Tritiated retinaldehydes

Labeling with tritium in position 15 could easily be accomplished by reduction of retinaldehyde with sodium borotritide (Mayer and Isler, 1971) or of retinoic acid esters with lithium aluminum tritide, and, again, oxidation of the tritiated retinol (Kaegi et aL, 1982c) to retinaldehyde-15- H. Because of the favorable isotope effect, most of the isotope should stay attached to the aldehyde group. However, Futterman et aL (1979) found that all-frany-retinaldehyde-15- H is inadequate as a tracer for 11-c/y-retinaldehyde formation in a biological system. 

In general, recrystallization (when feasible) is the best method of purifying radiolabeled retinoids. Perry et aL (1982) found that when all-tran -retinoic acid was tritiated at very high specific activity, it had to be extensively purified by repeated recrystallization before it could be stored for any period of time. On the other hand, tritiated all-rran -retinaldehyde could not be obtained isomerically pure by recrystallization alone (Kaegi et aL, 1982a). 

---