Synthesis of polyhydroxysterols (I): synthesis of 24-methylenecholest-4-en-3beta,6beta-diol, a cytotoxic natural hydroxylated sterol

A decade of lessons in the activation of ArIL2 species

Hypervalent iodine(iii) compounds of the general structure ArIL2 are widely used as oxidizing agents for a variety of applications across both organic and inorganic chemistry. Considerable work has been done on the activation of these compounds by tuning the ligands at the iodine centre. This perspective summarises the work of our and other groups on rectification of historically misidentified iodine(iii) reagents of this class, and the syntheses of activated species. Recent advances focusing on increasing the oxidative capacity of I(iii) moieties using Lewis and Brønsted acids and Lewis bases as well as the activation of halogens with I(iii) are discussed.

Synthesis and antitumor activity of some cholesterol-based selenocyanate compounds

The introduction of selenium-containing functional groups into steroids to study the biological activities of related derivatives is rarely reported in the literature. In the present study, using cholesterol as raw material, four cholesterol-3-selenocyanoates and eight B-norcholesterol selenocyanate derivatives were synthesized, respectively. The structures of the compounds were characterized by NMR and MS. The results of the in vitro antiproliferative activity test showed that the cholesterol-3-selenocyanoate derivatives did not exhibit obvious inhibitory on the tested tumor cell lines. However, the B-norcholesterol selenocyanate derivatives obtained by structural modification of cholesterol showed good inhibitory activity against the proliferation of tumor cell. Among them, compounds 9b-c, 9f and 12 showed similar inhibitory activity against tested tumor cells as positive control 2-methoxyestradiol, and better than Abiraterone. At the same time, these B-norcholesterol selenocyanate derivatives displayed a strong selective inhibitory against Sk-Ov-3 cell line. Except for compound 9g, the IC₅₀ value of all B-norcholesterol selenocyanate compounds against Sk-Ov-3 cells was less than 10 µM, and compound 9d was 3.4 µM. In addition, Annexin V-FITC/PI double staining was used to analyze the cell death mechanism. The results showed that compound 9c could induce Sk-Ov-3 cells to enter programmed apoptosis in a dose-dependent manner. Furthermore, the in vivo antitumor experiments of compound 9f against zebrafish xenograft tumor showed that 9f displayed obvious inhibitory effect on the growth of human cervical cancer (HeLa) xenograft tumor in zebrafish. Our results provide new thinking for the study of such compounds as new antitumor drugs.

On the potential intermediacy of PhIBr2 as a brominating agent

PhIBr2 has been invoked as a brominating agent, however PhIBr2 does not appear to exist but rather forms PhI and Br2, with Br2 being responsible for bromination.

Synthesis and cytotoxicity of A-homo-lactam derivatives of cholic acid and 7-deoxycholic acid

Using cholic acid and deoxycholic acid as starting materials, a series of 3-aza-A-homo-4-one bile acid and 7-deoxycholic acid derivatives were synthesized by the esterification, oxidation, reduction, oximation and Beckman rearrangement etc. The cytotoxicity of the synthesized compounds against MGC 7901 (human ventriculi carcinoma cell line), hela (human cervical carcinoma cell line), SMMC 7404 (human liver carcinoma cell line) were investigated. The results showed that bile acid and 7-deoxycholic-acid derivatives with 3-aza-A-homo-4-one configuration bearing a 6-hydroximino or 12-hydroximino group displayed a distinct cytotoxicity to Hela tumor cell line. In particular, the IC(50) values of the compounds 6 and 13 were 14.3 and 24.3 μmol/L against Hela human tumor cell line respectively. The information obtained from the studies may be useful for the design of novel chemotherapeutic drugs.

Cytotoxic derivatives of (22R,23R)-dihydroxystigmastane

(22R,23R)-22,23-dihydroxystigmast-4-en-3-one, (22R,23R)-22,23-dihydroxystigmast-4-en-3,6-dione, (22R,23R)-3beta,5alpha,6beta,22,23-pentahydroxystigmastane, (22R,23R)-5alpha,6alpha-oxido-3beta,22,23-trihydroxystigmastane, (22R,23R)-5beta,6beta-oxido-3beta,22,23-trihydroxystigmastane, and (22R,23R)-3beta,6beta,22,23-tetrahydroxystigmast-4-ene were synthesized. Their cytotoxicities were comparatively studied using the MCF-7 line of carcinoma cells of human mammary gland and cells of human hepatoma of the Hep G2 line.

