1-Lyxose, synthesis

The synthesis of diol 56 from L-lyxose is reported. Compound 56 constitutes a subunit of the toxin erythroskyrine <96JCS(P1)1323>. 

An elegant, stereospecific synthesis of two 2-chloro-2-deoxy-pentoses was achieved during the course of a study of the anomerization of chlorosulfated glycosyl chlorides.40 It had been found37 that attempts to anomerize /3-D-xylopyranosyl chloride 2,3,4-tri(chloro-sulfate) (14) with 0.25 mol-equivalent of aluminum chloride afforded the crystalline a-D anomer only in low yield formed also was another compound whose structure has been established40 to be that of 2-chloro-2-deoxy-a-D-lyxopyranosyl chloride 3,4-di(chlorosulfate) (16). The dichloro derivative 16 became the exclusive product when 1.5 mol-equivalents of aluminum chloride were used treatment of 16 with sodium iodide yielded crystalline 2-chloro-2-deoxy-D-lyxose. Similarly, a-D-lyxopyranosyl chloride 2,3,4-tri(chlorosulfate) (15) afforded 2-chloro-2-deoxy-a-D-xylopyranosyl chloride 3,4-di(chlorosuI-fate) (17). 

The Wohl degradation214 of suitably acetylated aldononitriles was used for the synthesis of 5-deoxy-L-arabinose,216 5-deoxy-D-lyxose,2W and 5-deoxy-D-ribose.217... 

A key reaction in the synthesis of the TIA alcohol 18 was the Suarez fragmentation (33) of the 2,3-O-isopropylidene-D-lyxose derivative 23 (34). Treatment of 23 with diiodobenzene diacetate (DIB) provided the 1,2-0-isopropylidene acetate 24 in 88% yield. Acetal exchange was effected by treatment of 24 with thiophenol and BF3.Et20 at -78 °C. Mild base hydrolysis of the product provided 18 in 90% yield from 24, and in 65% overall yield over the four one-pot operations for commercially available D-lyxose 22 (Scheme 3). 

The details on the preparation of the glycone synthon 16 have been described in the earlier report on 3 (24). The key reactions in this synthesis is the Suarez radical fragmentation of the 1,2-O-isopropylidene furanose 17 to give the 1-O-acetyl-1,2-isopropylidene 18 (35), and acetal exchange of 18 to the phenylthio monothioacetal 16 (Scheme 2). Overall, 16 is easily obtained on multi-gram scale (ca. 20 g), in 60% yield, over five steps from commercially available D-lyxose. 

Good diastereoselectivities were observed for the hetero Diels-Alder addition of homochiral 1,3-dienes with achiral acyl-nitroso dienophiles. An example is shown in Scheme 13.85 for the total synthesis of 4-amino-4,5-dideoxy-L-lyxose derivatives 300 and 301, potent inhibitors of a-L-fucosidase [160]. 

An optically pure cyclic analogue of aziridine-2-carboxylate ester was prepared from ribose via a Ph3P-promoted conversion of 3-azido-2-tosyl-D-xylofuranoside to its corresponding 2,3-aziridine (95) (Scheme 34) <93T90l>. The procedure is directly applicable to the synthesis of enantiomerically pure 2,3-aziridine carboxylate isomers from D-lyxose. 

Walker et al. have described by tliis method a seven-step synthesis of 4-thio-2-deox-y-i3-eri f/7ro-pentosc (37) from 2-dcoxy-D-erir/ira-pentosc via dithioacetals 35 and 36, involving inversion at C-4 by Mitsunobu reaction and final cyclization of the dithioacetal, accompanied by further inversion at C-4. Secrist et al.- have synthesized 39 from the ribose derivative 38 using the same method. Similarly, Imbach et al. have prepared 1,4-dithio-D-ribofuranosides 39 from L-lyxose and from D-ribose,and 1,4-dithio-L-lyxofuranosides 40 from D-ribose. Mackenzie... 

Lipides, 238, 239, 241-243, 261 Lipidosis, 239, 242, 243 Lobry de Bruyn-Alberda van Ekenstein transformation, 63, 291 acid catalysis of, 79 aldolization in, 77 base catalysis of, 79-81 catalysis of, by metal ions, 81 dealdolization in, 77 dehydration reactions in, 73 enzyme-catalyzed, 66, 70 formation of reductones in, 79 of or-hydroxy aldehydes, 71 mechanism of, 84 of noncarbohydrate a-ketols, 71 non-enzymic, 66, 67, 83 in paper chromatography, 81 rearrangement of carbon chain, 79 scope of, 65 of steroids, 72 use of, for synthesis, 82 Lyxonic acid, 3-deoxy-D-, 300 Lyxose, D-, condensation of, with urea, 218... 

Proline is a stable, nontoxic, cyclic, secondary pyrrolidine-based amino acid with an increased pK value. Thus, proline is a chiral bidentate compound that can form catalytically active metal complexes (Melchiorre et al. 2008). Bidentate means that proline has not only one tooth but also a second one to bite and react. The greatest difference to other amino acids is a Lewis-base type catalysis that facilitates iminium and enamine-based reactions. It is especially noteworthy that cross-aldol condensations of unprotected glycoladehyde and racemic glyceralde-hyde in the presence of catalytic amounts of the Zn-(proline)2 gave a mixture of pentoses and hexoses (Kofoed et al. 2004). Again, proline seems to play the decisive role. The conditions are prebiotic the reaction proceeded in water for seven days at room temperature. It is remarkable that the pentose products contained ribose (34%), lyxose (32%), arabinose (21%), and xylose (12%) and that all are stable under the conditions. Thus, the diastereomeric and enantiomeric selection observed support the idea that amino acids have been the source of chirality for prebiotic sugar synthesis. 

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