Total synthesis of polycavernoside A, a lethal toxin of the red alga Polycavernosa tsudai

[structure: see text] Two approaches to the synthesis of the aglycon 120 of polycavernoside A (1) were developed, only one of which was completed. The successful "second-generation" route assembled the aglycon seco acids 102 and 106 via Nozaki-Hiyama-Kishi coupling of aldehyde 70, prepared from methyl (S)-3-hydroxy-2-methylpropionate (72) and (S)-pantolactone (73), with vinyl bromide 71. The latter was obtained from a sequence which commenced from the silyl ether 24 of 3-hydroxypropionaldehyde and entailed cyclization of (Z)-zeta-hydroxy-alpha,beta-unsaturated ester 82. Regioselective Yamaguchi lactonization of trihydroxycarboxylic acids 102 and 106 and subsequent functional-group adjustments led to macrolactone 120, to which the fucopyranosylxylopyranoside moiety was attached. Stille coupling of the glycosidated aglycon 128 with dienylstannane 129 furnished polycavernoside A in a synthesis for which the longest linear sequence was 25 steps. The overall yield to lactone 120 was 4.7%.     

Three new vinyl acetylenes from the marine red alga laurencia

The structures of three new halogenated vinyl acetylenes are described which are natural products from various species of the red seaweed Laurencia. The structure of chlorofucin (1) isolated from Laurencia snyderae was determined by X-ray diffraction analysis. Poiteol (2) was isolated from Laurencia poitei and its structure was also determined by single crystal X-ray diffraction experiments. The structure of obtusenyne (3) was based on a combination of chemical and spectral methods. The ¹³C NMR spectra of these new compounds are presented and assignments made.     

Glandulaurencianols A–C,brominated diterpenes from the red alga, Laurencia glandulifera and the sea hare, Aplysia punctata

Glandulaurencianols A and B were isolated from the organic extract of the red alga, Laurencia glandulifera, collected from the island of Crete in South Greece. Investigation of the mollusk, Aplysia punctata, collected from the coast of Nea Makri, Central Greece, resulted in the isolation of glandulaurencianols A and C. The structures of the new metabolites, as well as their relative configurations, were established on the basis of thorough analyses of their spectroscopic data.     

New sesquiterpenes from the red alga Laurencia microcladia

Three new aromatic sesquiterpenes (1, 2, and 4), one new dimeric sesquiterpene of the cyclolaurane-type (3), one sesquiterpene alcohol of bisabolene type (8) along with three previously reported metabolites (5-7), were isolated from the organic extracts of Laurencia microcladia, collected from the Chios island in the North Aegean Sea. The structures of the new natural products, as well as their relative stereochemistries, were established by means of spectral data analyses, including 2D experiments. The cytotoxicity of the isolated metabolites was evaluated against five human tumor cell lines.     

Cytotoxic bromoditerpenes from the red alga Sphaerococcus coronopifolius

Three new brominated diterpenes (1, 2, 8), along with six previously reported metabolites (3-7, 9), were isolated from the organic extract of Sphaerococcus coronopifolius, collected in Palaiokastritsa bay at the west coasts of Corfu Island. The structures of the new natural products, as well as their relative stereochemistry, were established by means of spectral data analyses, including 2D experiments. The absolute stereochemistry of 2 and 4 as well as the structure revision of the previously reported metabolite 3 were established by X-ray crystallographic analyses. The cytotoxicity of the isolated metabolites was evaluated against the NSCLC-N6-L16 and A549 human lung cancer cell lines.     

Structural determination of carnosadine,a new cyclopropyl amino acid,from red alga Grateloupia carnosa

A new cyclopropyl amino acid, carnosadine, was isolated from red alga Grateloupia carnosa and the structure was determined to be 1-amino-2-guanidino-methylcylopropane-1-carboxylic acid from the results of NMR, mass spectrometry and coloring tests.     

Structures and absolute stereochemistry of nipponallene and neonipponallene, new brominated allenes from the red alga Laurencia nipponica

Two new natural brominated allenes named as nipponallene 1 and neonipponallene 2 were isolated from the red alga Laurencia nipponica, collected near the Russian shore of the Sea of Japan (Troitsa Bay). The structures and absolute stereochemistry of 1 and 2 were elucidated using NMR spectroscopy, chemical transformations, modified Mosher’s method and on the basis of biogenetic understanding.     

