Riboflavin pigments from

More than one century ago a yellow, fluorescent pigment was isolated from whey by Blyth In the subsequent years yellow pigments were extracted from various biological materials. Depending either on the source of isolation or the physical appearance, these natural products were named e.g. lactochrome , lycochrome , ovoflavin , lactoflavin , hepatoflavin , or verdoflavin . Later, it became evident that all these compounds are riboflavin (vitamin B2). 

Although crystalline riboflavin was not isolated until 1931 interest in this compound as a pigment dates back to 1881 in connection with the color in the whey of milk. In 19.31 riboflavin was isolated as a coenzyme-en/.yme complex from yeast by Warburg and Christian and was designated yeiioiv oxidation ferment. 

Apart from the derivatives of p-carotene, other pigments are the anthocyanins, the chlorophylls, cochineal, the betalaines, turmeric, caramel and riboflavin. In this account the historical background in brief, the chemistry of these pigments, their extraction from natural sources and their synthesis will be discussed. The present permitted natural substances and nature-identical synthetic materials (also described by the Food and Drugs Administration, the FDA, as colorants exempt from certification ) is quite small in number. Reference is also made to colourants no longer listed but which have an historical organic chemical significance such as for example brazilin and its relative haematoxylin. 

From certain higher fungi, e.g., Russula sp. pteridine pigments as well as fluorescent pteridines were isolated, which are closely related to riboflavin. Some of the russopteridines are represented by the following formulas ... 

More than 100 years ago a fluorescent compound was isolated first fi om whey, and later from different biological materials. When it Ijecame clear that the isolated yellow pigments, named lactochrome, ovoflavin, or lactoflavin, had a common structure, the new compound was named riboflavin (vitamin B2) (for historical review see 2). In the years between 1933 and 1935 the structure and the main chemical reactions of riboflavin were studied and the chemical synthesis was performed. Soon afterward, the coenzyme forms, flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), were isolated in pure form, and the structures were determined. In the last 50 years many flavoproteins were isolated and their physicochemical properties were studied. Succinate dehydrogenase was the first enzyme found with the prosthetic group (FAD) covalently bound to the protein. About 20 flavoproteins are now known to contain covalently bound coenzyme (mainly via carbon atom 8a) (3). In mammalian tissue, the number of covalently bound flavoproteins appears to be limited. 

Numerous flavins (and flavoproteins) that are derived from isoal-loxazine (9-58) are also biologically significant pigments. The most important representative of this group of pigments is riboflavin (vitamin B2), which is also used as a yellow food pigment. 

Among the lutrogen-containing derivatives isolated from polychaetes there is a series of pteridines derived from lumazin and thus related to vitamin B2 (riboflavin). Recall that some of the pteridine derivatives provide the white, yellow, orange and red pigments of the wings of butterflies and other insects. Biopterin is also a constituent of the royal jelly of bees. 

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