Diuretics -Chemistry & Proteins

1. Diuretics
Prepared and Submitted by
S.D.Shanmugakumar., M.Pharm., Ph.D
Associate Professor
Department of Pharmaceutical Chemistry
Jyothishmathi Institute of Pharmaceutical
Sciences, Thimmapur, Karimnagar – 505527
Telangana state

2. Introduction
Diuretics, sometimes called water pills, help rid your body of salt (sodium) and water. Most of
these medicines help your kidneys release more sodium into your urine. The sodium helps
remove water from your blood, decreasing the amount of fluid flowing through your veins and
arteries.
The word diuretic has a Greek stem, diu (through) oυρειη (to urinate), and a diuretic is defined as any
substance that increases urine flow and thereby water excretion. Diuretics are among the most
commonly used drugs and the majority act by reducing sodium chloride reabsorption at different sites
in the nephron, thereby increasing urinary sodium, and consequently, water loss.
Paintings found in the ruins of Pompeii have depictions of grapes, ivy, olives and sweet cherry – all of
these have diuretic properties described in the writing of Pliny the Elder (23–79 AD).3 A treatise published
in 1788 by Joseph Plenick (1735–1807) lists several hundred plants, of which 115 have diuretic properties,
including garlic, Chinese lantern, saffron, fennel, liquorice, sassafras and dandelion (Taraxacum
officinale).4 The latter derives its name from the French ‘dent de lion’ (tooth of the lion) on account of the
shape of its leaves which impart its diuretic property –probably because of that it is commonly called, in
French, ‘pissenlit’, literally ‘piss in bed’.5,6 Its diuretic properties are thought to be due to potash
(potassium carbonate, K2CO3.

3. From 1919 until the 1960s, the most effective
diuretics, used as the mainstay of treatment, were
the mercurials, but they are no longer used
because of their toxicity. Other options during this
period were osmotic diuretics like urea, mannitol
and sucrose, acidifying salts such as ammonium
chloride, xanthine derivatives and digoxin, which
has a diuretic effect in addition to its inotropic
effect. In 1937, Southworth realized that patients
treated with the antibiotic sulphanilamide not only
breathed deeply (they developed a mild metabolic
acidaemia) but also produced an alkaline urine,
with increased sodium and water excretion. Hence,
Sulphanilamide was found to be a carbonic
anhydrase inhibitor and by 1949, Schwartz11 had
successfully treated congestive heart failure
patients with sulphanilamide.

4. Carbonic Anhydrase inhibitors ( Classification of Diuretics)
Acetazolamide ; Methazolamide ;Dichlorphenamide.
Thiazides : Chlorothiazide, Hydrochlorothiazide,
Hydroflumethazide, Cyclothiazide.
Loop Diuretics : Furosemide, Bumetanide, Ethacrynic acid
Potassium Sparing diuretics : Spironolactone,
Triamterene, Amiloride
Osmotic Diuretics : Mannitol

5. Defects in CA2 are the cause of osteopetrosis autosomal recessive type 3 (OPTB3) [MIM:259730];
also known as osteopetrosis with renal tubular acidosis, carbonic anhydrase II deficiency
syndrome, Guibaud-Vainsel syndrome or marble brain disease. Osteopetrosis is a rare genetic
disease characterized by abnormally dense bone, due to defective resorption of immature bone.
The disorder occurs in two forms: a severe autosomal recessive form occurring in utero, infancy, or
childhood, and a benign autosomal dominant form occurring in adolescence or adulthood.
Autosomal recessive osteopetrosis is usually associated with normal or elevated amount of non-
functional osteoclasts. OPTB3 is associated with renal tubular acidosis, cerebral calcification
(marble brain disease) and in some cases with mental retardation.
Carbonic anhydrase

