Degradation of epothilones

Description

Epothilones of type C and type D belong to the art and are especially characterized by a C═C double bond at positions 12 and 13 and a hydrogen atom at position 12 (type C) or an alkyl group-(type D).

According to one embodiment the invention concerns a process for a degradation of an epothilone C or an epothilone D, wherein an epothilone C or an epothilone D is subjected to an olefin metathesis in the presence of ethylene and subsequently an optional ester hydrolysis (scheme I).

According to the invention the epothilone C or D can be a fermentation product.

According to another embodiment the invention concerns a process for the production of an epothilone of formula 9

wherein an epothilone of formula 2a (schemes I and II) is converted into compound of formula 3a (scheme II), the compound of formula 3a is reacted with a compound of formula 6 (which has been formed by reacting a compound of formula 4 with a compound of formula 5; scheme II) to give a compound of formula 7 by esterification (scheme II), the compound of formula 7 is reacted in the presence of a Grubbs catalyst to give a compound of formula 8a by deprotection (scheme II), the compound of formula 8a is converted into a compound of formula 8b by deprotection (scheme II), and compound of formula 8b is converted to a compound of formula 9 by epoxidation (scheme II).

Alternatively to the reaction sequence depicted in scheme I synthetic intermediates of type 3 may be obtained according to scheme III by

• 1) cleavage of the lactone of epothilone C or D with e.g. pig liver esterase (PLE) or, after protection of the 3,7-hydroxyl groups, with aqueous base to give 10 (this conversion is described in U.S. patent application Ser. No. 09/811,808, Mar. 19, 2001 by BMS/GBF),
• 2) optionally esterification with diazomethane and optionally protection of the 3,7-dihydroxyl groups to give 11,
• 3) olefin metathesis with an excess of an olefin, e.g. ethylene and a ruthenium or molybdenum metathesis catalyst and optionally protection of the 3,7-dihydroxyl groups to give 3b.

EXPERIMENTAL PART

12,13-seco-Epothilone C (2a)

450 mg of epothilone C (1) (0.95 mmol) were dissolved in 250 mL of dichloromethane, saturated with ethylene and after addition of 60 mg of Grubb's catalyst (PhCHRuCl₂[P(Cy)₃]₂ stirred for 24 hours. After addition of further 60 mg of catalyst and stirring for 24 hours the dark solution was evaporated to dryness and the residue purified by chromatography on silica with the solvent system hexanes/tert.-butylmethylester/methanol 80:20:1. The first fraction contained 360 mg (75%) of 2a, the second 100 mg (22%) of recovered starting material 1.

2a: ¹H-NMR (CDCl₃), 300 MHz): δ=6.95 (s, 19-H), 6.02 (s, 17-H), 5.89–5.64 (m, 12-H, 13-H), 5.16–4.89 (m, 12a-H₂, 13a-H₂), 5.37 (t, J=7 Hz, 15-H), 4.24 (ddd, J=10, 3, 3.5 Hz, 3-H), 3.36 (s, OH), 3.34 (d, J=8 Hz, 7-H), 3.25 (dq, J=1.5, 7 Hz, 8-H), 3.21 (d, J=3.8 Hz, OH), 2.70 (s, 21-H₃), 2.52–2.32 (m, 2-H₂, 14-H₂), 2.07 (d, J=1.5 Hz, 16-Me), 2.05–1.95 (m, 11-H₂), 1.8–1.1 (m, 6-H, 8-H, 9-H₂, 10-H₂), 1.18 (S, 4-Me), 1.10 (s, 4-Me), 1.04 (d, J=7 Hz, 6-Me), 0.83 (d, J=7 Hz, 8-Me).

ESI-MS (pos ions) m/z=506 [M+H⁺], CI-MS (NH₃ pos. ions) m/z=506 [M+H⁺] (22%), 380 (100%).

3,7-Di-[tert-buthyldimethyl-silyloxy]-4,4,6,8-tetramethyl-5-oxo-12-tridecenoic acid (3a)

To 330 mg (0.65 mmol) of 12,13-seco-epothilone C (2a) dissolved in 10 mL of THF were added with stirring 0.6 mL of NEt₃ and 0.6 mL of tert-butyldimethylsilyltriflate. After one hour the solvent was evaporated in vacuo. The residue was dissolved in 10 mL of THF, 70 mg of LiOH dissolved in 0.5 mL of water were added and the mixture stirred for 16 hours. The solvents were evaporated and the residue distributed between phosphate buffer of pH 5 and ethyl acetate. The organic layer was dried with MgSO₄ and evaporated to dryness. Preparative HPLC on RP-18 with the solvent system methanol/20 mmol ammonium acetate buffer pH 7 gave 235 mg (67%) of 3a as colorless viscous oil.

