New Dolabellane Derivatives from the Brown Alga Dictyota pardalis

Reinvestigation of the brown alga Dictyota pardalis f. pseudohamata CRIBB led to the crystallization of 1 and to the isolation of the two new dolabellane derivatives 2 and 3 . X-Ray analysis of 1 and 2 , together with detailed 1D-and 2D-NMR studies on 2 and 3 , allowed their structures to be elucidated as (1R*,3S*,7S*,11R*,4Z)-dolabella-4,8(17), 12(18)-triene-3,7-diol ( 1 ), (1R*,3S*,4S*,7S*,8S*,11R*,14R*,12E)-3,4:7,8-diepoxydolabe11-12-ene-14, 18-diol ( 2 ), and (1R*,3S*,4S*,7S*,8S*,11R*,14R*)-3,4:7,8-diepoxy-l,4,8,12,12-pentamethylbicyclo[9. 3. 0]tetra-decan-14-ol( 3 ).     

A New Bromophenol from the Brown Alga Leathesia nana

A novel bromophenol was isolated from ethanolic extract of the brown alga Leathesia nana S.et G. The structure was elucidated as (E)-3-(2,3-dibromo-4,5-dihydroxyphenyl)-2-methylpropenal by spectroscopic methods including IR, HREIMS, 1D and 2D NMR techniques.     

Glyceroglycolipids and Dipeptide Derivatives from the Brown Alga Sargassum naozhouense

Chemistry of Natural Compounds -     

A New Sesquiterpene-substituted Benzoic Acid from the Brown Alga Dictyopteris divaricata

A new sesquiterpene-substituted benzoic acid has been isolated from the brown Alga Dictyopteris divaricata Okam.Its structure was elucidated as 3-[(2-hydroxy-2,5,5,8a-tetramethyldecahydro-1-naphthalenyl)methyl]-4-hydroxybenzoic acid, named dictyvaric acid on the basis of spectroscopic methods including IR, HRFABMS, 1D and 2D NMR techniques.     

Isolation of 24-Hydroperoxy-24-Vinylcholesterol and Fucosterol from the Brown Alga Turbinaria Conoides

A highly cytotoxic hydroperoxysterol 24-hydroperoxy-24-vinylcholesterol (1) and fucosterol (2) were isolated from the brown alga Turbinaria conoides. Compound (1) was transformed into 29-hydroperoxystigmasta-5, 24(28)-dien-3β3-ol 3 in chloroform solution at ?5–0°C in quantitative yield. The latter compound has been shown to exhibit much stronger cytotoxicity toward cultured spleen lymphocytes stimulated by mitogen concanavalin A than toward normal spleen lymphocytes.     

Diterpenes from Xylopia langsdorffiana

The phytochemical investigation of Xylopia langsdorffiana A.St.‐Hil. & Tul . led to the isolation of eight diterpenes, i.e., of the four new compounds (5β,7β,8α,9β,10α,12α)‐atisane‐7,16‐diol 7‐acetate ( 1 ), named xylodiol 7‐acetate, (5β,8α,9β,10α,12α)‐16‐hydroxyatisan‐7‐one ( 2 ), named xylopinone, (3α,12Z)‐3‐hydroxy‐ent‐labda‐8(20),12,14‐trien‐18‐oic acid ( 3 ), named labdorffianic acid A, and 8,20‐epoxy‐13‐hydroxy‐ent‐labd‐14‐en‐18‐oic acid ( 4 ), named labdorffianic acid B, and of the four known compounds 5 – 8 , i.e., ent‐kauran‐16‐ol, ent‐kaur‐16‐en‐19‐oic acid, ent‐kaur‐16‐en‐19‐ol, and ent‐trachyloban‐18‐oic acid. The structures were established by IR, HR‐ESI‐MS, and NMR data analysis with the aid of 2D techniques.     

