Chemical Synthesis, Proton NMR. Parameters, Hydrogen‐ and Calcium‐Ion. Complexation of L‐γ‐Carboxyglutamyl‐L‐γ‐carboxyglutamic Acid and D‐γ‐Carboxyglutamyl‐L‐leucine

The purpose of this communication is to describe the preparation and some properties of the first two synthetic peptides containing D ‐ and L ‐γ‐carboxyglutamic acid. Use was made of N ‐protected γ,γ′‐di‐ t ‐butyl‐γ‐carboxyglutamic acids ( D , L , and DL ) described earlier [1 a]. Preliminary 1 H‐NMR. data (360 MHz) indicate a restricted rotation of the Gla side chain in the free amino acid as well as in the C‐terminal Gla of Gla‐Gla in H 2 O solution at acid pH. The proton dissociation from Gla and Gla‐Gla was studied by potentiometric titration and NMR. methods. The pH titration in the presence of Ca 2+ ions shows that Gla‐Gla has a much higher association constant for this cation than Gla. It is almost as great as that of prothrombin (pCa 2+ = 3.2 vs. 3.5).