these are 1- ( 1,4-oxathian-3-yl ) -5-fluorouracil ( 8 ) , 1- ( 4-oxo-1,4-oxathian-3-yl ) -5-fluorouracil ( two stereoisomers 9 and 10 , resolved by silica gel column chromatography , 1- ( 1,4-oxathian-3-yl ) -5-fluorouracil ( 11 ) , 1- ( 1,4-oxathian-2-yl ) -5-fluorouracil ( 12 ) , 1- ( 1,4-dithin-2-yl ) -5-flourouracil ( 15 ) , 1- ( 1,4-dithian-2-yl ) uracil ( 16 ) , 1- ( 1,4-dithian-2-yl ) thymine ( 17 ) , and 1- ( 1,4-dioxan-2-yl ) -5-fluorouracil ( 20 ) .
C0041917
uracil
C0016360
5-fluorouracil