Quinol epoxides fromp-cresol and estrone by photooxygenation and titanium(IV)- or vanadium(V)-catalyzed oxygen transfer

Photocatalytic Synthesis of para-Peroxyquinols: Total Synthesis of (±)-Stemenone B and (±)-Parvistilbine B

A photocatalytic method to selectively synthesize 4-hydroperoxy-2,5-cyclohexadienones from para-alkyl phenols is disclosed. This photosensitized singlet oxygen approach functionalized a variety of electronically diverse para-alkyl phenols in 27-99% isolated yields. Utilizing this dearomative oxidation, (±)-stemenone B and (±)-parvistilbine B were synthesized in 9 and 11 steps, respectively, from commercially available starting materials. Additional experiments revealed the dramatic influence of base and solvent on the selectivity while providing insight into the mechanism of this transformation.

Convergent total synthesis of (+)-calcipotriol: A scalable, modular approach to vitamin D analogs

A convergent approach for the total synthesis of calcipotriol (brand name: Dovonex), a proven vitamin D analog used for the treatment of psoriasis, and medicinally relevant synthetic analogs is described. A complete approach, not wedded to semisynthesis, toward both the A-ring and CD-ring is reported. From a retrosynthetic standpoint, hidden symmetry within the decorated A-ring is disclosed, which allowed for scalable quantities of this advanced intermediate. In addition, a radical retrosynthetic approach is described, which highlights an electrochemical reductive coupling as well as an intramolecular hydrogen atom transfer Giese addition to establish the 6,5-transcarbon skeleton found in the vitamin D family. Finally, a late-stage decarboxylative cross-coupling approach allowed for the facile preparation of various C20-arylated derivatives that show promising biological activity in an initial bioassay.

Iron salt-promoted oxidation of steroidal phenols by m-chloroperbenzoic acid: a route to possible antitumor agents

A new oxidant, containing m-chloroperoxybenzoic acid (MCPBA) and an iron salt, was developed and used for oxidation of steroidal phenols to a quinol/epoxyquinol mixture. Reaction was optimized for estrone, by varying initiators (Fe-salts), reaction temperature, time and mode of MCPBA application. A series of five more substrates (17β-estradiol and its hydrophobized derivatives) was subjected to the optimized oxidation, providing corresponding p-quinols and 4β,5β-epoxyquinols in good to moderate yields. The obtained epoxyquinols were additionally transformed by oxidation, as well as the acid-catalyzed oxirane opening. In a preliminary study of the antiproliferative activity against human cancer cell lines, all newly synthesized compounds expressed moderate to high activity.

Iron salt-promoted reaction of estrone and its derivatives with meta-chloroperoxybenzoic acid was developed and epoxyquinols were further transformed. Most compounds showed in vitro antiproliferative activity.

Atom Economical Photocatalytic Oxidation of Phenols and Site-Selective Epoxidation Toward Epoxyquinols

The discovery of a multiple-bond-forming process merging the singlet oxygen-mediated dearomatization of 3,4-disubstitued phenols and diastereo- and regioselective epoxidation is described. This one-pot strategy using a transition metal-free multicatalytic system comprised of rose bengal and cesium carbonate allowed the efficient formation of functionalized epoxyquinol products under mild conditions. Mechanistic investigations have been performed to shed the light on the key species involved in this transformation.

Multicatalytic dearomatization of phenols into epoxyquinols via a photooxygenation process

A multicatalytic photooxygenation of substituted phenols in the presence of rose bengal and cesium carbonate under green LED light is reported. This transformation enabled the introduction of both atoms of singlet oxygen and led to the one-pot synthesis of epoxyquinols in a stereoselective way.

Practical one-pot conversion of 17beta-estradiol to 10beta-hydroxy- (p-quinol) and 10beta-chloro-17beta-hydroxyestra-1,4-dien-3-one

An efficient one-pot procedure for the preparation of 10beta,17beta-dihydroxyestra-1,4-dien-3-one (p-quinol, 1, 75%) is reported, involving oxidation of 17beta-estradiol with potassium permanganate. Similar treatment of 17beta-estradiol with sodium chlorite led to 10beta-chloro-17beta-hydroxyestra-1,4-dien-3-one (2) in 44% yield along with smaller amounts 4-chloro-10beta,17beta-dihydroxyestra-1,4-dien-3-one (3), 2,10beta-dichloro-17beta-hydroxyestra-1,4-dien-3-one (4), and 4,10beta-dichloro-17beta-hydroxyestra-1,4-dien-3-one (5).

Synthesis and antiproliferative activity of A-ring aromatised and conduritol-like steroidal compounds

A simple approach to aromatization of steroidal quinols and epoxyquinols using a catalytic amount of TMSOTf is reported. Beside acetylation of the angular OH, the acid-catalyzed (TfOH) dienone-phenol rearrangement occurred affording "para" products, or in the case of blocked position 4, the acetoxy group 1,2-migration leads to the formation of "meta" products. Using epoxyquinol derivative as a substrate, the acetoxy group elimination was observed, followed by acid-catalyzed epoxy-ring opening and subsequent double bond migration, giving as a final product Delta(9,11)A-ring aromatized compounds. Synthesis of conduritol-like compounds and structure confirmation by X-ray crystallography of the precursor of steroidal conduritol is also described. In addition, the results of extensive antiproliferative screening against a panel of 60 cancer cell lines are presented.

Synthesis and antiproliferative activity of epoxy and bromo compounds derived from estrone

Based on biological properties of epoxyquinols from natural sources, bromo and epoxyquinols derived from estrone were synthesized and screened against Fem-X, HeLa and K(562) cell lines. Evidence was found that the bromine atom and the epoxy moiety significantly increase the antiproliferative activity within the series.