3- Pentulose L-threo

Ishizu et al.29H found that D-xylose and D-fructose react with aqueous calcium hydroxide to produce 13 lactonizable saccharinic and other acids. These were identified after separation by cellulose column and gas-liquid chromatography, and the Cs-saccharinic acids, 2-C-methyl-D-threonic acid (117) and 2-C-methyl-D-erythronic acid (118), were among those isolated. These authors299 later reported that L-sorbose reacts similarly, to generate 14 lactones, including the 2-C-methyl-L-xr/o o-l,4-lactone and 2-C-methyl-L-lyxono-1,4-lactone, which were also prepared from 1-deoxy-L-threo-pentulose via the cyanohydrin reaction. 

L-Arabinose —> L-arabinitol — L-threo-pentulose — xylitol — D-threo-pentulose —> D-threo-pentulose 5-phosphate — ... 

Scheme 18.—Biosynthesis of pyridoxol from l-deoxy-D-rfim>-pentulose and 4-hydroxy-L-threo-nine.

Hodge et al. (45) discussed mechanisms for formation of methyl furanones and related substances from Amadori compounds. They have been produced by heating D-ribose and D-ribose phosphate with ammonia (46 47). Hicks and Feather (48) demonstrated that the Amadori compound 1-benzylamino-l-deoxy-D-threo-pentulose dehydrates to 4-hy-droxy-5-methyl-3(2H)-furanone and it has also been identified as a degradation product of L-ascorbic acid. This compound is believed to be formed from ribose-5-phosphate, and gained prominence when it was isolated from beef by Tonsbeck et al. (49). It became more apparent as a precursor of meat flavor when Van den Ouweland and Peer (50) reacted it and its thio analog with HaS to produce a number of sulfur compounds, some of which had meaty odors. 

Acetamido-5-deoxy-D-threo-pentulose and 5-acetamido-5-deoxy-L-erythro-pentulose (204) are obtainable by the bacterial oxidation of 1-acetamido-l-deoxy-D-arabinitol and 1-acetamido-l-deoxy-D-ribitol, respectively. Both ketoses are crystalline, and show a strong carbonyl vibration in their infrared spectra. Accordingly, they exist in the acyclic form. Their isopropylidene acetals are likewise acyclic. Furthermore, 5-acetamido-5,6-dideoxy-L-xylo-hexulose (205), obtainable by bacterial oxidation, shows a great tendency to assume the acyclic structure. 5-Acetamido-5-deoxy-L-xi/io-hexulose (206) may be obtained by the bacterial oxidation of 2-acetamido-2-deoxy-D-glucitol it assumes, exclusively, the sterically more-favored pyranose form. ... 

Cordova and co-workers [163] reported simultaneously a similar approach for the synthesis of protected 4-amino-4-deoxy-threo-pentulose and 4-amino-4-deoxyfructose (O Scheme 32). The catalyst can be L-proline, other o -aminoacids, or alanine-tetrazole [126]. 

For succinate-grown yeast, extracts catalyze D-glucitol D-fiructose + L-xt/Zo-hexulose, D-mannitol <->D-fructose, D-arabinitol — threo-pentulose, and reduction of NAD with xylitol or erythritol.264... 

For D-glucitol-grown yeast, extracts catalyze D-glucitol — fructose + xyfo-hexulose, D-mannitol — fructose, xylitol — fhreo-pentulose, and D-arabinitol —< threo-pentulose, reduction of NAD with L-iditol or ribitol, and oxidation of NADH with D-fructose or L-xylo-hexulose.264... 