Analytical HPLC on Nucleosil RP-18 (260×5 mm) solvent system methanol/20 mmol ammonium acetate buffer pH 7, 1 mL/min, light scattering detector: R_t=5.5 min.

¹H-NMR (CDCl₃, 300 MHz): δ=5.78 (m, 12-H), 4.99, 4.92 (m, 13-H₂), 4.39 (dd, J=6.3, 3.4 Hz, 3-H), 3.79 (dd, J=7.2, 2.0 Hz, 7-H), 3.12 (dq, J=7.0 Hz, 8-H), 2.49 (dd, J=16.5, 3.5 Hz, 2-H_a), 2.32 (dd, J=16.5, 6.2 Hz, 2-H_b), 1.5–1.0 (m, 6-H, 8-H, 9-H₂, 10-H₂, 11-H₂), 1.2 (s, 4-Me), 1.07 (s, 4-Me), 1.04 (d, J=6.9 Hz, 6-Me), 0.91 (d, J=7.0 Hz, 8-Me), 0.89 (s, tBuSi), 0.88 (s, tBuSi), 0.09 (s, MeSi), 0.06 (s, MeSi), 0.05 (s, 2 MeSi).

ESI-MS (neg. ions) m/z=541 (M−H).

4-Bromo-2-methyl-thiazole (4)

1 g (2.05 mmol) 2,4-Dibromothiazole was dissolved in 25 mL anhydrous ether and the resulting solution was stirred under N₂ atmosphere at −78° C. To the solution was added n-BuLi (1.1 equivalent, 4.52 mmol, 2.82 mL of 1.6 M solution in hexane) and the stirring was continued for 1 h. To the reaction mixture was then added dropwise a solution of dimethylsulfate 1.16 mL (12.34 mmol) in 1 mL ether. After stirring for 4 h at −78° C. the reaction mixture was allowed to warm to room temperature and stirred for 14 h. The reaction mixture was diluted with a saturated solution of NaHCO₃ (10 mL). The aqueous layer was extracted with ether and the combined organic extracts were washed with a brine and dried over MgSO₄. Concentration under vacuum, and flash column chromatography (silica gel, 10:1 petroleum ether/ethyl acetate), yielded 0.52 g (70.6%) a yellow oil.

IR (KBr) 3122, 2923, 1485, 1441, 1252, 1178, 1085887, 834 cm⁻¹.

¹H-NMR (CDCl₃, 400 MHz): δ=7.02 (s, 1H), 2.71 (s, 3H).

¹³C-NMR (CDCl₃, 100.6 MHz): δ=167.31, 124.18, 116.11, 19.40. EI-MS (70 eV): m/z (%): 179 (93) [M+2H]⁺, 177 (100) [M+H]⁺, 169 (30), 164 (20), 159 (15).

HRMS (EI): calcd for C₄H₄BrNS 176.9251, found 176.9248

1-(2-methyl-thiazol-4-yl)-hex-5-en-1-yn-3-ol (6)

480 mg (2.68 mmol) 4-Bromo-2-methyl-thiazole (4) in 4 mL Et₃N was added to 131 mg (0.187 mmol) PdCl₂(PPh₃)₂ and the suspension was stirred 15 minutes under N₂ atmosphere at room temperature then 117 mg (0.614 mmol) CuI was added under N₂ atmosphere followed by dropwise addition of 283 mg alcohol 5 (A. B. Smith, III et al. JACS 120, 3935–3948 (1998)) in 1 mL Et₃N. The mixture was stirred for 15 minutes at room temperature and heated to 80° C. for 6 h. Concentration under vacuum, and flash column chromatography (silica gel, 3:2 petroleum ether/ethyl acetate), yielded 0.29 g (56%) a yellow oil. [α]=−29.1 (c=1 in chloroform)

IR (KBr): 3386, 3142, 2924, 1641, 1501, 1435, 1286, 1194, 1041, 993, 918 cm⁻¹.

