Synthesis of New Unexpected Stable Mixed Alkanoic, Phosphonic and Sulphonic (Dichloromethylene)bisphosphonic Anhydride Esters

New mixed alkanoic, phosphonic and sulphonic (dichloromethylene)bisphosphonic anhydride esters [(RO)2P(O)CCl2P(O)(OX)(O−Z+), (RO)2P(O)CCl2P(O)(OX)(OR) and (Z+O−)(RO)P(O)CCl2P(O)(OX)(O−Z+); X=C(O)R, P(O)(OR)2, SO2Me; R=CH3, C6H5, CH(CH3)2, (CH2)5CH3; Z=ammonium, Na+, K+)] were selectively synthesised, and characterised by NMR spectroscopy. These new compounds are stable and bear potential bioreversible bisphosphonate protecting groups.