Synthesis and in vitro biological activity of 4alpha-(2-propenyl)-5alpha-cholest-24-en-3alpha,12 alpha-diol, a 12alpha-hydroxyl analog of 4alpha-(2-propenyl)-5alpha-cholest-24-en-3alpha-ol: the latter is a potent activator of the low-density lipoprotein receptor promoter.

4alpha-(2-Propenyl)-5alpha-cholest-24-en-3alpha-ol (3) was shown recently in a Chinese hamster ovary (CHO) cell-based low-density lipoprotein receptor/luciferase (LDLR/Luc) assay to be a potent transcriptional activator of the LDL receptor promoter in the presence of 25-hydroxycholesterol. Because of the involvement of 12alpha-hydroxylation in the metabolism of cholesterol, we are interested in investigating the effect of introducing a 12alpha-hydroxyl group to 3 on the transcriptional activity of the LDL receptor promoter. Thus 4alpha-(2-propenyl)-5alpha-cholest-24-en-3alpha,12a lpha-diol (14), a 12alpha-hydroxyl analog of 3, was synthesized from deoxycholic acid via the formation of 12alpha-[[(tertbutyl)dimethylsilyl]oxy]-4alpha-( 2-propenyl)-5alpha-cholest-24-en-3-one (11). Test results show that 14 is inactive at concentrations of up to 20 microg/ml, compared to 3 with an EC30 value of 2.6 microM, in the CHO cell-based LDLR/Luc assay. Apparently introduction of a 12alpha-hydroxyl group abolishes the capability of 3alpha-sterol 14 to activate the transcription of the LDL receptor promoter. However, in the [1-14C-acetate]cholesterol biosynthesis inhibition assay in CHO cells, 14 at 10 microg/ml (23 microM) is shown to inhibit the cholesterol biosynthesis by 51% relative to the control cells. Our previous studies indicated that 3 showed a 38% inhibition, but 4alpha-(2-propenyl)-5alpha-cholestan-3alpha-ol (1) exhibited no inhibition in the same assay at 10 microg/ml. In summary the results indicate that, in addition to the 24,25-unsaturation, the 12alpha-hydroxyl group in 14 has also conferred an inhibitory effect on cholesterol biosynthesis in CHO cells; however, the inhibition of cholesterol biosynthesis by 14 does not lead to the transcriptional activation of the LDL receptor promoter.