| Polyhydroxysterols from natural marine products plays important roles in new-drug discovery and development due to their novel structure and bioactivities. The aim of this dissertation is to concisely and highly efficient construct 24-homo-?24(28)-steroidal sidechain from cholanate acid and synthesize the natural marine product--24-homo-?24(28)-cholesten- 3β,5α,6β-triol from hyodeoxycholic and asymmetric synthesis of 24R,28-dihydroxysteroids and 24S,28-dihydroxysteroids by Sharpless catalytic asymmetric dihydroxylation using 24-homo-?24(28)-steroids as substrates.First of all, 24-homo-?24(28)-steroids were synthesized in a yield of 70%~85% by Et3N-chelated TMEDA-assisted isopropylation from a variety of methyl cholanate and Wittig olefination.Secondly, the natural marine product--24-homo-?24(28)-cholestan-3β,5α,6β-triol was synthesized in 7 steps with a total yield of 53% using methyl hyodeoxycholanate as the starting material, 3β-(tetrahy-dropyran-2-yloxy)-cholest-5-ene-24-one as the key intermediate and Grignard isopropylation as the key step.Finally, 24R,28-dihydroxysteroids 24S,28-dihydroxysteroids was synthesized by using improved Sharpless catalytic asymmetric dihydroxylation.In summary, 24-homo-?24(28)-steroids were synthesized in two steps from methyl cholanate utilizing the intact sidechain of methyl cholanate. In the base of it, 24- homo-?24(28)- cholesten-3β,5α,6β-triol and 24R,28-dihydroxysteroids 24S,28-dihydroxysteroids were synthesized concisely and efficiently. |
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