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The unusual base-induced ring-enlargement of halomethylenecyclobutanes to 1-halocyclopentenes was examined with unsymmetrical and (13)C-labeled substrates to study regio- and stereochemical characteristics. Migration of a ring carbon atom (single migration) or simultaneous migration of a ring carbon atom and the halide (double migration) gives the ring-enlarged products. (13)C-labeling experiments established that both rearrangements occur with retention of configuration at the migrating center. These systems are suggested as models for the Fritsch-Buttenberg-Wiechell (FBW) rearrangement.

The synthesis of a simple analogue of salicylihalamide A with a truncated lactone ring (+/- 2) was achieved in 10 steps. Its cytotoxicity profile in the NCI 60-cell-line human tumor assay differed significantly from that of salicylihalamide A in both level and specificity.

A new proline-rich cyclodecapeptide, designated stylopeptide 2, has been isolated from a cytotoxic extract of the Papua New Guinea marine sponge Stylotella sp. and found to correspond to structure 1. The structural assignment was based on HRMS collision-induced dissociation tandem mass spectrometry (CID MS/MS), NMR spectroscopic data, and amino acid analysis, which led to assignment of the absolute configuration.

Clavosolides A-D (1-4), dimeric macrolides incorporating cyclopropyl, tetrahydropyranyl, and glycosidic ring systems, were isolated from the cytotoxic extract of a Philippines collection of the marine sponge Myriastra clavosa. The structures of the clavosolides, which occurred as only trace metabolites, were elucidated through extensive NMR spectroscopic analyses. Clavosolides A (1) and B (2) were recently reported metabolites from M. clavosa, while the unsymmetrical dimers clavosolides C (3) and D (4) had new structures.

A sevised regiochemistry and the absolute configuration are established for cartilagineol (formerly allo-isoobtusol). This revised structure renders cartilagineol the first example of the fourth stereochemical type of Laurencia-derived polyhalogenated chamigrene in support of current biogenetic theory. Earlier misassigned NMR data for ma'ilione is corrected.

Summary Rottnestol, a new hemiketal, was isolated from an Australian collection of the marine sponge Haliclona sp. Its structure was deduced as 3 from 1H, 13C, COSY, HMQC, HMBC and nOe NMR studies. Hemiketal 3 was readily converted to its epimer, 4, and the methyl ketal of 4.

A sevised regiochemistry and the absolute configuration are established for cartilagineol (formerly allo-isoobtusol). This revised structure renders cartilagineol the first example of the fourth stereochemical type of Laurencia-derived polyhalogenated chamigrene in support of current biogenetic theory. Earlier misassigned NMR data for ma'ilione is corrected.

A new cell growth inhibitory (P388 lymphocytic leukemia ED 50 0.8 μg/mL) cycloheptapeptide designated stylostatin 1 (1) has been isolated from the south Pacific Ocean sponge Stylotella aurantium Kelly-Borges and Bergquist. Structural determination was accomplished primarily by utilizing high-field 1 H-NMR (500 MHz) with appropriate 2D-NMR experiments and was confirmed by X-ray crystallographic analysis. The absolute configuration (established by chiral gas chromatographic analysis) and crystal structure conformation (with hydrogen bonding) for stylostatin 1 (1) were determined

Chemical investigation of the Philippines marine sponge Myriastra clavosa has resulted in the isolation of three new cyclic octapeptides, myriastramides A ( 1 ), B ( 2 ), and C ( 3 ). The structures of compounds 1–3 were assigned based on extensive NMR spectroscopic analyses and a series of degradation and derivatization studies.

Two novel, highly potent, cytotoxic macrolides, salicylihalamides A (1) and B (2), were isolated from the sponge Haliclona sp. This new macrolide class incorporates salicylic acid, a 12-membered lactone ring, and an enamide side chain. COMPARE pattern-recognition analyses of the NCI 60-cell mean graph screening profiles of 1 did not reveal any significant correlations to the profiles of known antitumor compounds in the NCI's “standard agent database”, thus supporting the conclusion that the salicylihalamides represent a potentially important new class for antitumor lead optimization and in vivo investigations.

