0000000000214430
AUTHOR
Agnieszka Macedowska
Conformational studies into N-methylation of alanine diamide models: A quantitative approach
Abstract A systematic theoretical analysis was performed on N -acetyl- l -alanine N ′-methylamide (Ac- l -Ala-NHMe) and the analogues methylated on the N-terminus (Ac- l -(Me)Ala-NHMe), C-terminus (Ac- l -Ala-NMe 2 ), and both N/C-termini (Ac- l -(Me)Ala-NMe 2 ), to evaluate the influence of methylation of the amide group on the conformational properties of the affected residues. The ϕ , ψ potential energy surfaces were calculated at the B3LYP/6-31+G**//HF/3-21G level of theory with inclusion of the solvent (water) effect (SCRF method). The conformers localised were fully optimised at the B3LYP/6-31+G** in vacuo. The accessible areas of the potential energy surfaces; the number of conformer…
Conformational properties of N-acetyl-N-methyl-alpha,beta-dehydroalanine N'-methylamide.
The conformational properties of Ac-Delta(Me)Ala-NHMe (N-acetyl-N-methyl-alpha,beta-dehydroalanine N'-methylamide), as the simplest model of N-methyl-alpha,beta-dehydroamino acids, was examined with theoretical methods and in comparison with Ac-DeltaAla-NHMe and Ac-DeltaAla-NMe(2). The N-terminal amide of the Delta(Me)Ala residue easily adopts the configuration cis and the torsion angles phi, psi are highly flexible. The Delta(Me)Ala residue is a conformational flexibilizer as compared to the parent DeltaAla, which is a conformational stiffener. This seems to be the reason why Delta(Me)Ala is found in small natural cyclic peptides, where it ensures the conformational flexibility necessary f…