STRUCTURE AND BIOSYNTHESIS OF VITAMIN C:
A white crystalline vitamin C6H8O6 found in citrus fruits tomatoes potatoes and leafy green vegetables and used to prevent scurvy. Also called vitamin C.
Vitamin C also known as L-Ascorbic acid L-xyloascorbic acid 3-oxo-L-gulofuranolactone (enol form) L-3-ketothreohexuronic acid lactone and antisorbutic vitamin has the chemical formula C6H8O6 and a molecular weight of 176.12. This 6-carbon molecule is structurally very similar to the sugar D-glucose (Fig. 1) a point of significance which will be addressed when considering the mode of action and mechanisms underlying Vitamin C's therapeutic effectiveness with diabetes and heart disease.
Vitamin C an essential nutrient found mainly in fruits and vegetables. The body requires it to form and maintain bones blood vessels and skin. Like other vitamins ascorbic acid is an organic compound. An organic compound is a substance that (1) occurs in living things or organisms (hence the word 'organic') and (2) contains the elements carbon and oxygen (hence the word 'compound' meaning combination of elements).
Ascorbic acid is a water-soluble vitamin one that cannot be stored by thebody except in insignificant amounts. It must be replenished daily.
190 - 192 °C (decomposes)
l L-Ascorbic acid;
l L-xyloascorbic acid;
l 3-oxo-L-gulofuranolactone (enol form);
l L-3-ketothreohexuronic acid lactone;
L-Ascorbic acid 2-[34-dihydro-2578-tetramethy1-2-
hydrogen phosphate] potassium salt
l It is odourless or almost odourless.
l It has a pleasant sharp acidic taste.
l It is freely soluble in water and sparingly soluble in ethanol.
l It is practically insoluble in ether and chloroform.
l Ascorbic acid has pKa values of 4.2 and 11.6.
l Ascorbic acid has a melting temperature of 190°C with decomposition.
l A solution of ascorbic acid in sodium hydroxide sodium carbonate or sodium bicarbonate has a pH of 5.5-7.0.
l A 5% solution in water has a pH of 2.2- 2.5.
l In impure preparations and in many natural products the vitamin oxidises on exposure to air and light.
Ascorbic acid should be protected from air and light and be stored in a tightly closednon-metallic container.
Proliferation of human skin fibroblasts was stimulated significantly by the presence of L-ascorbic acid 2-phosphate (Asc 2-P). The presence of Asc 2-P (0.1-1.0 mM) in the culture medium for 3 weeks enhanced the relative rate of collagen synthesis to total protein synthesis 2-fold as well as cell growth 4-fold. Coexistence of L-azetidine 2-carboxylic acid (AzC) an inhibitor of collagen synthesis attenuated both effects of Asc 2-P in a dose-dependent manner. Supplementation of the medium with Asc 2-P also accelerated procollagen processing to collagen and deposition of collagen in the cell layer. Among the acidic glycosaminoglycans (GAG) another major component of extracellular matrix (ECM) deposition of sulfated forms was increased by the additive. Electron microscopic observations showed multilayered rough endoplasmic reticulum-rich cells surrounded by dense ECM. These results indicate that Asc 2-P is useful in culture systems as a long-acting vitamin C derivative and also that it promotes reorganization of a three-dimensional tissuelike substance from skin fibroblasts in culture by stimulating collagen accumulation in the fibroblasts.
We performed the quantitative and qualitative analysis on the main disaccharide units of glycosaminoglycans produced by human dermal fibroblasts in the 3-dimensional culture supplemented with L-ascorbic acid 2-phosphate (Asc 2-p) comparing with the monolayer culture system. The addition of Asc 2-p rendered fibroblasts to the organization of the dermis-like 3-dimensional structure in vitro without any pre-treatments with the plastic dish. Main disaccharide units were analyzed using HPLC after 1-phenyl-3-methyl-5-pyrasolone (PMP) labeling. The addition of Asc 2-p significantly increased the total amount of main disaccharide units and furthermore the composition revealed it to be more similar to that of the dermis. This 3-dimensional culture may offer a simple and useful system to investigate the glycosaminoglycan metabolism of human dermal fibroblasts in vitro.
Chemical and Biological Properties of Vitamin C:
L-ascorbic acid or vitamin C (CAS #: [50-81-7]; MW=176.1; mp=193°C [dec]) is a natural compound whose peculiar antioxidant properties are used in biological systems and for the conservation of several different manufacts (1).
