Synthesis and in vitro biological activity of 4 alpha-(2-propenyl)-5 alpha-cholest-24-en-3 alpha-ol: A 24,25-dehydro analog of the hypocholesterolemic agent 4 alpha-(2-propenyl)-5 alpha-cholestan-3 alpha-ol

4 alpha-(2-Propenyl)-5 alpha-cholestan-3 alpha-ol (LY295427) was previously identified from a Chinese hamster ovary (CHO) cell-based low density lipop rotein receptor/luciferase (LDLR/Luc) assay to be a potent transcriptional activator of the LDL receptor promoter in the presence of 25-hydroxycholest erol. To investigate the effect of the 24,25-unsaturation in the D-ring sid e chain (desmosterol D-ring side chain) on antagonizing the repressing effe ct of 25-hydroxycholesterol, 4 alpha-(2-propenyl)-5 alpha-cholest-24-en-3 a lpha-ol (17), a 24,25-dehydro analog of LY295427, was thus synthesized from lithocholic acid via the formation of 3 alpha-[[(1,1-dimethylethyl)dimethy lsilyl] oxy]-4 alpha-(2-propenyl)-5 alpha-cholan-24-al (15). Test results s howed that 17 had an EC30 value of 2.6 mu M, comparable to 2.9 mu m of LY29 5427, in the CHO cell-based LDLR/Luc assay in the presence of 25-hydroxycho lesterol. Apparently, the built-in 24,25-unsaturation in the D-ring side ch ain of 17 had added little effect to antagonizing the repressing effect of 25-hydroxycholesterol. In the [1-C-14-acetate]cholesterol biosynthesis inhi bition assay, 17 at 10 mu g/ml (23 mu M) has been shown to inhibit the chol esterol biosynthesis in CHO cells by 38% relative to the vehicle control; w hereas LY295427 showed no inhibition in the same assay in our previous stud ies. In contrast to LY295427, the built-in 24,25-unsaturation in the D-ring side chain of 17 has conferred an inhibitory effect on cholesterol biosynt hesis in CHO cells. In summary, the observed LDL receptor promoter activity of 17 is related to its ability to prevent 25-hydroxycholesterol from exer ting the repressing effect via an undetermined mechanism and, in part, to i nhibit the cholesterol biosynthesis. (C) 1999 Elsevier Science Inc. All rig hts reserved.