Reactions of organotin compounds. VIII. The reactions of tin hydrides with perfluorovinyl silicon compounds

The reactions of trimethyltin hydride and dimethyltin dihydride with (CH3)3SiCF=CF2 and (CH3)2Si(CF=CF2)2 respectively have been investigated. Under thermal conditions, reaction led to organotin fluorides and fluorovinyl-silanes. However, under ultraviolet irradiation at 25°, addition products were isolated of which (CH3)3SiCFHCF2Sn(CH3)3 and (CH3)3SiCF[Sn(CH3)3]CF2H were fully characterized. Evidence is presented which shows that these addition products are formed by a free radical process and that their decomposition to organotin fluorides and fluorovinyl-silanes proceeds via a β-fluorine elimination. Spectroscopic data are presented for a number of new organo-silanes.

The introduction of the C-22-C-23 ethylenic linkage in ergosterol biosynthesis

Methods for the chemical synthesis of [23-(3)H(2)]lanosterol, [23,25-(3)H(3)]24-methyldihydrolanosterol and [24,28-(3)H(2)]24-methyldihydrolanosterol are described. It is shown that, in the biosynthesis of ergosterol from [26,27-(14)C(2),23-(3)H(2)]lanosterol by the whole cells of Saccharomyces cerevisiae, one of the original C-23 hydrogen atoms is lost and the other is retained at C-23 of ergosterol. It is also shown that 24-methyldihydrolanosterol is converted into ergosterol in good yield and without prior conversion into a 24-methylene derivative. On the basis of these results possible pathways for the formation of the ergosterol side chain from a 24-methylene side chain are discussed.

The biological conversion of 7-dehydrocholesterol into cholesterol and comments on the reduction of double bonds

It is shown that the 7-dehydrocholesterol reductase-catalysed conversion of 7-dehydrocholesterol into cholesterol (II), with a 105000g microsomal pellet of rat liver in the presence of [4-(3)H(2)]NADPH, results in the transfer of radioactivity to the 7alpha-position of cholesterol. When the conversion is carried out in the presence of tritiated water the label is introduced exclusively at the 8beta-position. However, when the conversion of 7-dehydrocholesterol into cholesterol is performed with a 500g supernatant of rat liver homogenate the radioactivity is incorporated at both the 7alpha- and the 8beta-position. Evidence is provided for the presence of an enzyme system in the 500g supernatant that catalyses an equilibration of hydrogen atoms between those at the 4-position of NADPH and those of water. The work with stereospecifically labelled cofactors shows that both the equilibrating system and the 7-dehydrocholesterol reductase utilize the 4B-hydrogen atom of NADPH. In the light of these results a mechanism for the reduction of carbon-carbon double bonds is discussed.

The transfer of hydrogen from C-24 to C-25 in ergosterol biosynthesis

1. A convenient synthesis of 3-hydroxytrisnorlanost-8-en-24-al and its conversion into [24-(3)H]lanosterol and [26,27-(14)C(2)]lanosterol is described. 2. A method for the efficient incorporation of lanosterol into ergosterol by the whole cells of Saccharomyces cerevisiae is also described. 3. It is shown that in the biosynthesis of ergosterol from doubly labelled lanosterol the C-24 hydrogen atom of lanosterol is retained in ergosterol. 4. On the basis of unambiguous degradations it is shown that the C-alkylation step in ergosterol biosynthesis is accompanied by the migration of a hydrogen atom from C-24 to C-25. 5. The mechanism for the biosynthesis of the ergosterol side chain is presented. 6. Mechanisms of other C-alkylation reactions are also discussed.

The stereochemistry of the hydrogen elimination in the biological conversion of cholest-7-en-3-beta-ol into cholesterol

1. The syntheses of Delta(7)-[4-(14)C]cholestenol (XVI, Scheme 3) and Delta(7)-[6alpha-(3)H]-cholestenol (XII, Scheme 2) are described. 2. The metabolism of doubly labelled Delta(7)-cholestenol (II, Scheme 1) by rat-liver homogenates was studied. 3. During the enzymic conversion of Delta(7)-cholestenol into cholesterol (IV, Scheme 1) the 6alpha-hydrogen atom of the former is lost and the overall reaction corresponds to a cis-elimination. 4. In the light of these results various mechanisms for the conversion of Delta(7)-cholestenol into cholesterol are discussed.