合成路线1

The sodium salt of triethyl methanetricarboxylate (I) was alkylated with 1,2-dibromoethane (II) to afford bromide (III). Subsequent condensation of 6-(methylamino)-2-chloropurine (IV) with bromide (III) in the presence of K2CO3 gave adduct (V). Mono-decarbethoxylation of tricarboxylate (V) upon treatment with NaOMe produced malonate (VI), which was further reduced to diol (VII) by means of NaBH4 in CH2Cl2-MeOH. Treatment of (VII) with tetrabenzyl pyrophosphate in the presence of LDA gave rise to the bis-phosphate ester (VIII). The benzyl groups of (VIII) were then cleaved employing boron trichloride, and the resulting phosphoric acid was purified through an ion-exchange resin in the presence of ammonium bicarbonate to furnish the title tetraammonium salt.