Pentoses derivatives

Beaupere and co-workers have proposed a short synthesis of 5-thio-o-pentopyr-anoses 93 applying a sequence of simple reactions starting from 5-bromopentono-1,4-lactones of type 27 (Scheme 27) [108, 109]. The latter were acetylated and subsequently converted into their corresponding S-S-acetyl-S-thio derivatives 91. Reduction of 91 into lactols 92 was followed by deprotection, furnishing the desired pentose derivatives 93 in good overall yields. 

The mass spectra of aldohexose diethyl dithioacetal pentaacetates resemble those of the corresponding pentose derivatives, but differ in the position of the U, V, W, and AA series, which are situated 72 mass units higher, due to addition of a CHOAc unit to the molecule. 

A 2-deoxy-3-0-methylpentose (corchsularose) was isolated, as the crystalline phenylhydrazone, from corchsularin,11 a bitter principle from the alcoholic extract of jute seeds. According to this investigation, the structure of the pentose derivative was adequately corroborated by the isolation of methoxysuccinic acid after permanganate oxidation. It seems remarkable, however, that a 2-deoxypentose derivative should withstand the conditions of hydrolysis (concentrated hydrochloric acid) which were employed to liberate it. 

Radical chain reactions can take place via organotin reagent without hydrogen donors such as allyltin [38, 39]. This methodology has been applied to synthesize some important chiral precursors of natural products (for example pseudomonic acid). Thus, the pentose derivative 35 affords the compound 36 with retention of configuration via the carbohydrate radical R- at C-4 position [Scheme 18]. 

Sell, D. R., and Monnier, V. M., End-stage renal disease and diabetes catalyze the formation of a pentose-derived crosslink from aging human collagen. J. Clin. Invest. 85, 380-384 (1990). 

A variant of this process was used to achieve a chain extension at C5 of a pentose derivative, allowing the construction of the oxahydrinden part of avermectins [59,156]. As shown in Scheme 11.49, the D-ribose derived aldehyde 217 was treated with ( )-trimethylcrotylsilane in the presence of BF3-Et20 [157]. This produced a mixture of three isomers in an 8.9 1.1 1.0 ratio, from which compound 218 was isolated in a yield of 78%. The subsequent steps allowed deoxygenation of the sugar ring to give the diol 219. This compound was, in turn, transformed into the... 

L-serine was converted into aminotetrose and pentose derivatives 51 and 52, respectively [66]. The anti diastereoselectivity observed for addition of 42 to the A, A -diprotected a-amino aldehyde... 

For the preparation of syn isomers, alcohol 62 has to be oxidized into the corresponding ketone, which is reduced with K-Selectride into the syn isomer 64. The a-amino aldehyde L-65, derived from L-serine, was converted into aminotetrose and pentose derivatives 66 and 71, respectively. The anti diastereoselectivity observed for 67 of 61 to the A, W-diprotected Q -amino aldehyde l-65 can be reversed to syn selectivity by using a W-monoprotected derivative [209,210]. 

Now the calculated values may be applied to additional, isomeric pentose derivatives. In the a-D-xylopyranose derivative the equilibrium is practically totally on the side of the 4Ci form (l ). Similarly, the p-D-arabinopyranose derivative totally adopts the 1C4 conformation (13). Consequently, neither... 

Pentose-based surfactants are not considered as toxic or harmful in acute toxicity tests. APP also have uses in dishwashing and laundry detergents, cosmetics, and cleaning products which are discharged into domestic wastewater after use and thus enter the aquatic environment. It has been shown that pentose derivatives have good kinetics of biodegradation compared with conventional surfactants [35]. The production of pentose-based surfactants requires 37 1% less fertilizers and 36-57%... 

For selective oxidations in the carbohydrate field, Heyns and coworkers have investigated the use of platinum catalysts in different forms. For reactions in which further oxidation of the desired product is probable (as, for example, in the oxidation of ketose and pentose derivatives ), a milder catalyst of 5 to 10% platinum on activated carbon is recommended. Care must be taken in the preparation of the catalyst otherwise, it is difficult to obtain catalysts of reproducible activity. The platinum is deposited on the carbon by hydrogenation or by reduction with formaldehyde or hydrazine sulfate. The catalyst prepared through formaldehyde... 

Nuclear magnetic resonance spectroscopy has revealed, somewhat surprisingly, that the anomers of l,2,4,6-tetra-0-acetyl-3-deoxy-D-gryl/iro-hex-2-enopyranoses (54, 55, R = CH2OAc) and the corresponding -D-g/ycero-pent-2-enopyranoses (54, 55, R= H) adopt different conformations which, from the observed/4,5 values (a-D anomers, about 9 Hz, /3-d anomers, about 1 Hz) must be close to those shown.50,51,106 Consideration of the pentose derivatives (54 and 55,... 

In work designed to develop syntheses of 3-deoxy-D-en/thro-pento-furanose compounds, Brown and Jones123 have studied additions to 3 - deoxy -1,2-0- isopropylidene - a - D - glycero - pent - 3- enodialdo -1,4-furanose (65, R = H), which was obtained by base-catalyzed elimination of p-toluenesulfonic acid from the corresponding 3-0-p-tolyl-sulfonyl-a-D-xyZo-pentose derivative. Partial, catalytic hydrogenation gave 3-deoxy-l,2-0-isopropylidene-/3-L-t/ireo-pentodialdo-l,4-fura-nose (66) which could, however, be isomerized, largely to the a-D-... 

Stereoselective synthesis of (+)-K252a (5) has been reported from a pentose derivative (Schemes 3 and 4). Esterification of the indole 3-acetic acid (27) with allyl bromide afforded the corresponding ester, which nnderwent regiospecific bromination with NBS to give the corresponding 2-bromoindole 28 whose glycosylation with l-chloro-2-deoxy-... 

C-3 in pentose derivatives, with ammonia as the attacking group, have been recorded. An exception to this general behavior was noted in the reaction of methyl 2,3-anhydro-/3-D-lyxofuranoside with benzylthiolate anion, which gave a 60% yield of the 2-thio-D-xylose derivative and a 40% yield of the 3-thio-D-arabinose isomer. 

---