A novel olefinic rearrangement. The enzymic conversion of cholesta-7,9-dien-3β-ol into cholesta-8,14-dien-3β-ol

1. [3alpha-(3)H]Cholesta-7,9-dien-3beta-ol is converted in high yield into cholesterol by a 10000g(av.) supernatant fraction of rat liver homogenate. 2. Incubation of cholesta-7,9-dien-3beta-ol with [4-(3)H]NADPH and rat liver microsomal fractions under anaerobic conditions resulted in (3)H being incorporated into the 14alpha-position of cholest-7-en-3beta-ol. 3. Under anaerobic conditions in the absence of NADPH cholesta-7,9-dien-3beta-ol was isomerized into cholesta-8,14-dien-3beta-ol by rat liver microsomal fractions.     

Synthesis of 14β-cholesta-5,7-dien-3β-ol

5, 7-Cholestadien-3β-ol was transformed into 14β-cholesta-5, 7-dien- 3β-ol in six steps. The inversion of the stereochemistry at C-14 was obtained by a selective protection of the Δ⁵ and the elaboration of the Δ⁷ double bond.     

Biotransformation of 5-en-3β-ol steroids by Mucor circinelloides lusitanicus

In this work, we report the mode of biotransformation of 5-en-3β-ol steroids using Mucor circinelloides lusitanicus for the first time. Here, we selected seven 5-en-3β-ol steroids as substrates. The main characteristic of the fungus was to introduce a 7α-hydroxyl group into substrates 1--5. With substrate 2, 3β, 7α, 11α-trihydroxypregna-5-en-20-one (2b) was obtained as the final product in good yield (46.4%). All the metabolites were determined by infrared spectra, high-resolution mass spectrometry, proton nuclear magnetic resonance, and carbon-13 nuclear magnetic resonance.     

Synthesis of 3β-hydroxy-androsta-5,7-dien-17-one from 3β-hydroxyandrost-5-en-17-one via microbial 7α-hydroxylation

The synthesis of 3β-hydroxy-androsta-5,7-dien-17-one from 3β-hydroxy-androst-5-en-17-one (dehydroepiandrosterone, DHEA) via microbial 7α-hydroxylation has been accomplished. At the first stage, 3β,7α-dihydroxy-androst-5-en-17-one was obtained in high yield (71.2%) using a strain of Gibberella zeae VKM F-2600, which was first applied for DHEA conversion. The further route included the substitution of 7α-hydroxyl group with chlorine followed by a dehydrochlorination stage, and required minimal purifications of the intermediate products. The steroids obtained at every step were characterized by TLC_,¹H NMR, MS, UV- and IR-spectrometry.The combination of microbial and chemical steps ensured 54.6% yield of the target 3β-hydroxy-androsta-5,7-dien-17-one from DHEA and can be applied for obtaining novel vitamin D derivatives.     

Sterol metabolism. XLIII. The oxidation of cholest-4-en-3β-ol by singlet molecular oxygen

The photosensitized oxidation of cholest-4-en-3β-ol in which singlet molecular oxygen is implicated yielded cholest-4-en-3-one and the isomeric epoxides 4α,5-epoxy-5α-cholestan-3-one and 4β,5-epoxy-5β-cholestan-3-one, the epoxides being formed in the ratio 3 : 1. Oxidation of cholest-4-en-3-one by alkaline hydrogen peroxide likewise yielded the isomeric 4,5-epoxides but in the ratio 1 : 7.4. Attempted use of cholest-4-en-3β-ol to intercept singlet molecular oxygen putatively generated in the disproportionation of hydrogen peroxide gave a very complex product mixture of over 50 components from which only cholest-4-en-3-one could be identified. However, neither isomeric 4,5-epoxycholestan-3-one was detected among the products. These data establish that it is unwarranted to infer the action of single molecular oxygen in systems containing cholest-4-en-3β-ol merely by product analysis where the product 4α,5-epoxy-5α-cholestan-3-one is formed.     

