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The asymmetric synthesis of polyunsaturated triene C18:3 n-3 and C18:3 n-6 methoxylated ether lipids (MEL) of the 1-O-alkyl-sn-glycerol type is described as possible structural candidates for a triene C18:3 MEL of an unknown identity found in a mixture of shark and dogfish liver oil. Their C18:3 hydrocarbon chains constitute an all-cis methylene skipped n-3 or n-6 triene framework, along with a methoxyl group at the 2′-position and R-configuration of the resulting stereogenic center. The methoxylated polyenes are attached by an ether linkage to the pro-S hydroxymethyl group of the glycerol backbone. The syntheses were based on the polyacetylene approach that involves a semi-hydrogenation of the resulting triynes. Both syntheses were started from our previously described enantio- and diastereomerically pure isopropylidene-protected glyceryl glycidyl ether, a double-C3 building block that was designed as a head group synthon for the synthesis of various types of MELs. [ABSTRACT FROM AUTHOR]

The asymmetric synthesis of a triene C18 : 3 n‐8 methoxylated ether lipid (MEL) of the 1‐O‐alkyl‐sn‐glycerol type is described by two different routes. The C18 : 3 hydrocarbon chain is attached by an ether linkage to the pro‐S hydroxymethyl group of the glycerol backbone, and constitutes an all‐cis methylene skipped triene framework, along with a methoxyl group in the 2'‐position and R‐configuration at the resulting chiral centre. The initial synthesis was based on the polyacetylene approach involving a semi‐hydrogenation of the resulting triyne. A modified approach based on a combined polyacetylene‐Wittig strategy was also successfully executed and an attempt made to compare and evaluate these strategies. Both syntheses were started from our previously described enantio‐ and diastereomerically pure isopropylidene‐protected glyceryl glycidyl ether, a double‐C3 building block designed as a head group synthon for synthesis of various types of MELs which was shown to suit the Wittig‐based approach very well. [ABSTRACT FROM AUTHOR]

This report describes the synthesis of reversed structured 1-O-alkyl-2,3-diacylsn-glycerols (DAGEs) possessing a pure saturated even number fatty acid (C6:0-C16:0) at the sn-2 position along with a pure EPA or DHA located at the terminal sn-3 position of the glycerol backbone of chimyl, batyl and selachyl alcohols. These adducts were synthesized by a highly efficient two-step chemoenzymatic process involving an immobilized Candida antarctica lipase to introduce pure EPA and DHA activated as oxime esters exclusively to the sn-3 terminal position of enantiopure chimyl, batyl and selachyl alcohols in excellent yields. The saturated fatty acids were subsequently incorporated to the remaining sn-2 position of the resulting 3-monoacylglyceryl ethers (3-MAGEs) using EDAC coupling agent in the presence of DMAP in very high to excellent yields (85%-98%). No losses of enantiomeric composition were observed during these processes. The multiple utilities of the resulting focused library of reversed structured DAGEs are discussed including how such compounds may possibly be utilized within the pharmaceutical area. [ABSTRACT FROM AUTHOR]

Abstract: The naturally occurring 1-O-alkyl-sn-glycerols and their methoxylated congeners, 1-O-(2′-methoxyalkyl)-sn-glycerols, are biologically active compounds, ubiquitously found in nature as diacyl glyceryl ether lipids and phosphoether lipids. The chief objective of this article is to provide a comprehensive and up to date review on such ether lipids. The occurrence and distribution of these compounds in nature are extensively reviewed, their chemical structure and molecular variety, their biosynthesis and chemical synthesis and, finally, their various biological effects are described and discussed. An unprecedented biosynthesis of the 2′-methoxylated alkylglycerols is proposed. The first synthesis of enantiopure (Z)-(2′R)-1-O-(2′-methoxyhexadec-4′-enyl)-sn-glycerol, the most prevalent 2′-methoxylated type alkylglycerol present in cartilaginous fish, is described. It was accomplished by a highly convergent five step process. [Copyright &y& Elsevier]

Abstract: A highly efficient two-step chemoenzymatic synthesis of enantiopure structured ether lipids of the 1-O-alkyl-2,3-diacyl-sn-glycerol type has been developed. Chimyl, batyl and selachyl alcohols possessing pure saturated fatty acid (SFA) attached to the sn-3 position and pure EPA and DHA attached to the sn-2 position were obtained under full regiocontrol. This was offered by mild conditions and a highly efficient lipase that operated at room temperature. High-resolution 1H NMR spectroscopy was used to monitor the progress of the reactions and to evaluate the full regiocontrol of the reactions involved by keeping track of all prospective adducts involved in these reactions. This was extended to preparation of a focused library of eight monoacyl intermediate adducts for all even-numbered SFA ranging from C2–C16 and the corresponding EPA and DHA structured diacyl glycerol ethers (DAGE) products for chimyl, batyl and selachyl alcohols, the total of 72 compounds. [Copyright &y& Elsevier]

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. Asymmetric synthesis of methoxylated ether lipids: Total synthesis of two monounsaturated C18:1 and a saturated C18:0 methoxylated ether lipid derivatives. [Display omitted] • First asymmetric syntheses of three methoxylated ether lipids, C18:1 n-14, C18:1 n-9, and C18:0. • Seven methoxylated ether lipid derivatives isolated and detected in shark liver oil. • Five previously known methoxylated ether lipids detected: C16:1 n-12, C16:0, C18:1 n-14, C18:0 and C22:6 n-3. • A novel C18:1 n-9 methoxylated ether lipid confirmed by total synthesis. • An unknown C18:3 methoxylated ether lipid detected. [ABSTRACT FROM AUTHOR]