RESUMO
The conformational space of protected amino acid HCO-Tryptophane-NH2 was explored by using a new optimization procedure, in order to localize the stable minima on its potential energy surface (PES). The genetic algorithm based on the Multi-Niche Crowding (MNC) technique was used initially to generate a set of optimized structures for title compound. Resulting structures from the genetic algorithm technique will be used hereafter as input conformers at a hierarchy of increasingly more accurate electronic structure calculations (RHF/6-31G+(d) and DFT/B3LYP/6-31G+(d) geometry optimizations). The lowest energy conformer γL(g+g+) presents a folded Backbone that is stabilized by strong hydrogen bond noted C7. This links the carbonyl oxygen of the formyl group and the hydrogen of the amine group. There are further interactions from one hand between the carbonyl oxygen of the formyl group and the neighboring CH group on the pyrrole ring and from other hand between the N-terminus hydrogen and the indole ring in accordance with the experimental results. This work includes also a comparison between the theoretical calculations and the experimental results of X-ray crystallography extracted from protein data bank (PDB).