6. Carbonic Anhydrase Inhibitors :
1. Carbonic anhydrase (CA) inhibitors are derived from the sulphonamides. Sulfonamide group (-
SO2NH2) is essential for its activity. It forms alkaline urine and also produces systemic acidosis.
The potent CA inhibitors have an aromatic group either Phenyl or heterocycle attached to
sulphamoyl group.
MOA : In carbonic anhydrase inhibitors, The primary site of action is proximal tubules.
They interfere with the reabsorption of Bicarbonate ions ( HCO3)
In the presence of carbonic anhydrase enzyme, Intracellularly Bicarbonate get converted in to Water and
Carbondioxide.
Further they combine to each other and form carbonic acid.
H2CO3 dissociates to form H+ and HCO3-.
The HCO3- is transported across the basolateral membrane. H+ ion secreted in the tubular lumen is in exchange
for Na+.
The H+ combines with a filtered bicarbonate to form carbonic acid, which immediately dissociates in to water
and carbondioxide. Accumulation of bicarbonate ion in the tubular lumen inhibits Sodium –H+ exchange and
Sodium reabsorption. The increase in the sodium concentration in the tubular fluid is compensated by sodium
chloride reabsorption in the later segments of the tubule. Hence the diuretic effect of the carbonic anhydrase is
achieved.

7. Acetazolamide
Acetazolamide is used with other medicines to reduce edema (excess fluid retention) and
to help control seizures in certain types of epilepsy.
N-(5-Sulfamoyl-1,3,4-thiadiazol-2-yl)acetamide
MOA : It depends on the inhibition of carbonic anhydrase, causing a
reduction in the availability of hydrogen ions for active transport in the
renal tubule lumen. This leads to alkaline urine and an increase in the
excretion of bicarbonate, sodium, potassium and water.
Uses : For adjunctive treatment of edema due to congestive heart
failure, drug induced edema, chronic simple glaucoma.

8. Docking of Acetazolamide

9. Methazolamide
N-(4-methyl-2-sulfamoyl-1,3,4-thiadiazol-5-yliden)
acetamide
MOA : Methazolamide is a potent inhibitor of
carbonic anhydrase. Inhibition of the
carbonic anhydrase in the ciliary process of
the eye decreases aqueous humour
secretion, persumably by slowing the
formation of bicarbonate ions with
subsequent reduction in sodium and fluid
transport.
Uses : For the treatment of chronic open – angle glaucoma and acute – closure glaucoma

10. Docking of methazolamide

11. Dichlorphenamide
4,5-Dichlorobenzene-1,3-disulfonamide
MOA : It reduces intraocular pressure by partially suppressing the
secretion of aqueous humor. Although the mechanism by which they
do this not fully understood. Evidence suggests that bicarbonate ions
are produced in the ciliary body by hydration of carbondioxide under
the influence of carbonic anhydrase and diffuse them in to the
posterior chamber which contains more sodium and bicarbonate ions
that does plasma and consequently hyper tonic.
Uses : For adjunctive treatment of chronic simple glaucoma, secondary
glaucoma and preoperatively in acute angle closure glaucoma.

12. Docking of
Dichlorphenamide

13. Thiazides
Thiazides are also called benzothiazides.
1.The 2nd position can tolerate the presence of small alkyl groups such as CH3.
2. Substituents with hydrophobic character in the 3rd position increases saluretic activity 1000
times.
3. Substituents include –CH2Cl, –CHCl2, –CH2C6H5, –CH2S, –CH2 –C6H5. The increase in saluretic
activity correlates with the lipid solubility.
Saturation of double bond between the 3rd and 4th position of nucleus increases the diuretic
activity approximately 3 fold to 10-fold. Example— Hydrochlorthiazide.
4. Hydrogen atom at the 2nd position is more acidic due to the presence of neighbouring electron
with-drawing the sulphone group.
A free sulphamoyl or potentially free sulphamoyl group at 7th postion is essential for activity. N7-
caproyl chlorthiazide is excreted as chorothiazide, the loss of sulphamoyl group eliminates the
diuretic effect, but not the antihypertensive action, example, diazoxide.
5. Direct substitution of the 4th, 5th, or 8th position with an ethyl group usually results in
diminished diuretic activity.
Substitution of the 6th position with an activating group is essential for diuretic activity. The
substiutents include Cl, Br, and CF3 groups.

