N-Acyl migration in ceramides

Chemoselective Esterification of Natural and Prebiotic 1,2-Amino Alcohol Amphiphiles in Water

In cells, a vast number of membrane lipids are formed by the enzymatic O-acylation of polar head groups with acylating agents such as fatty acyl-CoAs. Although such ester-containing lipids appear to be a requirement for life on earth, it is unclear if similar types of lipids could have spontaneously formed in the absence of enzymatic machinery at the origin of life. There are few examples of enzyme-free esterification of amphiphiles in water and none that can occur in water at physiological pH using biochemically relevant acylating agents. Here we report the unexpected chemoselective O-acylation of 1,2-amino alcohol amphiphiles in water directed by Cu(II) and several other transition metal ions. In buffers containing Cu(II) ions, mixing biological 1,2-amino alcohol amphiphiles such as sphingosylphosphorylcholine with biochemically relevant acylating agents, namely, acyl adenylates and acyl-CoAs, leads to the formation of the O-acylation product with high selectivity. The resulting O-acylated sphingolipids self-assemble into vesicles with markedly different biophysical properties than those formed from their N-acyl counterparts. We also demonstrate that Cu(II) can direct the O-acylation of alternative 1,2-amino alcohols, including prebiotically relevant 1,2-amino alcohol amphiphiles, suggesting that simple mechanisms for aqueous esterification may have been prevalent on earth before the evolution of enzymes.

Total synthesis of ceramides and β-O-glucosylceramides via intramolecular fatty acyl group migration

Fatty acyl group utilized as both protection and migratory group for the synthesis of ceramides and glucosylceramides.

A mass spectrometry-based method for the assay of ceramide synthase substrate specificity

The acyl composition of sphingolipids is determined by the specificity of the enzyme ceramide synthase (EC 2.3.1.24). Ceramide contains a long-chain base (LCB) linked to a variety of fatty acids to produce a lipid class with potentially hundreds of structural variants. An optimized procedure for the assay of ceramide synthase in yeast microsomes is reported that uses mass spectrometry to detect any possible LCB and fatty acid combination synthesized from unlabeled substrates provided in the reaction. The assay requires the delivery of substrates with bovine serum albumin for maximum activity within defined limits of substrate concentration and specific methods to stop the reaction and extract the lipid that avoid the non-enzymatic synthesis of ceramide. The activity of ceramide synthase in yeast microsomes is demonstrated with the four natural LCBs found in yeast along with six saturated and two unsaturated fatty acyl-coenzyme As from 16 to 26 carbons in length. The procedure allows for the determination of substrate specificity and kinetic parameters toward natural substrates for ceramide synthase from potentially any organism.

Studies on the synthesis of N'-acetyl aza-analogues of ganciclovir-unexpected liability of N'-(2-hydroxyethyl)-azanucleosides under basic conditions

The O'-pivaloyl diesters of N'-acetyl-azanucleosides were obtained from N-[1,3-di(pivaloyloxy)prop-2-yl]-N-(pivaloyloxymethyl)acetamide and a silylated nucleobase under Vorbruggen's conditions. Unexpectedly, de-pivaloylation of the diesters under basic conditions afforded the corresponding nucleobase and N-acetylserinol. Mechanistic investigations showed that these products result from the following cascade of spontaneous transformations initiated by the mono de-pivaloylation of the starting diesters. N'-Deacetylation of the resultant mono-esters via the intramolecular N-O acetyl migration is the key step of the cascade; the corresponding NH-azanucleosides in the form of O-acetyl-O'-pivaloyl diesters are formed. Fragmentation of these diester intermediates gives the nucleobase and O-acetyl-O'-pivaloylserinol. Conversion of the latter to N-acetylserinol involves the selective O-N acetyl migration followed by de-pivaloylation of the resulting N-acetyl-O-pivaloylserinol.

Biodiversity of sphingoid bases ("sphingosines") and related amino alcohols

"Sphingosin" was first described by J. L. W. Thudichum in 1884 and structurally characterized as 2S,3R,4E-2-aminooctadec-4-ene-1,3-diol in 1947 by Herb Carter, who also proposed the designation of "lipides derived from sphingosine as sphingolipides." This category of amino alcohols is now known to encompass hundreds of compounds that are referred to as sphingoid bases and sphingoid base-like compounds, which vary in chain length, number, position, and stereochemistry of double bonds, hydroxyl groups, and other functionalities. Some have especially intriguing features, such as the tail-to-tail combination of two sphingoid bases in the alpha,omega-sphingoids produced by sponges. Most of these compounds participate in cell structure and regulation, and some (such as the fumonisins) disrupt normal sphingolipid metabolism and cause plant and animal disease. Many of the naturally occurring and synthetic sphingoid bases are cytotoxic for cancer cells and pathogenic microorganisms or have other potentially useful bioactivities; hence, they offer promise as pharmaceutical leads. This thematic review gives an overview of the biodiversity of the backbones of sphingolipids and the broader field of naturally occurring and synthetic sphingoid base-like compounds.

Novel analogs of D-e-MAPP and B13. Part 2: signature effects on bioactive sphingolipids

Novel isosteric analogs of the ceramidase inhibitors (1S,2R)-N-myristoylamino-phenylpropanol-1 (d-e-MAPP) and (1R,2R)-N-myristoylamino-4'-nitro-phenylpropandiol-1,3 (B13) with modified targeting and physicochemical properties were developed and evaluated for their effects on endogenous bioactive sphingolipids: ceramide, sphingosine, and sphingosine 1-phosphate (Cer, Sph, and S1P) in MCF7 cells as determined by high-performance liquid chromatography-mass spectrometry (HPLC-MS/MS). Time- and dose-response studies on the effects of these compounds on Cer species and Sph levels, combined with structure-activity relationship (SAR) data, revealed 4 distinct classes of analogs which were predominantly defined by modifications of the N-acyl-hydrophobic interfaces: N-acyl-analogs (class A), urea-analogs (class B), N-alkyl-analogs (class C), and omega-cationic-N-acyl analogs (class D). Signature patterns recognized for two of the classes correspond to the cellular compartment of action of the new analogs, with class D acting as mitochondriotropic agents and class C compounds acting as lysosomotropic agents. The neutral agents, classes A and B, do not have this compartmental preference. Moreover, we observed a close correlation between the selective increase of C(16)-, C(14)-, and C(18)-Cers and inhibitory effects on MCF7 cell growth. The results are discussed in the context of compartmentally targeted regulators of Sph, Cer species, and S1P in cancer cell death, emphasizing the role of C(16)-Cer. These novel analogs should be useful in cell-based studies as specific regulators of Cer-Sph-S1P inter-metabolism, in vitro enzymatic studies, and for therapeutic development.