Ahh! Furane, I made some fluoro furanes. They are somewhat acid labile, very unstable compared to thiophene. They are only partially aromatic. You can see this on NMR, the signals are closer to vinylethers than aromatic signals. But if you dont plan to boil in HCl they are fine. But maybe you should spread out the structures more, phenyl, thiophene, furane, biphenyl. They are all lipophilic. The pyrimidinyl you suggested is more different, hydrophilic. Sometimes you gain affinity to a receptor just by making the molecule more lipophilic just because the drug want to get away from the water surrounding the receptor if the drug is lipophilic, the drug-receptor complex gets stabilized. We had this effect on the PETT-nnRT-inhibitors in our HIV-project. So it could be good to make lipophilic things, thats for sure and in your case the rest of the molecule is polar so it could be even more important in your project. But you are digging in the same place with these molecules, maybe the thiophene+biphenyl is enough to start with, the furane is so similar? Just a thought.