Chemoselective reduction of 1,4,6-cholestatrien-3-one and 1,4,6-androstatriene-3,17-dione by various hydride reagents

The chemoselectivity of rigid cyclic alpha,beta-unsaturated carbonyl group on the reducing agents was influenced by the ring size and steric factor. Cholesterol (cholest-5-en-3beta-ol) and dehydroepiandrosterone (DHEA) were oxidized with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone to form 1,4,6-cholestatrien-3-one and 1,4,6-androstatriene-3,17-dione. They were reduced with NaBH(4), lithium tri-sec-butylborohydride (l-Selectride), LiAlH(4), 9-borabicyclo[3.3.1]nonane (9-BBN), lithium triethylborohydride (Super-hydride), and BH(3) x (CH(3))(2)S in various conditions, respectively. Reduction of 1,4,6-cholestatrien-3-one and 1,4,6-androstatriene-3,17-dione by NaBH(4) (4 equiv.) produced 4,6-cholestadien-3beta-ol and 4,6-androstadiene-3beta,17beta-diol, respectively. Reduction by l-Selectride (12 equiv.) afforded 4,6-cholestadien-3alpha-ol and 4,6-androstadiene-3alpha,17beta-diol, chemoselectively. Reaction with Super-hydride (12 equiv.) produced 4,6-cholestadien-3-one and 3-oxo-4,6-androstadien-17beta-ol. Reduction of 1,4,6-cholestatrien-3-one by 9-BBN (14 equiv.) produced 1,4,6-cholestatrien-3alpha-ol, but 1,4,6-androstatriene-3,17-dione was not reacted with 9-BBN in the reaction conditions. Reaction of LiAlH(4) (6 equiv.) formed 4,6-cholestadien-3beta-ol and 3-oxo-1,4,6-androstatrien-17beta-ol. Reduction of 1,4,6-cholestatrien-3-one by BH(3) x (CH(3))(2)S (11 equiv.) gave cholestane as major compound and unlike reactivity of cholesterol, 1,4,6-androstatriene-3,17-dione by 8 equiv. of BH(3) x (CH(3))(2)S formed 3-oxo-1,4,6-androstatrien-17beta-ol. LiAlH(4) and BH(3) x (CH(3))(2)S showed relatively low chemoselectivity.

Epoxidation and reduction of DHEA, 1,4,6-androstatrien-3-one and 4,6-androstadien-3beta,17beta-diol

Dehydroepiandrosterone (DHEA) reacted with m-chloroperoxybenzoic acid (m-CPBA) to form 3β-hydroxy-5α,6α-epoxyandrostan-17-one (1), but it did not react with 30% H₂O₂. 1,4,6-Androstatrien-3,17-dione (2) was obtained from DHEA and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone in dioxane. Compound 2 was reacted with 30% H₂O₂ and 5% NaOH in methanol to give 1α,2α-epoxy-4,6-androstadien-3,17-dione (3), which was stereoselectively reduced with NaBH₄ to form 1α,2α-epoxy-4,6-androstadien-3β,17β-diol (7) and reacted with Li metal in absolute ethanol-tetrahydrofuran mixture to give 2-ethoxy-1,4,6-androstatrien-3,17-dione (8). Compound 2 was also epoxidized with m-CPBA in dichloromethane to afford 6α,7α-epoxy-1,4-androstadien-3,17-dione (4), which was reacted with NaBH₄ to synthesize 6α,7α-epoxy-4-androsten-3β,17β-diol (9). Compound 4 was reduced with Li metal in absolute ethanol-tetrahydrofuran mixture to form 7β-ethoxy-6α-hydroxy-1,4-androstadien-3,17-dione (10). Compound 2 was reduced with NaBH₄ in absolute ethanol to form 4,6-androstadien-3β,17β-diol (5), which was reacted with 30% H₂O₂ to give the original compound, but which reacted with m-CPBA to give 4β,5β-epoxy-6-androsten-3β,17β-diol (6).

