A novel ether core lipid with H-shaped C 80-isoprenoid hydrocarbon chain from the hyperthermophilic methanogen Methanothermus fervidus

Abstract

A new ether lipid core (designated as FU) was found in Methanothermus fervidus total lipid. Comparison with caldarchaeol showed lower mobility of FU on TLC and smaller molecular weight ( m/ z 1298) by 2 mass units on FAB-MS. Treatment of FU with HI followed by displacement with silver acetate afforded long chain alcohol acetate (ROAc), which was further saponified with mild alkali to its free alcohol (ROH). ROH is the long chain alcohol prepared from FU. The molecular weights of ROAc and ROH were shown by MS to be 1354 and 1186, respectively. These results suggested that the molecular formula of ROH was C 80H 162O 4, and ROH had four hydroxyl groups, and one molecule of ROH was bound with two molecules of glycerol by four ether linkages. Because FU was not oxidized by NaIO 4 and specific rotation [α] D of FU coincided with that of caldarchaeol, it seems that the ether linkages of FU are formed with hydroxyl groups of the sn-2 and sn-3 positions of each glycerol moiety. The structure of FU was suggested to be a modified caldarchaeol in which two hydrocarbon chains are bridged with a covalent bond. Although a few points remain to be elucidated before the final conclusion can be reached on the structure of FU due to difficulty in complete structure determination done even with every approach currently available, the most possible position of the bridge in FU hydrocarbon was proposed from the data of EI-MS of ROAc and 1 H -NMR of FU. The hydrocarbon chain looks like H-shaped C 80 isoprenoid.