O. Isler

Chemistry and Biochemistry of the K Vitamins

Publisher Summary The elucidation of the chemical basis of the K vitamins is because of the schools of Dam, Doisy, and Karrer, who succeeded in 1939 in isolating two pure compounds with vitamin K activity, namely vitamin K 1 (I) from alfalfa and vitamin K 2 (II) from putrefied fish meal. The structure of vitamin K 1 was proved by oxidative degradation and by synthesis to be 2-methyl-3-phytyl-1, 4-naphthoquinone, the side chain consisting of four isoprene units (4 ×5 = 20 C-atoms). It had been established that vitamin K 2 contains the same ring system with a longer and more unsaturated side chain. This chapter summarizes the progress in chemistry and biochemistry of the naturally occurring K vitamins and their close analogs. In addition, the chapter reviews the observed differences in action between K vitamins and menadione and an attempt is made to explain them on biogenetic considerations.

Chemistry of Vitamin E

Publisher Summary Vitamin E occurs in vegetable oils and acts as a biological antioxidant. It is distributed throughout the tissues of animals and man, and its deficiency causes a variety of syndromes in the animal organism. This chapter shows the preferred routes to specific labelings of vitamin E and has indicated the chemical research that is necessary for getting a final stereochemical insight into the tocopherol molecules. Similar investigations on related natural chromanols and ohromenols might help to elucidate their mutual biogenetic relationship. Furthermore, the reported chemical interconversions of trimethylphytylbenzoquinone into either α-tocopherol or 3,4-dehydro-α-tocopherol may indicate some biological interrelations, which might also be common to the related natural quinones, chromanols, and chromenols listed in this chapter.

Syntheses of vitamins K and related compounds with special reference to labeling.

Publisher Summary This chapter describes the structural relationships within a group of quinones widely distributed in nature and the art of building up these and similar structures in the laboratory. As many of these procedures are readily adaptable for tracer syntheses, they allow the preparation of molecules labeled at different sites and with different isotopes, thus providing useful tools for biochemical and pharmacological research. The biochemically important vitamins K, the ubiquinones, plastoquinones, and tocoquinones, comprise a series of naphtho- and benzo-quinone derivatives bearing an unsaturated side chain of several isoprene units that are linked together head to tail. The biologically important compounds of the ubiquinone and plastoquinone series are synthesized according to the methods discussed in the chapter. In addition, the conversion of quinones—for example, phylloquinone and ubiquirione-6—into the corresponding chroineriols without affecting the unsaturated side chain can be smoothly performed in boiling pyridine or with sodium hydride.

The Synthesis and Labeling of Vitamin A and Related Compounds

Publisher Summary Ever since the elucidation of the structure of vitamin A by Karrer, the synthesis of this rather unstable pentaene alcohol has been a challenge to chemists. Owing to patient and continuous efforts in many laboratories, there seems to be today an excellent picture of the possible synthetic routes to vitamin A. Although a wealth of information has been gathered on its synthesis, relatively little is known about the functions of vitamin A in the body. Knowledge on this subject broadened beginning with the advent of radioactive tracer methods. It therefore seems justified to take stock of the synthetic methods available, and to examine them as to their usefulness for the preparation of selectively labeled vitamin A compounds. These compounds will undoubtedly help the biochemists in their patient and often laborious investigations of the biological pathways that vitamin A and certain related compounds seem to control.

Total syntheses of carotenoids.

Publisher Summary Carotenoids occur universally in animals and plants and contribute to a large extent to the red and yellow coloring matter in foodstuffs. β-Carotene, one of the commonest natural pigments, is converted into vitamin A in the animal body. The close chemical relationship of vitamin A to the carotenoids is realized vitamin A is regarded as consisting of one-half of β-carotene plus the elements of water, and this relationship has been proved biologically by the transformation of β-carotene into vitamin A on passing through the intestinal wall. Many carotenoids can function as provitamin A, and it would appear that all vitamin A is formed from these substances. While oxidation of the central bond of the polyene system of carotenoids may lead to vitamin A, terminal oxidation gives carboxylic acids such as bixin and crocetin. By virtue of their closely related structures, it was obvious that, the same intermediaries could be used for the syntheses of vitamin A and carotenoids. The chapter summarizes total syntheses of carotenoids up to 1956.