Typical procedure. l,3,4-Tri-0-benzyl-5-0-triphenylmethyl-keto-D-threo-pentulose 1885 [1402, 1403] 2,3,5-Tri-O-benzyl-l-O-triphenylmethyl-D-arabinitol (5.0 g, 7.5 mmol) was dissolved in DMSO/acetic anhydride (3 2, vjv, 30 mL) and the solution was kept at room temperature for 18 h. Cold water (120 mL) was then added, the mixture was stirred for 30 min, and the aqueous phase was decanted off. The remaining yellowish syrup was washed twice with water and dissolved in hexane, and this solution was washed repeatedly with water, once with 10% aqueous silver nitrate solution, and concentrated under reduced pressure to yield 4.9 g of a syrup. Chromatography on 250 g of silica gel (0.05-0.20 mm, Merck no. 7734) eluting with benzene/diethyl ether (9 1, vjv) gave the product 1885, pure by TLC, as a syrup (4.3 g, 6.5 mmol, 87%) = -26.2° (c = 2.1, CHCI3). 

D-gluco-L-glycero-3-Octulose (34), the first naturally occurring 3-octulose reported, was Identified as the main constituent in aqueous extracts from Laurus nobilis leaves and buds, and evidence has been presented that 1-deoxv-D-threo-pentulose... 

Another synthesis, described in detail in Scheme 12, was devised specifically for the introduction of deuterium at both ends of l-deoxy-D-t/ireo-pentulose.21,22 Stannylene methodology was used twice, first for glycol splitting with phenyliodonium diacetate, under strictly neutral conditions (necessary to preserve the benzylidene acetal), and secondly to convert the sequence -CHOH-CD3 to CO-CD3 by brominolysis. The final, labeled pentulose was l-deo y-D-threo-(1-2H3, 5-2H)pentulose. 

This section is completed with a brief review of the synthesis and properties of this epimer (20) of the precursor of thiazole in bacteria. This pentulose is conveniently accessible by an unconventional route (Scheme 19). Methyl 2,3 4,6-di-O-isopropylidene-a-D-mannopyranoside, readily available from methyl ot-D-mannopyranoside, is converted to the ketonic glycoside by butyllithium in 91% yield, following a method first published by Klemer and Rodemeyer43 and scaled up by Horton and Weckerle.44 This was converted by means of lithium hydroxide in a water-ether mixture into 3,5-0-benzylidene-l-deoxy-D-eryf/iro-2-pen-tulose in 55% yield. Hydrolysis to the free pentulose (20) proceeded in 73% yield in aqueous acetic acid. This product was obtained as a syrup with a characteristic absorption band at 1705 cm 1 as a film. Thus, there is a fair proportion of the open-chain ketone under these conditions, as with the D-threo epimer.45... 

For succinate-grown yeast, extracts catalyze D-glucitol — xyZo-hexulose + glucose, D-mannitol — fructose + mannose, ribitol — ribose, xylitol — xylose + threo-pentu-lose, D-arabinitol — arabinose + fhreo-pentulose, and oxidation of NADPH with D-fructose, L-xyZo-hexulose, D-ribose, D-xylose, or L-arabinose.284... 

The D-2-pentuloses, o-erythro-l-ptn lulose (D-ribulose, 12) and o-threo-l-pentulose (D-xylulose, 13) are able to cyclize as 2-pentulofuranoses. The 2-ketopentoses are important metabolic intermediates in glycolysis.11... 

G.l.c.-m.s. of the isopropylldenated product mixture obtained by aldol condensation of glycolaldehyde and 1,3-dihydroxypropan-2-one allowed identification of erythro-2-pentulose, erythrose, threose, xylose, dendroketose and threo-2-pentulose. The ratio of these products varied with the base used, which included calcium, barium, and sodium hydroxides and the hydroxide ion form of Dowex-1 and Amberlite IRA-400. 

Fragment spectra that may be summed algebraically to predict the vacuum- u.v. c.d. spectra of certain pyranoid monosaccharides e.g. a- and P-L-arabinopyranose and methyl a-L-arabinopyranoside) have been presented. A limited number of these fragment spectra were used to calculate a large number of c.d. spectra that had been measured previously and to predict the c.d. spectra of other monosaccharides whose spectra have yet to be measured. The c.d. spectra of acyclic ketoses (e.g. D-threo- and D-cryr/tro-pentulose) show two overlapping bands of opposite sign at ca. 310 and 270 nm which can be related to the configuration at cUral centres. ... 

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