Steroids: partial synthesis in medicinal chemistry

Contents

• 1 Introduction

• 2 Estrogens

• 3 Androstanes

• 4 Pregnanes

• 5 Bile acids

• 6 Cholestanes

• 7 Vitamin D

• References

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Abstract

Covering: January to December, 2004

This article reviews the progress in the chemistry of the steroids that was published between January and December 2004. The reactions and partial synthesis of estrogens, androgens, pregnanes, cholic acid derivatives, cholestanes and vitamin D analogues are covered. There are 127 references.

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1 Introduction

This review follows the pattern of its predecessors¹ with sections on the major skeletal types of steroids. Reviews have appeared on the use of steroids in combinatorial chemistry,² on the synthesis and biological activity of cephalostatin analogues,³ on directing effects in the hydroboration of steroidal alkenes⁴ and on the solid phase epoxidation of steroidal alkenes with potassium permanganate and metal salts.⁵ The methods that are employed for the identification of anabolic steroids that are abused in sport, have been reviewed.⁶ Special issues of the Journal of Steroid Biochemistry and Molecular Biology have been devoted to vitamin D⁷ and to the role of steroids in prostate cancer and its treatment.^8,9

2 Estrogens

A number of novel syntheses of the estrane skeleton have been described¹⁰ including an enantioselective synthesis of estrone using a chiral oxazaborolidinium catalyst. A radical cascade cyclization has been used¹¹ in a new total synthesis of estrone whilst the steroid backbone has been formed¹² by a photo-induced domino-cyclization of silyl enol ethers.

A gas chromatography–mass spectrometric assay of estradiol, catechol estradiols and methoxyestradiol in plasma has been developed¹³ whilst isotope dilution GC–MS methods have been used¹⁴ in the detection of estrogens and phytoestrogens in urine. The differentiation of steroid epimers by mass spectrometric methods has been examined.¹⁵ The complete ¹H and ¹³C NMR assignments of some estradiols have been reported.¹⁶

A molecular dynamics simulation has been used¹⁷ to predict the binding affinities of estrogen analogues to the estrogen receptor. The need for selective targeting of estradiol dependent cancers has been discussed¹⁸ in the context of drug delivery systems for estrogenic hormone antagonists. 2-Methoxyestradiol has tumour growth inhibitory properties. In light of this, the anti-proliferative activity of 2-alkylsulfonyl estrogen derivatives has been examined.¹⁹ A series of 2-methoxyestradiol analogues, e.g.1, have been prepared²⁰ in order to study their effects on cell proliferation and cytotoxicity in human cancer cell lines.

The oxidative coupling of estradiol through the aromatic ring to give 2 using hydrogen peroxide and peroxidase²¹ and the bromination of estradiol with N-bromosuccinimide²² have been described. The stability of the catechol estrogens in the presence of copper(I) salts has been examined.²³ The anti-cancer agent, estramustane 3 has been synthesized²⁴ bearing deuterium labels on rings A and D. An industrial synthesis of a 4-chloro-11β-arylestradiol 4 has been described.²⁵

The way in which ICI 182780 5 binds to and regulates the estrogen receptor, has been examined.²⁶ A further series of estradiol derivatives bearing sulfur containing substituents at the C-7a and C-11β positions have been reported.²⁷ Some estradiol–taxol® conjugates have been prepared²⁸ in which the estradiol is linked to the taxol® through the C-11 and C-16 positions.

The modification of ring D of the estrogens has continued to be explored in the context of its effects on estrogen metabolism. A number of potential estrogenic inhibitors of the 17β-hydroxy-steroid dehydrogenase have been prepared including compounds bearing substituents at C-16²⁹ and lactones at C-16,²⁹e.g.6.³⁰ The Mitsunobu inversion of sterically hindered 17β-hydroxy steroids has been examined.³¹ An unusual iminium ion induced overall 1,5-hydride shift 7 → 9 has been observed³² involving a D-seco isoquinuclidine 8.

3 Androstanes

Studies on the androgen receptor as a potential target for the treatment of prostate cancer have been reported.³³ The use of anti-androgens in the endocrine treatment of prostate cancer has been discussed.³⁴ The loss of the androstane 19-methyl group in the aromatase sequence leading to the estrogens, has continued to be a topic of investigation with reports on the synthesis of 19-³H analogues of dehydroepiandrosterone.³⁵ The determination of the stereochemistry of the reduction of the 19-carbonyl group of the 3-deoxyandrogens 10 and 11 by sodium borohydride has led³⁶ to the preparation of some 19R- and 19S-labelled aromatase inhibitors. In both cases the 19S isomer predominated in the reduction. It is the 19-proR hydrogen which is lost on the aromatase oxidation to the aldehyde. The cleavage of the C(10)–C(19) bond of oxygenated androst-4-ene-3,6-diones (e.g.12 → 13) has been examined³⁷ under various conditions.