Two new brominated C15-acetogenins from the red alga Laurencia japonensis

Abstract

We report on the chemical characteristics of the red alga Laurencia japonensis, collected off the coast of Yoshio, Katsuura, Boso Peninsula, Japan. We isolated two new brominated C₁₅-acetogenins in this species, which we name katsuurenyne A (1) and katsuurenyne B (2), along with two already known halogenated terpenes [2,10-dibromo-3-chloro-α-chamigrene (7) and aplysiadiol (8)]. We extensively analysed spectral data (from IR, ESI-MS, 1D-NMR and 2D-NMR) to confirm the structure of these compounds.     

Two new C15 acetylenes from the marine red alga laurencia obtuse

Two new brominated C₁₅,-nonterpenoids which are unusual oxolane derivatives possessing a propargylic bromide side chain have been isolated from the red alga $\text{L. obtuse}$ and their structures were determined as 6 and 7. The ¹HNMR spectra of these new compounds are presented and assignments made.     

Neoirieone,a diterpenoid of a new skeletal class from the red marine alga Laurencia cf. Irieii

Neoirieone, a dibrominated diterpenoid of a new skeletal class, related to the irieol diterpenoids, has been isolated from Laurencia cf. irieii. The structure of neoirieone was elucidated by x-ray crystallographic analysis of its corresponding reduction product, neoirieol ($\text{7}$.     

Laurenidificin, a new brominated C15-acetogenin from the marine red alga Laurencia nidifica

<正>A new brominated C_(15)-acetogenin,namely,laurenidificin,was isolated from the marine red alga Laurencia nidifica.Its structure was determined on the basis of spectroscopic methods.     

Aldingenin A, new brominated sesquiterpene from red algae Laurencia aldingensis

A new brominated bisabolene derivative, aldingenin A, was isolated from red alga Laurencia aldingensis Saito et Womersley (Ceramiales, Rodophyta). Its structure was determined by analysis of spectroscopic data (¹H and ¹³C NMR, IR, MS), including bidimensional NMR (¹H-¹H COSY, HMQC, HMBC and NOESY) and biogenetic considerations.     

Dictyotadimer A, a new dissymmetric bis-diterpene from a brown alga of the genus Dictyota

A phytochemical investigation of a Mediterranean brown alga (Dictyota sp.) led to the isolation of a novel C₄₀bis-diterpene, named dictyotadimer A. The chemical structure of this unusual dissymmetric dimer, characterized by a C-C linkage between two different xenicane units, was elucidated by 1D and 2D NMR analyses together with HR-ESI mass spectrometry. The relative configuration of the two diterpenoid components was determined by NOESY NMR correlations and molecular modeling. A plausible biogenetic pathway of dictyotadimer A was also proposed.     

Study towards bioactive pyrone derivatives from the marine red alga Phacelocarpus labillardieri

Red algae of the genus Phacelocarpus labillardieri produce a structurally rather unique class of macrocyclic pyrone derivatives with phospholipase A₂ inhibiting properties and potential neuromuscular blocking activity. They were also shown to be potent feeding inhibitors for various marine herbivorous gastropods. Described herein is the first preparative study towards these conspicuous secondary metabolites. Their carbon skeleton has been assembled in a few straightforward steps using ring closing alkyne metathesis (RCAM) catalyzed by the Schrock alkylidyne complex (tBuO)₃WCCMe₃ to forge the meta-cyclophane core with high efficiency.     

A new labile bromoterpenoid from the red alga laurencia majuscula: Dehydrochloroprepacifenol

A new labile brominated chamigrene, dehydrochloroprepacifenol, was isolated from the red alga Laurencia majucula. The structure of this compound was determined by its spectral properties and low-temperature X-ray diffraction analysis.     

Laurallene,new bromoallene from the marine red alga Laurencia nipponica Yamada

Laurallene ($\text{1}$), a new brominated cyclic ether having a terminal allene moiety, has been isolated as a main constituent from the marine red alga $\text{Laurencia nipponica}$ Yamada (Rhodomelaceae, Rhodophyta) and its structure was determined by its physical and chemical properties.     

Laureepoxide,new bromo ether from the marine red alga Laurencianipponica Yamada

An interesting bromine containing compound, laureepoxide ($\text{1}$), has been isolated from $\text{L}$. $\text{nipponica}$ Yamada (Rhodomelaceae, Rhodophyta) and its structure has been determined by the chemical degradations and spectral properties.