Competitive inhibitors of type B ribose 5-phosphate isomerases: design, synthesis and kinetic evaluation of new d-allose and d-allulose 6-phosphate derivatives Original Research Article

This study reports syntheses of d-allose 6-phosphate (All6P), d-allulose (or d-psicose) 6-phosphate (Allu6P), and seven d-ribose 5-phosphate isomerase (Rpi) inhibitors. The inhibitors were designed as analogues of the 6-carbon high-energy intermediate postulated for the All6P to Allu6P isomerization reaction (Allpi activity) catalyzed by type B Rpi from Escherichia coli (EcRpiB). 5-Phospho-d-ribonate, easily obtained through oxidative cleavage of either All6P or Allu6P, led to the original synthon 5-dihydrogenophospho-d-ribono-1,4-lactone from which the other inhibitors could be synthesized through nucleophilic addition in one step. Kinetic evaluation on Allpi activity of EcRpiB shows that two of these compounds, 5-phospho-d-ribonohydroxamic acid and N-(5-phospho-d-ribonoyl)-methylamine, indeed behave as new efficient inhibitors of EcRpiB; further, 5-phospho-d-ribonohydroxamic acid was demonstrated to have competitive inhibition. Kinetic evaluation on Rpi activity of both EcRpiB and RpiB from Mycobacterium tuberculosis (MtRpiB) shows that several of the designed 6-carbon high-energy intermediate analogues are new competitive inhibitors of both RpiBs. One of them, 5-phospho-d-ribonate, not only appears as the strongest competitive inhibitor of a Rpi ever reported in the literature, with a Ki value of 9 μM for MtRpiB, but also displays specific inhibition of MtRpiB versus EcRpiB.