AU1311599A - Method of preparing 16alpha,17alpha-dialkylated steroids - Google Patents

Description

WO 99/28336 PCT/US98/23641 METHOD OF PREPARING 16a,17c-DIALKYLATED STEROIDS FIELD OF THE INVENTION 5 The present invention relates to methods of synthesizing 16c,17x dialkylated steroids. In particular, the present invention relates to methods of appending a 17a-alkyl substituent to a steroidal 16a-alkyl-17(20)-enyl-20-silyl ether. 10 BACKGROUND OF THE INVENTION 16c,17c-dialkylated steroids have desirable medicinal properties. See, for example, U.S. Patent No. 4,686,214; Cairns, et al., J. Chem. Soc., Perkin 15is Trans. 1, 1981:2306, and references cited therein. Previous syntheses of 16a,17a-dialkylated steroids have employed a one-step conjugate addition-enolate trapping method to accomplish the addition of the C16 and C17 alkyl groups. For example, see Schaub, et al., J. 20 Med. Chem., 10:789 (1967), and Cairns, et al., J. Chem. Soc., Perkin Trans. I, 1978:1594 and 1976:1558, disclosing alkyl Grignard conjugate addition reaction followed by an alkyl halide quench in a single reaction vessel. The one-step conjugate addition-enolate trapping method sometimes 2 gives the desired 16a,17a -dialkylated steroid in low yield and contaminated with polyalkylated side products. Such side products can be difficult to remove using conventional purification techniques, e.g., recrystallization: Cairns, et al., J. Chem. Soc., Perkin Trans. 1, 1981:2306 and 1978:1594. 3o Alternative methods of preparing 16x,17a-dialkylated steroids are desired.

WO 99/28336 PCT/US98/23641 SUMMARY OF THE INVENTION According to the present invention, steroidal 16a-alkyl-17(20)-enyl-20 silyl ethers are reacted with an enol silyl ether cleaving agent and an Salkylating agent to give the corresponding 16a, 17u.-dialkylated steroid. DETAILED DESCRIPTION OF THE INVENTION Enones of Formula I are known. The compounds of Formula I can be 10 prepared, for example, according to the methods cited or disclosed in commonly assigned, co-pending Patent Application No. PCT/US97/19276, titled "METHOD OF PREPARING 21-ALKYLATED PREGNA-1,4,16-TRIEN 3,20-DIONES," filed October 22, 1997, which claims priority from parent U.S. provisional application serial no. 60/029,312, filed October 25, 1996. 15 2121 21CH2 R 1 x =o 17 16 /Y 0 3 4 Q(I) wherein R 1 is H or CHR 4 R'; X is OSiR 7

R'R

9 or OC(=O)R 6 ; 20 Y is H, F, or CI; or X and Y taken together are a covalent bond; or X and Y taken together form an epoxide group: )No

R

4 , R' and R 6 are independently H or C 1 - C4 alkyl;

R

7 , R 8 and R 9 are independently C 1 - C4 alkyl; and 2 WO 99/28336 PCT/US98/23641 Q is H or CH 3 . Enol silyl ethers of Formula II can be prepared by addition of a stoichiometric organocuprate reagent and a silylating agent to enones of SFormula I, as described in Example 1 below. Alternatively, a catalytic organocuprate reagent can be used, as described by Horiguchi et al., Org. Synth., 73:123 (1995) for the case of copper-catalyzed Grignard addition to 16-dehydroprogesterone. Generally, it is desirable to conduct this addition reaction at low temperatures to increase the yield of the intended alkylation o10 product. Appropriate temperatures will be determined by those skilled in the art, but will typically range from 0 to -100 oC. In most instances, it is expected that temperatures ranging from -20 to -80 0C will be sufficient for the organocuprate addition reaction to selectively produce the intended product. 15 OSiR 7