The selective carbonylation of 2α,3α-epoxyandrostan-17-one to give 2β-carbomethoxy-3α-hydroxyandrostan-17-one 14 in the presence of a cobalt octacarbonyl catalyst, has been reported.³⁸ The hydroboration of 3-hydroxy-3-methylandrost-4-enes has been shown³⁹ to give 4β-hydroxy-3α-methyl-5β(H)-steroids (15 → 16) with the elimination of the 3-hydroxyl group irrespective of the stereochemistry at C-3. The β-face selective epoxidation of Δ⁵-steroids has continued to be of interest with reports⁴⁰ on the use of oxygen in the presence of a silica supported cobalt catalyst. Whereas treatment of 5α,6α-epoxy-3β-methanesulfonoxyandrostan-17-one with hydrobromic acid in glacial acetic acid afforded a 4-methylestratriene by a dienol–benzene rearrangement, the reaction with sulfuric acid led to the product 17 of a Westphalen backbone rearrangement.⁴¹ 3-Chloro-3,5-dienes 18 are easily prepared from the corresponding unsaturated ketones with oxalyl chloride. They have been shown⁴² to be oxidized with chromium trioxide to the corresponding Δ⁴-3,6-diones in good yield. The synthesis of some 3-hydroxy-3-methyl-6-oxoandrostanes has been reported.⁴³ The crystal structure has been described⁴⁴ of a trifluoroacetate bridged 5,6,7-π-allyl steroid palladium dimer 19 derived from the reaction of 3β-acetoxyandrost-5-en-17-one with palladium(II) trifluoroacetate.

11-Substituted androstanes have continued to attract interest. A cobalt mediated 2 + 2 + 2 cyclization of an allenediyne has been reported⁴⁵ to give the 11-aryl steroid skeleton. The reactivity of 11-oxo steroids, e.g.20, towards organometallic reagents⁴⁶ and the radical decomposition of oxalate esters⁴⁷ have been examined in the context of preparing 11-substituted derivatives. Further work has been reported on the preparation of 13,14-seco-steroids by the Grob fragmentation of 14α-hydroxy-17β-tosyloxy steroids, 21 → 22,⁴⁸ and by the lead tetra-acetate and iodine oxidation of 14α-hydroxy-17-keto steroids.⁴⁹ The reaction of (13S)-13-iodo-16β-methoxy-3α,5α-cyclo-13,14-secoandrostan-14,17-dione with hydroxylamine has been examined.⁵⁰

A simple synthesis of gestodene 23 from 18-methylestr-4-ene-3,17-dione has been reported.⁵¹ The detection of 17-alkyl substituted anabolic steroids by liquid chromatography and electrospray tandem mass spectrometry has been examined in relation to the abuse of these steroids.⁵² The microbiological hydroxylation of 17-methoxy steroids at C-6 and C-11 by the fungus, Cephalosporium aphidicola, has been reported.⁵³

The synthesis of the furanosteroidal antibiotic, viridin 24 has been achieved.⁵⁴ The biological activity of a library of viridin and wortmannin analogues as inhibitors of tumour cell growth has been examined.⁵⁵

4 Pregnanes

The synthesis and the effect of 3α-amino-5α-pregnan-20-one on the GABA receptor has been studied⁵⁶ in the context of the activity of pregnanes as neurosteroids. The synthesis and modification of 3β-steroidal glycosides of 3β,5α,6β-trihydroxypregnan-20-one has been reported.⁵⁷ Some 5α-hydroxy-6-ketopregnanes, e.g.25, have been examined⁵⁸ as analogues of brassinosteroid plant growth regulators. 17-Substituted pregnadienes have been prepared⁵⁹ as potential inhibitors of testosterone 5α-reductase. An unusual Δ²⁰-pregnene 26 which was obtained⁶⁰ from an octacoral, has been shown to be an inhibitor of the mitochondrial respiratory chain.

The hydrogenation of a C(20),C(22)-ketene dithioacetal has been used⁶¹ in the stereoselective synthesis of the unnatural C(20R) epimer of a C(22) aldehyde. The stereoselective reactions of the 20-dihydropyran 27 have been examined⁶² with the object of preparing compounds with modified steroidal side chains.

