Steroid Side Chain Research Articles

Highly Stereocontrolled Formal Synthesis of Brassinolide via Chiral Sulfoxide-Directed SN2‘ Reactions

An efficient stereocontrolled methodology for the preparation of the four contiguous chiral centers of the brassinosteroid side chain is described. Allylic mesyloxy sulfinyl steroids have been found to undergo highly stereoselective SN2‘ displacements when treated with cyanocuprates that provide the required acyclic stereocontrol in the key C-24 position of the steroidal side chain. Preparation of a direct precursor of brassinolide 1, as well as a precursor of naturally occurring (24R)-epibrassinolide, (+)-18, is carried out in two additional steps utilizing asymmetric dihydroxylations of (22E)-olefins (+)-2 and (+)-17. In this manner, a formal synthesis of this plant growth promoter has been completed, and the extension of the scope of this methodology has been explored providing a straightforward route to this family of steroids. Alternative routes to the key olefin (+)-2 are also outlined. Improved selectivity in the addition to aldehyde 7 for the preparation of the Cram (22R)-allylic hydroxy sulfoxides is achieved by controlling the chirality at sulfur or by a condensation−symmetric oxidation sequence employing the analogous vinyl sulfide reagent 22.

Novel pathways for elimination of cholesterol by extrahepatic formation of side-chain oxidized oxysterols

Recently, we described a new pathway whereby peripheral cells can eliminate intracellular cholesterol by conversion into the more polar oxysterols 27-hydroxycholesterol and 3 beta-hydroxy-5-cholestenoic acid. The latter steroids are easily excreted from the cells and transported to the liver for conversion into bile acids. Our attempts to evaluate the importance of this new mechanism are reviewed here and also our investigations on the possible presence of additional similar pathways for removal of extrahepatic cholesterol. Human alveolar macrophages in culture were shown to have a high capacity to convert cholesterol into 27-hydroxycholesterol and 3 beta-hydroxy-5-cholestenoic acid and to excrete these steroids into the culture medium. Treatment of the macrophages with cyclosporin A, an inhibitor of sterol 27-hydroxylase, reduced the excretion of the 27-hydroxylated products by more than 90%, with a concomitant accumulation of intracellular cholesterol. The quantitative importance of the mechanism in relation to reverse cholesterol transport was investigated in 14C-cholesterol labelled macrophages exposed to HDL. At very low concentrations of HDL, possibly similar to those present in tissues, the two pathways were about equally effective. At optimal concentrations of HDL, however, reverse cholesterol transport was about 10-fold more effective than the sterol 27-hydroxylase pathway. The net uptake of 27-oxygenated steroids by the liver was measured in volunteers by comparison of the levels in the hepatic vein with those in a peripheral artery. Approximately 20 mg of 27-oxygenated oxysterols was taken up by the liver during 24 hours. Quantitative conversion of these oxysterols into bile acids would correspond to 4% of the total bile acid formation. It is evident that this new pathway contributes significantly to cholesterol elimination. The possibility that the sterol 27-hydroxylase pathway is of importance for cholesterol homeostasis in the brain was investigated by measuring oxysterols in the internal jugular vein and in an artery of healthy volunteers. There was no net flux of 27-hydroxycholesterol from the brain into the circulation. There was, however, a significant flux of 24-hydroxycholesterol, corresponding to elimination of about 4 mg cholesterol/24 hours. This flux is higher than the estimated rate of synthesis of cholesterol in the human brain. To summarize, we have demonstrated two mechanisms for cholesterol elimination from extrahepatic cells by specific oxygenases capable of oxidizing the steroid side-chain. The efficiency of these mechanisms is based on the fact that side-chain hydroxylated cholesterol species are both translocated through lipophilic membranes and converted into bile acids at a much faster rate than cholesterol itself. The importance of the sterol 27-hydroxylase-mediated mechanism is illustrated by the fact that patients who lack this enzyme develop xanthomas and premature atherosclerosis in spite of normal levels of circulating cholesterol.

η3-π allylzirconocene derivatives: preparation of steroidal side chains

(E,E) η 3-π allylzirconocene derivative 7 was generated in situ under thermodynamically equilibrated conditions and subsequently reacted with acetone to give natural andlor unnatural steroidal side chains.