R

8

R

9 X CH2R R2 O . 0 (II) wherein R 2 is C1 - 04 alkyl, and is most preferably CH 3 ; and X, Y, Q, R 1 , R 7 , R 8 , and R 9 are as defined above. 20 Preferred compounds of Formula II are those where R 1 is CH 3 ; R 2 is

CH

3 ; Q and Y are H; X is OSiR 7

R

8

R

9 and R 7 , R 8 , and R 9 are CH 3 According to the methods of the present invention, enol silyl ethers of 2 Formula II are reacted in a suitable solvent with an alkylating agent, R 3

CH

2 Z, and an enol silyl ether cleaving agent to give the corresponding 16a,17(x 3 WO 99/28336 PCT/US98/23641 dialkylated steroid of Formula III. Subsequently, the protecting group at the 11-position can be removed ((OSiR'R'R' or OC(=O)R 6 ) --> OH) using known methods (e.g., U.S. Patent No. 4,012,510 and Cairns, et al., J. Chem. Soc., Perkin Trans. 1, 1981:2306), to obtain a medicinally useful 16c,17(a S dialkylated steroid.

CH

2 R -0 x XpCH 2R3 .nR2 OY 0 (1) wherein R 3 is H, C1 - C3 alkyl, C-CH, CH=CH 2 , or phenyl; and o10 X, Y, Q, R', and R 2 are as defined above. The general chemical methodology involved is known for other applications. See Kuwajima, et al., J. Am. Chem. Soc., 104:1025 (1982) (fluoride salt method); Patterson, et al., J. Org. Chem., 39:2506 (1974) and 15 Binkley, et al., J. Org. Chem., 40:2156 (1975) (lithium amide method). According to these references, such methods result in little formation of polyalkylated side products. The alkylating agents, R 3

CH

2 Z, suitable for use in the methods of the 20 present invention are known compounds. R 3 is selected from the group consisting of hydrogen, an alkyl group of up to three carbon atoms total, an ethenyl group, an ethynyl group, and a phenyl group. Preferably, R 3 is H. Z is CI, Br or I, and is preferably I. 4 WO 99/28336 PCT/US98/23641 The enol silyl ether cleaving agent is selected from the group consisting of a fluoride salt and lithium amide. A third type of known enol silyl ether cleaving agents, alkyllithium compounds, is not suitable for use in the methods of the present invention because such compounds preferentially Sreact with the 3-keto group rather than the 17(20)-enyl-20-silyl ether. In the event that a fluoride salt is chosen as the enol silyl ether cleaving agent, the fluoride salt is preferably a tetraalkylammonium fluoride compound. An especially preferred fluoride salt is benzyltrimethylammonium o10 fluoride. Suitable solvents for use with the fluoride salt embodiment of the present invention include tetrahydrofuran ("THF") and glyme. The preferred solvent for use with a fluoride salt is THF. In the case of a fluoride salt enol silyl ether cleaving agent, the alkylation reaction is preferably conducted in the presence of a suitable drying agent, such as zeolite molecular sieves (see Is Kuwajima, et al., J. Am. Chem. Soc., 104:1025 (1982)). If lithium amide is chosen as the enol silyl ether cleaving agent, the preferred solvent is liquid ammonia. A cosolvent, such as THF, is optionally employed. 20 The following examples are presented to illustrate further various aspects of the present invention, but are not intended to limit the scope of the invention in any respect. 2 EXAMPLE 1 Preparation of 16c,21-Dimethyl-110,20-bis(trimethylsiloxy)-pregna-1,4,17(20)-trien-3 one 30 a) Preparation of dilithium dimethyl(cyano)cuprate(l). Methyllithium (1.0 M in 9:1 cumene-THF, 4.0 mL, 4.0 mmol) was added dropwise via syringe over 5 min to a stirred, ice-cooled suspension of CuCN powder (187 mg, 2.09 5 WO 99/28336 PCT/US98/23641 mmol) in anhydrous THF (6.0 mL) under Ar, giving a clear, pale pink-purple solution of Me2Cu(CN)Li2 (0.2 M). b) Preparation of Pregna-1,4,16-trien-11p-ol-3,20-dione. 5 i) The method of Kovendi et al., Rev. Chim. (Bucharest), 27:467 (1976) was modified. Semicarbazide hydrochloride (7.1 mL of a 5% aq. solution, 3.2 mmol) was added to a stirred, 50 oC solution of 21 deoxyprednisolone (1.82 g, 5.29 mmol) [see U.S. Patent No. 3,033,873 and Vitali et al., Gazz. Chim. Ital., 96:1115 (1966)] in acetic acid (60 mL) under Ar. 1o The solution was heated to 75-80 0C (internal). After 2.7 h, another 4.7 mL of 5% aq. semicarbazide hydrochloride (2.1 mmol) was added. After 5.5 h at 75 oC, water (50 mL) was added and the solution was heated to 75 oC for 10 h and then to 90 oC for 1.5 h. The solution was cooled to room temperature, poured into 600 mL of water, stirred for 1 h, diluted with water to 1 L, stirred 15 for 0.5 h and filtered on a fritted Buchner funnel. The solid was dried at 80 oC for 3-4 h to a constant weight of 1.00 g (58%, nominal) of crude product, C21H2603. Proton NMR (CDCI3): d 1.22 (s, 3H, 18-H3); 1.48 (s, 3H, 19-H3), 2.27 (s, 3H, 20 21-H3); 1.0-2.7 (m, 12H); 4.38 (br q, 1H, J=2.5, H-11); 6.00 (s, 1H, H-4); 6.25 (dd, 1H, J=10 and 2, H-2); 6.66 (q, 1H, J=2, H-16); 7.32 (d, 1H, J=10, H-1). This material was converted in 75% yield to the known trimethylsilyl derivative, 11 P-(trimethylsiloxy)-pregna-1,4,16-trien-3,20-dione (Formula I 2 where X = OSi(CH 3

