Synthesis and biological activity of phosphonate analogues and geometric isomers of the highly potent phosphoantigen (E)-1-hydroxy-2-methylbut-2-enyl 4-diphosphate

Gammadelta-T-lymphocytes contribute to innate immunity and are selectively activated by nonpeptide phosphorylated molecules (so-called phosphoantigens) produced by organisms responsible for causing a broad range of infectious diseases. gammadelta-T-cells are also activated by synthetic phosphoantigens and are cytotoxic to tumor cells. Here we report the synthesis, NMR characterization, and comparative biological evaluation of new pyrophosphate, phosphonate, and pyrophosphonate monoesters whose structures correspond to isosteric analogues and stereoisomers of the highly potent isoprenoid metabolite ( E)-1-hydroxy-2-methylbut-2-enyl 4-diphosphate called HDMAPP (hydroxy-dimethyl-allyl pyrophosphate). Both pyrophosphate and pyrophosphonate series elicit promising gammadelta-T-cell stimulatory responses in vitro, the pyrophosphonate ester (C-HDMAPP) being by far more stable than its parent pyrophosphate ester (HDMAPP) with improved ADMET properties and a similar pharmacodynamic profile based on in vivo studies in nonhuman primate. In both series, we found that E-stereoisomers are the most active derivatives and that Z-stereoisomers show very marginal bioactivity levels. These results indicate that the use of bioisosteric analogues of HDMAPP may represent promising new leads for immunotherapy.