Additional analysis of chemical diversity in Laurencia nipponica (Ceramiales, Rhodophyta)

The red alga Laurencia nipponica Yamada (Rhodomelaceae, Ceramiales) is known to contain several chemical races, each of which is characterized by a particular, major halogenated secondary metabolite. Both field-collected and cultured plants of a population of this species found recently at Shikanoshima Island, Fukuoka Prefecture, southern Japan, produced C₁₅ bromoethers, (3E)-laureatin and (3E)-isolaureatin, and sesquiterpenoids, 2,10-dibromo-3-chloro-9-hydroxy-α-chamigrene and 2,10-dibromo-3-chloro-α-chamigrene. Laurencia nipponica can be referred to as a further chemical race that is characterized by the production of two C₁₅ bromoethers, (3E)-laureatin and (3E)-isolaureatin, and a sesquiterpenoid, 2,10-dibromo-3-chloro-9-hydroxy-α-chamigrene as major compounds.     

Two New Halogenated Compounds from the Marine Red Alga Laurencia nipponica Yamada from the Kunashiri and Etorofu Islands

The red alga Laurencia nipponica comprises various chemical races distributed relative to the ocean current in Japanese coastal areas. We investigated the chemical compositions and chemical races of L. nipponica distributed from the Kunashiri and Etorofu Islands, the confluence of the Soya warm current and Oya-shio cold current. Two new halogenated secondary metabolites, deacetylneonipponallene ( 1 ) and neopacifenol ( 2 ), along with four known compounds, deoxyprepacifenol ( 3 ), pacifenol ( 4 ), halo-chamigrene diether ( 5 ), and isolaurallene ( 6 ) were isolated from L. nipponica collected at Chikappunai, Kunashiri Island, while Zaimokuiwa (Kunashiri Island) and Sana (Etorofu Island) populations contained 3 , 7-hydroxylaurene ( 7 ), 2,10-dibromo-3-chloro-9-hydroxy-α-chamigrene ( 8 ), and (3Z)-laurefucin ( 9 ). The structures of 1 and 2 were established using spectroscopic methods. The chemical races of L. nipponica distributed in this area were divided into 6 - and 9 -producing races. Interestingly, both races contained 4 as an additional race-index, as well as its derivatives, 2 and 5 . To the best of our knowledge, this is the first example of a race comprising a mixture of two race-index compounds, suggesting that the convergence of two currents causes the production of new and diverse chemical races in this species.     

Antifouling Brominated Diterpenoids from Japanese Marine Red Alga Laurencia venusta Yamada

The marine red algal genus Laurencia has abundant halogenated secondary metabolites, which exhibit novel structural types and possess various unique biological potentials, including antifouling activity. In this study, we report the isolation, structure elucidation, and antifouling activities of two novel brominated diterpenoids, aplysin-20 aldehyde ( 1 ), 13-dehydroxyisoaplysin-20 ( 2 ), and its congeners. We screened marine red alga Laurencia venusta Yamada for their antifouling activity against the mussel Mytilus galloprovincialis. Ethyl acetate extracts of L. venusta from Hiroshima and Chiba, Japan, were isolated and purified, and the compound structures were identified using 1D and 2D NMR, HR-APCI-MS, IR, and chemical synthesis. Seven secondary metabolites were identified, and their antifouling activities were evaluated. Compounds 1 , 2 , and aplysin-20 ( 3 ) exhibited strong activities against M. galloprovincialis. Therefore, these compounds can be explored as natural antifouling drugs.     

A new species of Laurencia, L. omaezakiana (Ceramiales, Rhodophyta), from Japan

Laurencia omaezakiana Masuda, sp. nov. (Ceramiales, Rhodophyta) is described from Japan. It is characterized by the following set of features: (i) the production of four periaxial cells from each vegetative axial cell; (ii) a shift in branching from distichous to spiral; (iii) the presence of projecting superficial cortical cells near the apices of branches; (iv) the presence of longitudinally oriented secondary pit-connections between contiguous superficial cortical cells; (v) the presence of lenticular thickenings in the walls of medullary cells; (vi) the occurrence of 1–2 corps en cerise in each superficial cortical cell and a single corps en cerise in each trichoblast cell; and (vii) a parallel arrangement of tetrasporangia. Furthermore, it produces a characteristic triterpenoid (enshuol), which has not been detected in other species of Laurencia, as a major halogenated secondary metabolite. A synoptical key to the 23 species of Laurencia growing in Japan is given. Laurencia ceytanica J, Agardh and Laurencia heteroclada Harvey are excluded from the Japanese marine algalflora. The latter is a distinct species from Laurencia filiformis (C. Agardh) Montagne.     

