Ascorbic acid labeled with

There is evidence that tartaric acid in grapes has L-ascorbic acid as a major precursor. Thus, immature grapes fed with L-ascorbic acid labelled with at C-1 were found to have 72" of the C in the carboxyl carbon of tartaric acid. I he indications are that in L-ascorbic acid C-1 to C-4 end up as tartaric acid indeed, if C-6 is labelled with C none of it appears in the tartaric acid. However, the process in vines is by no means. simple and depends on a number of factors, including the extent of development of the plant, and is difl erent for different... 

The Reichstein-Gnissner synthesis has been used to prepare a number of labeled derivatives of L-ascorbic acid, starting with labeled D-glu-cose (36-40). This synthesis is not amenable to the preparation of analogues. 

Williams and Loewus (7) prepared l-[4- C]ascorbic acid by the method of Bakke and Theander (8) and showed that this form of specifically labeled ascorbic acid, like L-[l- C]ascorbic acid, was an effective precursor of tartaric acid in grape berries and grape leaves (Table I) (9). Over 98% of the was located in the carboxyl groups of labeled tartaric acid from l-[1- C]- or L-[4- C]ascorbic acid labeled leaves or berries. Only L-(-f)-tartaric acid was formed (10). The C2 fragment of this cleavage, as judged by studies with l-[6- C] ascorbic acid, was recycled into products of hexose phosphate metabolism (5,6,11,12). 

Virginia Creeper leaves were fed L-ascorbic acid with C in Cl, C4, C5, or C6 or on C6 (14). In each experiment, three compound leaves from the fifth position behind the tip of the vine were used. After a 24-h metabolic period, the distribution of radioisotope was determined (Table III). As in the grape, l-[1- C]- and l-[4- C]ascorbic acid produced carboxyl labeled tartaric acid. Virutally no radioisotope appeared in tartaric acid from the other l-[5- C]-, l-[6- C]-, or l-[6- H]ascorbic acid. The larger amount of C02 released by L-[l- C]ascorbic acid labeled leaves has been confirmed in subsequent studies. 

Within experimental limits, leaves labeled with l-[5- C]- or l-[6- C]ascorbic acid gave comparable results (Table III). Additively, the C in CO2, sugars, and malic acid accounted to 62-63% of that present in the leaves. Another 7% appeared in the residue as glycans. The total amount of C found in hexose or products of hexose metabolism of l-[5- C]- or L-[6- C]ascorbic acid labeled leaves was similar to that found in tartrate (and CO2) after labeling with l-[1- C]- or l-[4- C]-ascorbic acid. Cleavage of the carbon chain of ascorbic acid at the C4-C5 bond accounts for these observations. 

Fig. 11. Proposed pathway for the biosynthesis of L-ascorbic acid (with inversion of configuration) in plants using C-l-labeled D-glucose or C-l-labeled...

FIGURE 10.13 The TLC profiles of labeled peaks isolated from [U- C]ascorbic-acid-modified calf lens protein obtained from Bio-Gel P-2 chromatography. Peaks 2 to 7 were spotted on a preparative silica gel TLC plate and developed with ethanol/ammonia (7 3, v/v). The fluorescence in each lane was detected by irradiation with a Wood s lamp at 360 nm, and the pattern of radioactivity was determined by scanning the plate with AMBIS imaging system. (Reprinted with permission from Cheng, R. et al., Biochim. Biophys. Acta, 1537, 14-26, 2001. Copyright (2001) Elsevier.)... 

N5,N10-methenyltetrahydrofolate (with ascorbic acid) was adjusted to neutral pH, autoclaved, and stored at -20° C prior to column purification on DEAE and G-15 Sephadex. These labeled products are the biologically active diastereomers, and they are used to study the metabolism of folinic acid in cells, tissues, and animals. 

The bone becomes depleted of calcium salts when the urine is acidic over a relatively long period. This was shown by Goto (17) who fed rabbits large doses of hydrochloric acid. He then showed that urinary calcium loss occurred in concert with a marked reduction in mass of the skeletal system, and also that the total non-fat dry weight of bone decreased,implying a loss of bone matrix. A dose-dependent, dietary acid induced loss of labelled calcium from rat bone has been reported by Thorn and his coworkers (18). They demonstrated that in response to graded doses of ascorbic acid, cells in tissue culture, and bones in whole animals fed such doses were depleted of the labelled calcium. 

