1,1'-Dimethyl-1H,1'H-[4,4']bipyrimidinyl-6,6'-dione

1,3,7-trimethyl-8-(pyridin-2-yl)-xanthine

8-[2,2']Bipyridinyl-6-yl-1,3,7-trimethyl-3,7-dihydro-purine-2,6-dione

8,8'-bis-(1,3,7-trimethylxanthine)

4,4'-联吡啶