title: Complete stereochemistry of neamphamide A and absolute configuration of the beta-methoxytyrosine residue in papuamide B.
abstract: The absolute stereochemistry of the three unresolved structural components in neamphamide A (1) was determined to be (R)-beta-methoxy-L-tyrosine, (2R,3R,4S)-4-amino-7-guanidino-2,3-dihydroxyheptanoic acid, and (2R,3R,4R)-3-hydroxy-2,4,6-trimethylheptanoic acid. Stereochemical assignments were made by chemical degradation of 1, derivatization of the resulting products, and then spectroscopic and chromatographic comparison of the derivatives with synthetically prepared standards. Using the same analytical protocol developed for 1, the beta-methoxytyrosine residue in papuamide B (2) was found to be (R)-beta-methoxy-D-tyrosine. This represents a rare example of divergent stereochemistry in an unusual amino acid residue that is present in two closely related classes of peptides.
authors.affiliation: Molecular Targets Development Program, Center for Cancer Research, National Cancer Institute, Building 1052, Room 121, Frederick, MD 21702-1201, USA.
authors.forename: Naoya
authors.initials: N
authors.lastname: Oku
authors.forename: Ravi
authors.initials: R
authors.lastname: Krishnamoorthy
authors.forename: Alan G
authors.initials: AG
authors.lastname: Benson
authors.forename: Robert L
authors.initials: RL
authors.lastname: Ferguson
authors.forename: Mark A
authors.initials: MA
authors.lastname: Lipton
authors.forename: Lawrence R
authors.initials: LR
authors.lastname: Phillips
authors.forename: Kirk R
authors.initials: KR
authors.lastname: Gustafson
authors.forename: James B
authors.initials: JB
authors.lastname: McMahon
mesh_terms: D047630:Depsipeptides / Q000737:chemistry*; D008401:Gas Chromatography-Mass Spectrometry; D010456:Peptides, Cyclic / Q000737:chemistry*; D013237:Stereoisomerism; D014443:Tyrosine / Q000031:analogs & derivatives / Q000737:chemistry*
chemical_list: D047630:Depsipeptides; D010456:Peptides, Cyclic; C492416:neamphamide A; C474171:papuamide B; D014443:Tyrosine