14. MOA : Thiazides inhibit a Na-cl symport in the luminal membrane of the epithelial cells in the
distal convoluted tubule. Thus , thiazides inhibit Nacl reabsorption in the distal convoluted
tubule. Thiazides enhance ca++ reabsorption in the distal convulted tubule by inhibiting Na+
entry and thus enhancing the activity Na+-ca++ exchanger in the basolateral membrane of
epithelial cells.
ChloroThiazide 6-chloro-1,1-dioxo-1,2,4-benzothiadiazin-2-ide-7-sulfonamide

15. Hydrochlorthiazide
6-Chloro -1,1 dioxo -3,4 dihydro-2H -2,4 benzothiadiazine – 7-
sulfonamide
1. Hydrochlorothiazide, a thiazide diuretic inhibits water reabsorption
in the nephron by inhibiting the sodium – chloride symporter in the
distal convoluted tubule.
2. The sodium – chloride symporter transports sodium and chloride
from the lumen in to the epithelial cell lining the distal convoluted
tubule.
3. Sodium entry in to the cell is facilitated by Sodium – potassium
ATPase on the basolateral membrane.
4. By blocking the sodium – chloride symporter, hydrochlorothiazide
effectively reduces the osmotic gradient and water reabsorption
through out the nephron.
Uses : For the treatment of high blood pressure and management of edema.

16. Hydroflumethazide
1,1 dioxo -6 (trifluoromethyl)-3,4 –dihydro -2,4 benzothiadiazine 7-
sulfonamide
MOA : Hydroflumethazide is a thiazide diuretic that inhibits water
reabsorption in the nephron by inhibiting the soidum – chloride
symporter (SLCA3) in the distal convulted tubule, which is
responsible for 5% of total sodium reabsorption.
Uses : Adjunctive therapy in edema associated with congestive heart
failure.

17. Cyclothiazide
3-(bicyclo[2.2.1]hept-5-en-2-yl)-6-chloro-3,4-dihydro-2H-1,2,4-
benzothiadiazine-7-sulfonamide 1,1-dioxide
MOA : 1. It inhibits active chloride reabsorption at the early distal tubule via the
Na –Cl Co- transporter resulting an increase in the excretion of sodium, chloride
and water.
2. Thiazides like cyclo thiazide also inhibit sodium ion transport across
the renal tubular epithelium through binding to the thiazide sensitive sodium –
chloride transporter. This results in the increase in potassium excretion via the
sodium –potassium mechanism.
Uses : Cyclothiazide is indicated as adjunctive therapy in edema associated with
congestive heart failure, Hepatic cirrhosis and corticosteroid and estrogen
therapy.

18. Loop Diuretics
The diuretics that produce peak diuresis than other diuretics and act distinctly on renal tubular function (at loop of
henle) are called loop diuretics. There are two major classes of loop diuretics :
1. Sulfonamide derivatives : Furosemide, bumetanide and torsemide.
2. Non- Sulfonamide : Loop diuretic such as ethacrynic acid
MOA : Loop diuretics inhibit reabsorption of NaCl and Kcl by inhibiting the Na+-K+-2Cl symport in the luminal membrane
of the thick ascending limb of loop of Henle. Since TAL is responsible for the reabsorption of 35% of filtered sodium and
loop diuretics are highly effcacious, hence they are called high – ceiling diuretics.

19. Human Kidney

20. SEM of
Nephron
Barrier.

21. SEM of loop of Henle.

22. SAR of loop diuretics
1. The substituent at 1-position must be acidic, the carboxyl group
provides optimal diuretic activity, but other groups as tetrazole may have
diuretic activity.
2. A sulfamoyl group in the 5- position is essential for optimal high ceiling
diuretic activity.
3. The activating group in the 4th position can be Cl or CF3, a phenoxy,
alkoxy, aniline, benzyl or benzoyl group.
4. Substituents that can be tolerated on the 2-amino group series only
furfuryl, benzyl, thienyl methyl, benzyl.
5. Substituent on the 3-amino group series can very widely without
affecting optimal diuretic activity.

23. Furosemide
4-Chloro-2 ( Furan-2yl methyl) amino) 5-sulfamyl ) benzoic acid
Furosemide, a loop diuretic inhibits water reabsorption in the nephron by
blocking the sodium –potassium –chloride cotransporter in the thick
ascending limb of the loop of henle. The lumen becomes more hypertonic
which in turn diminishes the osmotic gradient for water reabsorption
through out the nephron.
Furosemide get metabolised in to 4-
chloro -5-Sulfamoyl anthranilliac acid.

