New nitrogenous eudesmane-type compounds isolated from the Caribbean sponge Axinyssa ambrosia

Medicinal Chemistry of Isocyanides

In eons of evolution, isocyanides carved out a niche in the ecological systems probably thanks to their metal coordinating properties. In 1859 the first isocyanide was synthesized by humans and in 1950 the first natural isocyanide was discovered. Now, at the beginning of XXI century, hundreds of isocyanides have been isolated both in prokaryotes and eukaryotes and thousands have been synthesized in the laboratory. For some of them their ecological role is known, and their potent biological activity as antibacterial, antifungal, antimalarial, antifouling, and antitumoral compounds has been described. Notwithstanding, the isocyanides have not gained a good reputation among medicinal chemists who have erroneously considered them either too reactive or metabolically unstable, and this has restricted their main use to technical applications as ligands in coordination chemistry. The aim of this review is therefore to show the richness in biological activity of the isocyanide-containing molecules, to support the idea of using the isocyanide functional group as an unconventional pharmacophore especially useful as a metal coordinating warhead. The unhidden hope is to convince the skeptical medicinal chemists of the isocyanide potential in many areas of drug discovery and considering them in the design of future drugs.

Cytotoxic Nitrogenous Terpenoids from Two South China Sea Nudibranchs Phyllidiella pustulosa, Phyllidia coelestis, and Their Sponge-Prey Acanthella cavernosa

A detailed chemical investigation of two South China Sea nudibranchs Phyllidiella pustulosa and Phyllidia coelestis, as well as their possible sponge-prey Acanthella cavernosa, led to the isolation of one new nitrogenous cadinane-type sesquiterpenoid xidaoisocyanate A (1), one new naturally occurring nitrogen-containing kalihinane-type diterpenoid bisformamidokalihinol A (16), along with 17 known nitrogenous terpenoids (2⁻15, 17⁻19). The structures of all the isolates were elucidated by detailed spectroscopic analysis and by the comparison of their spectroscopic data with those reported in the literature. In addition, the absolute stereochemistry of the previously reported axiriabiline A (5) was determined by X-ray diffraction (XRD) analysis. In a bioassay, the bisabolane-type sesquiterpenoids 8, 10, and 11 exhibited cytotoxicity against several human cancer cell lines.

New sesquiterpenoid isonitriles from three species of phyllidid nudibranchs

Chemical investigation of the two nudibranch species Phyllidiella pustulosa and Phyllidia ocellata collected in Queensland, Australia, provided new stereoisomers of 4-isocyano-9-amorphene (1) and of 10-isocyano-4-amorphene (2), respectively. A specimen of Phyllidia picta collected from Bali, Indonesia, contained the axane sesquiterpenoids pictaisonitrile-1 (3) and pictaisonitrile-2 (4). The planar structures were elucidated using 1D and 2D NMR spectroscopy, while relative configurations were established using NOESY correlations, coupling constant data, and comparison with literature data.

Marine Isonitriles and Their Related Compounds

Marine isonitriles represent the largest group of natural products carrying the remarkable isocyanide moiety. Together with marine isothiocyanates and formamides, which originate from the same biosynthetic pathways, they offer diverse biological activities and in spite of their exotic nature they may constitute potential lead structures for pharmaceutical development. Among other biological activities, several marine isonitriles show antimalarial, antitubercular, antifouling and antiplasmodial effects. In contrast to terrestrial isonitriles, which are mostly derived from α-amino acids, the vast majority of marine representatives are of terpenoid origin. An overview of all known marine isonitriles and their congeners will be given and their biological and chemical aspects will be discussed.

Trans-dimer D, a novel dimeric sesquiterpene with a bis-bisabolene skeleton from a Hainan sponge Axinyssa variabilis

A novel bisabolene sesquiterpene dimer named trans-dimer D (1) and its diastereoisomer trans-dimer C (2) reported in our previous work have been isolated as an inseparable mixture in a ratio of 1.5:1 from the South China Sea sponge Axinyssa variabilis. The structure of 1 was determined on the basis of extensive spectroscopic analysis and by comparison of its NMR spectral data with those of structurally related compounds. Compound 1 represents the fourth example of a sesquiterpene dimer with a bis-bisabolene skeleton.

