For an exact determination of the structure of the isomer (diastereomers and/or enantiomers), standards must be used. These standards are not commercially available, so they must be synthesized. The synthesis of individual PG isomers has been described several times. Two types of synthesis are possible, either total organic synthesis, based mainly on (R)-and (S)solketals, in which the respective isomers are obtained by multiple synthesis , or a reaction of phosphatidylcholine with (R)-and (S)-solketals in the presence of phospholipase D .