¹H-NMR (CDCl₃, 400 MHz): δ=7.26 (s, 1H), 5.98–5.88 (m, 1H), 5.23–5.16 (m, 2H), 4.62 (dd, J=11.9, 5.8 Hz, 1H), 2.68 (3H, S), 2.58–2.54 (2H, m), 2.39 (d J=6.1 Hz, 1H, OH)

¹³C-NMR (CDCl3, 75.5 MHz): δ=165.77, 136.20, 133.09, 122.48, 118.85, 89.53, 79.04, 61.84, 41.87, 19.10.

DCI-MS (NH₃): 211[M+NH₄⁺], 194[M+H⁺].

(1S)-1-[(2-Methyl-thiazole-4-yl)-1-ethynyl]-3-butenyl (3S, 6R, 7S, 8S)-3,7-di-[tert-butyldimethylsiloxy]-4,4,6,8-tetramethyl-5-oxo-12-tridecenoate (7)

99 mg (0.478 mmol)DCC was added at 0° C. to a solution of acid 200 mg(0.368 mmol), alcohol 79 mg (0.405 mmol) and 12 mg (0.09 mmol) DMAP in 10 mL CH₂Cl₂. The mixture was stirred for 15 min at 0° C. and for 16 h at room temperature. Concentration under vacuum, and flash column chromatography (silica gel, 10:1 petroleum ether/ethyl acetate), yielded 240 mg (91%) a yellow oil.

[α]=−45.8 (c=1 in CH₂Cl₂)

IR (KBr): 2929, 2856, 1742, 1697, 1641, 1472, 1253, 989 cm⁻¹.

¹H-NMR (CDCl₃, 400 MHz): δ=7.28 (s, 1H, thiazole H-5), 5.91–5.73 (m, 2H, H-12, H-3′),

5.58 (t, J=6.1 Hz, 1H, H-1′), 5.20–4.90 (m, 4H, H-13, H-4′), 4.38 (dd, J=6.3, 3.3 Hz, 1H, H-3), 3.74 (dd, J=6.8, 2.2 Hz, 1H, H-7), 3.11 (dq, J=6.8, 6.8 Hz, 1H, H-6), 2.67 (s, 3H, thiazole CH₃), 2.60 (t, J=6.6 Hz, 1H, H-2), 2.55 (dd, J=16.7, 3.5 Hz, 1H, H-2′), 2.29 (dd, J=17.0, 63 Hz, 1H, H-2′), 2.05–1.95 (m, 2H, H-11), 1.47–1.29 (m, 3H,) 1.17–1.08(m, 2H) (H-8, H-9, H-10), 1.21 (s, 3H, H-22), 1.05 (s, 3H, H-23), 1.03 (d, J=6.6 Hz, 3H, C6-CH₃), 0.89 (d, J=6.6 Hz, 3H, C8-CH₃), 0.88, 0.87(2s, 2x9H, OSiC(CH₃)₃), 0.089 (s, 3H, OSi(CH₃)₂), 0.032, 0.028, 0.024 (3s, 3x3H, OSi (CH₃)₂).

¹³C-NMR (CDCl₃, 100.6 MHz): 217.63, 170.84, 165.55, 138.97, 136.08, 132.23, 123.22, 118.91, 114.41, 85.67, 79.97, 73.76, 63.77, 53.38, 45.23, 40.20, 39.09, 38.87, 34.35, 34.00, 30.48, 27.11, 26.26, 26.07, 25.66, 24.97, 23.44, 19.89, 18.55, 17.66, 15.52, −3.61, −3.74, −4.20, −4.59

DCI-MS (NH₃): 735[M+NH₄⁺], 718[M+H⁺].

HRMS (DCI): calcd for C₃₉H₇₀N₂O₅SSi₂ 735.4622, found 735.4675.

(4S, 7R, 8S, 9S, 16S)-4,8-Di-tert-butyldimethylsilyloxy-5,5,7,9-tetramethyl-1-6-(2-(2-methyl-1,3-thiazol-4-yl)-1-ethynyl)-1-oxa-13-cyclohexadecen-2,6-dione, mixture of Z and E isomeres (8a)

To a solution of 190 mg (0.264 mmol) diene 7 in 66 mL CH₂Cl₂ was added 44 mg (0.053 mmol)

bis(tricyclohexylphosphine)benzylideneruthenium dichloride and the reaction mixture was stirred for 48 h at room temperature. Concentration under vacuum, and flash column chromatography (silica gel, 10:1 petroleum ether/ethyl acetate), yielded 95 mg (52%) of a yellow oil.

