title: Solution and solid-state structure of the diketopiperazine of tyrosyl-tetrahydroisoquinoline-3-carboxylic acid.
abstract: delta-Selective antagonism of [L-Tic2]-peptides, including the simple dipeptide Tyr-L-Tic-NH2, is linked to the Tyr-Tic-"recognition site". In order to gain further information on the conformational preferences of the Tyr-Tic-moiety we have undertaken a structural study of a cyclic analog, the diketopiperazine of Tyr-Tic. A conformational study of cyclo[-Tyr-Tic-], that is almost devoid of opioid activity, can also be useful to discriminate between the role of the two aromatic rings and of the basic nitrogen in determining antagonism. The structure of cyclo[-Tyr-Tic-] has been solved in a DMSO/water solution at 278 K by NMR spectroscopy and in the solid state by X-ray diffraction methods. The two informations are almost identical, with an arrangement of the aromatic rings rather different from that of the putative bioactive conformation of the parent linear dipeptide. This difference points to the importance of conformational effects and is in agreement with the hypothesis that the positive center may be not essential for antagonism.
authors.affiliation: Department of Chemistry, University of Naples Federico II, Italy.
authors.forename: M R
authors.initials: MR
authors.lastname: Ciajolo
authors.forename: G
authors.initials: G
authors.lastname: Balboni
authors.forename: D
authors.initials: D
authors.lastname: Picone
authors.forename: S
authors.initials: S
authors.lastname: Salvadori
authors.forename: T
authors.initials: T
authors.lastname: Tancredi
authors.forename: P A
authors.initials: PA
authors.lastname: Temussi
authors.forename: A
authors.initials: A
authors.lastname: Tuzi
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D054659:Diketopiperazines; D004121:Dimethyl Sulfoxide / Q000737:chemistry; D007546:Isoquinolines / Q000737:chemistry* / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000737:chemistry* / Q000378:metabolism; D010879:Piperazines / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D017465:Receptors, Opioid, delta / Q000037:antagonists & inhibitors*; D012995:Solubility; D013329:Structure-Activity Relationship; D044005:Tetrahydroisoquinolines; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D014961:X-Ray Diffraction
chemical_list: C097291:2-tyrosyl-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid; D054659:Diketopiperazines; D007546:Isoquinolines; D009842:Oligopeptides; D010879:Piperazines; D017465:Receptors, Opioid, delta; D044005:Tetrahydroisoquinolines; D014443:Tyrosine; D004121:Dimethyl Sulfoxide