Discovery of new antimalarial compounds from marine invertebrates

Marine invertebrates and algae were studied for their ability to produce secondary metabolites with potential utility for the treatment of malaria and other diseases. Extracts and pure compounds isolated from marine invertebrates were tested in vitro for antimalarial and other biological activity. Additional compounds were generated from the lead compound 10-isothiocyanato-4-amorphene by microbial transformation and semi-synthesis. Three compounds; halichondramide, sigmosceptrellin A and muqubilin (figure below) showed promising in vitro selectivity against malarial parasites (IC{dollar}sb{lcub}50{rcub}{dollar} = 1.9, 470 and 1,800 ng/mL, respectively). The most active compounds were tested for in vivo efficacy in mice to determine their in vivo effectiveness and toxicity. There is a significant reduction in the malarial parasitemia of halichondramide treated mice, though toxicity limits the tolerable dose. Natural abundance inverse detected {dollar}sp{lcub}15{rcub}{dollar}N NMR experiments were carried out on a variety of compounds to further characterize their chemical structures.; Isolation of pure compounds were primarily carried out using flash chromatography followed by high performance liquid chromatography (HPLC) on bonded stationary phases. The structures of pure compounds were elucidated using spectroscopic methods, especially nuclear magnetic resonance (NMR) spectroscopy. This information was used to perform database searches to help identify known compounds as early as possible. Homonuclear and heteronuclear two dimensional NMR was used, when needed, to identify new compounds. Mass spectrometry, infrared, ultraviolet spectroscopy and optical rotation were also used.; Besides the naturally occurring compounds, additional derivatives were produced by semi-synthesis (10-carbamate derivative) and microbial transformation (6-hydroxy derivatives) of 10-isothiocyanato-4-amorphene which was isolated from a Hawaiian sponge (Axinyssa sp.).; To aid in determining structures of nitrogen containing compounds, two dimensional {dollar}sp1{dollar}H-{dollar}sp{lcub}15{rcub}{dollar}N heteronuclear multiple bond correlation (HMBC) spectra were obtained. This technique has been used little because of limitations in spectrometer design and techniques. These studies show that {dollar}sp1{dollar}H-{dollar}sp{lcub}15{rcub}{dollar}N HMBC spectra can be readily obtained on a diverse array of compounds at natural abundance using a modern NMR spectrometer. Because most of the known antimalarial drugs contain nitrogen this technique may be a useful tool for characterizing new antimalarials. {dollar}sp{lcub}15{rcub}{dollar}N Chemical shifts are reported for keenamide A, keenamide B, 3 sceptrin alkaloids, 10-isothiocyanato-4-amorphene, and naamine D. Keenamide B, naamine D and debromosceptrin are unreported compounds.