No abstract

Six new polyaromatic alkaloids, lamellarin I (3), J (€9, K (7), L (9), M (11) and the triacetate (13) of lamellarin N, and four known alkaloids, lamellarin A (I), B (15), C (16) and the triacetate (14) of lamellarin D, have been isolated from the marine ascidian Didemnum sp. The structures were deduced by high-field n.m.r. spectroscopy including l 3 c -'~ shift-correlated two-dimensional ( 2~) n.m.r. experiments and n.0.e. measurements. The triacetates (8) and (10) of two of the compounds, lamellarin K (7) and lamellarin L (9), were dehydrogenated in high yield by treatment with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone in ethanol heated under reflux. The products obtained were identical in all respects to the triacetates of lamellarin M and N, respectively. The re-isolation of lamellarins A-D, which were previously obtained from the prosobranch mollusc Lamellaria sp., lends further support for the idea that these molluscs sequester the compounds from ascidians as food sources.Marine ascidians have proven to be rich sources of structurally diverse alkaloids, many of which exhibit a broad spectrum of biological activity.l Members from the family Didemnidae are generally highly coloured, encrusting organisms, colonial by habit, and characteristically contain chemical constituents which are derived from amino acids.2 The polyaromatic lamellarin alkaloids, for example, are probably derived from three tyrosine residues. It has also been suggested that the lamellarins may be distantly related to the tunichromes, reducing blood pigments isolated from the ascidian Ascidia nigra.l The lamellarin skeleton was first identified in an isolate from a prosobranch mollusc, Lamellaria sp., from pa la^,^ but has more recently been found in the didemnid ascidian Didemnum chartaceum from the Seychelles? Of the eight lamellarin-based alkaloids isolated to date, the structures of lamellarins A (1) and E (2) were elucidated by X-ray methods, while the Faulkner, D.

No abstract

The structures and absolute stereochemistry of four isomeric, cembranoid diterpenes derived from alcyoniid soft corals are reported. Two of these compounds, sarcophytoxide [1] and isosacrophytoxide [6], are known, but their diastereomeric counterparts [3] and [7] are here reported for the first time. High field nmr data are reported for all four compounds. The results of a single crystal X-ray structure determination of one of the isosarcophytoxides [71 permits unambiguous assignment of all four structures. A new cembranoid diterpene 15-hydroxycembra-1,3,7,11-tetraene [5] is reported.

No abstract

Eusynstyelamides A-C (1-3) were isolated from the Great Barrier Reef ascidian Eusynstyela latericius, together with the known metabolites homarine and trigonelline. The structures of 1-3, with relative configurations, were elucidated by interpretation of their spectroscopic data (NMR, MS, UV, IR, and CD). The NMR data of 1 were found to be virtually identical to that reported for eusynstyelamide (4), isolated from E. misakiensis, indicating that a revision of the structure of 4 is needed. Eusynstyelamides A-C exhibited inhibitory activity against neuronal nitric oxide synthase (nNOS), with IC(50) values of 41.7, 4.3, and 5.8 microM, respectively, whereas they were found to be nontoxic toward the three human tumor cell lines MCF-7 (breast), SF-268 (CNS), and H-460 (lung). Compounds 1 and 2 displayed mild inhibitory activity toward Staphylococcus aureus (IC(50) 5.6 and 6.5 mM, respectively) and mild inhibitory activity toward the C(4) plant regulatory enzyme pyruvate phosphate dikinase (PPDK) (IC(50) values of 19 and 20 mM, respectively).

Nine sesterterpenes 1-9 have been isolated from a Dictyoceratid sponge, Strepsichordaia lendenfeldi, collected on the Great Barrier Reef, Australia. Seven of these compounds are new, one [4] had been reported previously as a semisynthetic product, and one [5] had been isolated previously from Carteriospongia foliascens. Unambiguous 13C- and 1H-nmr assignments have been made for 1 based on extensive 1D and 2D high field nmr experiments, which enabled 13C-nmr assignments to be made for 2-9. Significant growth inhibitory effects with tested cancer cell lines are reported for compounds 1-8.

The soft coral Sinularia polydactyla has yielded six highly functionalized diterpenes. The known diterpenes pukalide (2) and 1-epithunbergol (3) were readily identified by spectral comparison with authentic samples. The new natural products 13 α-acetoxy-11β, 12β-epoxypukalide (4),13 α-acetoxypukalide (5) and its allylically rearranged isomer (6) were identified on the basis of 2D-n.m.r. experiments at 300 MHz and by spectral comparison with the known compounds pukalide (21, lophotoxin (8) and epoxypukalide (9). A minor, relatively unstable metabolite (7) is tentatively identified as a 3,4:5,6-bisepoxy derivative of (6). The biological implications of these findings are discussed.