Vitamins optical rotation

No racemization was observed when the electrode potential was scanned only to a value where the dianion is formed. Upon formation of the tetraanion, subsequent chemical reactions were found. With a slightly different electrolyte salt (Mc4NBF4 instead of BU4NF6), reversibility without racemization was found even up to the tetraanion formation. Further examples include the spectroelectrochemistry of vitamin D2 [139], which has been studied with a long pathlength cell similar to the design described by Zak et al. [44]. Optical rotary dispersion and CD of optically active polybithiophene that has been electropolymerized in a cholesteric electrolyte have been studied [140]. The optical rotation of this chiral polymer could be controlled via the electrode potential. 

Vitamin Ki isolated from natural sources has a very low optical rotation which can be interpreted theoretically (Beredjick and Schiirch, 1957). 

Thus, D (—) aldopentose is the five-carbon laevo-rotatory sugar derived from d (-f) glycerose L (+) ascorbic acid is the vitamin derived from Z (—) glycerose. It will be noticed that the direction of optical rotation of the derivatives is not necessarily the same as that of the parent compound. 

Figure 13 shows the structure and absolute configuration of (2R,3S)-(-) vitamin K3 epoxide. This epoxide, prepared in optically active form by us (70) in 1976, had been known as a racemate since 1939 (78). It has recently been implicated (79) in prothrombin biosynthesis (80). The absolute configuration as shown in Figure 13 is based on the work of Snatzke (76) and the absolute rotation is [ ]436 = — 124° (acetone) and [a] = 0° ( ) (acetone). 

Vitamin K2 compounds have about 75% of the potency of Kj and are synthesized by bacteria in the intestinal tract of humans and various animals. This vitamin can also be found in putrefied fish meat. Compounds of this family differ from phylloquinone in the number of isoprene units in the side chain and also in the degree of their unsaturation. Hence, the general term applied to them is menaquino-nes (Figure 7.5). Unlike vitamin Kj they are not capable of optical light rotation however, maximum activity was observed for the trans configuration of the side-chain double bonds. 

The rotation of vitamin Ki thesdzed from natural phytol was found to be = —0.71 st 0.02°, the determination being performed on the un-dflutid oily compound using sodium li t. Vitamin Ki from isophytol shows no rotation as, so far, only racemic isophytol has been produced by total [ thesis. The compounds of the Ki series have no optical activity. 

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