Inhibition of nucleoside transport by new analogues of 4-nitrobenzylthioinosine : Replacement of the ribose moiety by substituted benzyl groups

4-Nitrobenzylthioinosine (NBTI, 1) is a well-known inhibitor for the nucleoside transport protein ENT1. However, its highly polar nature is unfavorable for oral absorption and/or penetration into the CNS. In the search for compounds with lower polarity than NBTI we replaced its ribose moiety by substituted benzyl groups. Halogen, hydroxyl, (trifluoro)methyl(-oxy), nitro, and amine functionalities were among the substituents at the benzyl group. In general, substitution of the benzyl group resulted in a lower affinity for ENT1. Only 2-hydroxyl substitution showed a higher affinity. Most likely this is the result of hydrogen bonding. Substitution at the 2-position of the benzyl group with aryl groups was also addressed. Compared to parent compound carrying a 2-phenylbenzyl group, all synthesized analogues gave higher affinities. Introduction of fluoro, trifluoromethyl, methoxy, and hydroxyl groups at the phenyl group clearly showed that addition to the 4-position was preferable. Despite the highly different...