Autofluorescent fused-pyrimidine nucleosides: Synthesis and evaluation as permeants and inhibitors of human nucleoside transporters

Nucleosides with an aromatic five-membered ring heterocycle (N, O, or S) fused at C4–C5 of pyrimidin-2-one were prepared by ring closures with 5-(alkyn-1-yl)pyrimidin-2-one intermediates, heterocyclic atom replacements, and ring closure with a 5-aminocytidine derivative. Ultraviolet absorption and emission properties of the autofluorescent products enabled studies on permeation and inhibition of the trans-cellular trafficking effected by human equilibrative nucleoside transporters (hENTs). Some of the autofluorescent nucleosides were shown to be potent and selective inhibitors of human concentrative nucleoside transporters (hCNTs) in a companion study reported elsewhere.