The cyclization of N-benzyl-N'-propylurea (I) with cyanacetic acid (II) in hot acetic anhydride gives 6-amino-1-benzyl-3-propyluracil (III), which is nitrosated with NaNO2/acetic acid and reduced with sodium dithionite to yield 5,6-diamino-1-benzyl-3-propyluracil (IV). The cyclization of (IV) with cyclopentylcarbonyl chloride (V) by means of NaOH in refluxing ethanol affords 3-benzyl-8-cyclopentyl-1-propylxanthine (VI), which is acylated with pivaloyl chloride (VII)/Na2CO3 in DMF giving the expected 7-acyl derivative (VIII). The debenzylation of (VIII) by hydrogenation over Pd/C as usual yields 8-cyclopentyl-7-pivaloyl-1-propylxanthine (IX), which is condensed with 1-bromo-3-fluoropropane (X) by means of Na2CO3 in DMF to afford 8-cyclopentyl-3-(3-fluoropropyl)-7-pivaloyl-1-propylxanthine (XI). Finally, this compound is deprotected with NaOH in DMSO/water.

The reaction of 8-cyclopentyl-3-(3-hydroxypropyl)-1-propylxanthine (I) with Ts-Cl and TEA gives the corresponding tosylate (II), which is then radiolabeled by means of 18FK and Kryptofix to provide the target radiolabeled compound.