Glycosyldiacylglycerolipids from the Lichen Dictyonema glabratum

Three glycolipids (<BO>1</BO>−<BO>3</BO>) were isolated from the basidiolichen Dictyonema glabratum. Their carbohydrate and lipid components were structurally characterized using 1D ¹H and ¹³C and 2D NMR spectroscopy, complemented by mass spectrometry, as were the carbohydrate moieties formed on saponification. These were O-α-<SCP>d</SCP>-Galp-(1‘ ‘→6‘)-O-β-<SCP>d</SCP>-Galp-(1‘↔1)-2,3-diacyl-<SCP>d</SCP>-glycerol (<BO>2</BO>) and two others not previously found in lichens, O-β-<SCP>d</SCP>-Galp-(1‘↔1)-2,3-diacyl-<SCP>d</SCP>-glycerol (<BO>1</BO>) and O-α-<SCP>d</SCP>-Galp-(1‘ ‘‘→6‘ ‘)-O-α-<SCP>d</SCP>-Galp-(1‘ ‘→6‘)-O-β-<SCP>d</SCP>-Galp-(1‘↔1)-2,3-diacyl-<SCP>d</SCP>-glycerol (<BO>3</BO>). Each was saponified to give the free carbohydrates and its fatty acid methyl esters. The most abundant fatty acid esters in <BO>1</BO>−<BO>3</BO> was palmitic C<INF>16:0</INF>, but there was a wide variation of ester composition. Others present were C<INF>8:0</INF> and C<INF>14:0</INF> in <BO>1</BO>, C<INF>14:0</INF>, C<INF>15:0</INF>, C<INF>17:0</INF>, C<INF>18:0</INF>, C<INF>18:1</INF> (oleic), C<INF>18:2</INF> (linoleic), C<INF>22:0</INF>, and C<INF>24:0</INF> in <BO>2</BO>, and C<INF>8:0</INF>, C<INF>14:0</INF>, C<INF>18:0</INF>, C<INF>18:1</INF> (oleic), C<INF>18:2</INF> (linoleic), and C<INF>18:3</INF> (linolenic) in <BO>3</BO>. As in ascolichens, the glycolipids appear to arise from the phycobiont.