Search

Swinhoeisterols A (1) and B (2), two novel sterols with an unprecedented 6/6/5/7 ring system, were isolated from the sponge Theonella swinhoei. The structures and absolute configurations were elucidated by spectroscopic analysis, X-ray single-crystal diffraction, modified Mosher's method, and TDDFT/ECD calculations. The cytotoxicity of these compounds toward A549 and MG-63 cells encourages studies on their potential target using an inverse virtual screening approach. The predicted inhibitor of h(p300) was corroborated by an in vitro biological test.

The phylum Echinodermata, which comprises about 6,000 living species distributed in all seas from the tropics to the antarctic zone, is divided into five classes: Crinoidea (sea lilies and feather stars), Holothuroidea (sea cucumbers or holothurians), Echinoidea (sea urchins), Asteroidea (sea stars or starfishes) and Ophiuroidea (brittle stars). Among the echinoderms, sea cucumbers and starfishes invariably contain saponins which are generally responsible for their toxicity. Saponins, complex water soluble compounds composed of a carbohydrate moiety attached to a steroid or triterpenoid aglycone, have been isolated from a great number of terrestrial plants, but are uncommon animal constituents. In the animal kingdom they are almost ubiquitous in sea cucumbers and starfishes (1), while found only rarely in alcyonarians (2), gorgonians (3-5), sponges (6-10) and as potent shark-repelling compounds in fishes (11). Chemically, saponins from sea cucumbers are triterpenoid glycosides whereas those from starfishes are steroidal glycosides.

The present microreview highlights the recent goals reached by the application of a combined approach of NMR spectroscopy and quantum chemical methods in the structural studies of natural products. In particular, different case studies are reported, showing the comparison of calculated NMR parameters at the quantum mechanical (QM) theory level with experimental data for the configurational assignment of organic compounds. Moreover, it is shown that the QM–NMR approach can be used as a fast and convenient method to lead the total synthesis of complex natural products to the correct stereoisomer. Through recent analysis of the covalent complex formed between d(GACTAATTGAC)-(GTCAATTAGTC) and (+)-yatakemycin, the potential application of this hybrid method as a useful tool for the characterization of bioactive molecule–biopolymer interactions is presented.

Rosacelose, a new anti-HIV polysaccharide composed of glucose and fucose sulfate, has been isolated from an aqueous extract of the marine sponge Mixylla rosacea. Extensive use of 1H and 13C multidimensional NMR spectroscopy, combined with chemical analysis were used to establish a linear polysaccharide structure composed mainly of 4,6-disulfated 3-O-glycosylated α- d -glucopyranosyl and 2,4-disulfated 3-O-glycosylated α- l -fucopyranosyl residues (in a 3:1 molar ratio).

Dactylolide (1), a new cytotoxic 20-membered macrolide, was isolated from a marine sponge of the genus Dactylospongia collected off the coast of the Vanuatu islands. It co-occurred with other known bioactive macrolides: latrunculin A (2), laulimalide (3), isolaulimalide (4) and with the anthelminthic mycothiazole (5). The structure of 1, which is a minor metabolite, was elucidated by spectroscopy (mainly by 1D/2D NMR and MS techniques). It showed cytotoxic activity against the L1210 and SK-OV-3 tumor cell lines (63% and 40% inhibition at 3.2 μg/mL).

A new bromoindole alkaloid, named dragmacidin F ( 1 ) and structurally related to other dragmacidins previously described, was isolated from a marine sponge of the genus Halicortex collected off the southern coast of Ustica Island (Italy). Structural elucidation of 1 was achieved by an extensive spectroscopic study (mainly by 1D/2D-NMR and MS techniques). Compound 1 , containing an unprecedented carbon skeleton that is very likely derived from cyclization of a partially oxidized form of dragmacidin D ( 2 ), showed in vitro antiviral activity against HSV-1 (EC 50 =95.8 μM) and HIV-1 (EC 50 =0.91 μM), thus proving to be responsible for the antiviral property exhibited by Halicortex extracts.