CELL-WALL POLYSACCHARIDES FROM AUSTRALIAN RED ALGAE OF THE FAMILY SOLIERIACEAE (GIGARTINALES, RHODOPHYTA) - NOVEL, HIGHLY PYRUVATED CARRAGEENANS FROM THE GENUS CALLOPHYCUS

Cell-wall polysaccharides from six species of red algae of the genus C allophycus were mainly galactans comprised predominantly of galactose (Gal) and 3,6-anhydrogalactose (AnGal), and were rich in pyruvate and sulfate. The Fourier Transform Infrared (FTIR) spectra of the polysacc harides superficially resembled that of alpha-carrageenan (composed of the repeating disaccharide carrabiose 2-sulfate), with major bands of absorption indicative of if-linked AnGal, axial 2-sulfate on 4-linked AnGal, and unsulfated, 3-linked Gal. The FTIR spectra of solutions of Callophycus polysaccharides in D2O-phosphate buffer displayed absorpt ion, corresponding to the carboxylate anion of the pyruvate acetal sub stituent. Methylation analysis showed that 3,4,6-linked Galp (interpre ted as 4,6-pyruvated, 3-linked Galp) and 2,4-linked AnGalp (interprete d as 4-linked AnGalp 2-sulfate) were the dominant links, together with significant quantities of 3-linked Galp. Proton-decoupled C-13 nuclea r magnetic resonance (NMR) spectroscopy showed the polysaccharides to be composed predominantly of pyruvated carrageenans. The C-13 NMR spec tra were completely assigned by a J-modulated spin-echo pulse sequence and 2D experiments employing gradient Heteronuclear Multiple Bond Cor relation (HMBC), C-13/H-1 Heteronuclear Multiple Quantum Coherence (HM QC), and HMQC Total Correlation Spectroscopy (HMQC-TOCSY). The Calloph ycus galactans thus consist predominantly of the novel repeating disac charide 4',6'-O-(1-carboxyethylidene)carrabiose 2-sulfate and minor am ounts of the alpha-carrageenan repeating unit (carrabiose 2-sulfate), and other structural variations. (C) 1997 Elsevier Science Ltd.