Stereoselective synthesis of syn-α-methyl-β-hydroxy esters

Boron enolates of an ethyl ketone structurally related to erythrulose react with achiral aldehydes in a highly stereoselective fashion to yield 1,2-syn/1,3-syn stereoisomers. Oxidative cleavage of the aldol adducts yields enantiopure O-formylated syn-α-methyl-β-hydroxy esters, easily cleaved to the corresponding hydroxyl-free compounds. The aforementioned ketone behaves therefore as a chiral propionate enolate equivalent.     

Synthesis of 17α-bromovinyl- and 17α-iodovinylnortestosterone derivatives

Depending upon the reaction conditions, norethisterone (1) and its ketal 2 can be transformed with tributyltin hydride to either the (E)-or(Z)-17α-(2-tributylstannylvinyl)-nortestosterone derivatives 3, 8 and 13. Further treatment with N-bromo- or N-iodosuccinimide yields the corresponding (E)- and (Z)-17α-halovinyl steroids 6,7,10 and 11. Radio-labelled (Z)-17α-(2-iodovinyl)-nortestosterone was prepared by reaction of the 17α-stannylvinyl derivative 13 with Na¹²⁵I.     

Et_2AlCl-Mediated Reaction of α-4(20)-Epoxy-5α-hydroxy Taxinine B

The anticancer drug paclitaxel (Taxol@), a diterpenoid isolated from the bark of Taxusbrevghlia', is clinically used in the treatment of ovarian and breast cancers2. Since itsdiscovery in the 1960s, particularly in recent years, a large number of studies onchemistry and structure-activity relationship have been carried out and led to the generalconclusion that the function groups at C,, C,, C.,, C,.-,, and C,-CH, have modest butoften beneficial effects on its biological activity, while the …     

Stereocontrolled synthesis of D-α-hydroxy carboxylic acid from L-amino acids

Optically active D-α-hydroxy carboxylic acids are obtained from L-amino acids via L-α-halocarboxylic acids and their stereoselective reaction with cesium p-nitrobenzoate.     

Synthesis and transformations of the 20-substituted derivatives of 16α,17α-epoxy-5α-pregnane-3Β,21-diol-20-ones

A new and more effective sequence of reactions is proposed for the production of 16,17-isopropylidenedioxy-5-pregnane-3,21-diol-20-one. It uses methods previously unused for 5-H-steroids and involves 21-hydroxylation of 16,17-epoxy-5-pregnan-3-ol-20-one with diacetoxyiodobenzene and cis-opening of the obtained 21-hydroxy-16,17-epoxy-5-pregnane-3,21-diol-20-one by acetic acid in the presence of epoxycarbonylhydrazine, followed by condensation of the obtained product with acetone.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1185–1188, May, 1991.     

Fragmentation of β-hydroxy hydroperoxides

A β-hydroxy hydroperoxide was obtained through base-catalyzed disproportionation of a hydroperoxy endoperoxide available by singlet oxygenation of cyclohepta-1,4-diene. Vitamins E and C induce fragmentation of this β-hydroxy hydroperoxide generating aldehydes, especially in the presence of redox active metal ions such as those present in vivo, e.g., under conditions of "iron overload". This chemistry may contribute to the oxidative cleavage of polyunsaturated fatty acyls that produces similar aldehydes, which damage proteins and DNA through covalent adduction resulting in "oxidative injury".     

Simple Synthesis of 17α,20β-Dihydroxypregn-4-en-3-one

Reduction of 17-hydroxyprogesterone (1) with NaBH ₄ produces 17,20-dihydroxypregn-4-en-3-one (2) and pregn-4-en-3,17,20-triol (3)     

Bismuth(III) triflate-catalyzed rearrangement of 16α,17α-epoxy-20-oxosteroids. Synthesis and structural elucidation of new 16α-substituted 17α-alkyl-17β-methyl-Δ-18-norsteroids

The use of bismuth(III) triflate for the rearrangement of 16α,17α-epoxy-20-oxosteroids is reported. The reactions occur under truly catalytic conditions to afford novel 17α-alkyl-17β-methyl-Δ¹³-18-nor products bearing different O-containing substituents at C16. When the reaction is performed in the absence of acylation agent a mixture of isomeric 16α- and 16β-hydroxy derivatives is obtained, whereas when carried out in the presence of such reagents, the reaction selectively affords the corresponding 16α-acyl rearranged products. The chemoselective rearrangement of 5β,6β;16α,17α-diepoxy-20-oxopregnan-3β-yl acetate to afford a ‘backbone’ rearranged product bearing the 16α,17α-epoxide group is also reported. Some mechanistic considerations are provided. All rearranged products were the subject of comprehensive structural elucidation, by the use of X-ray crystallography and 2D NMR.     

Method for mild trimethylsilylation of the 14α-hydroxy group in ecdysteroids

In the reactions of poststerone derivatives and 20-hydroxyecdysone with (trifluoromethyl)trimethylsilane catalyzed by tetrabutylammonium fluoride, the 14-hydroxy group is readily subjected to trimethylsilylation.     

Kinetic resolution of racemic α-tert-alkyl-α-hydroxy esters by enantiomer-selective carbamoylation

Kinetic resolution of sterically hindered racemic α-tert-alkyl-α-hydroxy esters is performed by enantiomer-selective carbamoylation with the t-Bu-Box-Cu(II) catalyst (Box = bis(oxazoline)). The reaction with 0.5 equiv of n-C(3)H(7)NCO is carried out with a substrate-to-catalyst molar ratio of 500-5000 at -20 to 25 °C. The high enantiomer-discrimination ability of the catalyst achieves an excellent stereoselectivity factor (s = k(fast)/k(slow)) of 261 in the best case. A catalytic cycle for this reaction is proposed.     

