N,N'-methyleno-didemnin A from the ascidian Trididemnum solidum. Complete NMR assignments and confirmation of the imidazolidinone ring by strategic analysis of 1J(CH).

The complete NMR assignments of N,N'-methyleno-didemnin A from Trididemnum solidum Van Name 1902 are reported along with a strategic analysis of (1)J(CH) coupling constants that confirm the presence of the imidazolidinone ring.

Sagittamides A and B. Polyacetoxy long-chain acyl amino acids from a didemnid ascidian.

[structure: see text]. An unidentified tunicate from Pohnpei, Micronesia, yielded sagittamides A and B-compounds comprising a long-chain C26 dicarboxylic acid that acylates terminal L-valine and L-ornithine groups. The structures, which contain an unprecedented internal O-hexacetyl-1,2,3,4,5,6-hexaol moiety, were determined by combined spectroscopic analysis including mass spectrometry and 1D and 2D NMR and chemical degradation. The partial absolute stereochemistry of the new compounds was addressed by Marfey's analysis.

Occurrence of the alpha-glucosidase inhibitor 1,4-Dideoxy-1,4-imino-D-arabinitol and related iminopentitols in marine sponges.

The alpha-glucosidase inhibitor 1,4-dideoxy-1,4-imino-D-arabinitol (1) was isolated from two marine sponges collected in Western Australia and shown by LC-MS to be responsible for the alpha-glycosidase inhibitory activity in different sponge extracts collected over a wide geographic area. The configuration of 1 was determined by application of Marfey's method. The two most inhibitory extracts contained only 1, while the less inhibitory extracts contained 1,4-dideoxy-1,4-imino-D-xylitol (2) or the putative diastereomeric imino pentitols 3 and 4. The least active or inactive extracts showed no detectable imino pentitols. While both 1 and 2 are known from plants, this is the first report on the isolation and detection of 1 and 2 in marine invertebrates.

Progressive-convergent elucidation of stereochemistry in complex polyols. The absolute configuration of (-)-sagittamide A.

The absolute stereostructure of sagittamide A (1), a O-hexacetyl long-chain hexahydroxy-alpha,omega-dicarboxylic acid, was assigned using a progressive-convergent approach that integrates three powerful regimens for stereochemical analysis of acyclic natural products: J-based analysis, 13C NMR universal database comparisons, and exciton coupling circular dichroism.

New 3-oxo-chol-4-en-24-oic acids from the marine soft coral Eleutherobia sp.

Two novel cholic acid derivatives and three known steroids were isolated from an octocoral Eleutherobiasp. from Pohnpei Micronesia along with the known briareins minabein-1 (6), minabein-4 (7), minabein-6 (8), minabein-8 (9), and minabein-9 (10). X-ray crystallographic analysis of the known compound minabein-4 allowed assignment of its correct relative and absolute stereochemistry. Consequently, a different structure proposed for the same compound (named independently as nui-inoalide-D) is incorrect.