Diterpenes from Sideritis trojana

Six known ent-kaurene, a new ent-kaurane and a new pimarane diterpenes were isolated from Sideritis trojana. The structures of new compounds were determined as ent-7alpha-15beta,16beta-epoxykaurane (1), and ent-2alpha-hydroxy-8(14),15-pimaradiene (2) along with the known compounds siderol (3), sideridiol (4), 7-epicandicandiol (5), isocandol B (6), candol A acetate (7) ent-7alpha-acetoxykaur-15-ene (8) by IR, 1D and 2D NMR techniques and HRMS.     

Characterization of Two Light-Harvesting Subunits Isolated from the Brown Alga Pelvetia canaliculata: Heterogeneity of Xanthophyll Distribution

The main light-harvesting fraction from Pelvetia canaliculata was isolated on a sucrose density gradient from digitonin-solubilized chloroplasts. After further solubilization by dodecyl maltoside, the bulk fraction was separated into two subunits by preparative isoelectric focusing. The more acidic brown fraction was mainly composed of 22 kDa polypeptides having an apparent pI of 4.55. Its pigment composition was very simple, containing chlorophyll (Chi) a, Chi c and fucoxanthin. The in vivo spectral properties of fucoxanthin, namely a shift in light absorption to the green and efficient energy transmission to Chi a, were conserved in this subunit. No xanthophyll associated with photoprotection was found in this band, even when obtained from photoinhibited thalli. The less acidic green band contained predominantly 22 kDa polypeptides that were resolved into numerous components by denaturing isoelectric focusing. Its pigment composition was more complex, containing, in addition, pigments of the so-called xanthophyll cycle. In photoinhibited thalli, about half of the violaxanthin was converted into antheraxanthin and zeaxanthin. All the pigments of the xanthophyll cycle were specifically associated with this subunit, and it may thus have a central role in the thermal dissipation of the absorbed light energy as postulated for light-harvesting complex II isolated from green plants.     

Seasonal Variability of Volatilome from Dictyota dichotoma

Dictyotaceae, the large family of brown algae with the genus Dictyota as the richest one among them, produce a significant number of secondary metabolites, like diterpenes. The aim of this study was to investigate the variations in the composition of the volatile organic compounds (VOCs) of the brown alga Dictyota dichotoma collected from the Adriatic Sea. For the first time, both seasonal changes and the impact of air drying were examined. Headspace solid-phase microextraction (HS-SPME) on two fibres with different polarities and hydrodistillation (HD), followed by gas chromatography and mass spectrometry (GC-MS) analysis, was performed on both fresh (FrDd) and air-dried (DrDd) D. dichotoma. The major compounds of HS-FrDd were pentadecane and oct-1-en-3-ol. The percentage of pentadecane in HS-DrDd was increased up to 7.8 times in comparison with HS-FrDd. Principal component analysis (PCA) identified differences between the variability of data among fresh and dried samples over months and clearly dissociated the fresh May samples from the others in the HS-SPME results. The most abundant group of VOCs in HD were terpenes, with diterpenes isopachydictyol A and cembra-4,7,11,15-tetraen-3-ol as the major compounds. Diterpene pachydictyol A was also found and among sesquiterpenes and gleenol was the most abundant. Based on the dominant compound analyses, the PCA showed distinct separation of the fresh and dried samples, indicating similarities between the samples and allowing the establishment of typical VOCs significant for the chemotaxonomy of D. dichotoma.     

Diterpenes from the marine pulmonate trimusculus reticulatus

The marine pulmonate Trimusculus reticulatus contains 6β-isovaleroxylabda-8,13-dien-7α,15-diol (1) and 2α,7α-diacetoxy-6β-isovaleroxylabda-8,13-dien-15-ol (2). The diol 1 is found in the mucus produced by T. reticulatus that repels predatory sea stars.     

