Synthesis and structure-activity relationships of pyridoxal-6-arylazo-5 '-phosphate and phosphonate derivatives as P2 receptor antagonists

Novel analogs of the P2 receptor antagonist pyridoxal-5'-phosphate-6-phenyl azo-2',4'-disulfonate (PPADS) were synthesized. Modifications were made thr ough functional group substitution on the sulfophenyl ring and at the phosp hate moiety through the inclusion of phosphonates, demonstrating that a pho sphate linkage is not required for P2 receptor antagonism. Substituted 6-ph enylazo and 6-naphthylazo derivatives were also evaluated. Among the 6-phen ylazo derivatives, 5'-methyl, ethyl, propyl, vinyl, and allyl phosphonates were included. The compounds were tested as antagonists at turkey erythrocy te and guinea-pig taenia coli P2Y(1) receptors, in guinea-pig vas deferens and bladder P2X(1) receptors, and in ion flux experiments by using recombin ant rat P2X(2) receptors expressed in Xenopus oocytes. Competitive binding assay at human P2X(1) receptors in differentiated HL-60 cell membranes was carried out by using [S-35]ATP-gamma-S. A 2'-chloro-5'-sulfo analog of PPAD S (C14H12O9N3ClPSNa), a vinyl phosphonate derivative (C15H12O11N3PS2Na3), a nd a naphthylazo derivative (C18H14O12N3PS2Na2), were particularly potent i n binding to human P2X(1) receptors. The potencies of phosphate derivatives at P2Y(1) receptors were generally similar to PPADS itself, except for the p-carboxyphenylazo phosphate derivative C15H13O8N3PNa and its m-chloro ana log C15H12O8N3ClPNa, which were selective for P2X vs. P2Y(1) receptors. C15 H12O8N3ClPNa was very potent at rat P2X(2) receptors with an IC50 value of 0.82 mu M. Among the phosphonate derivatives, [4-formyl-3-hydroxy-2-methyl- 6-(2-chloro-5-sulfonylphenylazo)-pyrid-5-yl]methylphosphonic acid (C14H12O8 N3ClPSNa) showed high potency at P2Y(1) receptors with an IC50 of 7.23 mu M . The corresponding 2,5-disulfonylphenyl derivative was nearly inactive at turkey erythrocyte P2Y(1) receptors, whereas at recombinant P2X(2) receptor s had an IC50 value of 1.1 mu M. An ethyl phosphonate derivative (C15H15O11 N3PS2Na3), whereas inactive at turkey erythrocyte P2Y(1) receptors, was par ticularly potent at recombinant P2X(2) receptors. (C) 1998 Wiley-Liss, Inc. dagger