Abstract:Lyxo-phytosphingosine and erythro-sphingosine have been elaborated from a common intermediate. The key step in the reaction sequence involves stereo- and regiospecific functionalization of an olefin by intramolecular nucleophilic sulfinyl group participation.
“…Raghavan and Rajender described a procedure usinghydroxy-, -unsaturated sulfoxide for the synthesis of Lerythro-sphingosine [96]. The stereochemistry of the polar head was established by transformation of the double bond into bromohydrine which utilizes the sulfinyl moiety as an intramolecular nucleophile.…”
Section: Synthesis Of Sphingosinementioning
confidence: 99%
“…Assembling of the E-double bond provided intermediates of natural ceramides. Mesylate diol (96), requisite for the latter, improved synthesis, was prepared in five steps without chromatographic purification following a patented procedure [101]. The primary alcohol was protected as silyl ether.…”
Section: Synthesis Of Sphingosinementioning
confidence: 99%
“…Because its cross-metathesis suffered from low yields and undesirable side reactions, probably due to the interaction of the phosphine ligands with the azide group and/or metalmediated nitrene process, the azido group was reduced to amine and protected as an Fmoc carbamate. The orthogonally protected alkene (99) was obtained in 21% yield from the diol (96). Reaction of (99) with 1-pentadecene catalyzed by Grubbs' catalyst A delivered protected sphingosine (100) as a precursor for the synthesis of glycosphingolipids.…”
Ceramides are a complex group of lipids that has gained much attention as cell signaling molecules and skin barrier constituents. In the skin, these sphingolipids form a major part of the stratum corneum intercellular lipid matrix, which is the barrier for penetration of most compounds. The development of such a protective layer was a critical step in the evolution of life on a dry land. Moreover, prominent skin diseases such as psoriasis and atopic dermatitis are associated with diminished ceramide levels and may be effectively improved by exogenous ceramides or their analogues. Since ceramides are not obtained from natural sources in pure form, they are of synthetic interest since 1950's. In this review, we describe sphingosine syntheses from 1998 until 2008, and the synthetic approaches to the unique epidermal ceramides, including the 6-hydroxysphingosine-based ones, the alpha- and omega-hydroxy forms and the omega-acyloxy species. Moreover, the structural requirements of ceramides for a competent skin barrier are discussed, including acyl chain length, trans double bond, acyl alpha-hydroxyl, stereochemistry, omega-linoleyloxy species and ceramide conformation.
“…Raghavan and Rajender described a procedure usinghydroxy-, -unsaturated sulfoxide for the synthesis of Lerythro-sphingosine [96]. The stereochemistry of the polar head was established by transformation of the double bond into bromohydrine which utilizes the sulfinyl moiety as an intramolecular nucleophile.…”
Section: Synthesis Of Sphingosinementioning
confidence: 99%
“…Assembling of the E-double bond provided intermediates of natural ceramides. Mesylate diol (96), requisite for the latter, improved synthesis, was prepared in five steps without chromatographic purification following a patented procedure [101]. The primary alcohol was protected as silyl ether.…”
Section: Synthesis Of Sphingosinementioning
confidence: 99%
“…Because its cross-metathesis suffered from low yields and undesirable side reactions, probably due to the interaction of the phosphine ligands with the azide group and/or metalmediated nitrene process, the azido group was reduced to amine and protected as an Fmoc carbamate. The orthogonally protected alkene (99) was obtained in 21% yield from the diol (96). Reaction of (99) with 1-pentadecene catalyzed by Grubbs' catalyst A delivered protected sphingosine (100) as a precursor for the synthesis of glycosphingolipids.…”
Ceramides are a complex group of lipids that has gained much attention as cell signaling molecules and skin barrier constituents. In the skin, these sphingolipids form a major part of the stratum corneum intercellular lipid matrix, which is the barrier for penetration of most compounds. The development of such a protective layer was a critical step in the evolution of life on a dry land. Moreover, prominent skin diseases such as psoriasis and atopic dermatitis are associated with diminished ceramide levels and may be effectively improved by exogenous ceramides or their analogues. Since ceramides are not obtained from natural sources in pure form, they are of synthetic interest since 1950's. In this review, we describe sphingosine syntheses from 1998 until 2008, and the synthetic approaches to the unique epidermal ceramides, including the 6-hydroxysphingosine-based ones, the alpha- and omega-hydroxy forms and the omega-acyloxy species. Moreover, the structural requirements of ceramides for a competent skin barrier are discussed, including acyl chain length, trans double bond, acyl alpha-hydroxyl, stereochemistry, omega-linoleyloxy species and ceramide conformation.
“…For the synthesis of 5 , amino olefinic ester 3e underwent Os-catalyzed dihydroxylation in a diastereoselective manner 8 to produce the corresponding aminodiol 4 (92% yield), which was hydrogenated over Raney nickel, thus affording either the cyclized dihydroxy pyrrolidone 5 (dr = 1:5, 65% yield) or its triacetate derivative 7 , a building block found in sphingosines, depending upon the reaction conditions (Scheme ). 2 Synthesis of 2-Pyrrolidone 5 and Triacetate 7 …”
A novel and highly enantioselective method for the synthesis of gamma-amino-alpha,beta-unsaturated esters via tandem alpha-amination-Horner-Wadsworth-Emmons (HWE) olefination of aldehydes is described. The one-pot assembly has been demonstrated for the construction of functionalized chiral 2-pyrrolidones, subunits present in several alkaloids. [structure: see text]
The use of sulfones in organic chemistry, acting as an auxiliary group, is still a very important synthetic strategy, especially for the formation of carbon‐carbon single and double bonds. Once the synthetic objective is achieved, the sulfone gruop is usually removed from the molecule. This removal most commonly involves a reductive desulfonylation process with either replacement of the sulfone by hydrogen, or a process that results in the formation of a carbon‐carbon double bond when a β‐hydroxy or β‐alkoxy sulfone is employed.
This chapter is devoted to the replacement of the sulfone group by a hydrogen (reductive desulfonylation reactions), and reductive elimination reactions of Julia‐type substrates (Julia‐Lythgoe olefination process). The chapter addresses the full scope, generality, limitations, and synthetic applications of these reactions. The literature through most of 2007 is covered.
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