24. Binding Furosemide with protein PDB ID 3bl1
MRP4 is an ATP-dependent, unidirectional
efflux transporter belonging to the C
subfamily of the ABC protein superfamily. It
is expressed in the kidney, blood-brain
barrier (BBB), liver, and other tissues

25. Bumetanide
3-butylamino-4-phenoxy-5-sulfamoyl-benzoic acid
MOA : Bumetanide interferes with renal cAMP and /or inhibits the sodium –
potassium ATPase pump. Bumetanide appears to block the active reabsorption
of chloride and possibly sodium in the ascendingloop of henle. Altering
electrolyte transfer in the proximal tubule.
Uses : For the treatment of edema associated with congestive heart failure,
hepatic and renal disease including the nephrotic syndrome.

26. 2-(2,3 –dichloro -4 (2-methylidene butanoyl) phenoxy acetic acid
MOA : Ethacrynic acid inhibits symport of sodium, potassium and
chloride particularly in the ascending limb of henle, but also in the
proximal and distal tubules. This Pharmacological action results in
excretion of these ions, increased urinary output and reduction
extracellular fluid.Diuretics also lower blood pressure intially by
reducing plasma and extra cellular fluid volume.
Ethacrynicacid
Uses ; For the treatment of high blood pressure and edema caused by diseases like congestive heart failure, liver failure
and kidney failure.

27. Potassium sparing diuretics
Potassium –Sparing diuretics do not share any obvious chemical similarities, steroidal structure of the aldosterone
anatagonists. Those in clinical use include : Aldosterone antagonists- Spironolactone, eplerenone .
Epithelial sodium channel blockers – Amiloride, triametrene
Aldosterone anatgonists - Spironolactone
9-acetyl sulfanyl-2,15 – dimethyl spiro (oxolane -2,14-tetracycloheptadecan -6-
ene -5,5’ dione.
MOA : Spironolactone is a specific pharmacologic anatgonist of aldosterone,
acting primarily through competitive binding of receptors at the aldosterone –
dependent sodium –potassium exchange site in the distal renal convoluted
tubule. Spironolactone causes increased amounts of sodium and water to be
excreted.
Uses : Primarily to treat low –renin hypertension, hypokalemia and conn’s syndrome.

28. Epithelial sodium channel blockers
Amiloride
3,5 –diamino -6-chloro-N-(diaminomethylidene) Pyrazine -2-
carboxamide.
MOA: Amiloride works by inhibitiing sodium reabsorption in the distal
convoluted tubules and collecting ducts in the kidneys by binding to the
amiloride – sensitive sodium channels. This promotes the loss of
sodium and water from the body, but without depleting sodium
channels. This promotes the loss of sodium and water from the body
without depleting potassium. Amiloride exerts its potassium sparing
effect through the inhibition of sodium reabsorption at the distal
convoluted tubule, cortical collecting tubule and collecting duct.
Uses : Adjunctive treatment with thiazide diuretics.

29. Triametrene
6-phenyl pteridine -2,4,7 -triamine
MoA: Triamtrene inhibits the epithelial sodium channels on principal
cells in the distal convulted tubule and collecting tubule.Since
csodium reabsorption is inhibited, this increases the osmolarity in
the nephron lumen and decreases the osmolarity of the
interstititum. This potential promotes potassium excretion through
apical potassium channels, by inhibiting sodium reabsorption,
trimetrene also nhibits potassium excretion.
Uses : For the treatment of edema associated with congestive heart failure.

30. Osmotic diuretics

31. Mannitol
Hexane-1,2,3,4,5,6 -hexol
MoA : As a diuretic mannitol induces diuresis because it is not reabsorbed in the renal tubule, thereby increasing
the osmolaity of the glomerular filtrate, facilitating excretion of water and inhibiting the renal tubular
reabsorption of sodium, chloride and other solutes.
Uses : For the promotion of diuresis before irreversible renal failure becomes established.