Acetylation of 5-amino-N,N'-bis(2,3-dihydroxypropyl)-2,4,6-triiodoisophthalamide (I) in refluxing acetic anhydride in the presence of p-toluenesulfonic acid affords acetamide (II). The title compound is then obtained by alkylation of acetamide (II) with 1-chloro-3-methoxy-2-propanol (III). The selectivity in the alkylation at the acetamide N has been improved with the addition of several metallic cations, the best results being obtained with calcium ions.
In an improved method, the acetamido isophthalamide (I) is treated with boric acid and KOH to form the cyclic diborate tripotassium salt (II). Subsequent alkylation of (II) with 1-chloro-3-methoxy-2-propanol (III) yields regioselectively the N-alkylated acetamide (IV). The borate groups of (IV) are finally removed upon quenching with diluted HCl.
In a different strategy, the acetamido isophthalamide (I) is treated with boric acid and KOH to form the cyclic diborate tripotassium salt (II). Subsequent condensation of (II) with epichlorohydrin (III) yields the dimeric adduct (IV). The borate groups of (IV) are finally removed upon quenching with diluted HCl.
In an improved method, the acetamido isophthalamide (I) is treated with boric acid and KOH to form the cyclic diborate tripotassium salt (II). Subsequent alkylation of (II) with 2-chloroethanol (III) yields regioselectively the N-alkylated acetamide (IV). The borate groups of (IV) are finally removed upon quenching with diluted HCl.
Alternatively, 5-acetamido-2,4,6-triiodoisophthalic acid (I) is alkylated with 1-chloro-3-methoxy-2-propanol (II) to produce (III). After protection of the alcoholic hydroxyl group as the acetate ester (IV), the carboxyl groups are activated as the corresponding acid chloride (V) with SOCl2. Coupling of (V) with 3-amino-1,2-propanediol (VI) then produces the title amide.