Sesquiterpenoids of Laurencia majuscula (Ceramiales, Rhodophyta) from the Ryukyu Islands, Japan

Two populations of the red alga Laurencia majuscula (Harvey) Lucas (Rhodomelaceae, Ceramiales) from Taketomi Island and Hateruma Island, the Ryukyu Islands, Japan, have been characterized on the basis of both morphological features and halogenated secondary metabolite content. These populations have smaller and more slender thalli than those of other regions. Furthermore, the populations contain two chamigrane-type Sesquiterpenoids, (2R, 3R, 5S)-5-acetoxy-2-bromo-3-chlorochamigra-7(14),9-dien-8-one and (2R, 3R)-2-bromo-3-chlorochamigra-7(14), 9-dien-8-one, and a laurane-type sesquiterpenoid, debromoisolaurinterol, as secondary metabolites which are different from those previously reported from other populations. These results are consistent with the concept of ‘chemical races’ within a single species of Laurencia.     

Brominated metabolites from an Okinawan Laurencia intricata

Two halogenated C₁₅ acetogenins, itomanallenes A and B, with a terminal bromoallene moiety along with a halogenated sesquiterpene, itomanol, have been isolated from the red alga Laurencia intricata collected in Okinawan waters. Their structures were deduced from 1D and 2D NMR experiments including ¹H–¹H COSY, HSQC, HMBC, and NOESY methods. The alcohol corresponding to itomanallene B seems to be a plausible precursor of itomanallene A, which has an unusual 2,10-dioxabicyclo[7.3.0]dodecene skeleton. Itomanol was found to be a selinane-type bromosesquiterpenoid, and is the first example of a selinane to be isolated from Japanese Laurencia species.     

Laurencia majuscula var. elegans (Rhodophyta,Rhodomelaceae) is reinstated to specific rank as L. elegans

Laurencia majuscula has recently been determined to be conspecific with Laurencia dendroidea. To determine the correct taxonomic placement of its only non‐typical variety, L. majuscula var. elegans, mitochondrial COI‐5P and chloroplast rbcL gene sequences were analyzed and its phylogenetic position was inferred. Laurencia majuscula var. elegans consistently formed a well‐supported clade distinctly separate from the L. dendroidea clade. Molecular analyses revealed that L. majuscula var. elegans generally shows two distinct forms; a long‐branched form, and a compact form. Often the compact form has been identified as a different species based on morphology alone. Included in these analyses were topotype sequences of two species with which L. majuscula var. elegans is most often misidentified; Laurencia nidifica and Laurencia mcdermidiae. Laurencia nidifica formed a well‐supported clade separate from L. majuscula var. elegans. Laurencia mcdermidiae, however, formed a well‐defined clade sister to the L. majuscula var. elegans clade. Morphological comparisons were also made. It is concluded that L. majuscula var. elegans is morphologically distinct from L. dendroidea, L. nidifica, and L. mcdermidiae. It is proposed that L. majuscula var. elegans be reinstated to species level as L. elegans.     

Australian Laurencia majuscula (Rhodophyta,Rhodomelaceae) and the Brazilian Laurencia dendroidea are conspecific

Morphological and molecular studies have been undertaken on two species of the red algal genus Laurencia J.V.Lamouroux: Laurencia majuscula (Harvey) A.H.S. Lucas and Laurencia dendroidea J.Agardh, both from their type localities. The phylogenetic position of these species was inferred by analysis of the chloroplast‐encoded rbcL gene sequences from 24 taxa. In all phylogenetic analyses, the Australian Laurencia majuscula and the Brazilian L. dendroidea formed a well‐supported monophyletic clade within the Laurencia sensu stricto. This clade was divided into two subclades corresponding to each geographical region; however, the genetic divergence between Australian L. majuscula and Brazilian L. dendroidea was only 0–1.35%. Examination of the type specimens and sequences of freshly collected samples of both Laurencia majuscula and L. dendroidea show the two to be conspecific despite their disjunct type localities.     