Downeyoside A and B, Two New Sulphated Steroid Glucuronides from the Starfish Henricia downeyae

Two new sulphated polyhydroxylated steroid glucuronides. downeyoside A and B ( 1, 2), C-24 methyl epimers possessing an ethereal ring linking C-16 to C-22 of the steroid, were isolated from the starfish Henricia downeyae collected from the Gulf of Mexico. Their structures were determined by spectral analysis and the stereochemistry of the highly oxygenated steroid side chain was derived from NMR data combined with molecular dynamics calculation. Compounds 1 and 2 were tested against non-small-cell lung human carcinoma cells and found to be cytotoxic with IC50 of 60 μg/ml and 36 μg/ml, respectively.

ChemInform Abstract: Novel Methodology for the Introduction of a 22,23‐Diol Fragment in the Side Chain of Steroids.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Cavity depth and width effects on cyclophane-steroid recognition: molecular complexation of cholesterol and progesterone in aqueous solution

Recent X-ray crystal structures show that steroid-binding proteins contain deep hydrophobic cavities defined by aromatic amino-acid side chains which encapsulate steroid molecules. These cavities resemble the binding site of a synthetic macrotricyclic cyclophane receptor which we recently reported to form complexes with cholesterol in aqueous solution. The binding affinity of the cyclophane-cholesterol complex (Ka approximately 10(6) M-1, 295 K) is similar to that measured for the cholesterol complex of steroid-transport proteins such as sterol carrier protein-2 (SCP-2). Here we describe synthesis and binding studies of a related receptor with a cavity that is wider and 2 A deeper than that of the previous cyclophane, and a comparison of the steroid-binding affinity and selectivity of the two synthetic receptors. A new tricyclic cyclophane receptor with a 13 A deep cavity was synthesized to study the effect of increased cavity depth on receptor selectivity for steroids. NMR analysis demonstrated that this receptor provided increased steroidal side-chain encapsulation with a corresponding gain in binding free energy of 0.9 kcal mol-1 (in d4-methanol) as compared to our previously reported 11 A deep receptor. An unexpected consequence of the increase in cavity depth was a corresponding enlargement of the cavity width, as indicated both by steroid-binding studies and molecular modeling. This enlargement in cavity width increases binding affinity for saturated steroids while decreasing the association strength of unsaturated steroids such as cholesterol. In water, cholesterol binds to the new receptor with Ka approximately 1.5 x 10(5) M-1 and exhibits a significant complexation-mediated solubility increase. Small changes in steroid receptor dimensions have resulted in large differences in steroid selectivity and binding affinity. These results indicate that potentially large gains in steroid-binding free energy may be obtainable from complete hydrophobic encapsulation of the flexible aliphatic steroidal side chain. These results have implications for the design of synthetic receptor mimics of natural steroid binding proteins.

Synthesis of 1α,25-dihydroxy-22-thiavitamin D 3 and related analogs

The 22-thiolation reaction of the steroidal side chain and the synthesis of 1α,25-dihydroxy-22-thiavitamin D 3 and related analogs bearing side chains of different sizes in combination with 20-epi configuration are described.

ChemInform Abstract: A Unified Approach to the (22S)‐ or (22R)‐Hydroxy Steroid Side Chain: Lewis Acid Promoted Carbonyl‐ene Reaction with α‐Alkoxyaldehydes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Particulate binding sites for steroid hormones in subcellular fractions of the ovine corpus luteum: properties and hormone specificity

