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In switched-angle spinning spectroscopy ͑SAS͒ a sample is spun about different angles, ␤, relative to the magnetic field, during various periods of the experiment. In the present work, SAS is combined with two-dimensional exchange spectroscopy in order to correlate carbon-13 chemical shift tensors of the carbonyl ͑1͒ and hydroxyl ͑2͒ carbons of tropolone. Experiments were performed on a sample enriched to 25 at. % in each of these sites ͑at different molecules͒. At this level of enrichment the dominant exchange mechanism between the two sites involves spin diffusion. The experiment consists of a preparation period during which the sample spins at the magic angle and the magnetization of one of the sites is quenched by means of a selective pulse sequence. During the rest of the experiment the sample spins with its axis away from the magic angle except for a short period just before the detection where the axis is switched to the magic angle in order to select the magnetization to be detected. Experiments were performed for all four possible combinations of the initial and final magnetizations, thus providing chemical shift correlations between carbons 1,1Ј, 2, and 2Ј in the two magnetically inequivalent ͑but symmetry related͒ molecules in the unit cell. Combining these results with the known crystal structure of tropolone ͑neglecting a small tilt between the perpendicular to the molecular plane and the crystallographic c-axis͒ provides information on the orientation and magnitude of the chemical shift tensors of the two types of carbons. The principal values ͑in ppm͒ are xx 1 ϭ65, yy 1 ϭ33, zz 1 ϭϪ98, xx 2 ϭ77, yy 2 ϭ17, and zz 2 ϭϪ94. Assuming zz to be perpendicular to the molecular plane, the orientations of the yy 's are 12°off the C 1 ϭ0 bond ͑toward the hydroxyl carbon͒ for carbon 1 and 10°off the C 3 ϭC 2 bond ͑away from the carbonyl carbon͒ for carbon 2.

Alkaloids, which are generally basic N-containing compounds, have been found in a variety of natural sources. Recently, the interest in alkaloids from corals increased significantly due to their remarkable bioactivities. This review deals with the chemical structures and biological activities of alkaloids in corals. The literature has been covered up to June 2011, and a total of 102 alkaloids from the 51 publications are discussed and reviewed. Some of these compounds showed various biological properties, such as cytotoxic, antibacterial, insecticidal, antifouling, and other activities.

Two new avermectin derivatives, avermectins B1c and B1e (1 and 2, resp.), as well as two known compounds, avermectin B2a (3) and ivermectin A1a (4), were isolated from a Beibu Gulf gorgonian coral, Anthogorgia caerulea. The structures of the new compounds were established by detailed spectroscopic analysis and by comparison with spectral data of related known compounds. Compounds 1-4 showed moderate antifouling activities against the larval settlement of Balanus amphitrite.