Nobuhiro Yamawaki

Cytotoxic Glycosylated Fatty Acid Amides from a Stelletta sp. Marine Sponge

We have discovered new glycosylated fatty acid amides, stellettosides, from a Stelletta sp. marine sponge. They were detected through LC-MS analysis of the extract combined with the cytotoxicity assay of the prefractionated sample. Their planar structures were determined by analyses of the NMR and tandem FABMS data. Stellettosides A1 and A2 (1 and 2) as well as stellettosides B1-B4 (3-6) were obtained as inseparable mixtures. Careful analysis of the NMR and tandem FABMS data of each mixture, along with comparison of the tandem FABMS data with that of a synthetic model compound, permitted us to assign the structure of the constituents in the mixture. The absolute configuration of the monosaccharide unit was determined by LC-MS after chiral derivatization. The relative configurations of the vicinal oxygenated methines in the fatty acid chains were assigned by the (1)H NMR data of the isopropylidene derivative. The mixture of stellettosides B1-B4 (3-6) exhibit moderate cytotoxic activity against HeLa cells with an IC50 value of 9 μM, whereas the mixture of stellettosides A1 and A2 (1 and 2) was not active at a concentration of 10 μM.

Distance to Encountered Ships Estimated by Visual Observation during Cruises

Judging the distance between one’s own ship and other ships is more difficult at sea than on land, because landmarks or reference objects are scarce at sea. Although we can now measure the precise distance to an encountered ship using nautical instruments, such as a radar distance indicator or the automatic identification system, ship crews occasionally judge distances by visual observation, particularly in the case of obstacle avoidance. These estimated distances are typically used for making decisions regarding collision risk, and errors might be influenced by experience. In this study, we evaluate errors in the distance to encountered ships estimated by visual observation. Estimated distances were more precise for experienced crew than were those for trainees. There were tendencies to overestimate the distance to encountered ships with increasing ship size, and to underestimate the distance with decreasing actual range. The colour of the ship did not affect the estimated distance. These results may contribute to ensuring safe ship operation.

The structure of flow field at Yokogan-sone seamount

The structure of flow field around a tall seamount, called Yokogan-sone, which is located to the southwest of the Nansei Islands in the East China Sea was investigated with a combination of observations and a numerical model simulation. The flow field around the seamount was preliminarily measured using an acoustic Doppler current profiler (ADCP) in May 2003. It was found that a distinct westward current flowed above the south flank of the seamount at a depth below 200 m while a eastward current attributed to the Kuroshio dominated over the seamount. Current meter moorings around the seamount were deployed for about one month in May 2004 to discriminate contributions of oceanic and tidal currents to the flow field. The results indicated that oceanic currents flowing into Yokogan-sone changed as the Kuroshio flow path dynamically moved around, and tidal currents were variable both temporally and spatially around the seamount. The Princeton ocean model (POM) was used to simulate the flow field around the seamount. The simulation was driven by steady inflow and oscillatory elevation of the sea surface, corresponding to oceanic currents and tidal elevations, respectively. The simulation results successfully reproduced the westward flow above the south flank of the seamount in spite of the dominant eastward steady flow over the structure, whereas they did not show the considerable temporal and spatial variation of strength of the tidal components