Stereochemical relationships between phytol and phytanic acid, dihydrophytol and C18 ketone in Recent sediments

The relative stereochemistry of certain acyclic isoprenoid compounds has been determined from the following sources: two intervals from a core of bottom sediment of a eutrophic lake (Esthwaite Water, U.K.); a marshy shore sediment from a small lake on the watershed of Esthwaite; the bottom sediment of a tropical lagoon (U.S. Virgin Islands); a blue-green algal mat and its underlying reduced sediment (Shark Bay, Australia); a decayed blue-green alga (Microcystis aeruginosa) from Esthwaite Water and the products of alteration of phytol as sole carbon source by a bacterial culture from Esthwaite sediment. The stereoisomeric distributions indicate that 1. (i) in the earliest stages of diagenesis of phytol in Esthwaite sediment, reduction to the dihydrophytyl skeleton (free, esterified or bound) is biological, probably microbial, 2. (ii) by analogy with earlier studies of Esthwaite, the phytanic acid in the other sedimentary situations is compatible with an origin in phytol via biological processes; the variations in the distributions reflect the differences in the populations bringing about the conversion, 3. (iii) for the samples where 6,10,14-trimethylpentadecan-2-one was examined, the stereochemistry is compatible with an origin in phytol but no distinction can be made between the pathways of oxidation (biological or chemical), and 4. (iv) conversion of phytol by the bacterial isolate under conditions of low oxygen concentration produced 2(RS),6,10,14-trimethylpentadecan-2-ol as the major saturated alcohol; the likely route for its formation is via reduction of the corresponding ketone.