title: Calyxamides A and B, cytotoxic cyclic peptides from the marine sponge Discodermia calyx.
abstract: Cyclic peptides containing 5-hydroxytryptophan and thiazole moieties were isolated from the marine sponge Discodermia calyx collected near Shikine-jima Island, Japan. The structures of calyxamides A (1) and B (2), including the absolute configurations of all amino acids, were elucidated by spectroscopic analyses and degradation experiments. The structures are similar to keramamides F and G, previously isolated from Theonella sp. The analysis of the 16S rDNA sequences obtained from the metagenomic DNA of D. calyx revealed the presence of Candidatus Entotheonella sp., an unculturable δ-proteobacterium inhabiting the Theonella genus and implicated in the biosynthesis of bioactive peptides.
authors.affiliation: Graduate School of Pharmaceutical Sciences,  The University of Tokyo , 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Miki
authors.initials: M
authors.lastname: Kimura
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Wakimoto
authors.forename: Yoko
authors.initials: Y
authors.lastname: Egami
authors.forename: Karen Co
authors.initials: KC
authors.lastname: Tan
authors.forename: Yuji
authors.initials: Y
authors.lastname: Ise
authors.forename: Ikuro
authors.initials: I
authors.lastname: Abe
mesh_terms: D000596:Amino Acids; D000818:Animals; D000970:Antineoplastic Agents / Q000737:chemistry / Q000302:isolation & purification* / Q000494:pharmacology*; D004354:Drug Screening Assays, Antitumor; D007564:Japan; D007941:Leukemia P388; D015394:Molecular Structure; D010456:Peptides, Cyclic / Q000737:chemistry / Q000302:isolation & purification* / Q000494:pharmacology*; D011161:Porifera / Q000737:chemistry*; D047232:Theonella / Q000737:chemistry
chemical_list: D000596:Amino Acids; D000970:Antineoplastic Agents; D010456:Peptides, Cyclic; C571494:calyxamide A; C571495:calyxamide B