The practical synthesis of a methylenebisphosphonate analogue of benzamide adenine dinucleotide: Inhibition of human inosine monophosphate dehydrogenase (type I and II)

β-Methylene-BAD (8), a nonhydrolyzable analogue of benzamide adenine dinucleotide (BAD), was synthesized as potential inhibitor of human inosine monophosphate dehydrogenase (IMPDH). Treatment of 2',3'O- isopropylideneadenosine 5'-methylenebisphosphonate (15) with DCC afforded P¹,P⁴-bis(2',3'-O-isopropylideneadenosine) 5'-P¹,P²:P³,p⁴- dimethylenetetrakisphosphonate (17). This compound was further converted with DCC to an active intermediate 18 which upon reaction with 3.(2',3'-O- isopropylidene-β-D-ribofuranosyl)benzamide (19) gave, after hydrolysis and deisopropylidenation, the desired β-methylene-BAD (8) in'95% yield. In a similar manner, treatment of 18 with 2',3'-O-isopropylidenetiazofurin (21) followed by hydrolysis and aleprotection afforded β-methylene-TAD (5) in 91% yield. Compound 8 (IC₅₀ = 0.665 μM) was found to be a 6-8 times less potent inhibitor of IMPDH than 5 (IC₅₀ = 0.107 μM) and was almost equally potent against IMPDH type I and type II. Although TAD and β-methylene-TAD were bound by LADH with the same affinity, the binding affinity of 8 toward LADH (K(i) = 333 μM) was found to be 50-fold lower than that of the parent pyrophosphate 7 (K(i) = 6.3 μM).