absorbable Sulfonamides
[i] Topical Sulfonamides: Sulfadiazine Ag & Mafenide acetate.
[ii] Intestinal Sulfonamides
They are Prodrugs designed to be poorly absorbed “from small intestine”
 In large intestine  cleavages  free sulfonamide "active".
Used in treatment of intestinal infections, ulcerative colitis & reduction of
bowel flora.
Sulfa guanidine
NH2
NH2
SO2 NH
NH
Poorly absorbed [with additional basic
group]  not absorbed from GIT  high local
concentration
Synthesis:
NH2
NH
+
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N1-amidino
sulfanilamide
H2N
C
NH2
SO2 NH2
Sulphanilamide
Guanidine
-NH3
200o C/Pr.
Sulfaguanidine
N4-substituted Sulfonamides
Succinic
sulphathiazole
O
NH
C
Phthalyl
sulphathiazole
HOOC
O
O
CH2 CH2
OH
NH
HOOC
O
C
N
SO2 NH
Phthalyl
sulphacetamide
NH
C
N
S
2-(N4-succinyl
sulfanilamide) thiazole
SO2 NH
O
S
SO2 NH
C
CH3
2-(N4-phthalyl
N4-acetyl-N4-phthalyl
sulfanilamide) thiazole
sulfanilamide
They have additional acidic group  poorly absorbed from GIT.
They are prodrugs  activated in vivo by slow hydrolysis giving  local
concentration.
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Sulfasalazine
COOH
N
N
OH
SO2NH
N
5-[4-(2-pyridyl sulfamoyl) phenyl
azo] salicylic acid
 Water insoluble, broken in body
giving: 5-amino saicyclic acid
[anti-inflammatory] +
Sulfapyridine [carrier]  so,
USED IN ULCERATIVE COLITIS.
Synthesis:
NH2
HOOC
N2Cl
HO
NaNO2 / HCl
Salicylic acid
SO2 NH
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SO2 NH
N
N
Sulfasalazine
Combination of sulfonamides with Dihydrofolate
Reductase Inhibitor
Trimethoprim
Sulfonamides
PABA
Dihydropteroate Synthetase
DHFA
Dihydrofolate Reductase
THFA
Remember  :  THFA synthesis   purine & pyrimidine bases
synthesis   DNA synthesis  stop growth of bacteria.
NH2
Trimethoprim
N
N
NH2
O
CH2
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CH3
O
O
CH3
CH3
• It's potent anti-bacterial by inhibition of DHFR enzyme   stop
bacterial growth.
• Selective in action  100.000 times more active ≠ bacterial DHFR
relative to mammalian DHFR. [used for UTI]
• Combined with Sulfamethoxazole as both have the same
pharmacokinetic properties [t1/2 = hrs like that of sulfamethoxazole] 
excreted at about the same time. important condition for combination
between two drugs]
Trimethoprim combined with Sulfamethoxazole
[Sutrim] [Septazole] [Septrin]
The combination of a sulfonamide with trimethoprim causes
a sequential blockade of folic acid synthesis .
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Advantages of this combination:
(1) Synergism due to sequential blockage.
(2) Avoid development of resistance.
(3) Broader spectrum of activity.
Fansidar
(Sulfadoxine/pyrimethamine)
Combination of
Antibacterial Sulfadoxine [500 mg]
+ antimalarial Pyrimethamine [25 mg]
Inhibit folic acid synthesis by two different ways.
With schizonticidal effect.
Used for prophylaxis & treatment of chloroquine-resistant
P.falciparum
NH2
Cl
H3CO
SO2 NH
OCH3
Sulfadoxine
4-Amino-N-(5,6-dimethoxy-4pyrimidinyl)benzenesulfonamide
CH3
N
N
N
31
H2C
H2N
N
NH2
Pyrimethamine
5-(4-chlorophenyl)-6-ethyl2,4-pyrimidinediamine