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

1. The syntheses of Δ⁷-[4-¹⁴C]cholestenol (XVI, Scheme 3) and Δ⁷-[6α-³H]-cholestenol (XII, Scheme 2) are described. 2. The metabolism of doubly labelled Δ⁷-cholestenol (II, Scheme 1) by rat-liver homogenates was studied. 3. During the enzymic conversion of Δ⁷-cholestenol into cholesterol (IV, Scheme 1) the 6α-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 Δ⁷-cholestenol into cholesterol are discussed.     

Ergosta-5,23-dien-3β-ol and ergosta-7,23-dien-3β-ol,two new sterols from Zea mays etiolated coleoptiles

Ergosta-5,23-dien-3β-ol and ergosta-7,23-dien-3β-ol were identified for the first time in maize etiolated coleoptiles. They represent more than 11 % of the total 4-desmethyl sterol fraction. It is suggested that they could play some role in the biosynthesis of 24-methyl sterols of this material.     

Cycloart-25-en-2β-ol from Euphorbia nivulia

A new tetracyclic triterpene cycloart-25-en-3β-ol (9β,19-cyclolanost-25-en-3β-ol) and cyclolaudenol, have been isolated from Euphorbia nivulia.     

Cyclization of squalene-2,3-epoxide to 10α-cucurbita-5,24-dien-3β-ol by microsomes from Cucurbita maxima seedlings

Labelled 10α-cucurbita-5,24-dien-3β-ol was obtained from [3-³H]squalene-2,3-epoxide incubated with microsomes of Cucurbita maxima seedlings. By contrast the lanostane triterpenoids [2-³H]cycloartenol, [2-³H]parkeol and their corresponding derivatives [2,12-³H]11-ketocycloartenol and [2-³H]24,25-dihydro-90α,11a-epoxyparkeol, incubated under the same conditions, gave no rearranged products with a cucurbitane skeleton. These results suggest that biosynthesis of cucurbitane triterpenoids from squalene-2,3-epoxide occurs through direct cyclization without the intermediacy of lanostane-type triterpenoids such as cycloartenol or parkeol. Labelled cycloartenol, α-amyrin, β-amyrin and 24-methylenecycloartanol were also obtained from [3-³H]squalene-2,3-epoxide in the same enzymatic system yielding labelled 10α-cucurbitadienol.     

Role of the “thrombocytoids” in capsule formation in the dipteran Calliphora erythrocephala

Of the three hemocyte types present in the blood of Calliphora, only one participates in capsule formation around implanted cellophane. This hemocyte, the thrombocytoid, shows in the blood a tendency to dissociate into numerous small cytoplasmic fragments, comparable to the mammalian megakaryocyte. This tendency is dramatically increased during the process of encapsulation. Most of the intact thrombocytoids and the numerous fragments participating in capsule formation do not show any particular modifications in their cytoplasm during this process, which corresponds to a mere sequestration of the implant. Dense material, resulting from necrotic cell debris and hemolymph lipoproteins, is often observed between the cellophane and encapsulating thrombocytoids, which apparently participate in the resorption of this material.     

4α-Methyl-5α-cholest-8(14)-en-3β-ol from the seeds of Capsicum annuum

A 4α-methylsterol was isolated from the seeds of Capsicum annuum and was identified as 4α-methyl-5α-cholest-8(14)-en-3β-ol. This seems to b     

The transformation of 10α-cucurbita-5,24-dien-3β-ol into cucurbitacin C by seedlings of Cucumis sativus

Labelled 10α-cucurbita-5,24-dien-3β-ol, the simplest tetracyclic triterpene with a cucurbitane skeleton, was transformed into cucurbitacin C in Cucumis sativus seedlings. This transformation has been previously postulated, but this is the first time it has been demonstrated to operate in plant tissues. Two other potential precursors of cucurbitacins, cycloartenol and parkeol, were incubated under the same conditions. Cycloartenol gave only the expected phytosterols whereas parkeol was recovered unchanged.     

5α-Stigmast-9(11)-en-3β-ol,a sterol from Costus speciosus roots

A new sterol isolated from Costus species roots has been characterized as 5α-stigmast-9(11)-en-3β-ol by spectroscopic data and chemical studies.     

