Sixth International Electronic Conference on Synthetic Organic Chemistry (ECSOC-6), 1-30 September

[A017]

Synthesis of Steroidal D-ring fused Isoxazolines of the Estrane-Series

Masao Imai,a Masataka Watanabe,a Shuntaro Mataka,b Thies Thiemannb*

 

Graduate School of Interdisciplinary Engineering Sciences and the Institute of Advanced Material Study, Kyushu University, 6-1, Kasuga-koh-en, Kasuga-shi, Fukuoka 816-8580, Japan E-mail: thies@cm.kyushu-u.ac.jp

 

In our quest for estrogens and anti-estrogens as ligands for the estrogen receptor ERa, the authors have studied steroid derived compounds such as 1, where an areno-unit has been fused to the D ring.[1] A number of steroidal D-ring fused heterocycles, both of the estrane and the androstane series, such as structures 2 - 4,[2,3] 6[4a,5,6] and 7[7] are known. Many of these molecules have been synthesized by intramolecular cyclization reactions such as by cyclization of steroidal b-ketohydrazones,[8] by a Domino-Heck-triene cyclization protocol[1] or by addition-cyclization sequences on steroidal ketoenamines.[3] A second approach uses an intermolecular cycloaddition, either of a 17-vinyl substituted 16,17-unsaturated steroid[9] as diene component or of an acceptor-substituted 16,17-unsaturated steroid as the ene-component[10] in a [4 + 2] cycloaddition for the preparation of areno- or alicyclo-annelated steroids such as 1 and 5 or in a [3 + 2] reaction to steroids annelated to a heterocycle, e.g, to 2, 3, 6 and 7. In the latter case, reactions of 16,17-unsaturated steroids with nitrilimines,[2a,c] diazoalkanes,[11] in the preparation of pyrazolo intermediates for cyclopropasteroids,[11c] and aryl azides[2b] as 1,3-dipoles have been carried out. In the isoxazolinosteroidal series, the addition of nitronic esters,[6] benzonitrile oxide[4] and acetonitrile oxide[4] to 16-dehydro-20-oxo steroids such as to 3b-hydroxy-20-oxopregna-5,16-diene under either Lewis acid catalysis[5] or under high pressure (14 Kbar)[6] is known to give compounds of type 6 and also one addition to estra-1,3,5(10),16-tetraene-3,17-diol 17-acetate[7] has been carried out, where not only the potential bioactivity of the compounds is of interest, but also their use as reactive intermediates to 16b-cyano substituted steroids[12] and other derivatives.[13] In this communication, the preparation of the novel substituted isoxazolinoestranes of type 8 via the 1,3-dipolar cycloaddition of nitrile oxides 15 to 3-methoxyestra-1,3,5(10),16-tetraene (1) is presented. These compounds are seen, after reductive opening of the oxazolidine-moiety, as precursors to estrane-oligopeptide hybrids.[3]

3-Methoxyestra-1,3,5(10),16-tetraene (11) itself was synthesized in a known procedure via methylation of the phenolic group at C-3,[14] conversion of the 17-keto derivative 9 to the corresponding tosylhydrazone 10 and direct conversion of 10 via Shapiro reaction[15,16] to the product.

 

 

The nitrile oxides were prepared in situ by dehydrochlorination of the corresponding hydroxamic chlorides, which are accessible in two steps from the carbaldehydes via the oximes. Formerly the reaction to the benzhydroxamic chlorides and related compounds was carried out with chlorine in [17] or with nitrosyl chloride in ether.[18] Here, the transformation has been carried out with N-chlorosuccinimide (NCS).[19]

