BACKGROUND OF THE INVENTION

The present invention is directed to novel taxanes which have utility as antileukemia and antitumor agents.

The taxane family of terpenes, of which taxol is a member, has attracted considerable interest in both the biological and chemical arts. Taxol is a promising cancer chemotherapeutic agent with a broad spectrum of antileukemic and tumor-inhibiting activity. Taxol has a 2'R, 3'S configuration and the following structural formula:

wherein Ac is acetyl. Because of this promising activity, taxol is currently undergoing clinical trials in both France and the United States.

Colin et al. reported in U.S. Patent No. 4,814,470 that taxol derivatives having structural formula (2) below, have an activity significantly greater than that of taxol (1) .

R' represents hydrogen or acetyl and one of R' ' and R' ' ' represents hydroxy and the other represents tert-butoxy- carbonylamino and their stereoisomeric forms, and mixtures thereof. The compound of formula (2) in which R' ' is hydroxy, R' ' ' is tert-butoxycarbonylamino having the 2'R, 3'S configuration is commonly referred to as taxotere.

Although taxol and taxotere are promising chemotherapeutic agents, they are not universally effective. Accordingly, a need remains for additional chemotherapeutic agents.

SUMMARY OF THE INVENTION

Among the objects of the present invention, therefore, is the provision of novel taxane derivatives which are valuable antileukemia and antitumor agents. Briefly, therefore, the present invention is directed to taxane derivatives of the formula:

wherein

R _x is phenyl or p-nitrophenyl-, R ₃ is furyl or thienyl,

T _α is hydrogen, hydroxyl protecting group, or -COT ₂ ,

T ₂ is H, Ci-C ₆ alkyl, C ₂ -C ₆ alkenyl, C ₂ -C ₆ alkynyl or monocylic aryl, Ac is acetyl, and

E ₁ and E ₂ are independently selected from hydrogen, hydroxy protecting groups and functional groups

which increase the water solubility of the taxane derivative.

Other objects and features of this invention will be in part apparent and in part pointed out hereinafter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the present invention, it has been discovered that compounds having structural formula (3), in general, and structural formulas (4), (5), and (6), in particular show remarkable properties, in vitro, and are valuable antileukemia and antitumor agents. Their biological activity has been determined _in vitro, using tubulin assays according to the method of Parness et al., J.. Cell Bioloσv, 91: 479-487 (1981) and human cancer cell lines, and is comparable to that exhibited by taxol and taxotere.

Taxanes having formulas (4), (5) and (6) which have the 2'R, 3'S configuration may be obtained by reacting a β-lactam with metal alkoxides having the taxane tetracyclic nucleus and a C-13 metallic oxide substituent to form compounds having a β-amido ester substituent at C-13. The β-lactams have the following structural formula:

wherein

R _x is phenyl or p-nitrophenyl,

R ₂ is a hydroxy protecting group, and

R ₃ is furyl or thienyl. β-lactams (7) can be prepared from readily available starting materials, as is illustrated by the following reaction scheme:

OLi

/

R ₅ S iO OCH ₂ CH ₃ R ₅ SiO 0CH ₂ CH ₃

N—TMS

R_,CHO .— t

reagents

(a) lithium diisopropyl amide, tetrahydrofuran ("THF" ), -780C to -50OC;

(b) lithium hexamethyl disilazane, THF, -78°C to 0OC;

(c) THF, -78°C to 25oC, (2h) ; and

(d) triethylamine and an acyl chloride.

The 3-hydroxyl protecting group shown in the above reaction scheme is -SiR ₅ wherein R ₅ is trialkyl or triaryl such as triethyl. The 3-hydroxyl may be protected with other standard protecting groups such as 1-ethoxyethyl, or 2, 2,2-trichloroethoxymethyl . Additional hydroxy protecting groups and the synthesis thereof may be found in "Protective groups in Organic Synthesis" by T.W. Greene, John Wiley & Sons, 1981.

The racemic β-lactams may be resolved into the pure enantiomers prior to protection by recrystallization of the corresponding 2-methoxy-2- (trifluoromethyl) phenylacetic esters. However, the reaction described hereinbelow in which the β-amido ester side chain is attached has the advantage of being highly diastereo-

selective, thus permitting the use of a racemic mixture of side chain precursor.

The metal alkoxides having the taxane tetracyclic nucleus and a C-13 metallic oxide substituent have the following structural formula:

wherein ^r T ₁ is hydrogen, hydroxyl protecting group, or -C0T ₂ ; T ₂ is H, Ci-Cg alkyl, C ₂ -C ₆ alkenyl, C ₂ -C ₆ alkynyl or monocylic aryl; T ₃ is hydrogen or a hydroxy protecting group; and M is a metal, preferably selected from the group comprising Group IA, Group IIA and transition metals, most preferably, Li, Mg, Na, K or Ti.

