The haliclonacyclamines, cytotoxic tertiary alkaloids from the tropical marine sponge Haliclona sp

2D-NMR spectroscopic data is reported for the haliclonacyclamines A - D (1)-(4) and for two bismethiodide adducts (5) and (6). The structures of two new alkaloids, haliclonacyclamines C (3) and D (4), which are the 15,16-dihydro analogues of the haliclonacyclamines A (1) and B (2) are described. Revised assignments deduced by 2D-INADEQUATE spectroscopy are presented for (1) and (2). The alkene substituent in the C,, spacer group of (2) and (4) is positioned between C27-C28 by NMR, and confirmed by x-ray structural analysis for (2). Metabolite (3) has a C25-C26 double bond. (C) 1998 Elsevier Science Ltd. All rights reserved.

Antifungal alkyl amino alcohols from the tropical marine sponge Haliclona n. sp.

Three new amino alcohols presumably deriving from L-alanine were isolated from the tropical marine sponge Haliclona n. sp. and characterized by 2D NMR, while a fourth amino alcohol was characterized as an acetamide derivative. Relative stereochemistry was deduced from the NMR characteristics of oxazolidinone derivatives and absolute stereochemistry secured by preparation and analysis of an MPA ester. The amino alcohol fraction from Haliclona n. sp, acts as an antifungal agent and inhibits the development of larvae of the ascidian Herdmania curvata.

Advanced precursors in marine biosynthetic study. Part 2: The biosynthesis of isocyanides and isothiocyanates in the tropical marine sponge Axinyssa n.sp.

The biosynthetic origins of the isocyanide and isothiocyanate groups in 9-isocyanop upukeanane (2) and 9-isothiocyanato-pupukeanane (3) are investigated by incorporation of [C-14]-labelled advanced precursors into the sponge Axinyssa n.sp. (C) 2001 Elsevier Science Ltd. All rights reserved.

New chlorinated peptides from the tropical marine sponge Dysidea sp.

Five new chlorinated peptides (5)-(9) have been isolated from a Dysidea sp. and identified by two-dimensional NMR spectroscopy. The absolute stereochemistry of the metabolites was deduced by chemical correlation with S-(-)-4,4,4-trichloro-3-methylbutanoic acid (10) and with an alcohol (11). (C) 2001 Elsevier Science Ltd. All rights reserved.

Advanced precursors in marine biosynthetic study. Part 3: The biosynthesis of dichloroimines in the tropical marine sponge Stylotella aurantium

The biosynthetic origins of the dichloroimine group in the stylotellanes A and B 1,2 have been investigated by incorporation of [C-14]-labeled farnesyl isocyanide 7 and farnesyl isothiocyanate 3 into the sponge Stylotella aurantium. (C) 2002 Elsevier Science Ltd. All rights reserled.

Biosynthetic pathways to isocyanides and isothiocyanates; precursor incorporation studies on terpene metabolites in the tropical marine sponges Amphimedon terpenensis and Axinyssa n.sp.

The biosynthetic origins of the isocyanide and isothiocyanate functional groups in the marine sponge metabolites diisocyanoadociane (1), 9-isocyanopupukeanane (10) and 9- isothiocyanatopupukeanane (11) are probed by the use of [C-14]-labelled precursor experiments. Incubation of the sponge Amphimedon terpenensis with [C-14]-labelled thiocyanate resulted in radioactive diisocyanoadociane ( 1) in which the radiolabel is specifically associated with the isocyanide carbons. As expected, cyanide and thiocyanate were confirmed as precursors to the pupukeananes 10 and 11 in the sponge Axinyssa n. sp.; additionally these precursors labelled 2-thiocyanatoneopupukeanane ( 12) in this sponge. To probe whether isocyanide-isothiocyanate interconversions take place at the secondary metabolite level, the advanced precursor bisisothiocyanate 17 was supplied to A. terpenensis, but did not result in significant labelling in the natural product isocyanide 1. In contrast, in the sponge Axinyssa n. sp., feeding of [C-14]-9-isocyanopupukeanane (10) resulted in isolation of radiolabelled 9- isothiocyanatopupukeanane 11, while the feeding of [C-14]-11 resulted in labelled isocyanide 10. These results show conclusively that isocyanides and isothiocyanates are interconverted in the sponge Axinyssa n. sp., and confirm the central role that thiocyanate occupies in the terpene metabolism of this sponge.

