Conformations of cis- and trans-2,3-methanomethionine stereoisomers in the tripeptide mimic system Ac[cyclo-M]NHiPr.
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abstract
Quenched molecular dynamics (QMD) was used to simulate low-energy conformers of the tripeptide mimics Accyclo-MetNHiPr, where the 2.3-methanomethionine is the cis-derivative (2R,3S)-cyclo-Met and the trans-derivative (2R,3R)-cyclo-Met. Variations of the favored omicron, upsilon values. and differences between the simulated preferred conformations for the two structures, were rationalized and discussed. Physical data for the cis-derivative (NMR, CD and FT-IR) gave no conclusive evidence for any preferred conformation. However for the trans-derivative, Ac(2R,3R)-cyclo-MetNHiPr, the physical data suggests that a conformer with partial helical structure is favored. This work provides details of how the rigidly constrained side chain and cyclopropane of 2,3-methanoamino acids can be used to manipulate phi, psi values in a logical fashion.