In principle, from the addition of 15 to 11 two regioisomers can be derived. Previously, there has been some confusion as to whether only one or two regioisomers and as to which regioisomers form in the addition of nitrile oxides to pregnolone derived compounds, where in the end it was reported that both regioisomers can form,[20] but with the isomer in which the oxygen of the former nitrile oxide is bonded to the more heavily substituted carbon atom being by far the major isomer. While in both the pregnolone derived molecules and estra-1,3,5(10),16-tetraene-3,17-diol 17-acetate the 16,17-olefinic moiety possesses a different degree of substitution at the two ends, the stereochemical demand in 11 is marked by the substituents of the neighboring carbon atoms within the steroidal frame. Thus, a priori it was not quite clear to what degree the stereochemical demand in 11 would affect the ratio of regioisomers RC1/RC2 formed in the reaction. The regioisomers RC1/RC2 can be readily identified by 1H NMR spectroscopy. In both regioisomers, the absorption frequencies of H16 and H17 are well separated and show clear d(oublet) [H17] and ddd-patterns [H16]. Also, the absorption of H15 is well separated and coupling between H16 and both H17 and H15 can be made out by 1H-1H COSY experiment. In the addition experiments often both regioisomers could be observed, with RC1 being the dominant isomer in all cases.

For the 1-pyrenyl substituted 16b-RC1, the signal for H16 is significantly broadened and shifted by d 0.4 ppm when compared to H16 of 16a-RC1 and of 16e-RC1. The electronic nature of the aryl substituent on the 1,2-oxazolino moiety has an influence, albeit a small influence, on the shift of H16 (see 16d-RC1 for an up-field shift of d 0.1 ppm). Moreover in 16b-RC1, for the 1,2-oxazolino moiety as well as for part of the pyrene substituent a double set of carbon signals can be observed, where the shift difference in the two sets of signals is marginal. Additionally, shifts of C16 and C17 of 16b-RC1 and 16a-RC1 and others are very similar. As simple modeling of 16b-RC1 shows, the pyreno substituent may not be freely rotating at rt and the authors suggest that the double sets of C-signals as well as the broadening of H16 may be due to 16b-RC1 rotamers.

The determination of the endo-stereoselectivity of the addition reaction can be based on NOE-spectroscopical experiments on the cycloadducts, which showed H16, H17 and the angular C18-methyl group on the same face of the molecule, thus clearly indicating that the dipole reacted from the a-face of the molecule, as would be expected.

Studies on the estrogenicity and cytotoxicity of these compounds are underway.

 

 

Typical experimental procedure:

To pyrenehydroxyiminoyl chloride (14b) (374 mg, 1.34 mmol) in dry CH2Cl2 (30 mL) was added triethylamine (163 mg, 1.61 mmol) at 0‹C. After 5 min, 3-methoxyestra-1,3,5(10),6-tetraene (11) (300 mg, 1.12 mmol) was added to the solution, which was subsequently stirred for 4h. The reaction mixture was poured into water (50 mL) and extracted with CH2Cl2 (3 X 20 mL). The organic layer was dried over anhydrous MgSO4 and concentrated in vacuo. The residue was subjected to column chromatography on silica gel (hexane/ether 1:2) give 16b-RC1 (572 mg, 61%); IR (KBr) n 2936, 2858, 1610, 1501, 1452, 1357, 1280, 1253, 1240, 909 cm-1; 1H NMR (270 MHz, CDCl3) d 0.91 (s, 3H, CH3), 2.73 (m, 2H), 3.74 (s, 3H, OCH3), 4.39 (m, 1H), 4.80 (d, 1H, 3J 8.2 Hz); 6.56 (d, 4J 2.3 Hz); 6.70 (dd, 1H, 3J 8.6 Hz, 4J 2.3 Hz); 7.19 (d, 1H, 3J 8.6 Hz), 7.94 - 8.20 (m, 9H); 13C NMR* (67.8 MHz, DEPT 90, DEPT 135) d 17.63 (+, CH3), 25.98 (-), 28.05 (-), 29.56 (-), 31.84 (-), 38.22 (+, CH), 43.25 (+, CH), 47.35 (+, CH), 53.66 (+, C16, CHrotA), 53.74 (+, C16, CHrotB), 53.89 (Cquat), 55.11 (+, OCH3), 92.84 (+, C17, CHrotA), 93.00 (+, C17, CHrotB), 111.41 (+, CH), 113.71 (+, CH), 126.31 (+, CH), 132.25 (Cquat), 137.63 (Cquat), 157.41 (Cquat, C3), 160.03 (Cquat, C=NrotA), 160.17 (Cquat, C=NrotB); MS (FAB, 3-nitrobenzyl alcohol) m/z (%) 513 (MH+, 4); HRMS Found: 512.2593. Calcd. for C36H34O2N: 512.2590 (EI). *For clarity, C-values for the pyrene unit are not listed.

