Threonic acid

A technique based on ozonation, in contrast, provides information on the stmcture of the lignin side chain by degrading the aromatic rings (33). Thus the side chain of the dominant stmcture ia all native lignins, the arylglycerol—P-aryl ether moiety, can be obtained ia the form of erythronic and threonic acids. Ozonation proves to be an elegant method for determination of the stereospecificity ia lignin. 

High antiscorbutic power is also reported to be shown by a derivative of L-ascorbic acid in which the enolic hydroxyl group at C2 is replaced by an amino group. 3,4-Isopropylidene-L-threonic acid (LX), prepared from 5,6-isopropylidene-L-ascorbic acid, is converted into the 2-acetyl-3,4-isopropylidene-L-threonyl chloride (LXI) and this is then allowed to react with the sodium derivative of ethyl malonate. 

The bromodeoxyaldonolactones have been used for the preparation of aminodeoxy aldonic acids and aminodeoxy sugars via azido derivatives (45,46). Likewise, a- and /J-aminopolyhydroxy acids have been prepared by treatment of the bromodeoxyaldonolactones with liquid ammonia (47). Thus, 3-amino-3-deoxy-D-threonic acid and 3-amino-3-deoxy-D-arabin-onic acid (40b) were obtained from 2-bromo-2-deoxy-L-threono- or D-xy-lono-1,4-lactone (38). It was shown that 2,3-epoxy carboxamides (namely, 39) are intermediates of the reaction. Heating at 90° for long periods led to the 3-amino-3-deoxyaldonamides, which upon acid hydrolysis yielded the corresponding aldonic acids. 

Five pentosaccharinic acids were formed when D-xylose was treated with calcium hydroxide. This mixture included 2-C-methyl-D-threonic acid and 2-C-methyl-D-erythronic acid, the structures of which were... 

Displacement of the bromine atom in 4-bromo-4-deoxy-DL-threonic acid (7) with silver acetate gave15 DL-threonic acid (10). 

DL-Threonic acid (10) seemed to be a promising source of DL-threose. Therefore, other routes to 10 were elaborated. By a procedure consisting of five steps" 2-propenal (acrolein) — vinylglycoloni-trile — ethyl vinylglycolate — ethyl 4-bromocrotonate — 3-hydroxy-crotonic acid — 10, DL-threonic acid was obtained in an overall yield of 4.1%. Another synthesis of 10 was achieved17 in six steps starting... 

DL-Threose was prepared19 from DL-threonic acid (10) in a slightly modified way. Benzoylation of 10 yielded 2,3-di-O-benzoyl-DL-threono-1,4-lactone (lib), instead of the desired 2,3,4-tri-O-benzoyl-DL-threonic acid. When DL-threonamide (15a) was used19 as the substrate, the 2,3,4-tri-O-benzoyl derivative 15b could be readily prepared. Deamination of 15b with nitrous acid, preparation of the acid chloride, and Rosenmund reduction of the latter, followed by deben-zoylation of the product, afforded DL-threose in good yield. 

L-erythronic acids, respectively, and D-xylose to D-threonic acid.44 Isbell et al. elucidated the mechanism of this process45 (see the following Chapter). Degradation to a lower aldonic acid can be achieved by oxidation of an unsaturated sugar derivative. The method of Reichstein et al.46 for the preparation of L-threono-1,4-lactone by permanganate oxidation of 5,6-0-isopropylidene-L-ascorbic acid was improved by Perel and Dayton to afford the crystalline lactone in 65% yield.47... 

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. 

The structure of 138 was elucidated, shortly after its isolation, in extensive contributions by many groups. Several important discoveries relating to its constitution were reported in 1933, the same year in which the first successful synthesis was described (see Refs. 274, 324). Thus, the group at the University of Birmingham335 found that the primary oxidation product of 138, the 2,3-diulosono-lactone 148 (dehydroascorbic acid), could be quantitatively oxidized by sodium hypoiodite to generate oxalic acid and L-threonic acid (Scheme 16), which was identified as the crystalline tri-O-methyl-L-threonamide. These results established the stereochemical relationship between 138 and L-gulonic (and L-idonic) acid. The work that provided support for the structure of L-ascorbic acid has been summarized in several reviews.274,336... 

Disaccharides and polysaccharides are also oxidized by the same degradative oxidation at first they react rapidly then, when the point of branching is reached, they react much more slowly. When subjected to similar oxidations, ascorbic acid affords threonic acid and oxalic acid, and 2-deoxy sugars yield 2-deoxyaldonic acids and lower alditols. 

Two papers have thrown light on the finer structure of Appel s diacetal. First, Gatzi and Reichstein141 oxidized it with potassium permanganate in alkaline solution and obtained a diethylidene-L-xylonic acid, together with a monoethylidene-L-threonic acid. The ethylidene group in the latter compound was shown to span positions 2 and 4, from which they concluded that the parent diacetal was 1,3 -diethylidene-D-sorbitol (XXXI). Secondly, Bourne and Wiggins117 hydrolyzed the... 

The colonial sea anemone Anthopleura elegantissima responds with characteristic contraction to a pheromone released by wounded conspecifics. This alarm response is highly characteristic, includes rapid bending and shortening of the tentacles and depression of the oral disk. In 1975, by extensive ion exchange column chromatography, (3-carboxy-2,3-dihydroxy-A(A(Af-trimethyl)-l-propanaminium chloride (50) was isolated as a pure crystalline substance.116 It showed alarm pheromone activity with a median concentration of 0.35 nmol 1 1 and was named anthopleurine. Comparison of spectral data between natural and synthetic compounds revealed that anthopleurine had a structure of 4-amino-4-deoxy-L-threonic acid betaine hydrochloride.117... 

Note 4. Ozonation times have varied from as short as 4 min for model compounds to as long as 60 min for wood meal. With wood meals, the yields of erythronic and threonic acids were highest at 40min. 

The dihydroxy lactone from L-threonic acid is prepared from L-dibenzoyl tartaric anhydride by catalytic hydrogenation over palladium. The substituted anhydride is formed from tartaric acid and benzoyl chloride. 

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