A cyclic depsipeptide, georgamide (1), was isolated from an Australian cyanobacterium and characterized by spectroscopic means. The constituent units were five amino acid residues, one each of L-Thr, L-Pro, L-Val, N-Me-L-Val, and N-Me-L-Phe, and two hydroxy carboxylic acids, 2(S)-hydroxy-3(R)-methylpentanoic acid and the unusual 2,2-dimethyl-3-hydroxy-7-octynoic acid. The stereochemistry was determined by hydrolysis of the peptide followed by derivatization and HPLC comparison with standard samples.

Several new compounds were isolated from the organic extract of the cyanobacterium Microcoleus lyngbyaceus, and their structures were determined by spectroscopic means. Polychlorinated acetamidoalkynes and alkanes were the major metabolites. 6-Acetamido-1,1,1-trichloroundecane, a positional isomer of the naturally occurring 5-acetamido-1,1,1-trichloroundecane, was synthesized in six steps from delta-decanolactone.

Serinol derivatives 4a and 4b were isolated from an Australian blue-green alga and characterized by spectroscopic means. Their absolute stereochemistry was established by chemical methods.

Seven new sesquiterpenes, majapolenes A [1] and B [2], majapolone [3], and majapols A [4], B [5], C [6], and D [7], were isolated from a Philippine collection of Laurencia majuscula. With the exception of majapolene B [2], all compounds were isolated as inseparable diastereomeric mixtures. Structure elucidation was achieved by spectroscopic methods. Majapolene A [1], a dioxabicyclo[2.2.2]-alkene, displayed modest activity in the NCI 60-cell line cytotoxicity screen. Majapolene A was also found as a major component of a Philippine collection of Laurencia caraibica.

The novel phorbol ester 12-deoxyphorbol 13-(3E,5E-decadienoate) [1] was isolated as the anti-HIV principle of Excoecaria agallocha leaves and stems collected in northwest Australia. The structure was determined by spectral means. Compound 1 was also a potent displacer of [3H]-phorbol dibutyrate from rat brain membranes.

Kahukuenes A [4] and B [5], new diterpenoids possessing an unprecedented prenylated chamigrene structure as part of a decalin ring, were isolated from the Hawaiian marine alga Laurencia majuscula. Spectroscopic methods, including extensive 1D and 2D nmr studies, were used to establish the structure and relative stereochemistry of these two secondary metabolites.

A new cytotoxic tribrominated chamigrene with a dibromohydrin functionality was isolated from an undetermined species of red alga, Laurencia sp. Its structure was determined by spectroscopic methods.

The syn and anti stereoisomers of 3-ethoxy-2-methyl-2-vinylcyclobutanone were prepared. Reinterpretation of the literature 13C spectra led to an inversion of the original structure assignments. Confirmation of relative stereochemistry was provided by NOE difference experiments. Copyright © 2001 John Wiley & Sons, Ltd.

Two new sesquiterpenoid metabolites have been characterized from a Jamaican variety of the marine alga Laurencia obtusa. These are 2-chloro-3-hydroxy-α-chamigren-9-one, with an unusual cis-relationship of the heteroatoms at the 2,3-positions, and its intramolecular conjugate addition derivative possessing a cineole moiety fused to a cyclohexane ring.

Enyne 1 was isolated from the marine red alga Laurencia majuscula , and its structure was elucidated by spectroscopic means. 1 is the first 2,2′- bis -tetrahydrofuran lauroxane to be found as a Laurencia metabolite.

3-(13-Methylhexadecyloxy)-1,2-(S)-propanediol ( 6 ) and 3-(15-methyloctadecyloxy)-1,2-(S)-propanediol ( 7 ) were isolated from an Aaptos species of marine sponge from Taiwanese waters and characterized by spectroscopic methods. Homolog 6 was independently synthesized.

Possible mechanisms by which the C2-unit of the tryptamine bridge of condylocarpine-type alkaloids can be lost to give the uleine skeleton are considered. A terminally-oxidized β-C2 substituent on an α-methyleneindoline system could not be cleaved, but a β-C3 acid unit fragmented readily.