Δ^2,4,6‐Cholestatrien. Beitrag zum Mechanismus der HBr‐Abspaltung aus 7‐Brom‐cholesterylbenzoat

Abstract

Bei der HBr-Abspaltung aus 7-Brom-cholesterinester zur Herstellung von 7-Dehydro-cholesterin, dem Provitamin D, , wurde neben diesem noch d4>6-Cholestadien-3-ol (VII) als Nebenprodukt isoliertl). Kiirzlich haben Ottke & ~$~g~~~n 2 )durch Einwirkung von N-Bromsuccinimid auf Cholesterylacetat und direkte HBr-Abspaltung &us dem rohen Bromierungsprodukt mit s-Collidin nach der Methode von Bernstein und Mitarbeitern,) ein neues Nebenprodukt isoliert, welchem die Struktur eines Bicholestatriens zukommen soll. Ein Bhnliches, wenn nicht identisches Bicholestatrien erhielt Hafex4) bei der Einwirkung von N-Bromsuccinimid auf d6-i-Cholestadien.I m Laufe unserer Untersuchungen iiber die HBr-Abspaltung aus 7-Brom-cholesterylbenzoat mit Calci~mhydroxyd~) in siedendem Xylol beobachteten wir im rohen Reaktionsprodukt regelmassig einen Stoff mit einem deutlichen Maximum im UV. bei 307 mp. Die Ausbeuten an diesem Korper variierten stark, je nach Reaktionsbedingungen zwischen 10 und 38 yo6). Durch chromatographische Trennung des verseiften Rohproduktes an A1,0, liess sich dieser in Kristallen erhalten; ihm kommt sehr wahrscheinlich die Formel eines ~I2~4~Wholestatriens (XVII) zu (siehe unten). Daneben wurden 7-Dehydro-cholesterin (V) (bis zu max. 40Yo6)), 7/?-Oxy-cholesterin (XII)7)s) und in sehr kleiner

Reactivity Studies on Natural Products: V. Rates of Borohydride Reduction of Some Ring a and B Steroid Ketones

“…However in the present work 95y0 of the @-isomer was isolated and this is in agreement with the observations that cholesta-4,6-dien-3-one (20) and cholest-1-en-3-one (21) give essentially the @-isomer. In the present work 58y0 of cholestan-7@-01 was formed in the reduction of cholestan-7-one.…”

Steroidal Sapogenins. XIV.1 Δ4, 6-22-Isospirostadien-3β-Ol and Δ2, 4, 6-Isospirostatriene

“…A similar, stereospecific reduction has recently been observed ( 14) with 4• 6-cholestadien-3-one. The synthetic 4• 6-dien-3/S-ol and derivatives (IVa-c) agreed fairly well in their properties with the by-products isolated earlier (7) in the dehydrobromination of VI, and the dextrorotatory shift of the synthetic dienol IVa as compared to the 5> '-isomer coincided with that reported in the literature for other series (3,8,14,15). As has already been demonstrated with 4• 6-cholestadien-3/3-ol (16), Oppenauer oxidation of the dienol IVa regenerated the dienone III.…”

“…3 The correct 3• 5• 7-cholestatriene was recently prepared by Gould, et al, (18) who showed that such a compound was characterized by a strongly negative rotation ([a]D -122°), ultraviolet absorption maxima at 302.5, 315, and 330 µ, and by the uptake of only two moles of hydrogen upon catalytic hydrogenation (the 7,8-double bond not being reduced). Eckhardt's triene (17), on the other hand as was recently confirmed by Schmutz, Schaltegger, and Sanz (14), exhibits a much more positive rotation ([a]D -13.5°), and ultraviolet absorption maxima at 295, 305 µ, and an inflection at 320 µ, in excellent agreement with the maxima observed for our triene V. As pointed out by the Swiss workers (14), the physical data, the fact that the triene takes up three moles of hydrogen, and that it forms an adduct with maleic anhydride, all support a 2•4 *• 6-cholestatriene structure. We have independently reached the same conclusion with regard to the structure of the triene isolated in the sapogenin series, since the latter (V) takes up three moles of hydrogen with formation of 22-isoallospirostan (VII) (19) and also yields a well crystallized adduct (VIII) with maleic anhydride.…”

“…Lowenbein (20), in a recent patent has claimed extremely high yields of crystalline 7-dehydrocholesterol, by treatment of 7-bromocholesterol esters with alkaline earth hydroxides in a mixture of xylene and nitrobenzene. This claim could not be duplicated by Schmutz, Schaltegger, el al., (14), who in addition to 7-dehydrocholesterol always isolated appreciable amounts of 2•4• 6-cholestatriene. We have had similar experiences on applying some of Lowenbein's conditions to 7-bromo-A6-22-isospirosten-30-ol acetate (VI) and in the experimental section there is reported an experiment with magnesium oxide, in which 2 •4 6-22-isospirostatriene (V) was the principal product.…”

Sterol Composition of the Mollusk Aulacomya ater

“…It is interesting to note the appearance of the steroidal hydrocarbon whose mass spectral analysis points to a triunsaturated cholestane (13), cholesta-2,4,6-triene or cholesta-1,4,6-triene. The imprecise determination is due to the fact that it is not possible to distinguish between the mass spectra of both compounds because of the normal isomerization that occurs when polyunsaturated hydrocarbons are analyzed by electron impact mass spectrometry (14). Otherwise, these known compounds (15)(16)(17) are, to our knowledge, unprecedented as natural products and we do not know whether they exist as natural compounds or are artifacts of the extraction procedure.…”