Polar Metabolites of the Tropical Green SeaweedCaulerpa taxifolia Which Is Spreading in the Mediterranean Sea: Glycoglycerolipids and Stable Enols (α\=Keto Esters)

Abstract

Examination of the polar components of the green seaweed Caulerpa taxifolia (Vahl) C. Agardh, which is heavily spreading in the northeastern Mediterranean, led to two families of compounds. The new (2R)‐3‐O‐β‐D‐galactopyranosyl‐1‐O‐[(7Z,10Z,13Z)‐hexadeca‐7,10,13‐trienoyl]‐2‐O‐[(9Z,12Z,15Z)‐octadeca‐1,12,15‐trienoyl]‐sn‐glycerol (2) was isolated in low abundance, like the analogues 1 and 3 already known from freshwater cyanobacteria. The acyl positions in 1 – 3 were determined by enzymatic methods and the absolute configuration from the O‐galactosylglycerol obtained upon alcaline methanolysis. More abundant were the (4‐hydroxyphenyl)‐ and (3,4‐dihydroxyphenyl)pyruvic acid methyl esters, occurring in the enol (Z) forms 13a and 14a accompanied by very minor (E) forms 13b and 14b. The latter became predominant on UV irradiation of 13a or 14a, allowing the determination of the C=C configuration of these isolatable, stable enols from 1H,13C NMR couplings (larger H−C(3)/C(1) coupling constant in the (E) than in the (Z) isomer). Contrary to literature implications, the O‐galactosylglycerolipids 1 – 3 lack any cholinergic or histaminergic activity; similarly, enols (= α‐keto esters) 13 and 14 or terpenoids of this seaweed were also devoid of such biological activities (see Table).

Tensioactive Compounds from the Aquatic Plant Ranunculus fluitans L. (Ranunculaceae)

“…Thus, the structure of7 was established as (2S)-3-O-b-d-galactopyranosyl-1,2-di-O-[(9Z,12Z,15Z)-octadeca-9,12,15-trienoyl]-sn-glycerol, the optical rotation being consistent with reported data[13]. This MGDG has been identified earlier from the cyanobacterium Phormidium tenue and the green seaweed Caulerpa taxifolia[24] [25].TheESI-MS of 8 (positive-ion mode) showed a quasi-molecular ion at m/z 955 ([M NH 4 ] ), a signal at m/z 938 ([M H] ), and characteristic fragments at m/z 776 ([M À 162] ) and 614 ([M À 162 À 162] ). The a-d-(1 3 6)linkage of the two galactosyl residues was evidenced by 13 C-NMR data (C(1'''') at d 100.62 and C(6''') at d 67.77).…”

“…Structure elucidation of the glycoglycerolipids was carried out by means of ESI LC/ MS experiments, 1 H-and 13 C-NMR spectral measurements, GC analysis of the fatty acid methyl esters, and by comparison with reference data [24] [25]. The number of signals for anomeric C-atoms in the 13 C-NMR spectra of the glycoglycerolipids showed 7 to be a monoglycoside, while 8 was the corresponding diglycoside.…”

“…Diacylglycerol galactosides are ubiquitous metabolites occurring primarily in the mitochondrial membrane of higher plant cells [26]. More recently, MGDGs and DGDGs have been isolated from dinoflagellates and cyanobacteria [24] [25]. The reason for their exceptionally high content in R. fluitans, however, is not understood at the moment.…”

“…These findings were corroborated by the presence of a resonance for C(1''') (105.36 ppm) in the 13 C-NMR spectrum. The remaining 13 C-NMR data were in perfect accordance with literature data for monogalactosyl-1,2-diacylglycerols (MGDG)[24] [25]. GC Analysis of the fatty acid methyl esters obtained from 7 by methanolysis showed the presence of linolenoyl residues in 7.…”

Glycolipids from macroalgae: potential biomolecules for marine biotechnology?

“…Distinct sulfonoglycolipid fractions were isolated from the basidiolichen Dyctionema glabratum (Sassaki et al, 2001) and from the red algae Chondria armata (AlFadhli et al, 2006). Glycoglycerol lipids occur widely in green seaweeds (Mancini et al, 1998), cyanobacteria (Reshef et al, 1997), marine dinoflagellates (Oshima, et al, 1994) and the freshwater alga Chlorella vulgaris (Morimoto et al, 1995).…”