Vitamin labeled, preparation

Specifications and standards for various vitamin E forms and preparations for use in pharmaceutical appHcations ate given in the United States Pharmacopeia (52). AH products should contain not less than 96.0% or more than 102.0% of the appropriate form. The products must be labeled to indicate both the chemical and stereochemical forms contained in the product. 

Label claims for tocopherol levels in preparations can be based on milligrams or International Units. Only the RRR or all-rac-International Units ate also used in some reference books and compendia, eg. Food Chemicals Codex (40,53), which is of particular importance for specifications for food fortification. 

Vitamin B12s reacts rapidly with alkyl iodides (e.g., methyl iodide or a 5 -chloro derivative of adenosine) via nucleophilic displacement to form the alkyl cobalt forms of vitamin B12 (Eq. 16-31). These reactions provide a convenient way of preparing isotopically labeled alkyl cobalamins, including those selectively... 

A control diet was prepared as follows Tha labelled egg-white protein was mixed with a basal diet in the proportion 2 98. The basal diet contained 10% casein, 10% sucrose, about 70% starch and 5% maizeoil, as well as vitamins and minerals. A small amount of [sHl-lysine was added to this mixture, giving a ratio of tritium to (11 C) dpm of approximately 10 1. The experimental diet was obtained by adding a small amount ot the glucose-lysine reaction mixture to the control diet. 

The 5,6-O-isopropylidene acetal (152) of L-ascorbic acid has been prepared,340 and von Schuching and Frye341 prepared the corresponding cyclohexylidene acetal. These compounds were found to be more resistant than L-ascorbic acid toward oxidation, and the parent acid can be readily regenerated by acid hydrolysis. The derivative was used in the synthesis of 14C-labeled vitamin C. The C-2 and C-3 enols of L-ascorbic acid or its acetone derivative (152) can be readily methylated with diazomethane, yielding the corresponding dimethoxy analogues. 

The nitroxidc (IV) (see Section I) was used as a spin label in connection with a study relevant to vitamin B12 coenzyme, which is of type Co (III)—R (R = 5 -deoxyadenosyl) and thus an analog of IV, but with a different axial group R (193). Compound (IV), which we may abbreviate Co(III) — R, was prepared from a Co(I) precursor Bi2s and R Br, and was found to bind to the enzyme ethanolaminc-ammonia-lyase (in this system ethanol-amine is converted to acetaldehyde). By ESR it was concluded that the active site is relatively close to the enzyme surface (sec also Section V,B). 

Discrimination among all of these is a trivial exercise. Both B vitamins and C were easily quantitated in prepared mixtures as expected [59], but it was also relatively easy to measure each one after its simple extraction into aqueous buffer from pharmaceutical preparations, as well as (in the case of vitamin C) from extracts of fruit, fruit juices, and vegetables. A very thorough inventory of tests for possible interferences was run and the resultant analytical data for the vitamins compared extremely well with the labelled contents on the packages of pharmaceutical products and with the data in compendia that list the average compositions of vitamins and other essential products in plant food materials [33]. Analysis of the major fat soluble D2 and D3 vitamins (ergocalciferol and cholecalciferol) has not progressed with the... 

The RIA described below is more convenient than the RRA for 1,25(0H)2D because a radioiodinated tracer eliminates the need for liquid scintillation, and the antiserum eliminates the need to prepare VDR from calf thymus. The RIA uses a previously developed antiserum with 1% to 2% cross-reactivity with the more abundant, non-1-hydroxylated vitamin D metabolites and a I-labeled tracer prepared from l,25(OH)2-24,25,26,27, tetranor-... 

I- cis- and 7,13-di-ciy-isomers of vitamin A [retinol (91)] have been prepared via the 1-cis photoisomerization product of the sulphone (94).62 Several isotopically labelled species of retinaldehyde and derivatives have been synthesized, including... 

More C-methylations follow this first one and the research during this period also set in place the next three intermediates beyond uro gen III 10 en route to vitamin B12 4, Scheme 18 [1,28,77,78]. They are precorrin-1 53 (or a tautomer of this structure), precorrin-2 12 and precorrin-3A 55 they can be seen as the mono-, di- and tri-methylation products of uro gen III 10, Scheme 18. The figures after the name precorrin correspond to the number of C-methyl groups introduced into uro gen III from SAM to generate that intermediate the reason for using 3A rather than just 3 will become clear later. When labelled forms of precorrin-2 12 and precorrin-3A 55 were incubated with a crude cell-free enzyme preparation from Pr. shermanii, they were converted into cobyrinic acid 58, a late precursor of vitamin B1 [ 1,28,11,78]. 

Despite large efforts to isolate new intermediates from Pr. shermanii lying beyond precorrin-3 A 55 on the pathway to B12, none were found. Also, following the approaches (i)-(iv) above, some putative later intermediates were prepared in labelled form but were found not to act as precursors of vitamin Bjj. It was clear that there were simply too many possible ways for the true pathway to go forward from precorrin-3A 55 to make this a realistic approach. A fresh approach was needed and the way the rapid advances over the past decade or so were achieved will be described in the remainder of this chapter. 

In 1963 radioactive vitamin D of high specific activity was successfully synthesized chemically This preparation was labelled in the 1 and 2 positions and pro-... 

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