5α-cholesta-7,24-dien-3β-ol as a major sterol of the male hamster reproductive tract

Marked variations in the 3β-hydroxysterol content of hamster spermatozoa were observed as they progress through the epididymis. Cholesterol is the major sterol of caputal spermatozoa while the concentration of precursors of cholesterol was higher than that of cholesterol in caudal spermatozoa. One of these precursors has been identified as desmosterol. A second sterol has now been identified as 5α-cholesta-7, 24-dien-3β-ol by GLC-MS and by NMR. Its concentration is approximately 3-fold higher than that of cholesterol. This 3β-hydroxysterol is also found in epididymal tissue.     

Sterol synthesis. Synthesis of 15-oxygenated 5α, 14β-cholest-7-en-3β-ol derivatives

Treatment of 3β-benzoyloxy-14α, 15α-epoxy-5α-cholest-7-ene with boron trifluoride-etherate gave, in 43% yield, 3β-benzoyloxy-5α, 14β-cholest-7-en-15-one with the unnatural C ring juncture. Reduction of the latter compound with lithium aluminum hydride gave 15α, 14β-cholest-7-en-3β, 15α-diol and 5α, 14β-cholest-7-en-3β, 15β-diol in 9% and 81% yields, respectively.     

Preparation of 3β,16β-dihydroxyandrost-5-en-17-one: Stabilization of its α-ketolic group toward alkali by formation of a semicarbazone

Alkaline hydrolysis of a 16β-acetoxy-17-oxo steroid is accompanied by almost complete rearrangement of the product to a 16-oxo-17β-hydroxy steroid. Hydrolysis can be achieved without rearrangement by 1) formation of a C-17 semicarbazone, 2) alkaline removal of the acetate group, and 3) removal of the semicarbazone group in the presence of pyruvic acid-acetic acid. By employing this technique, the title compound was obtained from its diacetate in a yield of 65%.     

The formation of cholest-5-ene-3β,26-diol as an intermediate in the conversion of cholesterol into bile acids by liver mitochondria

1. When [(14)C]cholesterol was incubated with rat liver mitochondria, radioactive 26-hydroxycholesterol, 3beta-hydroxychol-5-enoic acid and other bile acids were isolated from the incubation mixture. 2. In the absence of added 26-hydroxycholesterol, the specific radioactivity of the 26-hydroxycholesterol formed from [(14)C]cholesterol during the incubation was higher than that of the 3beta-hydroxychol-5-enoic acid. Addition of increasing amounts of 26-hydroxycholesterol led to a progressive fall in the specific radioactivity, and to a progressive increase in the mass, of the 3beta-hydroxychol-5-enoic acid recovered at the end of the incubation. 3. It is concluded that 26-hydroxycholesterol is an intermediate in the formation of 3beta-hydroxychol-5-enoic acid from cholesterol. 4. Comparison of the specific radioactivity of the 26-hydroxycholesterol formed in the incubation mixture with that of the added [(14)C]cholesterol indicates that endogenous cholesterol in mitochondria is accessible to cholesterol 26-hydroxylase.     

Δ5,7Sterols from the sponges Ircinia pipetta and Dysidea avara identification of cholesta-5,7,24-trien-3B-OL

• 1.1. Δ^5,7-sterols have been isolated as pure compounds from the marine sponges Ircinia pipetta (Dictyoceratida:Thorectidae) and Dysidea avara (Dictyoceratida:Dysideidae) by reverse phase HPLC and analyzed by GLC, u.v., mass spectrometry and ¹H-NMR.
• 2.2. Ircinia pipetta and D. avara have rather similar sterol compositions and contain predominantly Δ^5,7-sterols, accompaned by Δ⁵-sterols. Ergosterol, cholesta-5,7-dien-3β-ol and 24-ethylcholesta-5,7-dien-3β-ol are the major sterols in I. pipetta, while D. avara contains in addition to these three sterols, (24Z)-24-ethylcholesta-5,7,24(28)-trien-3β-ol as the fourth major sterol.
• 3.3. Cholesta-5,7,24-trien-3β-ol which previously was not isolated from a marine organism is also present.