The chemical nature of vitamin C

Abstract

HEXURONIc acid was discovered [1927] and isolated from plants and the adrenal cortex [1928] by Szent-Gyorgyi at the Biochemical Laboratory, Cambridge, and was investigated in regard to its function and chemistry [1928, 1930, 1931].Its chemical configuration has been studied by Haworth, Hirst and Reynolds [1932].The striking similarity of this substance with vitamin C was evident from the beginning.As far as it is known, its distribution in plants closely follows the distribution of the vitamin.The chemical properties of both substances agree and both are biologically active in minute quantities.As is known, hexuronic acid has strongly reducing properties and the reducing power of many plant extracts is mainly due to this substance.The close relation between vitamin content and reducing power has been empha- sised by Tillmans et al. [1932], whose careful work strongly suggested that the reducing power of plant extracts was in part due to the vitamin itself, which was identical with hexuronic acid.Tillmans and his co-workers claim to have shown that the vitamin content and the reducing capacity run on strictly parallel lines under many conditions.Furthermore they have shown that the reducing factor can be oxidised in two different ways, reversibly and irreversibly.They have succeeded in re- versing the oxidation of the reversible type by the application of reducing agents such as H2S.They observed that by the reversible oxidation the reducing factor becomes very labile and prone to undergo irreversible changes.The vitamin showed a closely analogous behaviour.On treatment with oxidis- ing agents, which produce a reversible oxidation of the reducing factor, the vitamin did not lose its activity, but became very labile.Tillmans and his collaborators were led to the conclusion that the reducing factor and the vitamin were in fact identical.As is known, hexuronic acid can be oxidised reversibly and irreversibly, the reversible form being readily again reduced by H2S.The agents reported by Tillmans to produce a reversible change in reducing factor also oxidise hexuronic acid reversibly.Agents, such as molecular oxygen, which produce an irreversible change in the reducing factor, also destroy hexuronic acid.