New Carbonic Anhydrase-II Inhibitors from Marine Macro Brown Alga Dictyopteris hoytii Supported by In Silico Studies

In continuation of phytochemical investigations of the methanolic extract of Dictyopteris hoytii, we have obtained twelve compounds (1–12) through column chromatography. Herein, three compounds, namely, dimethyl 2-bromoterepthalate (3), dimethyl 2,6-dibromoterepthalate (4), and (E)-3-(4-(dimethoxymethyl)phenyl) acrylic acid (5) are isolated for the first time as a natural product, while the rest of the compounds (1, 2, 6–12) are known and isolated for the first time from this source. The structures of the isolated compounds were elucidated by advanced spectroscopic 1D and 2D NMR techniques including ¹H, ¹³C, DEPT, HSQC, HMBC, COSY, NEOSY, and HR-MS and comparison with the reported literature. Furthermore, eight compounds (13–20) previously isolated by our group from the same source along with the currently isolated compounds (1–12) were screened against the CA-II enzyme. All compounds, except 6, 8, 14, and 17, were evaluated for in vitro bovine carbonic anhydrase-II (CA-II) inhibitory activity. Eventually, eleven compounds (1, 4, 5, 7, 9, 10, 12, 13, 15, 18, and 19) exhibited significant inhibitory activity against CA-II with IC₅₀ values ranging from 13.4 to 71.6 μM. Additionally, the active molecules were subjected to molecular docking studies to predict the binding behavior of those compounds. It was observed that the compounds exhibit the inhibitory potential by specifically interacting with the ZN ion present in the active site of CA-II. In addition to ZN ion, two residues (His94 and Thr199) play an important role in binding with the compounds that possess a carboxylate group in their structure.     

New Antibacterial Diterpenes from Pseudopterogorgia elisabethae

From the MeOH extract of Pseudopterogorgia elisabethae, collected from the Bahamas, four new diterpenes, elisabethin E ( 1 ), elisabethin F ( 2 ), pseudopterosin P ( 3 ), and pseudopterosin Q ( 4 ), were isolated and their structures established with the aid of extensive spectroscopic studies. Compounds 3 and 4 showed antibacterial activity selectively against the Gram‐positive bacteria Streptococcus pyogenes, Staphylococcus aureus, and Enterococcus faecalis.     

Unusual and Novel C11H16 Hydrocarbons from the Southern Australian Brown Alga Dictyopteris acrostichoides (Phaeophyceae)

Unusual and novel C₁₁H₁₆ olefins with (E)- or (E,E)-configuration instead of the previously known (Z)- or (E,Z)-configuration at the double bond(s) within the longer side chain are the main products of the Australian phaeophyte Dictyopteris acrostichoides. This configuration anomaly refers to all four series of alicyclic C₁₁H₁₆ hydrocarbons, namely the disubstituted cyclopentenes and cyclopropanes, as well as the monosubstituted cycloheptadienes and cyclopentenes. Chiral compounds within the above series have the same absolute configuration. The two (cyclopent-3-enyl)hexa-1, 3-dienes 11 and 13 are found for the first time. The absolute configuration and optical purity of the hydrocarbons are determined by gas chromatography on modified cyclodextrins as chiral stationary phases. The synthesis of chiral references via lipase-catalyzed resolutions is described.     

Two New Diterpenes from Solidago canadensis

Two new clerodane‐type diterpenes, solidagocanins A and B ( 1 and 2 , resp.), as well as two known compounds, mellein ( 3 ) and physcion ( 4 ), were isolated from the aerial parts of Solidago canadensis. The structures of the new compounds were elucidated by spectroscopic analyses, including 2D‐NMR techniques.     

New Myrsinol Diterpenes from Euphorbia prolifera

Four new myrsinol diterpenes, euphorprolitherins A-D (1-3, 5), were isolated from the ethanolic extract of the root of Euphorbia prolifera, along with a known one, SPr5 (4). The structures were elucidated on the basis of their spectroscopic evidences. The structure and relative stereochemistry of 1 were confirmed by X-ray crystallography.     

Two Labdane Diterpenes from Leonurus heterophyllus

The whole plant of Leonurus heterophyllus Sweet. (Lamiaceae), (Chinese name: Yi Mu Cao), is used in traditional Chinese medicine for treatment of gynaecological problems, including irregular menstruation, amenorrhea and postpartum heamorrhage1. About 40 l…