Sentence: Reaction of ( R ) - propanediol carbonate with 2,6-diaminopurine afforded exclusively ( R ) -9 - ( 2-hydroxypropyl ) -2,6-diaminopurine which was subsequently used for introduction of a phosphonomethyl residue using TsOCH 2 P ( O ) ( OiPr ) 2 or BrCH 2 P ( O ) ( OiPr ) 2 followed by deprotection of ester groups. 
 Section: background