Chapter 20. Pyrimidinomethylthiazole derivatives

Pyrimidinomethylthiazole derivatives are based on:

1. Thiamine chloride (bromide)

2. Thiamini chloridum (bromidum)

4-methyl-5-β-hydroxyethyl-N-(2-methyl-4-amino-5-methylpyrimidyl)-thiazolium bromide hydrobromide

Description

White crystalline substances with a yellow tint. They have a characteristic odor and are easily soluble in water (reaction of the medium is acidic, pH = 2.7-3.6).

3. Cocarboxylase hydrochloride

Cocarboxylasi hydrochloridum

It is a coenzyme, an ester of thiamine and phosphoric acid.

Description. It is a white crystalline powder, easily soluble in water. Reaction of the medium is acidic. Available in ampoules as a lyophilized powder. To be prepared ex tempore (because of its thermolability).

Identification

1. Salts of nitrogen-containing organic compounds: soluble in water, acidic reaction of the medium.

A) It is impossible to separate the base, because it is decomposed by alkali.

B) Precipitation with general alkaloid reagents. Thiamine bromide - a precipitate is quantitatively formed with silicotungstic acid.

2. Three pharmacopoeial reactions to the residue of phosphoric acid after acid hydrolysis of cocarboxylase with nitric acid:

1) + AgNO₃ ⇒ Ag₃РО₄ ↓ yellow precipitate;

2) + Mg²⁺ + NH₄Сl + NH₄OH ⇒ NH₄MgPO₄ ↓ white precipitate;

3) + (NH₄)₂MoO₄ → (NH₄)₃PO₄*12MoO₃ ↓ yellow precipitate.

3. To chloride and bromides - with AgNO₃.

4. A specific general group reaction: the formation of thiochrome.

Substance + water + 1 ml K₃[Fe(CN)₆] (oxidizing agent) + 1 ml 10% alkali (3 equivalents) + butanol or isoamyl alcohol (lighter than water) ⇒ shake ⇒ blue fluorescence appears in the upper layer in UV light (THIOCHROME) ⇒ add acid ⇒ coloration disappears ⇒ add more alkali ⇒ coloration reappears.

Stages

1. Neutralization of НBr: substance + NaOH ⇒ NaBr + water + [thiamine⁺]Br^-

2. Formation of thiazole base and pseudo base:

+ NaOH ⇒ -NaBr ⇒ :

3. Formation of the thiol form of thiamine:

4. Oxidation:

Thiochrome: blue fluorescence in UV. Authenticity and assay (fluorimetry).

Assay

1. Cocarboxylase hydrochloride ― neutralization. Т = NaOH. The indicator is thymolphthalein. Titrated HCl and two ОН^- M(1/z)= Mm/3.
2. Thiamine hydrochloride ― substance: acid-base titration in non-aqueous media, solvent: HCOOH + acetic anhydride, T = HClO₄; the indicator is crystal violet.
3. End product: [thiamine]ClO₄^-*HClO₄ ― thiamine diperchlorate (2 mol HClO₄) M(1/z)= Mm/2.

Other methods: SPM in UV, HPLC with a reference standard.