Ashgan Bishara

Taumycins A and B, Two Bioactive Lipodepsipeptides from the Madagascar Sponge Fascaplysinopsis sp.

Two closely related lipodepsipeptides, taumycins A and B (1 and 2) have been isolated from the Madagascar sponge Fascaplysinopsis sp. The two compounds have the same 12-membered oxodepsipeptide ring system in common. Both were toxic to brine shrimp larvae, and taumycin A (1 microM), but not taumycin B, inhibited growth of the human UT-7 leukemic cell line. The structure of the two compounds, likely to be derived from microorganisms, was established by MS and 1D and 2D NMR data.

Nardosinanols A-I and Lemnafricanol, Sesquiterpenes from Several Soft Corals, Lemnalia sp., Paralemnalia clavata, Lemnalia africana, and Rhytisma fulvum fulvum

Ten new sesquiterpenes, nardosinanols A-I ( 1- 9) and lemnafricanol ( 10), have been isolated from several Kenyan soft corals, i.e., from Lemnalia sp., Paralemnalia clavata, Lemnalia africana, and Rhytisma fulvum fulvum. The structures and relative stereochemistry of these compounds were elucidated by interpretation of MS, COSY ( (1)H- (1)H correlations), HSQC, HMBC, and NOESY NMR spectroscopic experiments and in the case of 5 also by chemical transformation to compounds 11 and 12. Nine compounds ( 1- 9) are based on the nardosinane skeleton ( 1- 6 are nardosinanes and 7- 9 nornardosinanes). Lemnafricanol ( 10) possesses a novel tricyclic skeleton. Compounds 3, 7, and 10 were found to be toxic to brine shrimp with LC 50 values of 4.0, 0.35, and 0.32 microM, respectively.

Tausalarin C: a new bioactive marine sponge-derived nitrogenous bismacrolide.

A novel nitrogenous bismacrolide, designated tausalarin C (1), was isolated from the Madagascar sponge Fascaplysinopsis sp. The structure of the compound was elucidated by interpretation of MS and 1D and 2D NMR spectra. It is suggested that tausalarin C is assembled from salarin A (2) and pretaumycin A. The relative configuration of the chiral centers of salarin A was determined by X-ray diffraction. Tausalarin C was found to inhibit proliferation of K562 leukemia cells. A possible biogenesis is discussed.

Salarin C, a member of the salarin superfamily of marine compounds, is a potent inducer of apoptosis

SummaryThe continuous emergence of new diseases and the development of drug-resistant cancers necessitate the development of new drugs with novel mechanisms of action. The richest marine source of natural anti-cancer products has been soft-bodied organisms that lack physical defenses against their predators, and hence rely on chemical defense mechanisms using cytotoxic secondary metabolites. Bio-guided (brine shrimp test) separation of CHCl3-CH3OH (1:1) extract from the Madagascar Fascaplysinopsis sp. sponge provided several new compounds. Here we focused on the biological activity of a panel of novel natural compounds, salarins A-J. Of these, salarin C was the most potent inhibitor of proliferation, as demonstrated on the K562 leukemia cell line. Salarin C-treated K562 cells underwent apoptotic death as monitored by cell-cycle analysis, annexin V/propidium iodide staining, cleavage of poly-ADP-ribose polymerase (PARP) and caspase 3, and caspase 9 levels. The experimental approach described herein is an essential step towards identifying the cellular pathway(s) affected by salarin C and producing potent synthetic derivatives of salarin C with potential future uses as basic research tools and/or drugs and drug leads.

Recent N-Atom Containing Compounds from Indo-Pacific Invertebrates

A large variety of unique N-atom containing compounds (alkaloids) without terrestrial counterparts, have been isolated from marine invertebrates, mainly sponges and ascidians. Many of these compounds display interesting biological activities. In this report we present studies on nitrogenous compounds, isolated by our group during the last few years, from Indo-Pacific sponges, one ascidian and one gorgonian. The major part of the review deals with metabolites from the Madagascar sponge Fascaplysinopsis sp., namely, four groups of secondary metabolites, the salarins, tulearins, taumycins and tausalarins.

Derivatives of Salarin A, Salarin C and Tulearin A—Fascaplysinopsis sp. Metabolites

Derivatives of salarin A, salarin C and tulearin A, three new cytotoxic sponge derived nitrogenous macrolides, were prepared and bio-evaluated as inhibitors of K562 leukemia cells. Interesting preliminary SAR (structure activity relationship) information was obtained from the products. The most sensitive functionalities were the 16,17-vinyl epoxide in both salarins, the triacylamino group in salarin A and the oxazole in salarin C (less sensitive). Regioselectivity of reactions was also found for tulearin A.