Tartrate from ascorbate

In plants, ascorbate is required as a substrate for the enzyme ascorbate peroxidase, which converts H202 to water. The peroxide is generated from the 02 produced in photosynthesis, an unavoidable consequence of generating 02 in a compartment laden with powerful oxidation-reduction systems (Chapter 19). Ascorbate is a also a precursor of oxalate and tartrate in plants, and is involved in the hydroxylation of Pro residues in cell wall proteins called extensins. Ascorbate is found in all subcellular compartments of plants, at concentrations of 2 to 25 mM—which is why plants are such good sources of vitamin C. 

Section V Stabilising Agents Recommended none are recommended Tolerated citric, tartaric, malic, ascorbic, fiimaric acids from nonsynthetic sources according to BATF standards. Low temperatures for tartrate stabilisation (cold stabilisation). Flash pasteurisation with technical justification Prohibited potassium ferrocyanide, synthetic citric acid, metatartaric acid, sorbic acid and sorbates... 

Further evidence that the tartaric acid arose from a G4 fragment of L-ascorbic acid corresponding to C3 through G6 was obtained from studies with l-[4- G]- and l-[6- C]ascorbic acid (Table IV) (9). The former was converted to carboxyl-labeled tartrate in grape and Virginia... 

The Pfeiffer effect, the outer-sphere interaction of a chiral substrate with a rapidly interconverting racemic solution of a chiral lanthanide complex, can be investigated by measurement of the luminescence dissymmetry factor (the ratio of circularly polarized luminescence to total luminescence) for Eu or Tb " complexes. Thus the racemic D chiral complexes [M(dpa)3], where M = Eu or Tb, interact in an outer-sphere manner with the following optically active spiecies cationic chiral transition metal complexes, ascorbic acid, aminocarboxylates, tartrates, amines and phenols. Association constants can be obtained from limiting values of the dissymmetry factors. In some cases, inner-sphere complexation can be demonstrated, as judged by changes in the general nature of the circularly polarized luminescence spectrum and pH irreversibility of the complexation. 

Figure 5 Calibration curves at 450 nm for tartrate ( ), malate (O), ascorbate (O), lactate ( ), succinate (A), and glucose ( ). (Reproduced from Ref. 18. WUey-VCH, 1999.)...

While the SnCb reduction method gives very sensitive results, it is susceptible to salt interference, and has only a short-lived colored product. For this reason, the ascorbic acid method is preferred to the Sn(II) method however, longer color development time is necessary when ascorbic acid alone is used. The Murphy and Riley [83] method introduced the use of antimonyl tartrate, which catalyzes the reduction step, suppresses the interference from silicate, and avoids problems of chloride interference. Consequently, this method is used as the basis for many batch and automated techniques in current use (see. Table 8.2 and Table 8.4). 

Retrosynthetic analysis demonstrated the need for a 1,2,3-butanetriol and a 1,2,3,4-butanetetrol with 2R, 3S chirality, which corresponds to that found in 2-deoxy-D-ribose. Our initial involvement with L-ascorbic acid (vide infra) led us to examine an equally accessible diastereomer, D-isoascorbic acid. While the former has been extensively studied, the same is not true for the latter. This could be due to early difficulties encountered in the preparation of 5,6-(9-protected derivatives. Unlike their counterparts from L-ascorbic acid, which are equally accessible from / -tartrates, chirons derived from D-isoascorbic acid are not easily obtained from other natural sources. They can be available from w. y( -tartrates only when differentiation between the two carboxyl groups is feasible. 

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