Phytochemical studies of the southern Australian marine alga, Laurencia elata

Chemical profiling of the southern Australian marine alga Laurencia elata (Rhodomelaceae) employing on-flow and stop-flow HPLC–NMR methodology followed by off-line chemical investigations resulted in the isolation of two C₁₆ chamigrenes, cycloelatanene A and B together with three previously reported sesquiterpenes, (3Z)-chlorofucin, pacifenol and elatenyne. The chemical structures were elucidated via detailed spectroscopic analyses.     

DIVERSITY OF HALOGENATED SECONDARY METABOLITES IN THE RED ALGA LAURENCIA NIPPONICA (RHODOMELACEAE,CERAMIALES)1,2

Many morphologically similar, but chemically distinct, populations have been found in the marine red alga Laurencia nipponica Yamada (Rhodomelaceae, Ceramiales) growing in Japan. Each chemical type is characterized by a specific end-product of halogenated secondaly metabolite synthesis: chamigrane-type sesquiterpenoids such as prepacifenol and halochamigrene epoxide and C₁₅ bromoethers such as laurencin, laureatin, isoprelaurefucin, epilaurallene, and kumausallene. These seven types of secondary metabolite syntheses remained the same in the wild and under various culture conditions. Because bromoethers and terpenoids are probably synthesized by different metabolic pathways, it is virtually certain that different sets of enzymes participate in their synthesis. Prepacifenol- and laureatin-producing populations were selected as representatives of terpenoid and bromoether groups, respectively. F₁ tetrasporophytes derived from crosses between reciprocal, female and male gametophytes of prepacifenol- and laureatin-producing strains bore both types of metabolites, suggesting that the genes Producing these enzyme systems are encoded by nuclear genomes. The F₁ gametophytes resulting from the reciprocal crosses produced either prepacifenol or laureatin, and the four individuals derived from spore tetrads (a set of tetraspores derived from a single tetrasporangium) produced either prepacifenol or laureatin in a 1:1 ratio, indicating that genes participating in terpenoid synthsis and those participating in bromoether synthesis are on different loci of homologous chromosomes and are segregated at meiosis (tetrasporogenesis). One individual of this interpopulational F₁ gamtophyte produced both parental types of metabolite, perhaps indicating the occurrence of a recombination type. Natural hybrid individuals, including such recombination-type gametophytes, were found in a sympatric locality at which these two chemical types occur. F₁ tetrasporophytes derived from crosses between respective prepacifenol- and laureatin-producing strains and their F₁ gametohytes produced only parental-type metabolite-producing plants. These results indicate that the diverse chemical types can be referred to as races (chemical races).     

Habitat characteristics and seasonal changes of Laurencia brongniartii (CeramiaIes, Rhodophyta) in Kagoshima, Southern Japan

The seasonal change in size of Laurencia brongniartii was observed for the year 2002 at Banshobana Park, Satsuma Peninsula and Tsuchihama Beach, Amami Oshima, both in Kagoshima Prefecture, Japan. Additionally, the vertical distribution of this species was also studied at Tsuchihama Beach (second site), where the largest populations were found. Maximum lengths were observed in October ‐ November with a size of 100 ± 6 mm at Banshobana Park and 111 ± 5 mm at Tsuchihama Beach. Line‐transects conducted at Tsuchihama Beach, were analyzed to determine the vertical distribution of L. brongniartii due to depth and the slope of the substrate. Alga was found growing in areas restricted to low levels of light.     

Taxonomic notes on Laurencia mariannensis (Rhodomelaceae, Rhodophyta)

The marine red alga Laurencia mariannensis Yamada (Rhodomelaceae, Ceramiales) is characterized by pale rose-red, softly fleshy, slender, terete axes (up to 600 μm in diameter), arising from a loosely entangled, stoloniferous basal system among species that have the following combination of features: the presence of longitudinally orientated secondary pit-connections between contiguous superficial cortical cells; the presence of projecting superficial cortical cells at the upper portions of branches; and the presence of lenticular thickenings in the walls of medullary cells, Furthermore, the presence of two or three corps en cerise per superficial cortical cell and one per trichoblast cell may characterize the species.     

