Showing papers by "William Fenical published in 2008"

Marine actinomycetes: a new source of compounds against the human malaria parasite.

Abstract: Background Malaria continues to be a devastating parasitic disease that causes the death of 2 million individuals annually. The increase in multi-drug resistance together with the absence of an efficient vaccine hastens the need for speedy and comprehensive antimalarial drug discovery and development. Throughout history, traditional herbal remedies or natural products have been a reliable source of antimalarial agents, e.g. quinine and artemisinin. Today, one emerging source of small molecule drug leads is the world's oceans. Included among the source of marine natural products are marine microorganisms such as the recently described actinomycete. Members of the genus Salinispora have yielded a wealth of new secondary metabolites including salinosporamide A, a molecule currently advancing through clinical trials as an anticancer agent. Because of the biological activity of metabolites being isolated from marine microorganisms, our group became interested in exploring the potential efficacy of these compounds against the malaria parasite.

Biosynthesis and structures of cyclomarins and cyclomarazines, prenylated cyclic peptides of marine actinobacterial origin.

Abstract: Two new diketopiperazine dipeptides, cyclomarazines A and B, were isolated and characterized along with the new cyclic heptapeptide cyclomarin D from the marine bacterium Salinispora arenicola CNS-205. These structurally related cyclic peptides each contain modified amino acid residues, including derivatives of N-(1,1-dimethylallyl)-tryptophan and delta-hydroxyleucine, which are common in the di- and heptapeptide series. Stable isotope incorporation studies in Streptomyces sp. CNB-982, which was first reported to produce the cyclomarin anti-inflammatory agents, illuminated the biosynthetic building blocks associated with the major metabolite cyclomarin A, signifying that this marine microbial peptide is nonribosomally derived largely from nonproteinogenic amino acid residues. DNA sequence analysis of the 5.8 Mb S. arenicola circular genome and PCR-targeted gene inactivation experiments identified the 47 kb cyclomarin/cyclomarazine biosynthetic gene cluster (cym) harboring 23 open reading frames. The cym locus is dominated by the 23 358 bp cymA, which encodes a 7-module nonribosomal peptide synthetase (NRPS) responsible for assembly of the full-length cyclomarin heptapeptides as well as the truncated cyclomarazine dipeptides. The unprecedented biosynthetic feature of the megasynthetase CymA to synthesize differently sized peptides in vivo may be triggered by the level of beta oxidation of the priming tryptophan residue, which is oxidized in the cyclomarin series and unoxidized in the cyclomarazines. Biosynthesis of the N-(1,1-dimethyl-2,3-epoxypropyl)-beta-hydroxytryptophan residue of cyclomarin A was further illuminated through gene inactivation experiments, which suggest that the tryptophan residue is reverse prenylated by CymD prior to release of the cyclic peptide from the CymA megasynthetase, whereas the cytochrome P450 CymV installs the epoxide group on the isoprene of cyclomarin C post-NRPS assembly. Last, the novel amino acid residue 2-amino-3,5-dimethylhex-4-enoic acid in the cyclomarin series was shown by bioinformatics and stable isotope experiments to derive from a new pathway involving condensation of isobutyraldehyde and pyruvate followed by S-adenosylmethionine methylation. Assembly of this unsaturated, branched amino acid is unexpectedly related to the degradation of the environmental pollutant 3-(3-hydroxyphenyl)propionic acid.

Salinipyrones and pacificanones, mixed-precursor polyketides from the marine actinomycete Salinispora pacifica.

Abstract: Chemical examination of a phylogenetically unique strain of the obligate marine actinomycete Salinispora pacifica led to the discovery of four new polyketides, salinipyrones A and B (1, 2) and pacificanones A and B (3, 4). These compounds appear to be derived from a mixed-precursor polyketide biosynthesis involving acetate, propionate, and butyrate building blocks. Spectral analysis, employing NMR, IR, UV, and CD methods and chemical derivatization, was used to assign the structures and absolute configurations of these new metabolites. Salinipyrones A and B displayed exactly opposite CD spectra, indicating their pseudoenantiomeric relationship. This relationship was shown to be a consequence of the geometric isomerization of one double bond. The phenomenon of polyketide module skipping is proposed to explain the unusual biosynthesis of the salinipyrones and the pacificanones.

Engineered biosynthesis of antiprotealide and other unnatural salinosporamide proteasome inhibitors.

Abstract: A new shunt in the phenylalanine biosynthetic pathway to the nonproteinogenic amino acid L-3-cyclohex-2'-enylalanine was exploited in the marine bacterium Salinispora tropica by mutagenesis to allow for the genetic engineering of unnatural derivatives of the potent proteasome inhibitor salinosporamide A (2) such as antiprotealide (1).