Biosynthetic pathways to dichloroimines; precursor incorporation studies on terpene metabolites in the tropical marine sponge Stylotella aurantium

The biosynthetic origin of the dichloroimine functional group in the marine sponge terpene metabolites stylotellanes A ( 3) and B ( 4) was probed by the use of [C-14]-labelled precursor experiments. Incubation of the sponge Stylotella aurantium with [C-14]-labelled cyanide or thiocyanate resulted in radioactive terpenes in which the radiolabel was shown by hydrolytic chemical degradation to be associated specifically with the dichloroimine carbons. Additionally, label from both precursors was incorporated into farnesyl isothiocyanate ( 2). A time course experiment with [ 14C]cyanide revealed that the specific activity for farnesyl isothiocyanate decreases over time, but increases for stylotellane B ( 4), consistent with the rapid formation of farnesyl isothiocyanate ( 2) from inorganic precursors followed by a slower conversion to stylotellane B ( 4). The advanced precursors farnesyl isothiocyanate ( 2) and farnesyl isocyanide ( 5) were supplied to S. aurantium, and shown to be incorporated efficiently into stylotellane A ( 3) and B ( 4). Feeding of [C-14]-farnesyl isothiocyanate ( 2) resulted in a higher incorporation of label than with [C-14]-farnesyl isocyanide ( 5). Farnesyl isocyanide was incorporated into farnesyl isothiocyanate in agreement with labelling studies in other marine sponges. Both farnesyl isocyanide and isothiocyanate were further incorporated into axinyssamide A ( 11) as well as the cyclized dichloroimines (12)-(14), ( 16) that represent more advanced biosynthetic products of this pathway. These results identify the likely biosynthetic pathway leading to the major metabolites of S. aurantium.

Cellular origin of chlorinated diketopiperazines in the dictyoceratid sponge Dysidea herbacea (Keller)

The tropical marine sponge Dysidea herbacea (Keller) contains the filamentous unicellular cyanobacterium Oscillatoria spongeliae (Schulze) Hauck as an endosymbiont, plus numerous bacteria, both intracellular and extracellular. Archaeocytes and choanocytes are the major sponge cell types present. Density gradient centrifugation of glutaraldehyde-fixed cells with Percoll as the support medium has been used to separate the cyanobacterial symbiont from the sponge cells on the basis of their differing densities. The protocol also has the advantage of separating broken from intact cells of O. spongeliae. The lighter cell preparations contain archaeocytes and choanocytes together with damaged cyanobacterial cells, whereas heavier cell preparations contain intact cyanobacterial cells, with less than 1% contamination by sponge cells. Gas chromatography/mass spectrometry analysis has revealed that the terpene spirodysin is concentrated in preparations containing archaeocytes and choanocytes, whereas nuclear magnetic resonance analysis of the symbiont cell preparations has shown that they usually contain the chlorinated diketopiperazines, dihydrodysamide C and didechlorodihydrodysamide C, which are the characteristic metabolites of the sponge/symbiont association. However, one symbiont preparation, partitioned by a second Percoll gradient, has been found to be devoid of chlorinated diketopiperazines. The capability to synthesize secondary metabolites may depend on the physiological state of the symbiont; alternatively, there may be two closely related cyanobacterial strains within the sponge tissue.

