ABSTRACT
A series of six arginine-glycine-aspartate (RGD) cyclopeptide analogues containing a C(alpha)-di- or trifluoromethylamino acid (alpha-Dfm or alpha-TfmAaa) at different positions of the ring were synthesized. All peptides were obtained in two diastereomeric forms, which were separated by HPLC. In vitro biological tests of the new cyclopeptides P were carried out in comparison with their corresponding cyclopeptides R lacking the alpha-fluoromethyl group. Five out of the six compounds P-I (containing (S)-alpha-Tfm-Aaa) showed activities in the nanomolar range, while the P-II compounds (containing (R)-alpha-Tfm-Aaa) were much less active or totally inactive. Only cyclo[RGDf-(S)-alphaTfmV] (P1-I) was found to be significantly more active than its model compound cyclo(RGDfV) (R1). The three-dimensional structure in water and DMSO was determined by NMR techniques and molecular dynamics (MD) calculations, but it was not possible to highlight significant differences in the backbone conformation of the peptides examined. Significant interproton distances, derived from nuclear Overhauser effect (NOE) experiments, were used to determine the absolute configuration of the side chains.
Subject(s)
Amino Acids/chemistry , Fluorine , Oligopeptides/chemical synthesis , Peptides, Cyclic/chemical synthesis , Dimethyl Sulfoxide , Integrin alphaVbeta3/chemistry , Integrins/chemistry , Magnetic Resonance Spectroscopy , Models, Molecular , Molecular Conformation , Oligopeptides/chemistry , Peptides, Cyclic/chemistry , Receptors, Vitronectin/chemistry , Stereoisomerism , Structure-Activity Relationship , WaterABSTRACT
N(alpha)-Protected alpha-amino acid bromides were easily generated in situ with 1-bromo-N,N-2-trimethyl-1-propenylamine from the corresponding amino acids under very mild conditions. o-Nbs and the azido moieties proved to be compatible with these overactivated halides and were successfully applied in difficult peptide bond formations. N-Deprotection methods and the total step-by-step solution synthesis of a peptide containing up to seven consecutive L-(alphaMe)Valine residues are also reported. The assembly of this homopeptide was achieved in a short time and in very high yields by the azido/bromide system in a single repetitive operation.
