An extract of the marine bryozoan Caulibugula intermis, collected in the Indo-Pacific off Palau, produced a distinct pattern of differential cytotoxicity in the National Cancer Institute's 60 cell line antitumor screen. Bioactivity-directed fractionation of the extract provided six new compounds, caulibugulones A-F (1-6). The structures of these novel metabolites were determined by spectrochemical analyses including LC-MS, HRFABMS, 1-D and 2-D NMR experiments, and by comparison with related compounds. The structures of compounds 2 and 3 were confirmed by chemical interconversion. The isolated compounds exhibited IC(50)'s of 0.03-1.67 microg/mL against murine tumor cells in an in vitro cytotoxicity assay.
Unusual amino acids such as beta-methoxytyrosine (beta-MeOTyr), allo-threonine (allo-Thr) and allo-isoleucine (allo-Ile) were derivatized with N-alpha-(2,4-dinitro-5-fluorophenyl)-L-alaninamide (FDAA), 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl isothiocyanate (GITC), (S)-N-(4-nitrophenoxycarbonyl)phenylalanine methoxyethyl ester (S-NIFE), or o-phthalaldehyde/isobutyryl-L-cysteine (OPA-IBLC), and then separated via reversed-phase high-performance chromatography followed by UV and electrospray ionization mass spectrometry detection. FDAA generally showed the highest enantioselectivity but the lowest sensitivity among the chiral derivatizing agents (CDAs) investigated. The detection limit of FDAA-derivatized amino acids was in the low picomolar range. Although the enantioselectivity of FDAA derivatives was generally quite high, its selectivity among beta-MeOTyr isomers was poor. The best separation of beta-MeOTyr stereoisomers was achieved with S-NIFE. Due to the complex relationships between the investigated CDAs, stereochemical analyses using a combination of two or more of the CDAs gave the most reliable results for a given separation problem. In general, the methods described are selective and reliable, and are being applied to the analysis of unusual amino acids as they occur in marine peptides.
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