Asymmetric synthesis of methoxylated ether lipids: Total synthesis of two monounsaturated C18:1 and a saturated C18:0 methoxylated ether lipid derivatives

The report describes the first asymmetric synthesis of three derivatives of methoxylated ether lipids (MELs) of the 1-O-alkyl-sn-glycerol type present in the liver oil of various species of cartilaginous fish, all three possessing eighteen-carbon hydrocarbon chains in their ether entity. Two of them were already known, the saturated C18:0 and the monounsaturated C18:1 n-14 MELs, whereas the third one is a novel monounsaturated C18:1 n-9 MEL. All three were isolated and detected by LC-MS studies of a MEL sample obtained from dogfish and shark liver oil. The structural identity of the novel one was unequivocally confirmed to be the C18:1 n-9 MEL by its total synthesis after comparison based on their MS/MS spectra. Their synthesis made use of our previously described enantiopure isopropylidene-protected glyceryl glycidyl ether diastereomer, a double-C3 building block serving as a head group synthon in synthesis of various types of MELs. They were all obtained in high chemical and stereochemical purity and good overall yields.