 

References and Footnotes:

 

[1]       T. Thiemann, M. Watanabe, S. Mataka, New J. Chem. 2001, 25, 1104.

[2]               [2a]B. Green, K. Sheu, Steroids 1994, 59, 479; [2b]B. Green, D.-W. Liu, Tetrahedron Lett. 1975, 33, 2807; [2c]B. Green, B. L. Jensen, P. L. Lalan, Tetrahedron 1978, 34, 1633.

[3]               M. Watanabe, M. Matsumoto, S. Mataka, T. Thiemann, in preparation for submission in Steroids.

[4]               [4a]T. P. Culbertson, G. W. Moersch, W. Neuklis, J. Heterocyclic Chem. 1964, 1, 280. This revised the structural assignment given in a previous report, see: [4b]W. Fritsch, G. Seidl, H. Ruschig, Justus Liebigs Ann. Chem. 1964, 677, 139; [4c]U. Stache, W. Fritsch, H. Ruschig, Justus Liebigs Ann. Chem. 1965, 685, 228; [4d]J. Fajkos, J. A. Edwards, Synthesis 1974, 63.

[5]               I. S. Levina, E. I. Mortikova, A. V. Kamernitzki, Synthesis 1974, 562.

[6]               A. V. Kamernitzki, I. S. Levina, E. I. Mortikova, V. M. Shitkin, B. S. El'yanov, Tetrahedron 1977, 33, 2135.

[7]               G. Gerali, C. Parini, G. C. Sportoletti, A. Ius, Farmaco 1969, 24, 231.

[8]               F. Sweet, J. Boyd, O. Medina, L. Konderski, G. L. Murdock, Biochem. Biophys. 1991, 180, 1057.

[9]               R. Skoda-Földes, G. Jeges, L. Kollar, J. Horvath, Y. Tuba, J. Org. Chem. 1997, 62, 1326.

[10]           [10a]DD Pat. 277684 (Kasch, H.; Ponsold, K.; Kaufmann, G., 11.4.1990); Chem. Abstr. 1991, 114, 82261v; [10b]DD Pat. 251143 (Ponsold, K.; Kasch, H.; Kurischko, A.; Stölzner, W.; Kamernitzki, A.; Levina, I.; Nikitina, G.; Korchow, W., 4.11.1987); Chem. Abstr. 1988, 109, 73751 z); [10c]K. Ponsold, H. Kasch, A. V. Kamernitski, I. S. Levina, D. S. El'yanov, V. M. Zhalin, J. Prakt. Chem. 1986, 328, 903.

[11]           Cf., [11a]U. Eberhardt, Pharmazie 1975, 30, 22; [11b]DD Pat 122520 (Eberhardt, U.; VEB Jenapharm, 16.7.1975); Chem. Abstr. 1977, 87, 102536; [11c]A. V. Kamernitski, T. N. Galakhova, I. S. Livina, B. S. El'yanov, V. S. Bogdanov, E. G. Cherepanova, Izv. Akad. Nauk SSSR, Ser. Khim. 1985, 1893.

[12]           [12a]G. W. Moersch, E. L. Wittle, W. A. Neuklis, J. Org. Chem. 1965, 30, 1272; [12b]G. W. Moersch, E. L. Wittle, W. A. Neuklis, J. Org. Chem. 1967, 32, 1387.