Cembranoid diterpenes from the Caribbean sea whip Eunicea knighti

Three new cembranoid diterpenes, knightol (1), knightol acetate (2), and knightal (3), along with the known asperdiol (4) and asperdiol acetate (5), were isolated as major compounds from the sea whip Eunicea knighti collected from the Colombian Caribbean. The structures and absolute configurations of 1-5 were determined on the basis of spectroscopic analyses and by a combination of chemical and NMR methods, multiple correlations observed in a ROESY experiment, and using the modified Mosher method. Additionally, five semisynthetic compounds, 6-10, obtained during the chemical transformations of the natural compounds are here reported for the first time. All compounds were tested for antimicrobial activity against marine bacteria associated with heavily fouled surfaces and were also screened for antiquorum sensing (QS) activity. Compounds 1, 3, and 8 showed significant antimicrobial activity against bacterial isolates, and 1, 3, 7, and 8 showed excellent anti-QS inhibition activity measured by means of bioluminescence inhibition with biosensor model systems.

Isothiocyanate sesquiterpenes from a sponge of the genus axinyssa

The chemical study of a sponge of the genus Axinyssa collected in the Gulf of California has led to the isolation of the new bicyclic sesquiterpenes axinisothiocyanates A-L ( 1- 12) together with the known compounds (1 R,6 S,7 S,10 S)-10-isothiocyanato-4-amorphene ( 13), (4 R*,5 R*,7 S*,10 R*)-4-isocyanoeudesm-11-ene, (-)-epipolasin A, and (+)-aristolone. The structures of the new metabolites have been established by spectroscopic techniques, including the analysis of pyridine-induced 1H NMR chemical shifts. The cytotoxic activity has been tested against three human tumor cell lines.

Isolation and Synthesis of (−)-(5S)-2-Imino-1-methylpyrrolidine-5- carboxylic Acid from Cliona tenuis: Structure Revision of Pyrostatins

[reaction: see text] (-)-(5S)-2-Imino-1-methylpyrrolidine-5-carboxylic acid (1), previously reported as the N-acetyl-beta-d-glucosaminidase inhibitor pyrostatin B, has been isolated from the organic extracts of the burrowing sponge Cliona tenuis. The structure of 1, including its absolute stereochemistry, was characterized from its spectral data and chemical transformations and confirmed by total synthesis. The synthesis of 1 reveals that the structure of pyrostatin B has been incorrectly assigned. Comparison of NMR spectral data strongly suggests that pyrostatins A and B are identical to 5-hydroxyectoine and ectoine, respectively.

Marine pharmacology in 2001-2: antitumour and cytotoxic compounds

During 2001 and 2002, marine antitumour pharmacology research aimed at the discovery of novel antitumour agents was published in 175 peer-reviewed articles. The purpose of this paper is to present a structured Review of the antitumour and cytotoxic properties of 97 marine natural products, many of them novel compounds that belong to diverse structural classes, including polyketides, terpenes, steroids, and peptides. The organisms yielding these bioactive compounds comprise a taxonomically diverse group of marine invertebrate animals, algae, fungi and bacteria. Antitumour pharmacological studies were conducted with 30 structurally characterised natural marine products in a number of experimental and clinical models which further defined their mechanisms of action. Particularly potent in vitro cytotoxicity data generated with murine and human tumour cell lines was reported for 67 novel marine chemicals with as yet undetermined mechanisms of action. Noteworthy, is the fact that marine anticancer research was sustained by a collaborative effort, involving researchers from Australia, Brazil, Canada, Denmark, Egypt, France, Germany, Italy, Japan, Netherlands, New Zealand, The Philippines, Russia, Singapore, South Korea, Thailand, Taiwan, Turkey, Spain, Switzerland, Taiwan, Thailand, Turkey, and the United States. Finally, this 2001-2 overview of the marine pharmacology literature highlights the fact that the discovery of novel marine antitumour agents has continued at the same pace as during 1998, 1999 and 2000.

New nitrogenous Germacranes from a Thai marine sponge, Axinyssa n. sp

Two new germacrane sesquiterpenes, including (1Z,4Z)-7alphaH-11-aminogermacra-1(10),4-diene (1) and N,N'-11-bis[(1Z,4Z)-7alphaH-germacra-1(10),4-dienyl]urea (2), were isolated from a Thai marine sponge Axinyssan. sp. collected from the Andaman Sea. The structure elucidations of 1 and 2 were accomplished by means of 1D and 2D NMR, MS, and IR spectroscopy. Only 1 exhibited strong antimicrobial activity against Staphylococcus aureus, Bacillus subtilis, and Candida albicans.

(-)-Axinyssene: a novel cytotoxic diterpene from a Japanese marine sponge Axinyssa sp

[structure: see text] A novel diterpene, (-)-axinyssene, was isolated from the Japanese marine sponge Axinyssa sp. The structure of (-)-axinyssene was determined on the basis of spectroscopic and synthetic evidence to be 1-methyl-4-[(4E)-5',9'-dimethyl-1'-methylene-4',8'-decadienyl]-(4S)-cyclohexene. (-)- and (+)-axinyssene showed mild cytotoxicity against acute promyelocytic leukemia, HL-60 cells.