A spectroscopic and molecular modeling study on novel pseudopeptides exhibiting biological activity

Abstract

A series of pseudopeptides, containing two fluorophores, such as naphthalene (N) and indole (I), and exhibiting interesting biological activity as tachykinin receptor antagonists, were investigated by electronic absorption, CD and steady-state fluorescence experiments. In polar solvents (e.g. methanol), bioactivity is coupled with a stacked, charge-separated complex between I and N, the amount of which depends on the stereochemical features and conformational mobility of the central scaffold in the molecules examined. This agrees with the idea that dipolar charged, spatially close, aromatic moieties are important topochemical elements in the mechanism of action of these receptor antagonists. Molecular mechanics calculations allowed us to build up hypothetical, low-energy conformations of a few representative pseudopeptides, whose structural features are consistent with the experimental findings.

Structural features and conformational equilibria of 310‐helical peptides in solution by spectroscopic and molecular mechanics studies

“…In the past years we successfully studied the structural features of short, ordered peptides in solution by a combined approach of fluorescence resonance energy transfer experiments 3 and molecular mechanics calculations 4, 5. This implies that the compounds examined had to carry two fluorophores, which is often the case for bioactive peptides or drugs6 and proteins (tryptophan, tyrosine, etc. ), one acting as a donor and the other one as an acceptor.…”

Positive Photocatalysis of a Diels−Alder Reaction by Quenching of Excited Naphthalene−Indole Charge-Transfer Complex with Cyclohexadiene

“…Interestingly, as the concentration of InH was increased, the fluorescence of NP decreased, and a new emission band was observed at wavelengths longer than those of NP fluorescence (see Figure ). The excitation spectrum at λ em = 388 nm evidenced that the species responsible for the emission between 370 and 450 nm was not a ( 1 NP*−InH) exciplex but an excited NP−InH charge transfer ( 1 CT*) complex absorbing between 300 and 370 nm, with λ max at 344 nm (see Figure and Scheme i,ii). ,, From the monoexponential fluorescence decay (see inset in Figure ) 1 CT* lifetime was estimated as ca. 3 ns; it was only slightly (although linearly) dependent on [InH], evidencing a weak interaction between 1 CT* and InH (Scheme iii).…”