[13]           G. Gerali, C. Parini, A. Ius, G. C. Sportoletti, Farmaco 1969, 24, 299.

[14]           R. A. W. Johnstone, M. E. Rose, Tetrahedron 1979, 35, 2169.

[15]           11 has also been prepared by treatment of 10 with LiALH4: [15a]L. Caglioti, M. Magi, Tetrahedron 1963, 19, 1127. C-17 deuterated and tritiated 3-methoxyestra-1,3,5(10),6-tetraene has also been prepared by Shapiro reaction of xx: [15b]M. Saljoughian, H. Morimoto, C. Than, P. G. Williams, Tetrahedron Lett. 1996, 37, 2923.

[16]           Other methods of preparing 11 have been reported: a.) via the less readily accessible estra-1,3,5(10)-trien-3,16-diol-16-tosylate: [16a]M. N. Huffman, M. H. Lott, A. Tillotson, J. Biol. Chem. 1955, 217, 203; b.) via pyrolysis (300‹C) of estra-3,17b-diol dibenzoate: [16b]V. Prelog, L. Ruzicka, P. Wieland, Helv. Chim. Acta 1946, 27, 250.

[17]           Y. Iwakura, M. Akiyama, K. Nagakubo, Bull. Chem. Soc. Jpn. 1964, 37, 76.

[18]           [18a]Y. Iwakura, K. Uno, S. Shiraishi, T. Hongu, Bull. Chem. Soc. Jpn. 1968, 41, 2954; [18b]Y. H. Chiang, J. Org. Chem. 1971, 36, 2155; [18c]A. Battaglia, A. Dondoni, O. Exner, J. Chem. Soc., Perkin Trans 2 1972, 1911.

[19]           C. J. Peake, J. H. Strickland, Synth. Commun. 1986, 16, 763.

[20]           A. Ius, C. Parini, G. Sportoletti, G. Vecchio, G. Ferrara, J. Org. Chem. 1971, 36, 3470.

