Three series of non-isoprenoidal dialkyl glycerol diethers in cold-seep carbonate crusts

Three novel series of non-isoprenoidal dialkyl glycerol diethers with an in ferred sn-1,2 stereochemistry were tentatively identified in carbonate crus ts precipitated from methane-rich bottom-waters and pore-waters associated with Mediterranean mud volcanoes. In the first series of diethers, an 11,12 -methylenehexadecyl moiety is ether-bound at the sn-2 position of the glyce rol group, and in diethers from the second series, an anteiso pentadecyl gr oup is ether-bound at the sn-2 position. In the third and minor series a pe ntadecyl moiety is ether-bound at the sn-2 position. In all series, ether-b ound C-14-C-17 alkyl units (either n-alkyl, branched alkyl, alkylcyclohexyl or methylenealkyl) occur at the sn-1 position. The two major series are al so distinguished by their delta C-13 values, which differ by 15-30 parts pe r thousand at the sites studied. Only the minor series has been previously reported in sediments. Members of the second and third series are similar t o diethers containing C-16-C-18 iso, anteiso, and n-alkyl units present in the thermophilic bacteria Thermodesulfobacterium commune, Ammonifex degensi i and Aquifex pyrophilus. The first series is unique, in that diethers poss essing alkyl chains that contain a cyclopropane ring have never been report ed. (C) 2001 Elsevier Science Ltd. All rights reserved.