)

3 ; Y = Q = H), as described in U.S. Patent No. 4,012, 510. ii) The method of Kovendi et al., Rev. Chim. (Bucharest), 27:467 (1976) was modified. Semicarbazide hydrochloride (4.75 mL of a 5.0 % aq. solution, 2.14 mmol) was added to a stirred solution of 21-deoxyprednisolone 3o (2.15 g, 6.25 mmol) [see U.S. Patent No. 3,033,873 and Vitali et al., Gazz. Chim. Ital., 96:1115 (1966)] in acetic acid (72 mL) under Ar. The solution was 6 WO 99/28336 PCT/US98/23641 heated to 80-85 0C (bath) for 4.2 h. Water (75 mL) was added and heating (85 0C bath) was continued for 5.5 h. The solution was cooled to 23 oC over 11 h, poured into water (850 mL), cooled in ice (to 7 oC) and filtered on a fritted Bichner funnel. The solid was dried under vacuum to give 1.40 g S(69%, nominal) of crude product, C21H2603. Proton NMR (CDCI3): d 1.22 (s, 3H, 18-H3); 1.48 (s, 3H, 19-H3), 2.27 (s, 3H, 21-H3); 1.0-2.7 (m, 12H); 4.38 (brq, 1H, J=2.5, H-11); 6.00 (s, 1H, H-4); 6.25 (dd, 1H, J=10 and 2, H-2); 6.66 (q, 1H, J=2, H-16); 7.32 (d, 1H, J=10, H-1). 10 This material was converted in 83% yield to the known trimethylsilyl derivative, 11 P-(trimethylsiloxy)-pregna-1,4,16-trien-3,20-dione (Formula I where X = OSi(CH 3

)

