While not intending to be bound by any theory of operation, when y is I in the exemplary phosphate-containing progroups Rp, it is believed that the phosphate-containing prodrugs are converted in vivo by enzymes such as phosphatases, lipases and/or esterases to the corresponding hydroxymethylamines, which are then further metabolized in vivo by the elimination of formaldehyde to yield the active 2,