[21]           Typical spectral and analytical data is as follows - (16a-RC1) mp 204 - 205‹C; IR (KBr) n 2938, 2858, 1610, 1501, 1455, 1358, 1314, 1234, 1034, 911, 765, 689 cm-1; 1H NMR (600 MHz, CDCl3) d 0.90 (s, 3H, CH3), 3.77 (s, 3H, OCH3), 4.07 (dd, 1H, 3J 8.2 Hz, 3J 8.3 Hz), 4.71 (d, 1H, 3J 8.2 Hz), 6.61 (d, 1H, 4J 2.5 Hz), 6.71 (dd, 1H, 3J 8.8 Hz, 4J 2.5 Hz), 7.22 (d, 1H, 3J 8.8 Hz), 13C NMR (67.8 MHz, CDCl3) d 17.57, 28.06, 28.14, 29.76, 31.82, 38.40, 43.29, 47.04, 47.19, 50.24, 55.22, 94.21, 111.52, 113.83, 126.43, 126.97, 128.75, 129.31, 129.74, 132.43, 137.77, 157.52, 159.10; MS (70 eV) m/z (%) 387 (M+, 100); HRMS Found: 387.2203; Calcd. for C26H29O2N: 387.2203; (16a-RC2) 1H NMR (395 MHz, CDCl3) d 1.04 (s, 3H, CH3), 1.39 - 1.60 (m, 7H), 1.75 (ddd, 2J 13.4 Hz, 3J 12.6 Hz, 3J 4.8 Hz), 1.90 - 1.93 (m, 1H), 2.13 - 2.17 (m, 1H), 2.22 (dd, 2J 13.4 Hz, 3J 5.7 Hz), 2.84 - 2.86 (m, 2H), 3.75 (s, 3H, OCH3), 3.86 (d, 1H, 3J 8.9 Hz), 5.29 (dd, 1H, 3J 8.9 Hz, 3J 4.8 Hz), 6.61 (d, 1H, 4J 2.9 Hz), 6.66 (dd, 1H, 3J 8.6 Hz, 4J 2.9 Hz), 7.06 (d, 1H, 3J 8.6 Hz), 7.36 - 7.41 (m, 3H), 7.64 - 7.67 (m, 2H); (16d-RC1) IR (KBr) n 2924, 2860, 1609, 1500, 1255, 916, 868, 798 cm-1; 1H NMR (270 MHz, CDCl3) 0.89 (s, 3H, CH3), 1.26 - 2.41 (m, 11H), 2.50 (s, 3H, CH3), 2.83 (m, 2H), 3.77 (s, 3H, OCH3), 3.95 (m, 1H), 4.66 (d, 1H, 3J 8.2 Hz), 6.61 (m, 1H), 6.72 (m, 2H), 6.93 (d, 1H, 3J Hz), 7.21 (d, 1H, 3J 8.5 Hz); d 13C NMR (67.8 MHz, DEPT 90, DEPT 135) d 15.55 (+, CH3), 17.47 (+, CH3), 26.02 (-), 28.12 (-), 29.76 (-), 31.79 (-), 31.99 (-), 38.37 (+, CH), 43.23 (+, CH), 47.04 (+, CH), 47.17 (Cquat), 55.20 (+, OCH3), 94.17 (+, CH), 111.48 (+, CH), 113.82 (+, CH), 125.50 (+, CH), 126.41 (+, CH), 128.01 (+, CH), 129.95 (Cquat), 132.42 (Cquat), 137.75 (Cquat), 143.00 (Cquat), 155.24 (Cquat), 157.50 (Cquat); MS (70 eV) m/z (%) 407 (100); HRMS Found: 407.1922; Calcd. for C25H29O2NS: 407.1919; (16e-RC1): mp 233 - 235‹C; IR (KBr) n 2930, 2862, 1605, 1567, 1518, 1505, 1345, 1238, 923, 906, 852 cm-1; 1H NMR (270 MHz, CDCl3) d 0.92 (s, 3H, CH3), 1.33 - 2.03 (m, 10H), 2.38 (m, 1H), 2.43 (m, 1H), 2.82 (m, 2H), 3.76 (s, 3H, OCH3), 4.07 (m, 1H), 4.80 (d, 1H, 3J 8.3 Hz), 6.61 (d, 1H, 4J 2.7 Hz), 6.71 (dd, 1H, 3J 8.6 Hz, 4J 2.7 Hz), 7.21 (d, 1H, 3J 8.6 Hz), 7.87 (d, 2H, 3J 8.3 Hz), 8.26 (d, 2H, 3J 8.3 Hz). 13C NMR (67.8 MHz, CDCl3, DEPT* 90, DEPT 135) d 17.52 (+, CH3), 25.95 (-), 28.10 (-), 29.67 (-), 31.75 (2C, -), 38.29 (+, CH), 43.27 (+, CH), 47.22 (2C, +, CH and Cquat), 49.56 (+, CH), 55.20 (+, OCH3), 95.43 (+, CH), 111.57 (+, CH), 113.83 (+, CH), 124.04 (+, CH, 2C), 126.39 (+, CH), 127.54 (+, CH, 2C), 132.14 (Cquat), 135.52 (Cquat), 137.64 (Cquat), 148.24 (Cquat), 157.57 (Cquat), 157.73 (Cquat); MS (EI, 70 eV) m/z (%) 432 (M+, 100); HRMS Found: 432.2043; Calcd for C26H28O4N2: 432.2049. *The assignment of the C-signals has been aided by DEPT experiments (DEPT = Distortionless Enhancement of Polarisation Transfer), where (+) denotes primary and tertiary carbons, (-) secondary carbons and (Cquat) quaternary carbons.