DEVELOPMENTS IN THE CHEMISTRY OF VITAMINS
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III. VITAMIN B 2
While synthesis had satisfactorily settled the identity of vitamin B 1 , vitamin
B 2 appeared to be made up of at least two major components which produced
different physiological effects, one having the power to prevent or cure the cessa-
tion of growth while the other affected the peculiar disease known as pellagra.
While these two factors occur associated together in the natural vitamin B 2 con-
centrate and are difficult to separate, the important discovery has been made in
the course of the last three years that the growth-promoting factor of vitamin B 2
belonged to a class of yellow-colouring matters called "flavins," a number of which
has been isolated from different sources, e.g., egg-white (ovoflavin), whey (lacto-
flavin), liver (hepatoflavin), kidneys (renoflavin), and even urine (uroflavin), which
were all very similar in properties, displaying a strong yellowish green flourescence
in aqueous solutions and being generally stable towards mineral acids and oxidis-
ing agents but decomposed by alkalis and by irradiation. The crystalline orange-
brown lactoflavin obtained by Kuhn from whey (nearly 1 grm. from 5,400 litres)
which represented the most active preparation of the growth-promoting factor of
vitamin B 2 had been intensively studied during the last year leading to important
developments taking place in the chemistry of these flavins. The investigation
of the products obtained by the irradiation of lactoflavin in alkaline and alcoholic
solution was followed by the recognition of these bodies as alloxazine derivatives and
the establishment of their constitutional formulae by syntheses. From these de-
compositions a complete picture of the structure of lactoflavin was deduced, a
pentose chain being considered on chemical grounds to be attached to the position
9 in the alloxazine ring.
The immediate outcome of these researches was the identification of the
natural lactoflavin with 6, 7-dimethyl-9, d-ribo-flavin by the exhaustive study of
the chemical and biological properties of all the eight possible stereo-isomeric
pentose-flavins which had been synthesised. The excellent yields of these products
obtained by Kuhn and his collaborators by their processes of synthesis and the
strong growth-promoting actions of both the 6, 7-dimethyl and the 7-methyl-9,
d-ribo-alloxazines encourage the hope that these would be available in quantity
for medical practice in the near future. The interesting discovery of the new
yellow-oxidation enzyme in yeast juice by Warburg and Christian has now been
proved to be made up of lactoflavin phosphoric ester associated, with a protein,
the growth-promoting factor of vitamin B 2 , thus becoming the prosthetic group
in Warburg's oxidation enzyme. It is highly important to know this relationship
for a proper understanding of the physiology of vitamin B 2 action, inasmuch as
it appears to indicate that this vitamin is needed for the elaboration of an essential
enzyme concerned with biological oxidations, which the animal organism by it-
self is incapable of synthesizing.
With regard to the other factor of the " B 2 complex ", namely, the anti-pellagra
or the anti-dermatitis component, very little is known as yet about its chemical