We have described previously the presence of binding sites in particulate fractions of the porcine corpus luteum (CL) which were specific for progesterone. We now demonstrate the presence of similar progesterone-specific binding sites in particulate fractions of the ovine CL. Preincubation of ovine luteal membranes with radiolabelled steroids demonstrated binding of progesterone and pregnenolone to a low-density particulate fraction (1.07–1.09 g/cm 3). Preincubation with digitonin perturbed the buoyant density of this fraction (to1.10–1.14 g/cm 3) without causing release of steroid. Androgens and oestrogens did not bind appreciably to control luteal membranes, but were bound when preincubated with digitonin. In contrast, steroid conjugates (oestrone sulfate, pregnanediol glucuronide), cortisol, fatty acids (arachidonic acid, prostaglandin F 2α) and cholesterol ester failed to bind to ovine luteal membranes, with or without digitonin pretreatment. The effects of digitonin on steroid binding led us to examine its effects on steroid binding to ovine luteal membrane fractions in vitro. Specific progesterone binding was absent in the absence of digitonin, even at very high membrane concentrations. However, binding of 3H-labelled progesterone was stimulated 5–15-fold in a dose-dependent fashion by increasing digitonin concentrations, reaching a plateau at about 100 μM. In the presence of digitonin, [ 3H]progesterone binding increased linearly with luteal membrane concentration. Other detergents, saponins and cardiotonic steroids tested did not stimulate progesterone binding to ovine luteal membranes. [ 3H]Progesterone binding was dependent on the pH, duration and temperature of incubation. Unlabelled progesterone decreased binding of [ 3H]progesterone (half-maximal displacement of specific binding (IC 50) at about 60 nM) whereas androgens were less potent (IC 50, 500–3300 nM), whilst a wide range of other steroids and inhibitors of steroidogenic enzymes were neffective, except at very high concentrations. Similarly, a number of progesterone receptor agonist and antagonist analogues failed to compete for progesterone binding to luteal membranes, suggesting that these binding sites were unrelated to progesterone receptors. Modifications to the 3,4, 5 and 11 positions of progesterone, removal of the steroid side-chain or aromatization of the A-ring decreased binding potency dramatically, whereas changes to the 17 or 20 positions had relatively minor effects. Our results indicate the presence of a low density particulate fraction in ovine corpora lutea which contains specific binding sites for endogenous and exogenous progesterone.

Synthesis and biological activity of 28-homobrassinolide and analogues

28-Homobrassinolide has been synthesized from stigmasterol in an overall yield of 21%. The biological activity of 28-homobrassinolide, brassinolide, 24-epibrassinolide, 22 S,23 S,24-epibrassinolide, and 22 S,23 S,28-homobrassinolide have been compared in the soybean epicotyl elongation assay. All the steroids except 22 S,23 S,28-homobrassinolide exhibited a similar biological activity, but the latter compound was substantially less active. There appears to be a correlation between biological activity and overall dimensions of the steroidal side chain.

ChemInform Abstract: A Novel Method for Stereospecific Generation of Natural C‐17 Stereochemistry and Either C‐20 Epimer in Steroid Side Chains by Palladium‐Catalyzed Hydrogenolysis of C‐17 and C‐20 Allylic Carbonates.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Lactol‐Ene Reaction: An Efficient Access to the Synthesis of 22R,25‐ Dihydroy Steroid Side Chains.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

A novel method for stereospecific generation of natural C-17 stereochemistry and either C-20 epimer in steroid side chains by palladium-catalyzed hydrogenolysis of C-17 and C-20 allylic carbonates.

The allylic alcohol, obtained by the reaction of C-17-keto steroid with isopropenyllithium, was converted to carbonate. Its hydrogenolysis with triethylammonium formate affords C-17β-isopropenyl group. Steroid side chain units were introduced by the reaction of C-20 keto steroid with (E) and (Z) alkenyl lithiums. The natural epimer at C-20 in steroid side-chains was generated stereospecifically by the palladium-catalyzed hydrogenolysis with triethylammonium formate of C-20 (Z) allylic carbonates, and the unnatural configuration was generated by the C-20 (E) allylic carbonate.

Egg-jelly signal molecules for triggering the acrosome reaction in starfish spermatozoa.

It was in the early 1950s that J.C. Dan discovered the acrosome reaction in sea urchins, starfishes and several other marine invertebrates at Misaki Marine Biological Station on the Pacific coast of Japan. We now know that in many animals including mammals the acrosome reaction is an essential, and probably the most central, change in spermatozoa for fertilization. Starfish spermatozoa undergo the acrosome reaction upon encountering the jelly coat consisting of glycoproteins, steroid saponins, oligopeptides and inorganic components. To induce the acrosome reaction, three egg jelly components act in concert on the spermatozoa: a highly sulfated glycoprotein named acrosome reaction-inducing substance (ARIS), a group of sulfated steroidal saponins named Co-ARIS, and a group of glutamine-rich tetratriacontapeptides named sperm activating peptide (SAP). The action of ARIS is quite species-specific due to the specificity of ARIS-receptors in a restricted domain of the sperm surface and depends very much on sulfated saccharide chains. Co-ARIS is not much species-specific and its action depends on the sulfate group and steroid side chain. SAPs have a ring of 25 residues and increase the intracellular pH of spermatozoa. None of them can induce the acrosome reaction by itself in normal sea water, but ARIS does induce it in high Ca2+ or high pH sea water. Although a combination of ARIS and either Co-ARIS or SAP induces the acrosome reaction in normal sea water, all three are required to mimic the full activity of dissolved jelly coat.

