Physically ribavirin is similar to the sugar D-ribose from which it is derived. It is freely soluble in water, and is re-crystallized as fine silvery needles from boiling methanol. It is only sparingly soluble in anhydrous ethanol.
Classically ribavirin is prepared from natural D-ribose by blocking the 2', 3' and 5' OH groups with benzyl groups, then derivatizing the 1' OH with an acetyl group which acts as a suitable leaving group upon nucleophilic attack. The ribose 1' carbon attack is accomplished with a 1,2,4 triazole-3-carboxymethyl ester, which directly attaches the 1' nitrogen of the triazole to the 1' carbon of the ribose, in the proper 1-β-D isomeric position. The bulky benzyl groups hinder attack at the other sugar carbons. Following purification of this intermediate, treatment with ammonia in methanolic conditions then simultaneously deblocks the ribose hydroxyls, and converts the triazole carboxymethyl ester to the carboxamide. Following this step, ribavirin may be recovered in good quantity by cooling and crystallization.
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