Steroidal tetrahydroxyoxazineones, e.g.28, have been examined⁶³ as inhibitors of testosterone 5α-reductase. A number of heterocyclic steroids have been prepared from dehydropregnenolone acetate and D-secopregnenes including the tetrahydroquinoline analogue 29.^64,65 The stereoselective addition of pyridyl lithium to a C-22 aldehyde has been reported.⁶⁶ The effect of the modified steroid backbone of 5β-methyl-19-norpregn-9-enes on their biotransformation by Cephalosporium aphidicola, has been examined.⁶⁷

An historical account has been given⁶⁸ of the development of the Merck process for the synthesis of cortisone from bile acids. Some novel spironolactone analogues have been detected⁶⁹ as impurities in commercial preparations of spironolactone. The flexibility of the progesterone receptor binding pocket has been explored⁷⁰ using crystal structures of norethindrone and mometasone furoate 30 complexes. The synthesis and glucocorticoid activity of a series of 17-furoate esters, e.g.31,⁷¹ and of some C-21 nitroesters of prednisolone,⁷² have been explored. The products, including 32, from the photodegradation of the anti-inflammatory steroid loteprednol etabonate, have been identified.⁷³

The synthesis of the biologically active cardenolides has been reviewed.⁷⁴ Bufalin is a bioactive constituent of the Chinese drug Chan-Su, which shows potent anti-cancer activity. A number of cytotoxic bufadienolides have been obtained⁷⁵ from bufalin by microbial hydroxylation with Mucor spinosus.

5 Bile acids

The partial synthesis of 3α,7α,14α-trihydroxy-5β-cholan-24-oic acid has been described.⁷⁶ The C-14α hydroxyl group was introduced by oxidation with dimethyldioxirane. The farnesol X receptor is activated by endogenous bile acids and plays a variety of physiological roles related to the modulation of gene transcription. Some further bile acid analogues based on 33 and derived from chenodeoxycholic acid have been examined⁷⁷ in this context. Bile acid conjugates, e.g.34 of mifepristone have been synthesized⁷⁸ as liver selective glucocorticoid antagonists for the treatment of type 2 diabetes.

The synthesis and X-ray crystal structures have been reported^79–81 of a number of dinorcholane derivatives. The X-ray crystal structure of the monoethyl oxalate ester of 3α-hydroxy-5β-cholan-24-oic acid has been described.⁸² Some lithocholic acid derivatives have been synthesized.⁸³ The hydrogen bonding network of 3-oxo-12α-hydroxy-5β-cholan-24-oic acid has been predicted⁸⁴ from X-ray evidence.

The remote functionalization of 3-oxo-bile acids by oxidation with 2,6-dichloropyridine N-oxide catalysed by a ruthenium porphyrin has been shown⁸⁵ to lead to lactonization at C-20 as in 35. Conjugates of gadolinium complexes with bile acids have been considered⁸⁶ as hepatocyte directed contrast agents for magnetic resonance imaging.

6 Cholestanes

A series of gradient enhanced selective NMR experiments have been used⁸⁷ to assign the ¹H NMR signals of stigmasterol. The synthesis of cholest-1-en-3-one from the 2α-iodo-3-ketone by oxidation of the iodine with per-acid has been described.⁸⁸ A series of spirostane analogues of the brassinosteroids have been prepared⁸⁹ by the homogeneous potassium permanganate dihydroxylation of 2,3-enes. The oxidation of Δ²-, Δ^2,4- and Δ^4,6-cholestenes with ruthenium tetroxide to form diols and ketols, e.g.36 has been reported.⁹⁰

Methods for the attachment of glycosyl units at the C-3 of diosgenin have been examined.^91,92 The synthesis of some spirostenols based on diosgenin which prevent β-amyloid induced neurotoxicity has been reported.⁹³ Cholesterol surrogates containing a benzophenone moiety have been synthesized⁹⁴ as potential photo-affinity labels for measuring cellular sterol efflux and HDL formation.

The design of chiral dimesogens containing cholesteryl groups for use in liquid crystals has been reviewed.⁹⁵ The (2π + 2π) photo-cycloaddition of cholesteryl cinnamate to methyl phenanthrene-9-carboxylate has been examined⁹⁶ in the context of stereoselectivity in the liquid crystalline phase. The dimethylaminobenzoate group linked to cholesterol has been used⁹⁷ to examine the microenvironment of gel fibrils by fluorescence methods.

Iron picolinate complexes have been used in the stereoselective allylic 7α-hydroxylation of cholesteryl acetate with oxygen.⁹⁸ The antibacterial and cytotoxicity of 7α- and 7β-spermidinyl cholesterol analogues, e.g.37, has been reported.⁹⁹ A 7-hydroxy sterol 38 from a soft coral, has been shown¹⁰⁰ to possess testosterone 5α-reductase inhibitory activity.

