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Chemistry of Isoniazid
Isoniazid is a simple chemical structure with a pyridine ring and a hydrazide group. The synthesis of this chemical compound was done by two scientists at Charles University in Prague in 1912, but the medicinal use was not discovered. Their findings were published but gained immense importance only after their use was later found for anti TB purposes.
The synthesis of Isoniazid takes place by the oxidation of 4-methyl pyridine. This forms isonicotinic acid, a single ringed structure. In the second step, isonicotinic acid is heated with anhydrous hydrazine (NH2NH2) to make a new compound, isonicotinic acid hydrazide (INH) or Isoniazid. It is very important to know the structure-activity relationship of Isoniazid. This is the scope of work under medicinal chemists who are very vigilant of teeny tiny changes. This is because even the slightest change can change the complete properties of the compound and destroy its therapeutic activity.
The compound has one membered ring with Nitrogen inside, making the ring called pyridine. There is a carbamide functional group attached to one of the corners of the pyridine ring. The functional group is further attached with another Nitrogen. One nitrogen group carries two hydrogen groups, while the second Nitrogen has only one hydrogen group. If these hydrogen atoms are replaced by an alkyl group or the position of the hydrogen atoms is changed and shifted to any other position, the therapeutic activity of Isoniazid is completely lost.
Let us suppose hydrogen is replaced with an isopropyl group, the compound would exhibit some psychomotor stimulant activity, but the compound would be inactive for the expected anti TB activity. Any other substitution, removal, or addition of a hydrogen atom or any other group would simply lead to the inactivation of Isoniazid as a therapeutic compound.
