Oceanapiside, a Marine Natural Product, Targets the Sphingolipid Pathway of Fluconazole-Resistant Candida glabrata.

Oceanapiside (OPS), a marine natural product with a novel bifunctional sphingolipid structure, is fungicidal against fluconazole-resistant Candida glabrata at 10 µg/mL (15.4 µM). The fungicidal effect was observed at 3 to 4 h after exposure to cells. Cytological and morphological studies revealed that OPS affects the budding patterns of treated yeast cells with a significant increase in the number of cells with single small buds. In addition, this budding morphology was found to be sensitive in the presence of OPS. Moreover, the number of cells with single medium-sized buds and cells with single large buds were decreased significantly, indicating that fewer cells were transformed to these budding patterns, suggestive of inhibition of polarized growth. OPS was also observed to disrupt the organized actin assembly in C. glabrata, which correlates with inhibition of budding and polarized growth. It was also demonstrated that phytosphingosine (PHS) reversed the antifungal activity of oceanapiside. We quantified the amount of long chain-bases (LCBs) and phytoceramide from the crude extracts of treated cells using LC-ESI-MS. PHS concentration was elevated in extracts of cells treated with OPS when compared with cells treated with miconazole and amphotericin B. Elevated levels of PHS in OPS-treated cells confirms that OPS affects the pathway at a step downstream of PHS synthesis. These results also demonstrated that OPS has a mechanism of action different to those of miconazole and amphotericin B and interdicts fungal sphingolipid metabolism by specifically inhibiting the step converting PHS to phytoceramide.

Zwittermicin A: synthesis of analogs and structure-activity studies.

Analogs and diastereomers of the natural product zwittermicin A were prepared. SAR studies of these compounds reveal the antifungal activity to be dependent singularly upon the natural constitution and configuration.

(+)-Zwittermicin A. Rapid assembly of C9-C15 and a formal total synthesis.

A short, enantioselective synthesis of the C9-C15 portion of (+)-zwittermicin A is reported that exploits directional functionalization of the known hepta-2,5-diyne-1,7-diol by partial reduction of the two triple bonds followed by Sharpless asymmetric epoxidation and boron-directed double ring-opening with sodium azide under Miyashita conditions. Subsequent desymmetrization of the C(2)-symmetric diazidotetraol product converges upon (-)-3--the enantiomer of the key intermediate of our earlier structural proof and synthesis of (-)-zwittermicin A--and constitutes a formal synthesis of (+)-zwitttermicin A.

Structure elucidation at the nanomole scale. 1. Trisoxazole macrolides and thiazole-containing cyclic peptides from the nudibranch Hexabranchus sanguineus.

A single specimen of Hexabranchus sanguineus, a nudibranch from the Indo-Pacific that is known to sequester kabiramides B and C and other trisoxazole macrolides, yielded new kabiramide analogues, 9-desmethylkbiramide B and 33-methyltetrahydrohalichondramide, and two new unexpected thiazole-containing cyclic peptides in submicromolar amounts. The structures of these cyclic peptides were determined by analyses of 1D and 2D NMR spectra recorded with a state-of-the-art 1 mm (1)H NMR high-temperature superconducting microcryoprobe, together with mass spectra. In addition to two proline residues, each peptide contains a thiazole- or oxazole-modified amino acid residue, together with conventional amino acid residues. All of the amino acid residues were l, as determined by Marfey's analysis of the acid hydrolysates of the peptides. This is the first report of cyclic thiazole peptides from H. sanguineus. Since thiazole-oxazole-modified peptides are typically associated with cyanobacteria and tunicates, the finding may imply a dietary component of the H. sanguineus that was previously overlooked.

Highly polar spiroisoxazolines from the sponge Aplysina fulva.

Two new highly polar brominated spiroisoxazolines, araplysillin N9-sulfamate (1) and an N-[5S,10R)-7,9-dibromo-10-hydroxy-8-methoxy-1-oxa-2-azaspiro[4.5]deca-2,6,8-triene-3-carboxy]-4-aminobutanoic acid (2), were isolated from a sample of Aplysina fulva collected in the Florida Keys. The absolute stereostructures of the new compounds were determined from analysis of MS, 1H and 13C NMR, and CD spectroscopy. Compound 2 provides a structural clue that may unify the biosynthesis of brominated spiroisoxazolines.

Asymmetric synthesis of diastereomeric diaminoheptanetetraols. A proposal for the configuration of (+)-zwittermicin a.

[structure: see text] A proposed absolute configuration for the 7 stereocenters in (+)-zwittermicin A is described based on asymmetric synthesis of six diastereomeric 2,6-diamino-1,3,5,7-heptanetetraols corresponding to the C9-C15 segment, pairwise 13C NMR chemical shift difference analysis of the models with the natural product, interpretation of enantiospecificity of the serine loading domain of the zwittermicin A biosynthetic gene cluster, and degradation of the natural product.

Stereochemical heterogeneity in Verongid sponge metabolites. Absolute stereochemistry of (+)-fistularin-3 and (+)-11-epi-fistularin-3 by microscale LCMS-Marfey's analysis.

The absolute configurations of fistularin-3, 11-epi-fistularin-3, and a related bis-oxazolidinone were determined by microscale hydrolysis followed by derivatization with 1-fluoro-2,4-dinitrophenyl-5-l-alaninamide. Samples of fistularin-3 from Verongid marine sponges collected in the Great Barrier Reef (Australia), Baía de Todos os Santos (Brazil), and the Key Largo, Florida (USA) varied in configuration at C11, a phenomenon that may be attributed to the involvement of stereochemically promiscuous hydroxylase enzymes. Variability in C11 configuration in fistularin-3 samples may have been overlooked in previously reported encounters due to the similarity of spectroscopic properties of fistularin-3 and 11-epi-fistularin-3 and their coelution under chromatographic conditions. Stereochemical heterogeneity at C11 in fistularin-3 samples suggests a possibility of a native biotransformation of suitable precursor in Verongid sponges by their associated microbial flora.

A cytotoxic carotenoid from the marine sponge Prianos osiros.

Investigations of the marine sponge Prianos osiros, collected in Pohnpei, gave a new cytotoxic acetylenic carotenoid, (3R,3'R,5S)-3,3',5,19'-tetrahydroxy-7',8'-didehydro-gamma,epsilon-carotene-8-one. The absolute configuration of this carotenoid was solved by interpretation of IR, MS, and 2D NMR spectra and application of the modified Mosher's method. Compound 1 is cytotoxic toward cultured human colon tumor cells, HCT 116 (IC(50) 4.38 microg/mL).

(2S,3R)-2-aminododecan-3-ol, a new antifungal agent from the ascidian Clavelina oblonga.

A new antifungal agent, (2S,3R)-2-aminododecan-3-ol (1), has been isolated from the ascidian Clavelina oblonga collected in Brazil. The structure of 1 was established by analysis of spectroscopic data, including absolute stereochemistry determined by circular dichroism analysis of the dibenzoyl derivative 2. Compound 1 displayed antifungal activity against Candida albicans ATCC 10231 with a MIC of 0.7 mug/mL and against Candida glabrata with a MIC of 30 microg/mL.