Synthesis of and Glycosidation by 2-Deoxy-2-Fluoro-D-Mannopyranose

Synthesis of ether lipids: natural compounds and analogues

Ether lipids are compounds present in many living organisms including humans that feature an ether bond linkage at the sn-1 position of the glycerol. This class of lipids features singular structural roles and biological functions. Alkyl ether lipids and alkenyl ether lipids (also identified as plasmalogens) correspond to the two sub-classes of naturally occurring ether lipids. In 1979 the discovery of the structure of the platelet-activating factor (PAF) that belongs to the alkyl ether class of lipids increased the interest in these bioactive lipids and further promoted the synthesis of non-natural ether lipids that was initiated in the late 60's with the development of edelfosine (an anticancer drug). More recently, ohmline, a glyco glycero ether lipid that modulates selectively SK3 ion channels and reduces in vivo the occurrence of bone metastases, and other glyco glycero ether also identified as GAEL (glycosylated antitumor ether lipids) that exhibit promising anticancer properties renew the interest in this class of compounds. Indeed, ether lipid represent a new and promising class of compounds featuring the capacity to modulate selectively the activity of some membrane proteins or, for other compounds, feature antiproliferative properties via an original mechanism of action. The increasing interest in studying ether lipids for fundamental and applied researches invited to review the methodologies developed to prepare ether lipids. In this review we focus on the synthetic method used for the preparation of alkyl ether lipids either naturally occurring ether lipids (e.g., PAF) or synthetic derivatives that were developed to study their biological properties. The synthesis of neutral or charged ether lipids are reported with the aim to assemble in this review the most frequently used methodologies to prepare this specific class of compounds.

Synthesis of (1-->4)-linked 2-deoxy-2-fluoroglucose oligomers. 1

[reaction: see text] Thioglycosides of natural monosaccharides are readily converted into their corresponding chlorides by diphenylchlorosulfonium chloride. This reagent can likewise effect the conversion of the more stable 4-chlorophenylthio 2-deoxy-2-fluoroglucose derivatives into chloride glycosyl donors. On the basis of this activation strategy, it was possible to assemble unnatural oligosaccharides composed of 2-fluorodeoxy sugars.

NMR spectra of fluorinated carbohydrates

Recent advances in structural and conformational analysis of fluorinated carbohydrates by NMR spectroscopy are reviewed. Characteristic 1H, 13C, and 19F NMR chemical shifts and coupling constants for selected examples are given and the spectral data of a series of fluorinated carbohydrates were collected in continuation of the review of Csuk and Glänzer [Adv. Carbohydr. Chem. Biochem., 46 (1988) 73-177].

The synthesis of 2,3-dideoxy-2-fluoro-3-C-methylpentose-containing nucleosides via [3,3]-sigmatropic rearrangements

[3,3]-Sigmatropic rearrangement of in situ-formed [O,O]-silyl ketene acetals of butenyl fluoroacetates was used as the key step in the synthesis of racemic 2,3-dideoxy-2-fluoro-3-C-methylpentofuranoses. The product pentofuranoses were transformed further into pyrimidine and purine nucleosides. The conformations of the synthetic carbohydrates were confirmed by single-crystal X-ray diffraction studies and indicated that previous structural assignments made by NMR were in error.

The synthesis and characterisation of 2-O-(6-O-L-glycero-alpha,beta-D-manno-heptopyranosyl-alpha-D-glucopyran osyl)-alpha,beta-D-glucopyranose

The title compounds were synthesised, and appropriate derivatives were characterised by GLC, GLC-MS, and NMR spectroscopy. The GLC and GLC-MS data proved 2-O-(6-O-L-glycero-alpha-D-manno-heptopyranosyl-alpha-D-glucopyranosyl)- D- glucopyranose to be a constituent of the outer-core region of the lipopolysaccharide from Escherichia coli K-12, indicating the heptosyl residue to be linked to the terminal glucopyranose residue.

A facile formation of 2,5-anhydro sugars by ring contraction in methyl hexopyranoside 2-triflates under conditions of nucleophilic displacement

Reaction of methyl 3,4-O-isopropylidene-2-O-(trifluoromethylsulfonyl)-alpha-L-fucopyr anoside and its beta anomer with a variety of nucleophilic reagents under mild conditions led to displacement of the triflic ester group, with migration of the ring-oxygen atom to C-2 and entry of the nucleophile at C-1, to give good yields of 2,5-anhydro sugar derivatives. Reagents employed were hydrogen fluoride-triethylamine complex, methanol in the presence of sodium hydrogencarbonate, sodium benzoate, sodium azide, potassium thiocyanate, and sodium borohydride. The same type of substitutive ring-contraction also occurred in methyl 4-O-benzyl-3-O-(4-methoxybenzyl)-2-O-(trifluoromethylsulfonyl)-alp ha-L- fucopyranoside and methyl 4,6-dideoxy-3-O-(4-methoxybenzyl)-2-O-(trifluoromethylsulfonyl)-al pha-L-xylo- hexopyranoside. The reaction is discussed in light of a literature survey of the chemical behavior of hexopyranoside 2-sulfonates in general, and 2-triflates in particular. Direct SN2 displacements, eliminations, and such different kinds of rearrangement as have previously been observed with structural analogs were not encountered in the present study. However, there is some precedent, in hexopyranoside 2-triflates, for the facile rearrangement that the four representatives here investigated have been found to undergo. The synthesis of these triflates from L-fucose is described.

Stereospecific approach to the synthesis of [18F]2-deoxy-2-fluoro-D-mannose

The reaction of methyl 4,6-O-benzylidene-3-O-benzyl-2-O-trifluoromethanesulfonyl-beta-D- glucopyranoside in acetonitrile at 75 degrees C for 30 min with [18F]tetra-n-butylammonium fluoride, followed by silica gel column chromatographic purification, gave the corresponding [18F]methyl 4,6-O-benzylidene-3-O-benzyl-2-fluoro-beta-D-mannopyranoside with complete regio- and stereoselectivity (42% radiochemical yield). Hydrolysis of the radiolabeled fluoromannopyranoside intermediate with either 6 N HCl or 50% methanesulfonic acid for 30 min at 120 degrees C, followed by purification by column chromatography (ion retardation resin and neutral alumina), gave pure [18F]2-deoxy-2-fluoro-D-mannose ([18F]2-FDM) with an overall radiochemical yield (from [18F]fluoride ion) of 34%. Extension of this methodology to the no carrier added (nca) synthesis under phase transfer conditions (Kryptofix 222/K 18F/acetonitrile) gave nca [18F]2-FDM in a radiochemical yield of 75%. Purity and identity of the fluorinated products were confirmed by 1H and 19F NMR spectroscopy. The synthetic procedure described here permits for the first time the routine preparation of large amounts of [18F]2-FDM for tomographic studies.