Ionic liquid-promoted Wagner-Meerwein rearrangement of 16α,17α-epoxyandrostanes and 16α,17α-epoxyestranes

Ionic liquids 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim](+)[PF(6)](-)) and 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim](+)[BF(4)](-)) were found to promote an unusual Wagner-Meerwein rearrangement of steroidal 16α,17α-epoxides leading to unnatural 13-epi-18-nor-16-one derivatives as the main products. These compounds were isolated in good to excellent yields. 16α-Hydroxy-Δ(13)-18-norsteroids, the results of the usual rearrangement, were obtained as minor components of the reaction mixtures. The ionic liquid [bmim](+)[PF(6)](-) was shown to induce C-ring aromatization of 16α,17α-epoxyestranes due to the formation of HF, the hydrolysis product of [PF(6)](-). Increasing amounts of HF and [PO(2)F(2)](-) were detected by (19)F and (31)P NMR when the ionic liquid was reused. The structures of the steroidal products, 16-oxo-18-nor-13α-steroid derivatives, 16α-hydroxy-Δ(13)-18-norsteroids, and C-aromatic compounds were determined by two-dimensional NMR techniques and high-resolution mass spectrometry (HRMS). The ionic liquids were recirculated efficiently.     

Synthesis of nitrogen-containing derivatives of 17(20)-pregnenoic, 17β-hydroxypregnanoic,and 17α-hydroxypregnanoic acids as new potential antiandrogens

A general scheme for the synthesis of oxazoline and benzoxazole derivatives of [17(20)E]-21-norpregnene differing in the structure of the steroid moiety as well as amides of 17β-hydroxy-3-oxopregn-4-en-21-oic and 17α-hydroxy-3-oxopregn-4-en-21-oic acids was developed. The scheme involved synthesis of the steroid building blocks (appropriately protected derivatives of pregn-17(20)-en-21-oic, 17β-hydroxypregnan-21-oic, and 17α-hydroxypregnan-21-oic acids) and subsequent transformation of these building blocks into the target compounds. Following the developed scheme, synthesis of new nitrogen-containing steroid derivatives exhibiting antiandrogenic activity was enabled.     

Synthesis of cyclicβ-silylenones via oxidative rearrangement of tertiaryα-hydroxy allylsilanes with PCC

An oxidative rearrangement of cyclic tertiary a-hydroxy allylsilanes has been carried out in refluxing ClCH₂CH₂Cl with pyridinium chlorochromate（PCC）.The reaction provides a convenient method to synthesize cyclicβ-silylenones in modest to excellent yields.     

Synthesis and Transformations of 20-Isoxazolylsteroids with Modified D Ring: I. Synthesis of 16α,17α-Epoxyderivatives

Synthesis of 16,17-epoxy-20-isoxazolylsteroids was carried out starting with dehydropregnenolone acetate. Transformation procedures for preparation therefrom of open-chain compounds were considered. Physico-chemical characteristics of compounds synthesized were investigated.     

The structure of 16, 17β-epoxy-17α-pregn-5-en-3β-ol-20-one monohydrate

The structure of the title compound (1) has been studied by means of X-ray diffraction. The region of cycleD in epoxide1 was compared with that of the 16,17-epoxy derivatives of progesterone and pregnenolone (studied previously) as well as with that of the respective 16,17- and 16,17-cyclopropano analogs. In contrast to the 16,17-epoxy-20-oxo derivatives, in compound1 the electron conjugation of the epoxide ring with the CH₃CO group at C(17) is partly disrupted. Moreover, the steric congestion at C(17) is significantly less pronounced in 16,17-epoxide1 than in its 16,17-counterpart. Both of these factors, especially steric decongestion, are favorable for nucleophilic attack at C(17) in the molecule of1. The X-ray diffraction data do not contradict the previously advanced mechanism of epoxide ring opening in 16,17- and 16,17-epoxy-20-oxo steroids by nucleophilic reagents.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 401–405, February, 1993.     

N-Hydroxymethyl derivatives of α-amino aldehydes used for the stereoselective syntheses of β-amino-α-hydroxy acids

The N-hydroxymethyl derivatives of α-amino aldehydes 1 were utilized for the effective synthesis of several β-amino-α-hydroxy acid derivatives in a one-pot process starting from the corresponding α-amino aldehydes. Properly protected methyl esters 3 were prepared in 65–79% yields from α-amino aldehyde derivatives 1 with more than 20:1 stereoselectivity. The application of suitably protected β-amino-α-hydroxy esters was shown by an efficient synthesis of the bioactive peptide, bestatin, and its more potent analogue, AHPBA-Val, in high yields from ent-3a.     

Characterization of 17α-hydroxysteroid dehydrogenase activity (17α-HSD) and its involvement in the biosynthesis of epitestosterone

Background  

Epi-testosterone (epiT) is the 17α-epimer of testosterone. It has been found at similar level as testosterone in human biological fluids. This steroid has thus been used as a natural internal standard for assessing testosterone abuse in sports. EpiT has been also shown to accumulate in mammary cyst fluid and in human prostate. It was found to possess antiandrogenic activity as well as neuroprotective effects. So far, the exact pathway leading to the formation of epiT has not been elucidated.