Process for preparing 1,3-dipropyl-8-(3-oxocyclopentyl)-xanthine

A process for preparing 1,3-dipropyl-8-(3-oxocyclopentyl)-xanthine comprising the steps of:

• a) reacting a mixture of 1,4-dioxaspiro[4,4]nonan-7-carboxylic acid and carbonyldiimidazole with 5,6-diamino-1,3-dipropyluracil, under basic conditions, in the presence of aqueous calcium hydroxide;
• b) isolating, as an intermediate, the 1,3-dipropyl-8-[(1,4-dioxaspiro[4,4-nonan-7-yl)]-xanthine thus produced;
• and,
• c) hydrolyxing the dioxolane protecting group, with acid, to obtain 1,3-dipropyl-8-(3-oxocyclopentyl)-xanthine.