Efficient solution phase synthesis and use of multiple O‐phosphothreonyl‐containing peptides for calcium phosphate binding studies

Abstract
The protected phosphothreonine derivative Boc‐Thr(PO3Ph2)‐OH was prepared in high yield from Boc‐Thr‐OH by a simple three‐step procedure which involved 4‐nitrobenzylcarboxyl protection, either phosphorotriester (diphenyl phosphorochloridate) or “phosphite‐triester” (diphenyl N.N‐diethylphosphoramidite) phosphorylation of the thrconine hydroxyl group of Boc‐Thr‐ONb followed by hydrogenolytic carboxyl deprotection. The three Thr(P)‐containing peptides, H‐Thr(P)‐Glu‐Glu‐NHMe.TFA, H‐Thr(P)‐Thr(P)‐Glu‐Glu‐NHMe.TFA and H‐Thr(P)‐Thr(P)‐Thr(P)‐Glu‐Glu‐NHMe.TFA, were prepared in high yield by the use of Boc‐Thr(PO3Ph2)‐OH in the Boc mode of peptide synthesis (mixed anhydride method) followed by platinum‐mediated hydrogenolytic deprotection of the Thr(PO33Ph2)‐containing peptides. The use of the phosphopeptides in calcium phosphate binding studies showed that the triple Thr(P)‐cluster was a basic structural requirement, since only the pentapeptide was able to bind calcium phosphate efficiently.

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