This compound can be obtained by two differents ways: 1) By condensation of 6-allyl-N-[3-(dimethylamino)propyl]ergolin-8-beta-caboxamide (I) with ethyl isocyanate (II) in refluxing toluene. 2) By condensation of 6-allylergolin-8-beta-carboxylic acid (III) with N-ethyl-N'-[3-(dimethylamino)propyl]carbodiimide (IV) in refluxing THF.
The synthesis of tritiated cabergoline by two similar routes has been described: 1) The acylation of 6-nor-dihydrolysergic acid methyl ester (I) with propargyl bromide yields the corresponding 6-propargyl derivative (II), which is hydrogenated with tritium gas over Pd/C in the presence of quinoline to give the ditritiated 6-allyl derivative (III). This compound is treated with 3-(dimethylamino)propylamine at 120 C, yielding the amide (IV), which is finally treated with ethyl isocyanate. 2) The reaction of the propargyl derivative (II) with 3-(dimethylamino)propylamine as before gives the amide (V). The reaction of (V) with ethyl isocyanate gives compound (VI), which is then hydrogenated with tritium as before.
The synthesis of [14C]-cabergoline has also been described: The reaction of 6-allylergoline-8beta-carboxylic acid methyl ester (I) with hydrazine in refluxing methanol gives the hydrazide (II), which by reaction with NaNO2-HCl in water is converted to the amine (III). The reaction of (III) again with NaNO2-HCl in water, followed by reaction with SnCl2, affords the chloro derivative (IV), which is condensed with [14C]-CNK in refluxing ethanol-water yielding the nitrile (V). Hydrolysis of (V) with NaOH in refluxing ethanol affords the acid (VI), which is finally condensed with N-ethyl-N'-[3-(dimethylamino)propyl]carbodiimide in DMF.