Synthesis of pyridoxal phosphate derivatives with antagonist activity at the P2Y13 receptor

We have synthesized a series of derivatives of the known P2 receptor antagonist PPADS (pyridoxit-5'-phosphate-6-azo-phenyl-2.4-disulfonate) and examined their ability to inhibit functional activity of the recombinant human P2Ytt nucleotide receptor expressed in 1321N1 human astrocytoma cells co-expressing G alpha(16) protein (AG32). Analogues of PPADS modified through substitution of the phenylazo ring, including halo and nitro substitution, and 5'-alkyl phosphonate analogues were synthesized and tested. A 6-benzyl-5'-methyl phosphonate analogue was prepared to examine the effect of stable replacement of the azo linkage, The highest antagonistic poteney was observed for 6-(3-nitrophenylazo) derivatives of pyridoxal-5'-phosphate, The 2-chloro-5-nitro analogue (MRS 2211) and 4-chloro-3-nitro analogue (MRS 2603) inhibited ADP (100 nM)-induced inositol trisphosphate (IP3) formation with pIC(50) values of 5.97 and 6.18, respectively, being 45- and 74-fold more potent than PPADS. The antagonism of MRS 2211 was competitive with a pA(2) value of 6.3. MRS2211 and MRS2603 inhibited phospholipase C (PLC) responses to 30 nM 2-methylthio-ADP in human P2Y(1) receptor-mediated 1321N1 astrocytoma cells with IC50 values of > 10and 0.245 mu M, respectively. Both analogues were inactive(> 10 mu M) as antagonists of human P2Y(12) receptor-mediated PLC responses in 1321N1 astrocytoma cells, Thus. MRS2211 displayed > 20-fold selectivity as antagonist of the P2Y(13) receptor in comparison to P2Y(1) and P2Y12 receptors, while MRS2603 antagonized both P2Y(1) and P2Y(13), receptors. (c) 2005 Elsevier Inc. All rights reserved.