The cytotoxic sterols, 24-methylenecholesta-3β,5α,6β,19-tetraol and 24-methylenecholest-5-ene-3β,7α- and 3β,7β-diols have been synthesized^101,102 from stigmasterol. The 22-spiroketal of diosgenin has been removed¹⁰³ by a Clemmensen reduction to afford 3β,16β,26-trihydroxycholest-5-ene, 39. This methodology has also been used to produce deuteriated samples. The rearrangement of a 23-oxo-spirostane to a 22-oxo-23-spiroketal 40 has been investigated¹⁰⁴ and the structure of the product established by X-ray crystallography.

The ecdysone relatives, viticosterone E 41¹⁰⁵ and the 22R/S epimers of 2α,3α,20,22-tetrahydroxy-5α-cholestan-6-one¹⁰⁶ have been synthesized and the binding of the latter to the ecdysterone receptor has been examined. A number of brassinosteroid relatives have been synthesized and their biological activity evaluated.^107,108 (26,27-²H₆)-Brassinosteroids have been prepared¹⁰⁹ for metabolic studies. The preparation of 1α,25-diacetoxy-3β-hydroxycholesta-4,6-diene 42 from a 5,7-diene has been reported.¹¹⁰

Efficient methods for the separation of lanosterol and dihydrolanosterol from commercial mixtures and for the preparation of epimerically pure derivatives have been described.^111,112

7 Vitamin D

The proceedings of the 12th Vitamin D Workshop have been published.⁷ Some new derivatives of 1α,25-dihydroxy-19-norvitamin D₃¹¹³ and 2-methylene analogues¹¹⁴ have been synthesized and their therapeutic potential has been discussed.¹¹⁵ Some 2-functionalized analogues of 1α,25-dihydroxyvitamin D₃ have been shown to be¹¹⁶ potent inducers of cell differentiation and some further 2α-(ω-hydroxyalkoxy)-analogues have also been synthesized.¹¹⁷ C(3)-Carbamate derivatives of 1α,25-dihydroxyvitamin D₃ showed¹¹⁸ a low affinity for the vitamin D receptor. The amide analogue 43 has been synthesized.¹¹⁹ The side chain lactam 44 has been reported¹²⁰ to be a vitamin D antagonist.

Calcitriol analogues with two different side chains at C(20) have been synthesized¹²¹ and their use as probes of the vitamin D receptor has been explored.¹²² The crystal structure of the vitamin D nuclear receptor liganded with the vitamin D side chain analogue calcipotriol 45, has been determined¹²³ in order to provide an insight into the biological activity of these analogues.

24-Sulfone¹²⁴ and sulfoxime analogues, e.g.46¹²⁵ of 1α,25-dihydroxyvitamin D₃ have been synthesized. The latter have low calcemic activity and are powerful inhibitors of the 24-hydroxylase involved in the catabolism of vitamin D. A number of other vitamin D derivatives have been synthesized.^126,127

