Experimental and theoretical studies on the conformational properties of cis- and trans-4,5-methano-L-prolines
It is well known that 4,5-methano-L-prolines have different conformational properties and characteristics than proline. The flattening of the pyrrolidine ring plays a role in the stability and conformation of L-proline methanologs. Thus, extensive studies have been conducted to analyze the structural differences and folding patterns of cis- and trans-4,5-methano-L-prolines and their oligomers in correlation with the n→π∗ electron delocalization between the adjacent carbonyls of amide and ester groups. In this thesis, the n→π∗ stabilization of each derivative is analyzed, disclosing additional structural properties of 4,5-methano-L-prolines. NMR spectroscopic studies revealed the spatial characteristics of cis- and trans-4,5-methano-L-prolines in correlation to the amide trans : cis isomerization equilibrium in different solvents. In addition, the tendency of diketopiperazine formation from the cis-cis, trans-trans, and mixed trans,cis-4,5-methano-L-proline dimers reflected the importance of the n→π∗ stabilization on the conformation and folding characteristics.
polyproline trans : cis isomerization diketopiperazine Methanoproline