Abstract: Phosphates play a crucial role in a wide range of biological processes. Numerous efforts have been devoted to molecular recognition, transport and catalytic hydrolysis of phosphate^1-4. Recent reports have shown that molecules containing several hydrogen-bonding group directed into a cleft or cavity can effectively recognize phosphate^5,6. We now report a new family of pseudo-cyclopeptides 1-4 as receptors for phosphomonoester, which were synthesized by the reaction of pyridine 2,6-dicarbonyl dichloride with cystine bis-peptides(H₂N-Xaa-Cyst-Xaa-NH₂) dimethylester leading to a variety of 1+1 cystine-based cyclic peptides with the general structure cyclo(Py-CONH-Xaa-Cyst-Xaa-NHCO-) (Cyst=L-cystine dimethyl ester; Xaa=amino acid X) and identified by conventional spectroscopic methods⁷.