Synthesis of diastereoisomeric peptides incorporating cycloglutamic acids. Substrate specificity of vitamin K-dependent carboxylation

Solution conformation of alpha, beta or gamma-methylglutamyl-containing derivatives as probes of vitamin K-dependent carboxylase using molecular modelling and nuclear magnetic resonance

In the present study, the conformational behaviour of methyl substituted N-BOC glutamic acid methyl esters (2M, 3T, 3E, 4T, 4E) has been completely characterized through combined NMR and molecular modeling studies. Hetero- and homonuclear coupling constants were measured in order to assign the remaining diastereotopic methylene protons at C(3) and/or C(4), and used for comparison with theoretical data. In parallel, the complete conformational analysis of these analogues has been achieved using molecular mechanics and molecular dynamics (MD) methods. The conformation of the glutamyl residue is established by the excellent agreement between the experimental and calculated side chain scalar coupling constants. The theoretical NMR data were calculated taking into account all the accessible conformations and using the averaging methods appropriate for internal motions. There is a significant influence of the methyl group on the conformational behaviour and on the biological relevance of these structures. Steric effect or electrostatic interaction may also have a considerable influence in stabilizing a conformational population in D2O solution. The conformational preferences of those different analogues in aqueous and methanol solution are discussed in the light of biological results obtained on the vitamin K-dependent carboxylase system.