Comparative actinomycete diversity in marine sediments

Abstract: The diversity of cultured actinomycete bacteria was compared between near- and off- shore marine sediments. Strains were tested for the effects of seawater on growth and analyzed for 16S rRNA gene sequence diversity. In total, 623 strains representing 6 families in the order Actino- mycetales were cultured. These strains were binned into 16 to 63 operational taxonomic units (OTUs) over a range of 97 to 100% sequence identity. The majority of the OTUs were closely related (>98% sequence identity) to strains previously reported from non-marine sources, indicating that most are not restricted to the sea. However, new OTUs averaged 96.6% sequence identity with previously cul- tured strains and ca. one-third of the OTUs were marine-specific, suggesting that sediment commu- nities include considerable actinomycete diversity that does not occur on land. Marine specificity did not increase at the off-shore sites, indicating high levels of terrestrial influence out to 125 km from shore. The requirement of seawater for growth was observed among <6% of the strains, while all members of 9 OTUs possessed this trait, revealing a high degree of marine adaptation among some lineages. Statistical analyses predicted greater OTU diversity at the off-shore sites and provided a rationale for expanded exploration of deep-sea samples. A change in community composition was observed, with the number of Micromonospora OTUs increasing in the off-shore samples. UniFrac (see http://bmf2.colorado.edu/unifrac) statistics support a difference in community composition between near- and off-shore locations. Overall, 123 of 176 strains had distinct 16S rRNA gene sequences, indicating a high level of actinomycete diversity in marine sediments.

The Marinopyrroles, Antibiotics of an Unprecedented Structure Class from a Marine Streptomyces sp.

Abstract: Cultivation of an obligate marine Streptomyces strain has furnished the marinopyrroles A and B, densely halogenated, axially chiral metabolites that contain an uncommon bispyrrole structure. X-ray analysis of marinopyrrole B showed that the natural product exists as an atropo-enantiomer with the M-configuration. Though configurationally stable at room temperature, M-(−)-marinopyrrole A can be racemized at elevated temperatures to yield the non-natural P-(+)-atropo-enantiomer. The marinopyrroles possess potent antibiotic activities against methicillin-resistant Staphylococcus aureus.

Genome sequencing reveals complex secondary metabolome in the marine actinomycete Salinispora tropica

Abstract: Recent fermentation studies have identified actinomycetes of the marine-dwelling genus Salinispora as prolific natural product producers. To further evaluate their biosynthetic potential, we analyzed all identifiable secondary natural product gene clusters from the recently sequenced 5,184,724 bp S. tropica CNB-440 circular genome. Our analysis shows that biosynthetic potential meets or exceeds that shown by previous Streptomyces genome sequences as well as other natural product-producing actinomycetes. The S. tropica genome features nine polyketide synthase systems of every known formally classified family, non-ribosomal peptide synthetases and several hybrid clusters. While a few clusters appear to encode molecules previously identified in Streptomyces species, the majority of the 15 biosynthetic loci are novel. Specific chemical information about putative and observed natural product molecules is presented and discussed. In addition, our bioinformatic analysis was critical for the structure elucidation of the novel polyenemacrolactam salinilactam A. This study demonstrates the potential for genomic analysis to complement and strengthen traditional natural product isolation studies and firmly establishes the genus Salinispora as a rich source of novel drug-like molecules.

An N-acyl homolog of mycothiol is produced in marine actinomycetes.

Abstract: Marine actinomycetes have generated much recent interest as a potentially valuable source of novel antibiotics. Like terrestrial actinomycetes the marine actinomycetes are shown here to produce mycothiol as their protective thiol. However, a novel thiol, U25, was produced by MAR2 strain CNQ703 upon progression into stationary phase when secondary metabolite production occurred and became the dominant thiol. MSH and U25 were maintained in a reduced state during early stationary phase, but become significantly oxidized after 10 days in culture. Isolation and structural analysis of the monobromobimane derivative identified U25 as a homolog of mycothiol in which the acetyl group attached to the nitrogen of cysteine is replaced by a propionyl residue. This N-propionyl-desacetyl-mycothiol was present in 13 of the 17 strains of marine actinomycetes examined, including five strains of Salinispora and representatives of the MAR2, MAR3, MAR4 and MAR6 groups. Mycothiol and its precursor, the pseudodisaccharide 1-O-(2-amino-2-deoxy-α-d-glucopyranosyl)-d-myo-inositol, were found in all strains. High levels of mycothiol S-conjugate amidase activity, a key enzyme in mycothiol-dependent detoxification, were found in most strains. The results demonstrate that major thiol/disulfide changes accompany secondary metabolite production and suggest that mycothiol-dependent detoxification is important at this developmental stage.

Ammosamides as anticancer agents

Abstract: A compound having the general the general structure I is provided: (Formula I), wherein Z is a substituent selected from a group consisting of S and O; X is a substituent selected from a group consisting of Cl, Br, I, OH and NH2; each of R 1 and R 2 is a substituent independently selected from a group consisting of H, a linear, cyclic or branched, substituted or unsubstituted C 1 -C 6 alkyl, a substituted or unsubstituted aryl, and a substituted or unsubstituted heteroaryl; and each of Y and Y 1 is a substituent independently selected from a group consisting of H and C(O)—C 6 H 4 —Br.