Regioselective esterification of polyhydroxylated steroids by Candida antarctica lipase B

The regioselectivity of Candida antarctica lipase B towards the acetylation of polyhydroxylated steroids has been systematically investigated. The enzyme showed a mark preference forthe alcoholic moieties on the A ring and on the steroidal side chain, making it possible the selective acylation at the positions 3 or 21 of polyhydroxy steroids. Acylation with the synthetically useful ester choloroacetate and levulinate was also accomplished, whereas esterification with benzoate and pivaloate as unsuccessful.

Sapogenins and dimethyldioxirane: A new entry to cholestanes functionalized at the side chain

A new and simple opening of the sapogenin spiroketal side chain by DMDO as oxyfunctionalizing agent, with the aim to get an easy approach to steroidal functionalized side chains from natural compounds available in large amounts, is reported.

A unified approach to (22S)- or (22R)-hydroxy steroid side chain: Lewis acid-promoted carbonyl-ene reaction with α-alkoxyaldehydes

A Lewis acid-promoted carbonyl-ene approach to either (22S)- or (22R)-hydroxy steroid side chain is described.

Human hepatoblastoma cells (HepG2) and rat hepatoma cells are defective in important enzyme activities in the oxidation of the C27 steroid side chain in bile acid formation

We have examined the ability of HepG2 human hepatoblastoma cells and 7800 C1 Morris rat hepatoma cells to convert 3 alpha, 7 alpha, 12 alpha-trihydroxy-5 beta-cholestanoic acid (THCA) and 3 alpha, 7 alpha-dihydroxy-5 beta-cholestanoic acid (DHCA) to cholic acid and chenodeoxycholic acid, respectively. Cell extracts from both these cell lines could neither form cholic acid from THCA nor from the activated form, THCA-CoA. This suggests that both cell lines are defective in two enzyme activities involved in the pathway, the microsomal THCA-CoA ligase and the peroxisomal THCA-CoA oxidase. Furthermore, we show that the subsequent enzymes are active in the conversion to bile acids, because the product of the THCA-CoA oxidase, 3 alpha, 7 alpha, 12 alpha-trihydroxy-5 beta-cholest-24-enoyl-coenzyme A (delta 24-THCA-CoA) or delta 24-THCA in the presence of THCA-CoA ligase, are converted to cholic acid by both cell lines. HepG2 cells were able to slowly form chenodeoxycholic acid and cholic acid from 5 beta-cholestane-3 alpha, 7 alpha-diol and 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol, respectively, in 24- and 96-h incubations. The rate of cholic acid formation was lower than the rate for chenodeoxycholic acid and there was a clear accumulation of THCA. 7800 C1 Morris cells had no ability to form cholic acid or chenodeoxycholic acid after 96 h incubation. We conclude that these two cell lines have defects in two enzyme activities involved in the peroxisomal oxidation in bile acid formation, the microsomal THCA-CoA ligase and the peroxisomal THCA-CoA oxidase.

ChemInform Abstract: Studies on Steroidal Plant‐Growth Regulators. Part 29. Osmium Tetroxide‐Catalyzed Asymmetric Dihydroxylation of the (22E,24R)‐ and the (22E,24S)‐24‐Alkyl Steroidal Unsaturated Side Chain.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Stereochemistry and physiological significance of hydroxylation of vitamin D side chain

Stereochemical aspect of side chain hydroxylation (C-23, C-24, and/or C-26 positions) of vitamin D 3 is described. The effect of the configuration of hydroxy group on biological activities is emphasized. Stereochemistry of vitamin D hydroxylation is compared with that of other natural hydroxylated steroids. Conformation of steroid side chain is also discussed