Fluorination of Naturally Occurring N⁶-Benzyladenosine Remarkably Increased Its Antiviral Activity and Selectivity.

Recently, we demonstrated that the natural cytokinin nucleosides N⁶-isopentenyladenosine (iPR) and N⁶-benzyladenosine (BAPR) exert a potent and selective antiviral effect on the replication of human enterovirus 71. In order to further characterize the antiviral profile of this class of compounds, we generated a series of fluorinated derivatives of BAPR and evaluated their activity on the replication of human enterovirus 71 in a cytopathic effect (CPE) reduction assay. The monofluorination of the BAPR-phenyl group changed the selectivity index (SI) slightly because of the concomitant high cell toxicity. Interestingly, the incorporation of a second fluorine atom resulted in a dramatic improvement of selectivity. Moreover, N⁶-trifluoromethylbenzyladenosines derivatives (9-11) exhibited also a very interesting profile, with low cytotoxicity observed. In particular, the analogue N⁶-(3-trifluoromethylbenzyl)-adenosine (10) with a four-fold gain in potency as compared to BAPR and the best SI in the class represents a promising candidate for further development.