Antioxidants should be labelled on the retail package with the specific chemical name or with the EC number. The legislation of member states of the EU is influenced by the decision taken within the EC. Some food standards are fully based on EC Directives and some are still based on national considerations. There may be differences between European states, for instance, the utilisation of ascorbic acid as antioxidant for egg products is permitted in France but prohibited in Germany. These differences concern usually the utilisation of antioxidants in various food commodities. The specification of antioxidants mentioned in EC Directives are respected by all member states. But it is still generally required that individual countries of the European Union as well as the central organisation should be approached. The requirements appearing in the EC Directives on additives must be applied by the member states. This means in the first place that for those categories of additives for which a Community positive list exists, member states may not authorise any additives which do not appear on the positive list. 

Less frequently used at present is electron spin resonance spectroscopy, which is based on the use of spin probes as model componnds or covalent spin labeling of drugs. Microviscosity and micropolarity of the molecnlar environment of the probe can be derived from electron spin resonance spectra. Moreover, the spectra allow us to differentiate isotropic and anisotropic movements, which result from the incorporation of the probe into liposomal structures. Quantitative distribution of the spin probes between the internal lipid layer, the snrfactant, and the external water phase is to be determined noninvasively. On the basis of the chemical degradation of drugs released from the lipid compartment, agents with reductive features (e.g., ascorbic acid) allow us to measure the exchange rate of the drugs between lipophilic compartments and the water phase [27,28]. 

Acetamido-2-deoxy-D-glucose is a component of a mucopolysaccharide hyaluronic acid. It has been demonstrated, by PET imaging with the corresponding F labeled compound, that this glucose derivative is incorporated into the connective tissue at the interface of a tumor and healthy tissue. Thus, it can be used as a tumor label. 6-[ F]-6-Deoxy-L-ascorbic acid also deserves attention, as it maintains the antioxidant properties of ascorbic acid. Thus, it can be useful to smdy the biochemical... 

Figure 6.19 Preparation of sugars labeled with F 2-[ F]-2-deoxytalose, N-[ F]-fluoroacetyl-D-glucosamine, and 6-fluoro-6-deoxy-L-ascorbic acid.

Calculate the amount of ascorbic acid in each sample. Does it agree with the label on the bottle ... 

By adding l4C-labelled sodium cyanide to L-threo-pentos-2-ulose (9), L-[l-14C]ascorbic acid was prepared (see Scheme 2) having an activity592-596 of 2.1 x 108 counts, min-1, mg-1. L-Xylose was prepared by the sequence shown in Scheme 21. The resulting L-xylose was oxidized with cupric acetate to 9 in 40-50% yield. In the second procedure, [1-14C]1 (specific activity 0.1 /iCi. mg-1) was purified by way of 5,6-O-cyclohexylidene-L-ascorbic acid.596... 

Uniformly labelled 1 was prepared by the Reichstein-Griissner synthesis (see Scheme 4), starting with unifonnly labelled D-glu-cose.597-599 L-[2,3,4,5,6-14C]Ascorbic acid was prepared 800 from L-[U-14C]xylose by way of L-threo-pentos-2-ulose (9) (see Scheme 2). The L-[U-14C]xylose was prepared from D-[U-,4C]glucitol by using the route shown in Scheme 21. 

The 5,6-O-isopropylidene acetal (152) of L-ascorbic acid has been prepared,340 and von Schuching and Frye341 prepared the corresponding cyclohexylidene acetal. These compounds were found to be more resistant than L-ascorbic acid toward oxidation, and the parent acid can be readily regenerated by acid hydrolysis. The derivative was used in the synthesis of 14C-labeled vitamin C. The C-2 and C-3 enols of L-ascorbic acid or its acetone derivative (152) can be readily methylated with diazomethane, yielding the corresponding dimethoxy analogues. 

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