An experimental approach to study the biosynthesis of brominated metabolites by the red algal genus Laurencia

The production of labeled brominated metabolites with radioactive ⁸²Br in Laurencia species was investigated as part of a study of the biosynthesis of halogenated metabolites from species belonging to the red algal genus Laurencia (Rhodomelaceae, Ceramiales). Radiobromide [⁸²Br], thin-layer chromatography (TLC), and TLC–autoradioluminography (ARLG) were used. When cultured in artificial seawater medium (ASP₁₂NTA including Na⁸²Br) under 16:8 h light:dark (LD) illumination cycles for 24 h, each of the strains of Laurencia, Laurencia japonensis Abe et Masuda, Laurencia nipponica Yamada (laurencin-producing race and laureatin-producing race), and Laurencia okamurae Yamada, produced species- (or race-) specific ⁸²Br-containing metabolites. In the case of the laurencin-producing race of L. nipponica, laurencin and deacetyllaurencin were found to be produced in approximately 1:1 ratio, though laurencin is the major metabolite in the wild sample. Furthermore, when cultured in the dark, the production rates of brominated metabolites in Laurencia spp. were found to be diminished. The present study strongly indicates that the use of radiobromine [⁸²Br] in combination with the TLC–ARLG method is an effective approach for investigating the biosynthesis of brominated metabolites in Laurencia.     

Chemical races in the red alga Laurencia nipponica (Rhodomelaceae, Ceramiales)

Genetic variation in the synthesis of halogenated secondary metabolites in the Japanese marine red alga Laurencia nipponica Yamada (Rhodomelaceae, Ceramiales) has been investigated in laboratory crossing experiments and chemical analyses, F₁ tetrasporophytes and F₁ gametophytes resulting from crosses within chemical races produced major metabolites characteristic of these races. F₁ tetrasporophytes derived from reciprocal interracial crosses produced: (i) both parental types of secondary metabolites; (ii) either of the parental types; or (iii) a further major compound in addition to both parental types or in addition to either of the parental types. The latter cases suggest that hybrid-specific products were formed by the combined enzymatic complements of the parents, as F₁ gametophytes derived from these interracial F₁ tetrasporophytes yielded one or other of their parental products in an approximate 1:1 ratio. The population structure was analyzed at localities in Hokkaido, where two of the chemical races occur sympatrically. At Usujiri (Minami-kayabe), where the prepacifenol race and the laureatin race were sym-patric, hybrid gametophytes (recombination type) were found in high frequency in addition to hybrid tetra sporophytes, which strongly suggests that a new, pre-pacifenol/laureatm race is beginning to be produced by natural hybridization and recombination. By contrast, at Oshoro Bay, where the laurencin race and the epi-lauraliene race grew together, the interracial hybrids were rare: only a few tetrasporophytes (probably F₁ generation) were found, suggesting that racial integrity may be retained by habitat segregation and/or the absence of recombination-type gametophytes.     

Halogenated diterpenoids from the red alga Laurencia nipponica

Chemical compositions of three collections of the red alga Laurencia nipponica from the western part of the Sea of Japan were studied. One of them contained a series of the previously known sesquiterpenoids. Another one gave C15 bromoallene ethers, predominantly. Finally, two new halogenated diterpenes, 15-bromoparguer-9(11)-ene-16-ol and 15-bromoparguer-7-ene-16-ol, were isolated from the third collection of the same species. Structures of these diterpenoids were established by 1D and 2D NMR (1H-1H COSY, DEPT, HMQC, HMBC and NOESY) along with molecular calculations for conformations having lowest energies and mass spectroscopy. Diversity and variability of halogenated secondary metabolites in L. nipponica were discussed.     