A sponge/dinoflagellate association in the haplosclerid sponge Haliclona sp.: cellular origin of cytotoxic alkaloids by Percoll density gradient fractionation

Light-microscopic and electron-microscopic studies of the tropical marine sponge Haliclona sp. (Or der: Haplosclerida Family: Haliclonidae) from Heron Island, Great Barrier Reef, have revealed that this sponge is characterized by the presence of dinoflagellates and by nematocysts. The dinoflagellates are 7-10 mu m in size, intracellular, and contain a pyrenoid with a single stalk, whereas the single chloroplast is branched, curved, and lacks grana. Mitochondria are present, and the nucleus is oval and has distinct chromosomal structure. The dinoflagellates are morphologically similar to Symbiodinium microadriaticum, the common intracellular symbiont of corals, although more detailed biochemical and molecular studies are required to provide a precise taxonomic assignment. The major sponge cell types found in Haliclona sp, are spongocytes, choanocytes, and archaeocytes; groups of dinoflagellates are enclosed within large vacuoles in the archaeocytes. The occurrence of dinoflagellates in marine sponges has previously been thought to be restricted to a small group of sponges including the excavating hadromerid sponges; the dinoflagellates in these sponges are usually referred to as symbionts. The role of the dinoflagellates present in Haliclona sp. as a genuine symbiotic partner requires experimental investigation. The sponge grows on coral substrates, from which it may acquire the nematocysts, and shows features, such as mucus production, which are typical of some excavating sponges. The cytotoxic alkaloids, haliclonacyclamines A and B, associated with Haliclona sp. are shown by Percoll density gradient fractionation to be localized within the sponge cells rather than the dinoflagellates. The ability to synthesize bioactive compounds such as the haliclonacyclamines may help Haliclona sp. to preserve its remarkable ecological niche.

Climate change, coral bleaching and the future of the world's coral reefs

Sea temperatures in many tropical regions have increased by almost 1 degrees C over the past 100 years, and are currently increasing at similar to 1-2 degrees C per century. Coral bleaching occurs when the thermal tolerance of corals and their photosynthetic symbionts (zooxanthellae) is exceeded. Mass coral bleaching has occurred in association with episodes of elevated sea temperatures over the past 20 years and involves the loss of the zooxanthellae following chronic photoinhibition. Mass bleaching has resulted in significant losses of live coral in many parts of the world. This paper considers the biochemical, physiological and ecological perspectives of coral bleaching. It also uses the outputs of four runs from three models of global climate change which simulate changes in sea temperature and hence how the frequency and intensity of bleaching events will change over the next 100 years. The results suggest that the thermal tolerances of reef-building corals are likely to be exceeded every year within the next few decades. Events as severe as the 1998 event, the worst on record, are likely to become commonplace within 20 years. Most information suggests that the capacity for acclimation by corals has already been exceeded, and that adaptation will be too slow to avert a decline in the quality of the world's reefs. The rapidity of the changes that are predicted indicates a major problem for tropical marine ecosystems and suggests that unrestrained warming cannot occur without the loss and degradation of coral reefs on a global scale.

Parallel processing and image analysis in the eyes of mantis shrimps

The compound eyes of mantis shrimps, a group of tropical marine crustaceans, incorporate principles of serial and parallel processing of visual information that may be applicable to artificial imaging systems. Their eyes include numerous specializations for analysis of the spectral and polarizational properties of light, and include more photoreceptor classes for analysis of ultraviolet light, color, and polarization than occur in any other known visual system. This is possible because receptors in different regions of the eye are anatomically diverse and incorporate unusual structural features, such as spectral filters, not seen in other compound eyes. Unlike eyes of most other animals, eyes of mantis shrimps must move to acquire some types of visual information and to integrate color and polarization with spatial vision. Information leaving the retina appears to be processed into numerous parallel data streams leading into the central nervous system, greatly reducing the analytical requirements at higher levels. Many of these unusual features of mantis shrimp vision may inspire new sensor designs for machine vision