8 References

1. J. R. Hanson, Nat. Prod. Rep., 2005, 22, 104.
2. R. Maltais, M. R. Tremblay, L. C. Crobanu and D. Poirier, J. Comb. Chem., 2004, 6, 443.
3. T. Flessner, R. Jautelat, V. Scholz and E. Winterfeldt, Prog. Chem. Org. Nat. Prod., 2004, 87, 1.
4. J. R. Hanson, J. Chem. Res., 2004, 1.
5. J. A. R. Salvador and J. R. Hanson, J. Chem. Res., 2004, 513.
6. G. J. Trout and R. Kaslauskas, Chem. Soc. Rev., 2004, 33, 1.
7. J. Steroid Biochem. Mol. Biol., 2004, 89, 1–633.
8. J. Steroid Biochem. Mol. Biol., 2004, 92, 219–325.
9. F. Labrie, L. Cusan, J. Gomez, V. Luu-The, B. Candas, A. Belanger and C. Labrie, J. Steroid Biochem. Mol. Biol., 2004, 92, 337.
10. Q.-Y. Hu, P. D. Rege and E. J. Corey, J. Am. Chem. Soc., 2004, 126, 5984.
11. G. Pattenden, K. L. Reddy and A. Walter, Tetrahedron Lett., 2004, 45, 4027.
12. J. A. Bunte, S. Rinne and J. Mattay, Synthesis, 2004, 619.
13. L. C. Zacharia, R. K. Dubey and E. K. Jackson, Steroids, 2004, 69, 255.
14. H. Adlercreutz, P. Kiuru, S. Rasku, K. Wahale and T. Fotsis, J. Steroid Biochem. Mol. Biol., 2004, 92, 399.
15. M. Mak, E. Francsics-Czinege and Z. Tuba, Steroids, 2004, 69, 831.
16. P. Cruffreda, S. Casati and A. Manzocchi, Magn. Reson. Chem., 2004, 42, 360.
17. M. M. H. van Lipzig, A. M. ter Laak, A. Jongejan, N. P. E. Vermeulen, M. Wamelink, D. Geerke and J. H. N. Meerman, J. Med. Chem., 2004, 47, 1018.
18. T. Ameller, P. Legrand, V. Marsaud and J. M. Renoir, J. Steroid Biochem. Mol. Biol., 2004, 92, 1.
19. M. P. Leese, S. P. Newman, A. Purchit, M. J. Reed and B. V. L. Potter, Bioorg. Med. Chem. Lett., 2004, 14, 3135.
20. A. B. Edsall, A. K. Mohanakrishnan, D. Yang, P. F. Fanwick, E. Hamel, A. D. Hanson, G. E. Agoston and M. Cushman, J. Med. Chem., 2004, 47, 5126.
21. A. Pezzella, L. Lista, A. Napolitano and M. d'Ischia, J. Org. Chem., 2004, 69, 5652.
22. A. J. Lee, J. W. Sowell, W. E. Cotham and B. T. Zhu, Steroids, 2004, 69, 61.
23. P. A. Thibodeau, C. Pasquier and M. A. Gougerot-Pocidalo, Steroids, 2004, 69, 419.
24. D. Giribone and E. Fontana, J. Labelled Compd. Radiopharm., 2004, 47, 161.
25. D. Prat, F. Benedetti, C. F. Girard, L. N. Bouda, J. Larkin, C. Wehrey and J. Lenay, Org. Process Res. Dev., 2004, 8, 219.
26. M. W. Wang, R. J. Traystman, P. D. Hum and T. Liu, J. Steroid Biochem. Mol. Biol., 2004, 92, 51.
27. D. Spera, G. Cabrera, R. Fiaschi, K. E. Carlson, J. A. Katzenellenbogen and E. Napolitano, Bioorg. Med. Chem., 2004, 12, 4393.
28. C. Liu, J. S. Strobl, S. Bane, J. K. Schilling, M. McCracken, S. K. Chatterjee, R. Rahim-Bata and D. G. I. Kingston, J. Nat. Prod., 2004, 67, 152.
29. M. Berube and D. Poirier, Org. Lett., 2004, 6, 3127.
30. P. Bydal, S. Auger and D. Poirier, Steroids, 2004, 69, 325.
31. P. Tapolosanyi, J. Wolfling, E. Mernyak and G. Schneider, Monatsh. Chem., 2004, 135, 1129.
32. J. Wolfling, E. Frank, G. Schneider and L. F. Tietze, Eur. J. Org. Chem., 2004, 90.
33. A. F. Santos, H. Huang and D. J. Tindall, Steroids, 2004, 69, 79.
34. T. Tammela, J. Steroid Biochem. Mol. Biol., 2004, 92, 287.
35. I. Cerny, V. Pouzar, M. Budesinsky, M. Bicikova, M. Hill and R. Hampl, Steroids, 2004, 69, 161.
36. M. Numazawa, N. Sohtome and M. Nagaoka, Chem. Pharm. Bull., 2004, 52, 722.
37. M. Nagaoka and M. Numazawa, Chem. Pharm. Bull., 2004, 52, 983.
