660 660 [[(2~{R},3~{S},4~{R},5~{R})-5-[2,4-bis(oxidanylidene)pyrimidin-1-yl]-3,4-bis(oxidanyl)oxolan-2-yl]methoxy-oxidanyl-phosphoryl]oxy-[[(2~{S},3~{R},4~{S},5~{S},6~{R})-6-(hydroxymethyl)-3,4,5-tris(oxidanyl)oxan-2-yl]methyl]phosphinic acid 660