Studies toward the total synthesis of the cytotoxic sponge alkaloid pyrinodemin A

[structure: see text]. The syntheses of the proposed structure of pyrinodemin A (1) and its cis double bond positional isomer (C15'-C16') in racemic form are described. The key reaction involved an intramolecular nitrone/double bond cycloaddition. Our results suggest that neither 1 nor its double positional isomer is the correct structure of pyrinodemin A     

Synthesis of the Arctic sponge alkaloid viscosaline and the marine sponge alkaloid theonelladin C

The synthesis of Arctic sponge alkaloid viscosaline (1) is achieved by using the Zincke reaction as the penultimate step. A key synthetic intermediate theonelladin C (6), itself a marine sponge natural product, is synthesised efficiently using a four-step sequence.     

A short biomimetic synthesis of marine sponge alkaloid Pyrinadine A

The biomimetic synthesis of the marine sponge alkaloid Pyrinadine A, based on the oxidative dimerisation of hydroxylamine, is reported.     

Asymmetric total synthesis and absolute stereochemistry of the neuroactive marine macrolide palmyrolide A

The first asymmetric total synthesis and determination of the absolute configuration for the neuroactive marine macrolide palmyrolide A is described. The highlight of the synthesis is macrocyclization via trans-enamide formation catalyzed by copper(I) iodide and cesium carbonate. Comparison with the authentic spectral data confirms the synthesis of (+)-ent-palmyrolide A.     

Prianosin A,a novel antileukemic alkaloid from the okinawan marine sponge Prianos melanos

A novel alkaloid, prianosin A (1), with potent antineoplastic activity has been isolated from the Okinawan marine sponge Prianos melanos. Its absolute stereostructure was determined by single crystal x-ray diffraction analysis.     

Synthesis of marine sponge alkaloid hachijodine B and a comment on the structure of ikimine B and on the absolute configuration of niphatesine D

The syntheses of the proposed structures of hachijodine B 1, ikimine B 2 and niphatesine D 3 from S-citronellol are described. Our results suggest that the gross structures of hachijodine B and niphatesine D are correct, but that ikimine B was incorrectly assigned. We have also established that the previous absolute stereochemical assignment for niphatesine D is unreliable.     

Synthesis of CD-ring structure of cortistatin A, an anti-angiogenic steroidal alkaloid from marine sponge

Stereoselective synthesis of the CD-ring structure of cortistatin A (1), a novel anti-angiogenic steroidal alkaloid from Indonesian marine sponge, was achieved. The stereogenic tertiary carbon center bearing the isoquinoline moiety was constructed by 1,3-chiral transfer method using Johnson-Claisen rearrangement of the chiral allylic alcohol 5. Subsequent intramolecular Michael-aldol reaction afforded the targeted trans-hydrindane skeleton with moderate stereoselectivity.     

A new 3-alkylpyridine alkaloid from the marine sponge Haliclona sp. and its cytotoxic activity

A new alkaloid, 3-dodecyl pyridine containing a terminal cyano group (1), was isolated from the methanol extract of an Indonesia marine sponge Haliclona sp. Its chemical structure was determined by a combination of spectroscopic methods, including 1D and 2D NMR. Bioassay results indicated that compound 1 had moderate cytotoxity against tumour cell lines A549, MCF-7 and Hela with IC₅₀ values of 41.8, 48.4 and 33.2 μM, respectively.     

The absolute stereochemistry of grenadamide

3-(2S-Heptylcycloprop-1S-yl)propanoic acid 2-phenylethanamide was synthesised from cis-cyclopropan-1,2-dimethanol via enzymatic desymmetrisation of the dibutyrate; it gave identical NMR spectroscopic data to those reported for grenadamide but had an equal and opposite absolute rotation, indicating that the latter is the 2R,1R-enantiomer.     

Brominated polyunsaturated lipids and their stereochemistry from the Chinese marine sponge Xestospongia testudinaria

Chemical examination of the Chinese marine sponge Xestospongia testudinaria led to the isolation of 39 new brominated polyunsaturated compounds, which were designated with the trivial names xestospongienes A-Z and Z₁-Z₁₃. The structures of these compounds were elucidated by analyzing extensive spectroscopic (IR, MS, 1D, and 2D NMR) data and the results from CD spectral assignment, chemical conversion, and Mosher reaction.     

Spironaamidine, a new spiroquinone-containing alkaloid from the marine sponge Leucetta microraphis

Spironaamidine (1), a unique spiroquinone-containing alkaloid, was isolated from the marine sponge, Leucetta microraphis, along with two known imidazole alkaloids, naamidine H (2) and (9E)-clathridine 9-N-(2-sulfoethyl)imine (3). Spironaamidine (1) showed antimicrobial activity against Bacillus cereus.     

The absolute stereochemistry of crotonitenone

The configuration at C—4 of the novel casbenoid diterpene, crotonitenone (3), was determined by Horeau's method as (R) — hence the absolute stereochemistry of the molecule is as written in (3).     

Determination of the absolute stereochemistry of Etzionin

The absolute configuration of Etzionin, a marine peptide-like compound isolated in 1989 from a red tunicate collected from the Red Sea has been determined by a combination of synthetic and spectroscopic procedures. Finally, its absolute stereochemistry has been established as 3S,3′R.     

Establishment of the absolute configuration of the bioactive marine alkaloid eudistomin X by stereospecific synthesis

A stereospecific synthesis of both enantiomers of the marine alkaloid eudistomin X using the amino acid chiral pool is achieved. Comparison of ¹H and ¹³C NMR chemical shifts of the synthetic product as either the free base, mono-salt or disalt with those reported for the natural product established that the ascidian metabolite was originally characterised as a mono-salt and that the absolute configuration was (10R).     

Structure and absolute stereochemistry of syphonoside, a unique macrocyclic glycoterpenoid from marine organisms

The glycoterpenoid syphonoside (1) is the main secondary metabolite of both the marine mollusk Syphonota geographica and the sea-grass Halophila stipulacea, two Indo-Pacific species migrated to the Mediterranean Sea through the Suez Canal. The structure and the absolute stereochemistry of 1, which displays unique structural features, has been accomplished by using a combination of spectroscopic techniques, degradation reactions, and conformational analysis methods. Compound 1 was able to inhibit high density induced apoptosis in a number of human and murine carcinoma cell lines.     

Biomimetic synthesis of marine sponge metabolite spiculoic acid A and establishment of the absolute configuration of the natural product

The synthesis of spiculoic acid A (1) using a biomimetic Diels-Alder reaction is described; comparison of the specific rotation of the natural and synthetic material revealed that the enantiomer of the natural product has been synthesized.     

Ircinamine B, bioactive alkaloid from marine sponge Dactylia sp.

Ircinamine B was isolated from the marine sponge Dactylia sp., which was collected at Cape Sada in Japan. Based on extensive spectral analysis, the structures of the isolated metabolites were established. This novel compound showed moderate activity against the murine leukemia cell line P388 (IC₅₀ 0.28 μg/mL).     

Revised structure of tetrapetalone A and its absolute stereochemistry

The chemical structure of tetrapetalone A (1), a novel lipoxygenase inhibitor from Streptomyces sp., was revised by using the ¹H-¹⁵N HMBC technique. Furthermore, the absolute stereochemistry of all the asymmetric carbons in 1 was determined based on the detailed NOE data of 1 and its derivative.