No abstract

A specimen of Ianthella basta, collected from the Great Barrier Reef, Australia, has been found to contain the recently reported tetramer of bromotyrosine , bastadin-9 (6a), along with a new example of this structure class, bastadin-12 (9a). The structure for bastadin-12 (9a) was confirmed by detailed spectroscopic analysis and derivatization, and represents the first reported example of this structure class derived from an alternative oxidative cyclization . As earlier biosynthetic arguments to the structure elucidation of some bastadins were based on the premise that only one cyclization pathway was possible (leading to 13,32-dioxa-4,22-diazabastarane), the discovery of (9a) introduces an added dimension to the identification of new and known bastadins. Also isolated and identified as their methyl ethers were two new dimers of bromotyrosine, hemibastadin-1 (10) and hemibastadin-2 (11).

Using the HFDHE2 He-He potential of Aziz et al. [J. Chem. Phys. 90, 4330 (1979)] with the Faddeev-Yakubovsky theory, we have calculated the He atom-triatom scattering length and found 0 it to be -116 A. We reduced the s-wave two-body t matrix to a separable form through the unitary-pole approximation and did the same for the s-wave [3+1] and [2+2] suhamplitudes with the energy-dependent-pole approximation in our work. Also, the binding energies of all the states in the trimer and tetramer, and the atom-diatom scattering length, already determined in our previous work with other potentials, were recalculated for the new interaction. We found an excited trimer bound state, apparently not an Efimov state, near the atom-diatom threshold and an atom-diatom 0 scattering length of 195 A. A feature of our results was the absence of an excited state in the tetramer, but in its place, was a resonancelike state which led to the large atom-triatom scattering length.

We have applied the Fonseca-Redish-Shanley solvable model for three bodies, two heavy and one light, in two dimensions for two types of Yamaguchi form factors in order to determine if the Efimov Effect exists there. The long-range effective heavy-heavy interaction which we extract in each case does not support an infinite number of bound states. Our results therefore indicate that the effect does not manifest itself in two dimensions.

An Australian marine sponge Arenochalina mirabilis (Lendenfeld 1887) collected from the Great Australian Bight has been found to contain six tricyclic alkaloids, mirabilins A-F (5)-(10), isolated and identified as their N-acetyl derivatives (11)-(16). Structures for the mirabilins were secured by detailed spectroscopic analysis.