Radiolabeled Analogs

The recent advances in vitamin D metabolism and mode of action can be directly attributed to the synthesis of radiolabeled vitamin D derivatives of high specific activity. 

Original syntheses employed catalytic reduction of an appropriate 1,2-steroidal olefin with tritium gas and produced H-vitamin D3 of moderate specific activity (5—10 Ci/mmole) Analogs of higher specific activity (20-80 Ci/mmole) can 

Another convenient synthesis of radiolabeled vitamin D has involved exchange in TjO and reduction with NaBT4 of the 3-keto vitamin analog in which the triene has been reversibly protected as an iron carbonyl adduct [scheme (36)] (S. Yamada, H. K. Schnoes, and H. F. DeLuca, unpublished results). 

Even though synthetic vitamin D chemistry had its origins a half century ago, only now is the field beginning to develop with the innovative character apparent in other areas of organic chemistry. The organic chemist confronted with work in this area should always look forward to integrating new techniques and concepts in this well-established field. 

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Preparation of Labeled (9Z,11E) CLA Metabolites. Recently, [l- " C]-radiolabeled analogs of (6Z,9Z,ll )-octadecatrienoic and (8Z,llZ,13 )-eicosatrienoic acids, two metabolites of (9Z,11 ) CLA isomer, were obtained stereoselectively by Gnadig and co-workers (24). These syntheses were carried out using combinations of Wittig-type reactions as shown in Figure 6.7. 

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