New records of marine benthic algae from New South Wales, eastern Australia

Twenty‐four species of marine macroalgae are recorded from the mainland coast of New South Wales for the first time. One species, Laurencia platyclada Boergesen, represents a new record for Australia and the Pacific Ocean. Included in these new records is the introduced, invasive and cold‐tolerant strain of the green alga Caulerpa taxifolia, which was formerly known only as native, non‐invasive populations from Lord Howe Island. Based on published accounts, the composition of the marine benthic algae for the state of New South Wales now stands at 131 green, 140 brown and 449 red macroalgae. This baseline information adds significantly to our knowledge of the overall marine biodiversity of the state, as well as to the phycogeography of the southwestern Pacific region.     

New records of three marine red algae from Japan

Three species in the red algal order Ceramiales, Dasya longifila Masuda et Uwai (Dasyaceae), Endosiphonia horrida (C. Agardh) P. Silva (Rhodomelaceae) and Laurencia flexilis Setchell (Rhodomelaceae), are reported from Japan for the first time, and their morphological features are described along with taxonomic comments. Our findings point to the northernmost limit of geographic distribution of these species in the north‐western Pacific. Dasya longifila is characterized by small, sparsely corticated axes, long pseudolaterals in which intercalary cell divisions take place, and a small number of tetrasporangial stichidia and spermatangial branches per fertile pseudolateral. Endosiphonia horrida is characterized by frequently anastomosing branches that form a bush‐like tuft without a percurrent axis, inner cortical cells becoming the same length as the axial and periaxial cells, and luxuriously developed, unbranched trichoblasts. Laurencia flexilis is characterized by numerous cartilaginous rigid axes developing from a basal disc without creeping branches, the production of 4 periaxial cells per vegetative segment and the absence of longitudinally oriented secondary pit‐connections between contiguous superficial cortical cells.     

Agar from the red seaweed,Laurencia flexilis (Ceramiales,Rhodophyta) from northern Philippines

The worldwide production of the gelling agent agar mainly rely on the red algae of the order Gracilariales and Gelidiales for raw material. We investigate here the potential of a species from another red algal order, Ceramiales as an agar source. The agar from Laurencia flexilis collected in northern Philippines was extracted using native and alkali treatment procedures and the properties of the extracts were determined using chemical, spectroscopic and physical methods. The native agar, 26% dry weight basis, forms a gel with moderate gel strength (200 g cm^?2). Alkali‐treatment did not enhance the gel strength, indicating insignificant amounts of galactose‐6‐sulfate residue, the precursor of the gel‐forming 3,6‐anhydrogalactose (3,6‐AG) moieties. Furthermore, the Fourier transform infrared and chemical analysis showed low sulfate and high 3,6‐AG levels, not affected significantly by the alkali treatment. Nuclear magnetic resonance spectroscopic analysis revealed 3‐linked 6‐O‐methyl‐D‐galactose and 4‐linked 3,6‐anhydro‐L‐galactose as the major repeating unit of the native extract, with minor sulfation at 4‐position of the 3‐linked galactose residues. The native and alkali treated agars have comparably high gelling and melting temperatures, whereas the former exhibits higher gel syneresis. Laurencia flexilis could be a good source of agar that possesses physico‐chemical and rheological qualities appropriate for food applications. Due to the inability of alkali treatment to enhance the key gel qualities of the native extract, it is recommended that commercial agar extraction from this seaweed would be done without pursuing this widely‐used industrial procedure.     

Chemical composition of Laurencia spp. collected from the Seto Inland Sea of Japan

The chemical composition of three Laurencia spp., Laurencia sp., L. okamurae and L. saitoi, which were collected from the Seto Inland Sea of Japan, has been examined. Laurencia sp. collected from the coast of Matoba Park, Takehara, Hiroshima Prefecture, contained a brominated chamigrane-type sesquiterpene (1), named matobol, as the main metabolite. The structure of matobol was determined as (+)-(2R,3R,6R,10S)-2,10-dibromochamigr-7(14)-en-3-ol (1). This is the first time that the optically active 1 has been isolated from Laurencia. On the other hand, L. okamurae from the coast of Ikunoshima Island, Hiroshima Prefecture, produced laurinterol (2) that is a known cyclolaurane-type sesquiterpene characteristic to this species in Japan. L. saitoi from the coast of Matoba Park contained a known bromoallenic C₁₅-acetogenin, neolaurallene (3).