Fig. 1.

Structures and receptor specificities of heteroarotinoids. Heteroarotinoids are a class of retinoids that exhibit decreased toxicity in animal models due to the insertion of a heteroatom in the cyclic ring of the arotinoid structure. Specific structural alterations of the heteroarotinoid structure have been shown to alter the receptor specificities of the compounds. The synthesis and receptor specificity of each heteroarotinoid indicated here was described previously as follows. SHet100 (previously compound 18; ref. 31) activates all RARs in the nanomolar range but does not activate RXRs up to 10 μM. OHet72 (previously compound 6; ref. 32) activates RXRs in the nanomolar range but is inactive with RARs up to 10 μM. SHetA2 does not activate either RARs or RXRs (33).