38. A. Balazs, C. Benedek, G. Szalontai and S. Toros, Steroids, 2004, 69, 271.
39. C. Uyanik, J. R. Hanson, L. Nisius and P. B. Hitchcock, J. Chem. Res., 2004, 471.
40. S. M. Silvestre, J. A. R. Salvador and J. H. Clark, J. Mol. Catal., 2004, 219, 143.
41. S. G. Knights and J. R. Hanson, J. Chem. Res., 2004, 830.
42. I. Kiran and J. R. Hanson, J. Chem. Res., 2004, 208.
43. H. Chodounska, V. Pouzar, M. Budesinsky, B. Slavikova and L. Kohout, Steroids, 2004, 69, 599.
44. P. L. Ruddock, D. J. Williams and P. B. Reese, Steroids, 2004, 69, 193.
45. M. Petit, C. Aubert and M. Malacria, Org. Lett., 2004, 6, 3937.
46. V. Lecomte, E. Stephan, J. Vaissermann and G. Jaouen, Steroids, 2004, 69, 17.
47. V. Lecomte, E. Stephan, M. N. Rager and G. Jaouen, J. Org. Chem., 2004, 69, 3216.
48. V. A. Khripach, V. N. Zhabinskii, G. P. Fando, A. I. Kuchto, A. S. Lyakhov, A. A. Govorova, M. B. Groen, J. van der Louw and A. de Groot, Steroids, 2004, 69, 495.
49. V. A. Khripach, V. N. Zhabinskii, A. I. Kuchto, Y. Y. Zhiburtovitch, G. P. Fando, A. S. Lyakhov, A. A. Govorova, M. B. Groen, J. van der Louw and A. de Groot, Steroids, 2004, 69, 501.
50. V. A. Khripach, V. N. Zhabinskii, A. I. Kuchto, Y. Y. Zhiburtovitch, G. P. Fando, A. S. Lyakhov, A. A. Govorova, M. B. Groen, J. van der Louw and A. de Groot, Steroids, 2004, 69, 511.
51. P. Ferraboschi, P. Grisenti, A. Onofri and P. Prestileo, Synlett, 2004, 1838.
52. A. Leinonen, T. Kouranne, T. Kotiaho and R. Kostiainen, Steroids, 2004, 69, 101.
53. I. Kiran, J. R. Hanson and A. C. Hunter, J. Chem. Res., 2004, 362.
54. E. A. Anderson, E. J. Alexanian and E. J. Sorensen, Angew. Chem., Int. Ed., 2004, 43, 1998.
55. P. Wipf, D. J. Minion, R. J. Halter, M. I. Berggren, C. B. Ho, G. G. Chiang, L. Kirkpatrick, R. Abrahams and G. Powis, Org. Biomol. Chem., 2004, 2, 1911.
56. L. Matyas, A. Kasal, Z. B. Riera and C. E. Sunol, Collect. Czech. Chem. Commun., 2004, 69, 1506.
57. S. M. Wang, W. Z. Ge, H. M. Liu, D. P. Zou and X. B. Yan, Steroids, 2004, 69, 599.
58. D. G. Rivera, F. Coll and F. Leon, J. Chem. Res., 2004, 284.
59. M. Cabeza, E. Flores, I. Heuze, M. Sanchez, E. Bratoeff, E. Ramirez and V. A. Francoluge, Chem. Pharm. Bull., 2004, 52, 535.
60. M. L. Ciavatta, M. P. Lopez Gressa, E. Manzo, M. Gavagnin and S. Wadihulla, Tetrahedron Lett., 2004, 45, 7745.
61. B. P. Shingate, B. G. Hazra, V. S. Pore, R. G. Gonnade and M. M. Bhadbhade, Chem. Commun., 2004, 2194.
62. A. Magyar, Z. Szendi, P. Forgo, M. Mak, H. Gorls and F. Sweet, Steroids, 2004, 69, 35.
63. J. Wolfling, L. Hackler, E. Merriyak, G. Schneider, I. Toth, M. Szecsi, J. Julesz, P. Schars and A. Csampai, Steroids, 2004, 69, 451.
64. G. Schneider, J. Wolfling, E. Mernyak and I. Toth, Magy. Kem. Foly., 2004, 109, 40.
65. A. Magyar, J. Wolfling, M. Kubas, J. A. C. Seijo, M. Sevvana, R. Herbst-Immer, P. Forgo and G. Schneider, Steroids, 2004, 69, 301.
66. G. Visbal and A. Alvarez-Auler, Synth. Commun., 2004, 34, 533.
67. J. R. Hanson, P. B. Hitchcock and K. Yildirim, J. Chem. Res., 2004, 519.
68. S. H. Pines, Org. Process Res. Dev., 2004, 8, 708.
69. H. Chen, X. Y. Wang, Z. D. Yang and Y. C. Li, Steroids, 2004, 69, 647.
70. K. P. Madauss, S. J. Deng, R. J. H. Austin, M. H. Lambert, I. McLay, J. Pritchard, S. A. Short, E. L. Stewart, I. J. Uings and S. P. Williams, J. Med. Chem., 2004, 47, 338.
