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Structure elucidation and biosynthetic investigations of marine cyanobacterial secondary metabolites

This thesis details my investigations of marine cyanobacterial natural
products that resulted in the discovery of thirteen new secondary metabolites, the
isolation of over fifteen previously reported metabolites and the biosynthetic
investigation of two additional cyanobacterial compounds.
Two novel lipopeptides were identified from a Lyngbya majuscula and
Schizothrix sp. assemblage collected in the Fiji Islands. Somamide A is a
depsipeptide consisting of a hexanoate moiety extended by seven amino acids,
including two nonstandard units characteristic of cyanobacterial peptides. In
contrast, somocystinamide A is a unique linear disulfide dimer displaying potent
cytotoxicity against a mammalian neuroblastoma cell line.
The organic extract from a Puerto Rican L. majuscula proved remarkably
rich in chemistry, producing twelve known compounds as well as four new
secondary metabolites. Among these new isolates were the novel sodium channel
blocker antillatoxin B, a new chlorinated quinoline derivative and the new ��-pyrone
malyngamide T.
A collection of L. majuscula from Antany Mora, Madagascar, led to the
isolation of the previously reported antineoplastic agent dolastatin 16 and the
discovery of a new series of lipopeptides, the antanapeptins. These new
molecules are characterized by the presence of the unique ��-hydroxy acid 3-hydroxy-2-methyloctynoate, or its reduced double- or single-bond equivalent.
Wewakazole is a novel cyclic dodecapeptide isolated from a Papua New
Guinea collection of L. majuscula. This large molecule contains both a
methyloxazole and two oxazoles, residues rarely observed in marine
cyanobacterial metabolites. Extensive utilization of 1D and 2D NMR techniques
were required to elucidate the structure of this distinctive peptide.
Biosynthetic investigations of two halogenated cytotoxins were also
conducted on a cultured L. majuscula strain originally isolated from Hector Bay,
Jamaica. Stable isotope feeding experiments demonstrated that both jamaicamide
A and hectochlorin derive from mixed PKS and NRPS biosynthetic origins but are
comprised of primary precursors unique to each molecule. / Graduation date: 2003
Date06 August 2002
CreatorsNogle, Lisa Marie
ContributorsGerwick, William H.
Source SetsOregon State University
Detected LanguageEnglish

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