3 ; Y = Q = H), as described in U.S. Patent No. 4,012, 510. 15 c) Preparation of 21-Methyl-11 p-(trimethylsiloxy)-pregna-1,4,16-trien 3,20-dione. Lithium hexamethyldisilazide (estimated 0.9 M in THF, 2.1 mL, 1.9 mmol) was added over 8 min. to a stirred, cooled (-60 to -65 oC internal) solution of 11 (trimethylsiloxy)-pregna-1,4,16-trien-3,20-dione (0.73 g, 1.83 mmol) in THF 20 (12.0 mL) and HMPA (3.0 mL) under Ar. After a further 2 min, the cloudy pale-orange mixture was quenched rapidly with iodomethane (2.5 mL, 40 mmol) whereupon the temperature rose to -57 oC and the suspension cleared. The solution was warmed over 2 min to 10 oC, quenched with sat. KH2PO4, and partitioned with EtOAc. The organic solution was dried 25 (MgSO4), filtered and concentrated. The residue (1.9 g) was purified by chromatography (80 g silica, 25% to 50% EtOAc-hexanes) to give 0.62 g (82%) of the product, C25H3603Si, as an off-white solid, m.p. 178 - 182 0C (dec.). 30 Proton NMR (CDCI3): d 0.24 (s, 9H, Me3Si); 1.05 (t, 3H, J=7.3, Me-21); 1.18 (s, 3H, 18-H3); 1.41 (s, 3H, 19-H3); 1.0 - 2.8 (m, 11H); 2.6 (q, 2H, 21-H2); 7 WO 99/28336 PCT/US98/23641 4.37 (brq, 1H, J=2.5, H-11); 5.99 (s, 1H, H-4); 6.25 (dd, 1H, J=10 and 2, H 2); 6.64 (q, 1H, J=2, H-16); 7.12 (d, 1H, J=10, H-1). d) Addition. 5 To a stirred, cooled (-45 oC bath, MeCN-CO2) solution of 21-methyl-113 (trimethylsiloxy)-pregna-1,4,16-trien-3,20-dione (0.395 g, 0.96 mmol) in 9.0 mL of anhydrous THF under Ar was added via syringe chlorotrimethylsilane (0.50 mL, 4.0 mmol), followed by dropwise addition over 3 min of 5.0 mL (1.0 10 mmol) of the above cuprate solution. After 10 min, the mixture was quenched at -45 oC (bath) by rapid addition via syringe of a solution of 0.5 mL (12 mmol) of MeOH and 1.5 mL (11 mmol) of Et3N and warming to 0 oC. Water and EtOAc were added and the solution was stirred vigorously. The pH was adjusted from 9 to 7 with sat. KH2PO4 and stirring was continued for 0.5 h. SThe layers were separated and the organic solution was washed with water and brine, dried (MgSO4), filtered and concentrated. The residue was purified by chromatography to give 0.41 g (85.5%) of the desired product, C29H4803Si2, as a white solid. 20 Proton NMR (CDCI3): d 0.20 (s, 9H, Me3Si); 0.24 (s, 9H, Me3Si); 0.96 (d, 3H, J = 6.9, Me-16); 1.01 (t, 3H, J = 7.4, Me-21); 1.07 (s, 3H, 18-H3); 1.39 (s, 3H, 19-H3); 0.9-2.4 (m); 2.6 (br m, 3H, 20-H2 and H-16); 4.38 (br s, 1H, H 11); 6.01 (s, 1H, H-4); 6.28 (dd, 1H, J = 10 and 2); 7.12 ( d, 1H, J = 10). 2 Example 2 Preparation of 11 -(Trimethylsiloxy)-16c,17a,21-trimethylpregna-1,4-dien-3,20-dione (a). Preparation of reagents. A 3 gram sample of 30 benzyltrimethylammonium fluoride hydrate was dried at 55 oC /0.2 Torr (Abderhalden, MeOH) for 40 h, then transferred under Ar to an Ar-filled desiccator over P205. Molecular sieves (4A, 1/16 in. spheres) were dried at 8 WO 99/28336 PCT/US98/23641 250 oC (internal) for several hours and cooled in the desiccator. lodomethane was dried over 4A molecular sieves. (b). Alkylation. Molecular sieves (2.7 g) and benzyltrimethylammonium Fluoride (0.8 g) were weighed under Ar (glove bag) into an oven-dried (100 oC) 25-mL 2-neck round bottom flask containing a magnetic stir bar. THF (3.0 mL, freshly distilled from a potassium-benzophenone solution under Ar) was added via syringe and the mixture was stirred rapidly under Ar for 6 h. To the resulting paste was added via syringe a solution of 16c,21-dimethyl-11 P,20 0 bis(trimethylsiloxy)-pregna-1,4,17(20)-trien-3-one (47 mg, 0.094 mmol) in iodomethane (1.3 mL, 21 mmol). The mixture was stirred for 45 min at rt. Ethyl acetate was added and the suspension was filtered, rinsing well with ethyl acetate. The filtrate was washed with half-saturated brine, dried (MgSO4), filtered through a pad of Florisil with EtOAc and concentrated to 15 give 46.5 mg of an oil that solidified on standing. Crystallization from 12% EtOAc-hexanes (6 mL) at -25 oC followed by drying under vacuum at 75 oC afforded 26 mg (63%) of a white solid, C27H4203Si. Proton NMR (CDCI3): d 0.20 (s, 9H, Me3Si); 0.87 (d, 3H, J=7.2, Me-16); 0.94 20 (s, 6H, Me-17+18-H3); 1.04 (t, 3H, J=7.1, Me-21); 1.37 (s, 3H, 19-H3); 2.34 (q, 2H, J=7, 21-H2); 1.1-2.7 (m); 3.07 (m, 1H, H-16); 4.46 (brt, 1H, J=3, H 11); 6.00 (s, 1H, H-4); 6.27 (dd, 1H, J=10 and 2, H-2); 7.10 (d, 1H, J=10, H 1). The invention has been described by reference to certain preferred 25 embodiments; however, it should be understood that it may be embodied in other specific forms or variations thereof without departing from its spirit or essential characteristics. The embodiments described above are therefore considered to be illustrative in all respects and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing S description. 9