71. D. A. Sandham, L. Barker, D. Beattie, D. Beer, L. Bidlake, D. Bentley, K. D. Butler, S. Craig, D. Farr, C. Ffoulkes-Jones, J. R. Fozard, S. Haberthuer, C. Hawes, D. Hynx, S. Jeffers, T. H. Keller, P. A. Kirkham, J. C. Maas, L. Mazzoni, A. Nicholls, G. R. Pilgrim, E. Schaebulin, G. M. Spooner, R. Stringer, P. Tranter, K. L. Turner, M. F. Tweed, C. Walker, S. J. Watson and B. M. Cuenoud, Bioorg. Med. Chem., 2004, 12, 5213.
72. P. G. Baraldi, R. Romagnoli, M. C. Nunez, M. Perretti, M. J. Paul-Clark, M. Ferrario, M. Govoni, F. Benedini and E. Ongini, J. Med. Chem., 2004, 47, 711.
73. Y. Shirasaki, K. Inada, J. Inoue and M. Nakamura, Steroids, 2004, 69, 23.
74. G. Schneider and J. Wolfling, Curr. Org. Chem., 2004, 8, 1381.
75. M. Ye, G. Qu, H. Guo and D. Guo, J. Steroid Biochem. Mol. Biol., 2004, 91, 87.
76. G. Kakiyama, T. Iida, T. Goto, N. Mano, J. Goto and T. Nambara, Chem. Pharm. Bull., 2004, 52, 371.
77. R. Pellicciari, G. Costantino, E. Camaioni, B. M. Sadeghpour, A. Entrena, T. M. Willson, S. Fiorucci, C. Clerici and A. Gioiello, J. Med. Chem., 2004, 47, 4559.
78. T. W. von Geldern, N. Tu, P. R. Kym, J. T. Link, H. S. Jae, C. Lai, T. Apelquist, P. Rhonnstaad, L. Hagberg, E. Koehler, M. Grynfarb, A. Goos-Nilsson, J. Sanberg, M. Osterland, T. Barkhem, M. Hoglund, J. Wang, S. Fung, D. Wilcox, P. Nguyen, C. Jakob, C. Hutchins, M. Fornegardh, B. Kauppi, L. Ohman and P. B. Jacobsen, J. Med. Chem., 2004, 47, 4213.
79. L. Nahar and A. B. Turner, J. Chem. Res., 2004, 329.
80. P. J. Cox, L. Nahar, S. D. Sarker and A. B. Turner, J. Chem. Res., 2004, 192.
81. P. J. Cox, L. Nahar and A. B. Turner, J. Chem. Res., 2004, 372.
82. P. J. Cox, L. Nahar and A. B. Turner, J. Chem. Res., 2004, 691.
83. L. Nahar and A. B. Turner, J. Chem. Res., 2004, 747.
84. A. Jover, F. Meijide, V. H. Soto, J. V. Tato, E. R. Nunez, H. T. Ton-Nu and A. F. Hofmann, Steroids, 2004, 69, 379.
85. S. Ogawa, T. Iida, T. Goto, N. Mano, J. Goto and T. Nambara, Org. Biomol. Chem., 2004, 2, 1013.
86. P. L. Anelli, L. Lattuada, V. Lorusso, G. Lux, A. Morisetti, P. Morosini, M. Serleti and F. Uggeri, J. Med. Chem., 2004, 47, 3629.
87. P. Forgo and K. E. Kover, Steroids, 2004, 69, 43.
88. C. A. Horiuchi, S. J. Ji, M. Matsushita and W. Chai, Synthesis, 2004, 202.
89. D. G. Rivera, O. Pando, V. Leliebre-Lara, D. Coll, F. Leon and F. Coll, J. Chem. Res., 2004, 53.
90. D. Musumeci, G. N. Roviello and D. Sica, Steroids, 2004, 69, 173.
91. G. Gu, Y. Du and R. J. Linhardt, J. Org. Chem., 2004, 69, 5497.
92. S. Reicheneder and C. Unverzagi, Angew. Chem., Int. Ed., 2004, 43, 4353.
93. L. Lecanu, W. Yao, G. L. Teper, Z. X. Yao, J. Greeson and V. Papadopoulos, Steroids, 2004, 69, 1.
94. T. A. Spencer, P. Wang, D. Li, J. S. Russel, D. H. Blank, J. Huusjonen, P. E. Fielding and C. J. Fielding, J. Lipid Res., 2004, 45, 1510.
95. V. A. Mallia and N. Tamaoki, Chem. Soc. Rev., 2004, 33, 76.
96. H. Maeda, A. Horiuchi, N. Koshio and K. Mizuno, Chem. Lett., 2004, 33, 966.
97. Y. Iwashita, K. Sugiyasu, M. Ikeda, N. Fujita and S. Shinkai, Chem. Lett., 2004, 33, 1124.
98. I. Okamoto, W. Funaki, K. Nakaya, E. Kotani and T. Takeya, Chem. Pharm. Bull., 2004, 52, 756.
99. B. Choucair, M. Dherbomez, C. Roussakis and L. El-Kihel, Bioorg. Med. Chem. Lett., 2004, 14, 4213.
