Glucose to L-ascorbic acid

D-Glucose to L-Ascorbic Acid Fermentation. The direct heterotrophic fermentation of D-glucose to L-ascorbic acid with algae is... 

Recently a study of the D-glucose to L-ascorbic acid conversion in Virginia Creeper was completed in which Cl, C6, HI, or H6 labeled... 

Scheme 11.19. A representation of what is currently (2007) understood abont the pathway from D-glucose to L-ascorbic acid in plants. L-ascorbic acid is not biosynthesized by some mammals (including humans). EC nnmbers and some graphic materials provided in this scheme have been taken with permission from appropriate links in a URL starting with http // www.chem.qmul.ac.uk/iubmb/enzyme/.

No Carbon-Chain Inversion. This section will discuss the methods by which D-glucose has been converted to L-ascorbic acid without carbon-chain inversion. These syntheses of L-ascorbic acid from D-glucose without carbon-chain inversion involve the oxidation of D-glucose at Cl and C2, and the inversion of chirality at C5. 

Labeling studies indicate that in the conversion of D-glu-cose to L-ascorbic acid in plants, the carbon chain is conserved. Although the steps of biosynthesis are not clear, they involve oxidation at C-1, an internal oxidation of C-2 or C-3, and epimerization at C-5 of glucose. One possible sequence is as follows D-glucose is converted to D-glucosone, which compound to L-sorbosone, which compound to l-ascorbic acid (Loewus, 1988). 

These experiments demonstrate that in the conversion of D-glucose to L-ascorbic there was a complete inversion of the molecule, and likewise suggest that there was no rupture of the molecule in the process. This latter view is supported strongly by the similarity of the yields of radioactive ascorbic acid from either C-1 or C-6 labeled glucose. It is difficult to visualize how the same results could be achieved if the hexose molecule was first split and the parts then recombined to form a new six-carbon unit. 

Many fruits are important sources of vitamin C (Table 18.33). Its biosynthesis in plants starts from hexoses, e. g., glucose. It is postulated that following C-1 oxidation and cyclization to 1,4-lactone (II), the 5-keto compound (III) appears as an intermediary product which is oxidized to the 2,3-endiol (IV) then reduced stereospecifically to L-ascorbic acid (V) (cf. Formula 18.40). 

The lactone is oxidized to L-ascorbic acid. The L-designation of ascorbic acid refers to the configuration at C-5, which was C-2 in o-glucose and C-5 in L-gulonic acid. 

M.p. 190-192 C. The enolic form of 3-oxo-L-gulofuranolactone. It can be prepared by synthesis from glucose, or extracted from plant sources such as rose hips, blackcurrants or citrus fruits. Easily oxidized. It is essential for the formation of collagen and intercellular material, bone and teeth, and for the healing of wounds. It is used in the treatment of scurvy. Man is one of the few mammals unable to manufacture ascorbic acid in his liver. Used as a photographic developing agent in alkaline solution. 

Most current industrial vitamin C production is based on the efficient second synthesis developed by Reichstein and Grbssner in 1934 (15). Various attempts to develop a superior, more economical L-ascorbic acid process have been reported since 1934. These approaches, which have met with htde success, ate summarized in Crawford s comprehensive review (46). Currently, all chemical syntheses of vitamin C involve modifications of the Reichstein and Grbssner approach (Fig. 5). In the first step, D-glucose (4) is catalytically (Ni-catalyst) hydrogenated to D-sorbitol (20). Oxidation to L-sotbose (21) occurs microhiologicaRy with The isolated L-sotbose is reacted with acetone and sulfuric acid to yield 2,3 4,6 diacetone-L-sorbose,... 

In all plants and most animals, L-ascorbic acid is produced from D-glucose (4) and D-galactose (26). Ascorbic acid biosynthesis in animals starts with D-glucose (4). In plants, where the biosynthesis is more compHcated, there are two postulated biosynthetic pathways for the conversion of D-glucose or D-galactose to ascorbic acid. 

In animals, ascorbic acid is synthesized in the liver from o-glucose, by a pathway that initially involves specific enzymic oxidation of the primary alcohol function, giving o-glucuronic acid (see Section 12.8). This is followed by reduction to L-gulonic acid, which is effectively reduction of the carbonyl function in the ring-opened hemiacetal. 

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... 

L-Ascorbic acid (Figure 10.8) proved to be less recalcitrant than glucose and could be esterified with palmitic acid in the presence of CaLB in [BMIm][BF4] and similar ionic liquids [116, 117]. The equilibrium was shifted toward the product by applying a vacuum to remove the water, and undesirable precipitation of the reaction product on the biocatalyst was obviated by the addition of a hydrophobic phase such as hexane or polypropylene beads [116]. 

---