title: Synthesis, conformational analysis, and cytotoxicity of conformationally constrained aplidine and tamandarin A analogues incorporating a spirolactam beta-turn mimetic.
abstract: With the aim of studying the contribution of the beta II turn conformation at the side chain of didemnins to the bioactive conformation responsible for their antitumoral activity, conformationally restricted analogues of aplidine and tamandarin A, where the side chain dipeptide Pro8-N-Me-d-Leu7 is replaced with the spirolactam beta II turn mimetic (5R)-7-[(1R)-1-carbonyl-3-methylbutyl]-6-oxo-1,7-diazaspiro[4.4]nonane, were prepared. Additionally, restricted analogues, where the aplidine (pyruvyl9) or tamandarin A [(S)-Lac9] acyl groups are replaced with the isobutyryl, Boc, and 2-methylacryloyl groups, were also prepared. These structural modifications were detrimental to cytotoxic activity, leading to a decrease of 1-2 orders of magnitude with respect to that exhibited by aplidine and tamandarin A. The conformational analysis of one of these spirolactam aplidine analogues, by NMR and molecular modeling methods, showed that the conformational restriction caused by the spirolactam does not produce significant changes in the overall conformation of aplidine, apart from preferentially stabilizing the trans rotamer at the pyruvyl9-spirolactam amide bond, whereas in aplidine both cis and trans rotamers at the pyruvyl9-Pro8 amide bond are more or less equally stabilized. These results seem to indicate a preference for the cis form at that amide bond in the bioactive conformation of aplidine. The significant influence of this cis/trans isomerism upon the cytotoxicity suggests a possible participation of a peptidylprolyl cis/trans isomerase in the mechanism of action of aplidine.
authors.affiliation: Instituto de Química Médica (CSIC), Juan de la Cierva 3, E-28006 Madrid, Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: Gutiérrez-Rodríguez
authors.forename: Mercedes
authors.initials: M
authors.lastname: Martín-Martínez
authors.forename: M Teresa
authors.initials: MT
authors.lastname: García-López
authors.forename: Rosario
authors.initials: R
authors.lastname: Herranz
authors.forename: Félix
authors.initials: F
authors.lastname: Cuevas
authors.forename: Concepción
authors.initials: C
authors.lastname: Polanco
authors.forename: Ignacio
authors.initials: I
authors.lastname: Rodríguez-Campos
authors.forename: Ignacio
authors.initials: I
authors.lastname: Manzanares
authors.forename: Francisco
authors.initials: F
authors.lastname: Cárdenas
authors.forename: Miguel
authors.initials: M
authors.lastname: Feliz
authors.forename: Paul
authors.initials: P
authors.lastname: Lloyd-Williams
authors.forename: Ernest
authors.initials: E
authors.lastname: Giralt
mesh_terms: D000970:Antineoplastic Agents / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D047630:Depsipeptides / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D004354:Drug Screening Assays, Antitumor; D006801:Humans; D007769:Lactams / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D010456:Peptides, Cyclic; D017433:Protein Structure, Secondary; D013329:Structure-Activity Relationship
chemical_list: D000970:Antineoplastic Agents; D047630:Depsipeptides; D007769:Lactams; D010456:Peptides, Cyclic; C409142:tamandarin A; C098980:plitidepsin