cytidine 5'-{[hydroxy(2-hydroxyethyl)phosphonoyl]phosphate} + AH2 + 2 S-adenosyl-L-methionine = cytidine 5'-({hydroxy[(S)-2-hydroxypropyl]phosphonoyl}phosphate) + 5'-deoxyadenosine + L-methionine + A + S-adenosyl-L-homocysteine + 2 H(+) — reaction