PEP is a linear polymer of on average 13 repeat units of estradiol phosphate.[2] Each individual estradiol unit in the molecule is connected by its C3 and C17β hydroxyl groups to phosphoric acid linkers that are present between the estradiol moieties.[2] In contrast to estradiol, such a polymer is not possible with testosterone because testosterone has only one hydroxyl group and hence does not have the two hydroxyl groups necessary for linking the testosterone units together.[1] In PTPP, phloretin is used as a coupling agent to solve this problem and create a testosterone phosphate polymer.[1] Phloretin has four available hydroxyl groups present in its chemical structure.[1] A linear polymer of phloretin with phosphoric acid linkers is present as the backbone of the molecule, and testosterone moieties are connected to the free third and fourth hydroxyl groups of each phloretin unit also with phosphoric acid linkers.[1] As such, two testosterone moieties essentially "hang" or "dangle off" of each phloretin unit in the polymer, and these testosterone moieties are slowly cleaved from the polymer.[1]
^ abcdefghijklmUS patent 2928849, Hogberg Knut Bertil; Ferno Ove Birger & Linderot Torsten Ove Enok et al., "High-molecular weight derivatives of steroids containing hydroxyl groups and method of producing the same", published 15 March 1960, assigned to Leo Ab
