Thiazide Diuretics

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Most of the diuretics of the thiazide class are structurally related to antibacterial drugs of the sulfonamide class; however, these compounds exhibit no antibacterial activity.

Drugs of this group are derivatives of benzothiadiazine, and as a rule they are substituted at C7 of the benzol ring by a sulfonamide group and a chlorine atom, or by another electron-accepting group (trifluoromethyl) at C6. A hydrogenated thiadiazine ring of the benzothiadiazine system permits the introduction of various substituents at C3, which allows for a significant number of drugs to be created and to make specific correlations between structure and activity in this series of compounds. In particular, it has been established that in the majority of cases, reduction of the double bond at C3-C4 of thiazide drugs increases their diuretic activity.

The exact mechanism of action is not known; however, qualitatively, thiazide diuretics act analogously, and their differences are generally quantitative in character. The effector regions of thiazide diuretics are the distal nephron tubules. Drugs of this group inhibit reabsorption of sodium, chloride, magnesium, and calcium ions and cause increased excretion from the organism along with an osmotically equivalent amount of water. Thiazides are also effective in acidosis or alkalosis, inhibiting carbonic anhydrase in vitro, and lowering arterial pressure in hypertensive patients.

The antihypertensive effect of thiazides can be explained by their diuretic action, i.e. by lowering the volume of circulated blood. It is also possible that the antihypertensive action of thiazides occurs as a result of their spasmolytic action on the walls of vessels, possibly as a result of changing sodium ion contents in muscle fibers. Reactivity of the vascular system changes under thiazide action, and pressor reactions on vasoconstricting substances (adrenaline and others) are reduced. The majority of side effects of thiazides occur along with hypertension or electrolytic irregularities such as hyponatremia, hypkalemia, or hypo-magnesemia. Around 1% of patients using thiazide diuretics develop skin rashes. Thiazides are used either independently, or in combination with other antihypertensive drugs to treat hypertension.

In medical practice, the most frequently used are hydrochorthiazide, chorthiazide, ben-thiazide, bendroflumethiazide, hydroflumethiazid, polythiazide, trichlormethiazide, as well as related thiazides, but not those named chlortalidon, metolazone, and indapamide.

Chlorothiazide: Chlorothiazide, 1,1-dioxide 6-chloro-2H-1,2,4-benzothiadiazin-7-sulfon-amide (21.3.3) is synthesized in the exact same manner, is all thiazide diuretics. 3-Chloroaniline (or 3-trifluoromethylaniline) undergoes sulfoylchlorination by chlorosulfonic acid, forming 4,6-sulfonochloride-3-chloroaniline (21.3.1), the reaction of which with ammonia gives 4,6-sulfonylamido-3-chloroaniline (21.3.2). Heating this with formamide leads to formation of chlorothiazide (21.3.3) [9-11].

NH2 2 NH3

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  • Tauno Hull
    How to synthesize thiazide?
    3 years ago

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