Incorporation of fluoroprolines to proctolin: Study on the effect of a fluorine atom toward peptidic conformation

In spite of quite small steric perturbation, substitution of proline (Pro) in the target pentapeptide proctolin (Arg-Tyr-Leu-Pro-Thr) for (4R)- as well as (4S)-4-fluoroproline led to apparent alteration of the pyrrolidine ring structure which eventually resulted in the significant conformational change of the whole molecules which was assumed on the basis of their NOESY spectra.