Epoxidation and reduction of cholesterol, 1,4,6-cholestatrien-3-one and 4,6-cholestadien-3beta-ol

Many naturally occurring polyhydroxylated sterols and oxysterols exhibit potent biologic activities. This paper describes reagent and position selectivity of epoxidation and reduction of cholesterol derivatives. Cholesterol was reacted with m-chloroperoxybenzoic acid (m-CPBA) to form 5alpha,6alpha-epoxycholestan-3beta-ol, but in reaction with 30% H(2)O(2), it did not reacted. 1,4,6-cholestatrien-3-one was obtained from cholesterol and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone in dioxane. 1,4,6-cholestatrien-3-one was reacted with 30% H(2)O(2) and 5% NaOH in methanol to give 1alpha,2alpha-epoxy-4,6-cholestadien-3-one, which was stereoselectively reduced with NaBH(4) to form 1alpha,2alpha-epoxy-4,6-cholestadien-3beta-ol and reduced with Li metal in absolute ethanol to give 2-ethoxy-1,4,6-cholestatrien-3-one. And 1,4,6-cholestatrien-3-one was epoxidized with m-CPBA in dichloromethane to afford 6alpha,7alpha-epoxy-1,4-cholestadien-3-one, which was reacted with NaBH(4) to synthesize 6alpha-hydroxy-4-cholesten-3-one and reduced Li metal in absolute ethanol to form 2-ethoxy-1,4,6-cholestatrien-3-one, respectively. 1,4,6-cholestatrien-3-one was reduced with NaBH(4) in absolute ethanol to form 4,6-cholestadien-3beta-ol, which was reacted with 30% H(2)O(2) to leave original compound, but was reacted with m-CPBA to give 4beta,5beta-epoxy-6-cholesten-3beta-ol as the major product and 4beta,5beta-epoxy-6alpha,7alpha-epoxycholestan-3beta-ol as the minor product.

Synthesis of polyhydroxysterols (V): efficient and stereospecific synthesis of 24-methylene-cholest-5-ene-3beta,7alpha-diol and its C-7 epimer

This paper describes the efficient and stereospecific synthesis of cytotoxic dihydroxylated sterols, 24-methylene-cholest-5-ene-3beta,7alpha-diol 1, and its C-7 epimer, 24-methylene-cholest-5-ene-3beta,7beta-diol 2. The crux of the synthesis is that the selective allylic oxidation of 24-methylene-cholesteryl acetate proceeds to 24-methylene-7-keto-cholesteryl acetate without extensive byproduct formation from reaction at the Delta24(28) double bond. This methodology may be useful for the preparation of other oxysterols with non-standard side chains.

Synthesis of polyhydroxysterols (IV): synthesis of 24-methylene-cholesta-3beta,5alpha,6beta,19-tetrol, a cytotoxic natural hydroxylated sterol

The cytotoxic, polyhydroxylated sterol 24-methylene-cholesta-3beta,5alpha,6beta,19-tetrol (1), previously isolated from the soft corals Nephthea albida and N. tiexieral verseveldt, was synthesized using stigmasterol as the starting material by 10 steps in 9% overall yield. The spectral data and physical constants of 1 were identical with those of the natural product. This is the first report of the synthesis of 1.

Synthesis of polyhydroxysterols (III): synthesis and structural elucidation of 24-methylenecholest-4-en-3beta,6 alpha-diol

Using stigmasterol as the starting material, 24-methylenecholest-4-en-3beta,6 alpha-diol (2) was synthesized in eight steps in 13% overall yield. The introduction of the sterol side-chain was carried out using (3-methyl-2-oxobutyl)-triphenylarsonium bromide (11) and K(2)CO(3) in a solid-liquid phase-transfer Wittig reaction. Construction of the steroidal nucleus was finished by oxidation of 24-methylenecholest-5-en-3beta-ol (9) with pyridinium chlorochromate (PCC) in dichloromethane at ambient temperature and by reduction of 24-methylenecholest-4-en-3,6-dione (10) with NaBH(4) in the presence of CeCl(3).7H(2)O.