Alberto Fiecchi

Epimerization of α- to β-C-glucopyranosides under mild basic conditions

A number of β-C-glucopyranosides having an activated methylene or methine group bonded to the anomeric carbon are obtainable in quantitative yield from the corresponding α-isomers by simple equilibration catalysed by various bases at room temperature.

Polyethylene Glycols as Solvents for Anionic Activation: Synthesis of Thioacetates by Means of Potassium Thioacetate in Polyethylene Glycol 400

Abstract Recently, polyethylene glycols (PEGS) of various molecular weights have been proposed as solvent promoters for various reactions 1, 2. We wish to report on the use of PEG 400 as solvent for the anionic activation of potassium thioacetate, which could be used for the preparation of alkyl and benzyl thioacetates from the corresponding halides or alcohol derivatives. The method can be synthetically significant, since from thioacetates the corresponding thiols can be easily prepared under a variety of mild conditions 3.

Hydrogen Exchange and Double Bond Formation in Cholesterol Biosynthesis

The conversion of lanosterol║to cholesterol requires a considerable number of intermediary steps involving loss or uptake of hydrogen atoms and formation and migration of nuclear double bonds. Detailed discussions on the intermediary steps in cholesterol biosynthesis are reported in several reviews (Olson 1965; Frantz & Schroepfer 1967; Goad 1970). In the present report some mechanisms in the formation of cholesterol and its sterol precursors from lanosterol are discussed. The relation between in vitro and in vivo pathways of cholesterol biosynthesis and the composition and metabolism of sterols in biological tissues is underlined.

Synthesis of (2R,3S,22S,23S)-2,3,22,23-tetrahydroxy-B-homo-7-aza-5α-stigmastan-6-one, an aza-analogue of homobrassinolide

(2R,3S,22S,23S)-2,3,22,23-Tetrahydroxy-B-homo-7-aza-5α-stigmastan-6-one, an aza-analogue of homobrassinolide, has been synthesized starting with 5α-stigmasta-2,22-dien-6-one. Osmylation of the trimethylsilyl enol ether of this dienone afforded (2R,3S,7S,22S,23S)-2,3,7,22,23-pentahydroxy-5α-stigmastan-6-one, which by oxidation of the acyloin group, after protection of the glycolic systems, afforded (by esterification) an aldehydo ester, which is the key intermediate for the production of the final compound by reductive amination.

Stereoselective synthesis of crinosterol [(22E,24S)-ergosta-5,22-dien-3β-ol]

A stereoselective synthesis of crinosterol, (22E,24S)-ergosta-5,22-dien-3β-ol, was developed from (20S)-6β-acetoxy-3α,5-cycle-5α-pregnane-20-carbaldehyde using the Claisen rearrangement of an appropriate precursor of established absolute configuration.

The stereochemistry of hydrogen elimination in the biological conversion of 5α-cholest-8-en-3β-ol to 5α-cholest-7-en-3β-ol

Abstract The stereochemistry of 5α-cholest-8-en-3β-ol to 5α-cholest-7-en-3β-ol isomerization was studied in rat liver homogenates incubated in the presence of either 3(±)-2R-[2- 3 H 1 ]- or 3(±)-2S-[2- 3 H 1 ]-mevalonic acid lactone. The isolated radioactive 5α-cholest-7-en-3β-ol and cholesta-5,7-dien-3β-ol acetates were transformed into the mixtures of epimeric cis-5α-cholestane-3β,7,8-triol-3β-acetates and then into the mixtures of epimeric 5α-cholestane-3β,8-diol-7-one 3β-acetates. Radioactivity contents showed that during the biological isomerization the 7α-hydrogen of 5α-cholest-8-en-3β-ol is completely eliminated whereas the 7β-hydrogen is retained.

Biohydrogenation of unsaturated compounds by Saccharomyces cerevisiae. Part 2: (S)-(–)-Ethyl 4-hydroxy-3-methylbutanoate as a chiral synthon for the preparation of (25S)-26-hydroxycholesterol

(25S)-26-Hydroxycholesterol (1b) has been synthesized from stigmasterol (4a) and (S)-(–)-ethyl 4-hydroxy-3-methylbutanoate (2a), the latter having the necessary chirality for the synthesis of the steroidal side-chain.

C-Glucopyranosyl derivatives from readily available 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl chloride

Readily available 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl chloride smoothly reacts with various silyl enol ethers and silver(I) trifluoromethanesulphonate (triflate) to afford D-C-glucopyranosyl derivatives of α-configuration in high yields, whereas reaction with an electron-rich aromatic nucleophile yields the corresponding β-anomer.

A novel synthesis of 3β-hydroxy-5α-cholest-8(14)-en-15-one

Jones oxidation of 5α-cholesta-8,14-dien-3β-yl acetate furnishes 9α-hydroxy-15-oxo-5α-cholest-8(14)-en-3β-yl acetate (4a). Treatment of (4a) with zinc dust and sulphuric acid followed by saponification gives 3β-hydroxy-5α-cholest-8(14)-en-15-one. On the basis of chemical and spectroscopic evidence, the product obtained by oxidation of 5α-cholest-8,14-dien-3β olis formulated as 9α-hydroxy-5α-cholest-8(14)-ene-3,15-dione (4b) and not as 14α-hydroxy-5α-cholest-8-ene-3,7-dione (3) as reported by others.

β-Oxidative cleavage of octanoyl-and dodecanoyl-CoA in rat liver cytoplasm

Abstract[12-14C] Dodecanoyl-CoA and [8-14C] octanoyl-CoA were tested as substrates for shortening the chain by two carbon atoms using both the 105,000 x g soluble fraction and the sonicated mitochondrial fraction of rat liver homogenate as the enzyme source. Both substrates were metabolized by the cytoplasmic enzymes giving rise to the accumulation of intermediates of the β-oxidation process without formation of two carbon units from the methyl carbon of the acyl residue. A new method is described which allows quantitative estimation of volatile fatty acids formed by β-oxidation of dodecanoyl- and octanoyl-Coenzyme A.