Claims (9)

1. A method of preparing a 16a,17ao-dialkylated steroid of the formula CH 2 R 1 0 X ,,. CH 2 R 3 .nR2 0 Y Q wherein R 1 is H or CHR 4 R'; R 2 is C1 - C 4 alkyl; R 3 is H, C, - C 3 alkyl, C-CH, CH=CH 2 , or phenyl; 10 X is OSiR RR 9 or OC(=O)R 6 ; Y is H, F, or CI; or X and Y taken together are a covalent /o R 4 , R 5 and R 6 are independently H or C, - C4 alkyl; R 7 , R 8 and R 9 are independently C, - C4 alkyl; and 15 Qis H orCH 3 ; comprising reacting in a solvent an enol silyl ether of the formula OSiRTR 8 R 9 X CH, R , " ['"1" R 2 0 Q10 10 WO 99/28336 PCT/US98/23641 with an enol silyl ether cleaving agent and an alkylating agent of the formula R 3 CH 2 Z wherein R 3 is selected from the group consisting of hydrogen, a 5 Z is CI, Br or I.

2. The method of Claim 1 wherein R 1 is CH

3 ; R 2 is CH 3 ; Q and Y are H; X is OSiR'R'R' and R 7 , R 8 , and R 9 are CH 3 . 10 3. The method of Claim 1 wherein R 3 is H and Z is I.

4. The method of Claim 1 wherein the enol silyl ether cleaving agent is selected from the group consisting of a fluoride salt and lithium amide. 15

5. The method of Claim 4 wherein the enol silyl ether cleaving agent is a tetraalkylammonium fluoride salt.

6. The method of Claim 5 wherein the enol silyl ether cleaving agent is benzyltrimethylammonium fluoride. 20

7. The method of Claim 5 wherein the solvent is selected from the group consisting of tetrahydrofuran and glyme.

8. The method of Claim 7 wherein the solvent is tetrahydrofuran. 25

9. The method of Claim 4 wherein the enol silyl ether cleaving agent is lithium amide and the solvent is liquid ammonia. 11