C07F 9/65616

Heterocyclic compounds, e.g. containing phosphorus as a ring hetero atom containing systems of two or more relevant hetero rings condensed among themselves or condensed with a common carbocyclic ring or ring system, with or without other non-condensed hetero rings {containing the ring system having three or more than three double bonds between ring members or between ring members and non-ring members, e.g. purine or analogs}