(4S, 7R, 8S, 9S, 16S)-4,8-Dihydroxy-tert-5,5,7,9-tetra-methyl-1-6-[2-(2-methyl-1,3-thiazol-4-yl)-1-ethynyl)-1-oxa-13-cyclohexadecen-2,6-dione (8b), mixture of cis and trans isomere

A solution of 95 mg (0.137 mmol) lactone X in 12 mL CH₂Cl₂ at −20° C. was treated with 2 mL trifluoroacetic acid, and the mixture was stirred for 2 h at 0° C. After concentration under vacuum, the residue was diluted with EtOAC, washed with saturated NaHCO₃ solution and dried over MgSO₄. Concentration under vacuum, and separation by HPLC (80:20:3 hexane/t-BuOMe/MeOH), yielded 27 mg (42%) of the cis-hydroxy lactone 8b and 27 mg (42%) of the corresponding trans isomer.

[α]=−123 (c=1 in CH₂Cl₂)

¹H-NMR (CDCl₃, 400 MHz): δ=7.30 (s, 1H, H-19), 5.65 (dd,J=9.1, 2.9 Hz, 1H, H-15), 5.55–5.41 (m, 2H, H-12, H-13), 4.20 (dd,J=10.8, 2.7 Hz, 1H, H-3), 3.67–3.65 (m, 1H, H-7), 3.12 (dq, J=6.6, 2.0 Hz, 1H, H-6), 2.88–2.77 (m, 1H, H-14), 2.70 (s, 3H, H-21), 2.51 (dd, J=15.0 Hz, 10.9 Hz, 1H, H-2), 2.27 (dd,J=15.2, 2.8 Hz, 1H, H-2), 2.18–2.00 (m, 2H, H-11, H-14), 1.71–1.58 (m, 3H, H-8, H-9, H-10), 1.32 (s, 3H, H-22), 1.30–1.19 (3H, H-8, H-9, H-10), 1.18 (d, J=6.7 Hz, 3H, H-24), 1.07 (s, 3H, H-23), 0.98 (d, J=6.9 Hz, 3H, H-25)

¹³C-NMR (CDCl3, 75.5 MHz): δ=220.81, 169.96, 164.44, 134.16, 134.27, 123.75, 123.00, 86.13, 80.00, 74.38, 72.03, 64.11, 53.31, 41.74, 39.37, 38.71, 32.87, 32.37, 27.63, 27.47, 22.69, 19.18, 18.37, 15.46, 13.70.

16,17-Didehydro-16-desmethyl-epothilone A (9)

To a solution of 27 mg (0.058) of lactone (8b) 4 mL CH₂Cl₂ was added dropwise at −20° C. a solution of dimethyl dioxirane in acetone (2 equiv). Stirring was continued for 2 h at −20° C. Concentration under vacuum, and separation by HPLC (80:20:3 hexane/t-BuOMe/MeOH), yielded 17 mg (60%) of α-epoxide 9 and 9 mg (32%) of β-epoxide.

α-epoxide

[α]=−34 (c=1 in CH₂Cl₂)

IR (KBr): 3453, 2958, 2850, 1744, 1690, 1500, 1467, 1376, 1290, 1261, 1147, 979, 775 cm⁻¹.

¹³C-NMR (CDCl₃, 100.6 MHz): 220.55, 170.19, 166.12, 135.50, 123.28, 85.00, 80.56, 75.12, 73.59, 62.71, 57.17, 53.75, 52.67, 43.68, 38.69, 35.96, 32.67, 29.72, 26.56, 23.63, 21.12, 20.48, 19.16, 17.06, 14.46

EI-MS (70 eV): m/z (%): 477(27) [M+H]⁺, 421 (14), 389 (19), 378 (100), 364 (28), 346 (27), 328 (15).

β-epoxide

¹³C-NMR (CDCl₃, 75.5 MHz): δ=221.38, 170.03, 166.05, 135.70, 123.28, 85.13, 80.48, 73.24, 73.11, 62.24, 57.14, 55.31, 52.28, 42.89, 38.98, 37.53, 32.40, 31.82, 27.60, 27.01, 23.45, 20.62, 20.36, 16.38, 13.49.