The chemical study of the ascidian Aplidium haouarianum has led to the isolation of the new metabolites haouamines A (1) and B (2) which belong to a novel class of alkaloids. The structure of 1 was established by interpretation of its spectroscopic data and those of the N-methyl derivative 3, and confirmed by X-ray crystallographic analysis. The structure of 2 was deduced by spectroscopic study of its peracetyl derivative 2a. In solution each haouamine exists as an unseparable mixture of two interconverting isomers derived by the presence of a highly strained 3-aza-[7]-paracyclophane moiety in their structures. Compound 1 exhibits a selective cytotoxic activity against the HT-29 human colon carcinoma cell line.

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Four different types of marine natural compounds isolated from tunicates were found to inhibit human aldose reductase. They all are characterized by a heterocyclic system, and at least two phenolic groups are present in the structure. Two of the compounds tested showed an inhibitory potency 5/6-fold higher than that of the known AR inhibitor sorbinil. One notable structural feature of these active compounds is the lack of either the carboxylic acid or the spiro-hydantoin commonly present in the principal classes of currently used inhibitors.

The sponge Spongia agaricina from Tarifa, Cadiz, Spain, contains two new 9,11-secosterols, [3-0-deacetylluffasterol B (1) and 3-0-deacetyl-22,23-dihydro-24,28-dehydroluffasterol B (2)] and two new sesterterpenoids [12,16-di-epi-12-0-deacetyl-16-0-acetylfuroscalarol (3) and 16-epi-scalarolbutenolide (4)], in addition to the known compounds 5-15. The structures of all compounds were elucidated by interpretation of' spectroscopic data. The metabolites 1-3 showed significant cytotoxicity against four tumor cell lines (C50 1 microgram/mL).

Three new cyclic peroxides 5-7 and a new carboxylic acid ester 8 were isolated as minor metabolites from the hexane extract of a Plakinastrella species from the Philippines. The structures of compounds 5-8 were elucidated by interpretation of spectral data and by chemical interconversion, and the absolute stereochemistry of peroxide 6 was determined by application of Mosher's method to a derivative. Although the major compounds in the sponge showed activity against Candida albicans prior to decomposition, the minor metabolites 5-8 are essentially inactive.