Fig. 1 - CPK model of L-ascorbic acid (carbons oxygens and hydrogens are indicated blue green and yellow circles respectively).
The ascorbic acid molecule (see Fig. 1) contains four hydroxyl groups in positions 2 3 5 and 6; the -OH group in position 3 is acidic (pKa3=4.2) the hydroxyl in position 2 has pKa2=11.6 while those in position 5 and 6 behave as a secondary and primary alcoholic residue respectively (2).
The next figure illustrates the tautomeric equilibrium (see Fig. 2) where the C1=O and C3-OH groups interchange with the shift of the double bond.
Fig. 2 - Tautomeric equilibrium in L-ascorbic acid
Vitamin C is very sensitive to even slight heating to the light and to the action of oxidizing agents and metal ions.Vitamin C is readily oxidized especially in aqueous solutions by reacting with atmospheric oxygen and behaves as a two-electron donor:
Fig. 3 - Oxidation of L-ascorbic acid
Fig. 4 - Some ascorbic acid derivatives; R can be a fully saturated or unsaturated chain with a number of carbons ranging between 6 and 18.
Fig.10 shows that ascorbic acid esters incorporated into phospholipid vesicles (liposomes) significantly suppress the oxidation of the unsaturated components and produce an induction period after which the peroxidation proceeds with the same slope as in the absence of the radical scavenger .
The hydroxyls (OH) next to the bottom double bond are enols. One enol loses an electron pair becoming an oxonium group (=OH2 ) by creating a double bond to the carbon.
Movement of electron pairs in deprotonationSimultaneously the carbon-carbon bottom double bond (between the enols) transfers its bottom electrons to form a double bond to the next (two-oxygen) carbon. To give way the double bond electrons of the carbonyl are received by the carbonyl's oxygen to produce an enolate. The oxonium promptly deprotonates to produce a carbonyl and this loss of protons gives ascorbic acid its acidity. The overall reaction is enol deprotonation to produce an enolate where the negative charge of the resulting enolate counterion is delocalized over the system of carbonyl (C=O) and the double bond (C=C). This delocalization makes the counterion more stable and less likely to regain the proton.
Movement of electron pairs in deprotonation
It is interesting to note that ascorbic acid 6-O-alkanoyl-ascorbic acids (A thru F) and 56-octylidene-ascorbic acid (L) possess more or less the same reducing activity as determined with this colorimetric method. Their radical scavenging performances are comparable or even larger than those of some natural products such as tocopherol (K) caffeic acid and some components of naturali olive oils. Furthermore it is important to observe that the most active natural products possess two OH phenolic groups in position orto: this chemical structure can be easily compared to the presence of the two OH groups in ascorbic acid on both sides of the double bond. The two-headed derivatives (G thru J) show an almost negligible activity as well as the fluorinated compounds (M).
Ascorbic acid also rapidly inconverts into two unstable diketone tautomers by proton transfer although it is the most stable in the enol form. The proton of the enol is lost and reacquired by electrons from the double bond to produce a diketone. There are two possible forms 12-diketone and 13-diketone.
L-Ascorbic acid phosphate magnesium salt n-hydrate (APMg):
For several years Ascorbic acid and its fatty acid esters such as monostearate and dipalmitate have been used as an ingredient in cosmetics to prevent chloasma or freckles. Unfortunately the water in cosmetics deteriorates these ascorbates.
L-Ascorbic acid phosphte magnesium salt n-hydrate (APMg) is very stable in cream and lotion and is easily absorbed into the skin.
This high quality Vitamin-C derivative is now available from Wako and can be used in your new skin-lightening cosmetics.
1. Chemical structure
1. Easily soluble in waterinsoluble in organic solvents
2. Stable in cosmetics
3. Excellent absorption into the skin
4. After absorption into the skin APMg quickly turns to Vitamin C
and suppresses the skin pigmenting action by melanin.
pH (3% w/v % in water)
: 7.0 - 8.0
: max. 1 %
: max. 0.21 %
other sacorbate derivatives
: max. 3.5 %
: max. 20 ppm
: max. 2.5 %
: max. 2 ppm
: max. 29.0 %
free ascorbic acid
: max. 0.5 %
: min. 95.0 %