100. P. Radhika, M. Cabeza, E. Bratoeff and G. Garcia, Steroids, 2004, 69, 439.
101. W. Lu, L. Zeng and J. Su, Steroids, 2004, 69, 445.
102. W. Lu, C. Zhang, L. Zeng and J. Su, Steroids, 2004, 69, 803.
103. L. Alessandrini, P. Ciuffreda, E. Santaniello and G. Terraneo, Steroids, 2004, 69, 789.
104. M. K. Cyranski, J. Frelek, I. Jasirzebska and J. W. Morzycki, Steroids, 2004, 69, 395.
105. I. V. Galyautdinov, S. R. Nazmeeva, R. G. Savchenko, N. A. Ves'kina, D. V. Nedopekin and A. A. Fatykhov, Russ. J. Org. Chem., 2004, 40, 675.
106. B. Watanabe, Y. Nakagawa, T. Ogura and H. Miyagawa, Steroids, 2004, 69, 483.
107. S. Uesusuki, B. Watanabe, S. Yamamoto, J. Otsuki, Y. Nakagawa and H. Miyagawa, Biosci., Biotechnol., Biochem., 2004, 68, 1097.
108. F. M. Michelini, J. A. Ramirez, A. Berra, L. R. Galagovsky and L. E. Alche, Steroids, 2004, 69, 713.
109. A. P. Antonchick, B. Schneider, V. N. Zhabinskii and V. A. Khripach, Steroids, 2004, 69, 617.
110. S. D. van Arnum, B. K. Carpenter, D. R. Parrish and A. MacIntrye, J. Org. Chem., 2004, 69, 8529.
111. L. K. Kaviaradze, M. Manley-Harris and B. K. Nicholson, Steroids, 2004, 69, 227.
112. L. K. Kaviaradze, M. Manley-Harris and B. K. Nicholson, Steroids, 2004, 69, 697.
113. A. Glebocka, R. R. Sicinski and H. F. DeLuca, J. Steroid Biochem. Mol. Biol., 2004, 89, 25.
114. P. Grzywacz, L. A. Plum, W. Sicinska, R. R. Sicinski, J. M. Prahl and H. F. DeLuca, J. Steroid Biochem. Mol. Biol., 2004, 89, 19.
115. H. F. DeLuca, J. Steroid Biochem. Mol. Biol., 2004, 89, 67.
116. T. Fujishima, A. Kittaka, M. Kurihara, N. Saito, S. Honzawa, S. Kishimoto, T. Sugiura, K. Waku and H. Takayama, J. Steroid Biochem. Mol. Biol., 2004, 89, 89.
117. N. Saito, Y. Suhara, M. Kurihara, T. Fujishima, S. Honzawa, H. Takayanagi, T. Kozono, M. Matsumoto, M. Ohmori, N. Miyata, H. Takayama and A. Kittaka, J. Org. Chem., 2004, 69, 7463.
118. V. Gotor-Fernandez, S. Fernandez, M. Ferrero, R. Bouillon and A. Verstuyf, Bioorg. Med. Chem., 2004, 12, 5443.
119. Y. Suhara, K. Ono, A. Yoshida, T. Fujishima, N. Saito, S. Honzawa, S. Kishimoto, T. Sugiura, K. Waku, H. Takeyama and A. Kittaka, Heterocycles, 2004, 62, 423.
120. Y. Kato, Y. Nakano, R. Sano, A. Tanatani, H. Kobayashi, R. Shimazawa, H. Koshino, Y. Hashimoto and K. Nagasawa, Bioorg. Med. Chem. Lett., 2004, 14, 2579.
121. H. Maehr, M. R. Vskokovic, L. Adorini and G. S. Reddy, J. Med. Chem., 2004, 47, 6476.
122. H. Maehr, M. R. Vskokovic, L. Adorini and G. S. Reddy, J. Steroid Biochem. Mol. Biol., 2004, 89, 35.
123. G. Tocchini-Valentini, N. Rochel, J. M. Wurtz and D. Moras, J. Med. Chem., 2004, 47, 1956.
124. G. H. Posner, K. R. Crawford, H. W. Yang, M. Kahraman, H. B. Jeon, H. Li, J. K. Lee, B. C. Suh, M. A. Hatcher and T. Labonte, J. Steroid Biochem. Mol. Biol., 2004, 89, 5.
125. M. Kahraman, S. Sinishtaj, P. M. Dolan, T. W. Kensler, S. Peleg, V. Saha, S. S. Chuang, G. Bernstein, B. Korczak and G. H. Posner, J. Med. Chem., 2004, 47, 6854.
126. P. J. DeClercq, I. Murad, L. J. Gao, Y. J. Chen, D. V. Haver, M. van de Walle, A. Verstuyf, L. Verlinden, C. Verboven and R. Bouillon, J. Steroid Biochem. Mol. Biol., 2004, 89, 61.
127. E. Moman, D. Nicolletti and A. Mourino, J. Org. Chem., 2004, 69, 4615.

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