Gulono-1,

L-Gulono-g-lactone-6- C L-2-Oxogulono-g-lactone-6- C t-Ascorbic acid-6- C... 

L-Ascorbic acid, better known as vitamin C, has the simplest chemical structure of all the vitamins (Figure 18.30). It is widely distributed in the animal and plant kingdoms, and only a few vertebrates—humans and other primates, guinea pigs, fruit-eating bats, certain birds, and some fish (rainbow trout, carp, and Coho salmon, for example)—are unable to synthesize it. In all these organisms, the inability to synthesize ascorbic acid stems from a lack of a liver enzyme, L-gulono-y-lactone oxidase. 

In ketones existing largely as the enol, palladium may prove effective in minimizing hydrogenolysis, Hydrogen was added slereoselectively to the least hindered side of L-ascorbic add (3) to give L-gulono-1,4-lactone (4)... 

The major pathway probably proceeds via D-galacturonic acid and L-galactono-1,4-lactone, as these are converted to L-ascorbic acid by mitochondria prepared from peas and mung beans, but neither L-gulono-1,4-... 

Catalytic hydrogenation of the oxime of D-glucurono-6,3-lactone leads179 to simultaneous isomerization with formation of L-gulono-... 

XIII. Biological Role of the Gulono-1,4-lactones and Gulonic Acids.320... 

The following article summarizes the methods of synthesis for L-gu-lono-1,4-lactone (1), D-gulono-1,4-lactone (2), and the corresponding... 

The most efficient synthesis of L-gulono-1,4-lactone (1) entails the reduction of D-glucofuranurono-6,3-lactone (7), which can be obtained from D-glucose2 (see Scheme 1). Catalytic hydrogenation3-4 of 7 in the presence of Raney nickel afforded 1 in 81% yield. Alternatively, D-... 

A short synthesis of D-gulono-1,4-lactone (2) from the inexpensive and readily available D-xylose (34) was first reported by Fischer and Stahel,18 and subsequently by others,12,25-31 and is shown in Scheme 6. The addition of hydrogen cyanide to D-xylose (34) resulted in the formation of cyanohydrins 35 and 36 which, on hydrolysis, afforded a mixture of D-gulonic acid (4) and D-idonic acid (37). D-Gulono-1,4-lactone may be obtained in 30-33% yield by recrystallization of the reaction products. In a similar way, L-xylose (l-34) has been converted32,33 in high yield into a mixture of L-gulonic and L-idonic acids. 

It has also been reported that D-galactose can be isomerized with molybdic acid to a mixture containing D-talose and D-gulose, but the yields are low.34-35 A number of derivatives of gulono-1,4-lactone have been prepared that, by reduction, would provide selectively protected derivatives of gulose. These derivatives will be discussed in subsequent Sections of this article. 

The crystal structure of D-gulono-1,4-lactone (2) has been determined,42 and is closely approximated by formula 38. Interestingly, the conformation of the side chain in 38 differs from that in crystalline L-ascorbic acid,1 very probably because of different steric interactions between the 3- and 5-hydroxyl groups in 2 (that is, 38) and 6. Bridgman43 measured the compressibility of gulono-1,4-lactone crystals. 

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