Preferably, the metal alkoxides are prepared by reacting an alcohol having the taxane tetracyclic nucleus and a C-13 hydroxyl group with an organometallic compound in a suitable solvent. Most preferably, the alcohol is a protected baccatin III, in particular, 7-O-triethylsilyl baccatin III (which can be obtained as described by Greene, et al. in JACS 110: 5917 (1988) or by other routes) or 7,10-bis-O-triethylsilyl baccatin III.

As reported in Greene et al. , 10-deacetyl baccatin III is converted to 7-O-triethylsilyl-lO-deacetyl baccatin III according to the following reaction scheme:

(9) (10) a, T ₁₌ H b, T _: =COCH ₃

Under what is reported to be carefully optimized conditions, 10-deacetyl baccatin III is reacted with 20 equivalents of (C ₂ H ₅ ) ₃ SiCl at 23°C under an argon atmosphere for 20 hours in the presence of 50 ml of pyridine/mmol of 10-deacetyl baccatin III to provide 7-triethylsilyl-'10-deacetyl baccatin III (10a) as a reaction product in 84-86% yield after purification. The reaction product may then optionally be acetylated with 5 equivalents of CH ₃ C0C1 and 25 mL of pyridine/mmol of 10a at 0 OC under an argon atmosphere for 48 hours to provide 86% yield of 7-O-triethylsilyl baccatin III (10b) . Greene, et al. in JACS 110., 5917 at 5918 (1988).

The 7-O-triethylsilyl baccatin III (10b) is reacted with an organometallic compound such as n-butyllithium in a solvent such as tetrahydrofuran (THF) , to form the metal alkoxide 13-0-lithium-7-0-triethylsilyl baccatin III (11) as shown in the following reaction scheme:

T H F

O CO C _B H ₅

As shown in the following reaction scheme, 13-0-lithium-7-0-triethylsilyl baccatin III (11) reacts with β-lactam (7) in which R ₂ is triethyl silyl to provide an intermediate in which the C-7 and C-2' hydroxyl groups are protected with a triethylsilyl group. The triethyl- silyl groups are then hydrolyzed under mild conditions so as not to disturb the ester linkage or the taxane substituents.

11

wherein

R _: is phenyl or p-nitrophenyl, and

R ₃ is phenyl.

Both the conversion of the alcohol to the metal alkoxide and the ultimate synthesis of the taxane derivative can take place in the same reaction vessel. Preferably, the β-lactam is added to the reaction vessel after formation therein of the metal alkoxide.

Compounds of formula (1) of the instant invention are useful for inhibiting tumor growth in animals including humans and are preferably administered in the form of a pharmaceutical composition comprising an effective antitumor amount of compound of the instant invention in combination with a pharmaceutically acceptable carrier or diluent.

Antitumor compositions herein may be made up in any suitable form appropriate for desired use; e.g., oral, parenteral or topical administration. Examples of parenteral administration are intramuscular, intravenous, intraperitoneal, rectal and subcutaneous administration.

The diluent or carrier ingredients should not be such as to diminish the therapeutic effects of the antitumor compounds.

Suitable dosage forms for oral use include tablets, dispersible powders, granules, capsules, suspensions, syrups, and elixirs. Inert diluents and carriers for tablets include, for example, calcium carbonate, sodium carbonate, lactose- and talc. Tablets may also contain granulating and disintegrating agents such as starch and alginic acid, binding agents such as starch, gelatin and acacia, and lubricating agents such as magnesium stearate, stearic acid and talc. Tablets may be uncoated or may be coated by unknown techniques; e.g., to delay disintegration and absorption. Inert diluents and carriers which may be used in capsules include, for example, calcium carbonate, calcium phosphate and kaolin.

Suspensions, syrups and elixirs may contain conventional excipients, for example, methyl cellulose, tragacanth, sodium alginate; wetting agents, such as lecithin and polyoxyethylene stearate; and preservatives, e.g., ethyl- p-hydroxybenzoate.

Dosage forms suitable for parenteral administration include solutions, suspensions, dispersions, emulsions and the like. They may also be manufactured in the form of sterile solid compositions which can be dissolved or suspended in sterile injectable medium immediately before use. They may contain suspending or dispersing agents known in the art.

The water solubility of compounds of formula (3) may be improved by modification of the C2' and/or C7 substituents to incorporate appropriate functional groups, E _α and E ₂ . For increased water solubility, Ej and E ₂ may independently be hydrogen and -COGCOR ¹ wherein

G is ethylene, propylene, -CH=CH-, 1,2-cyclohexane, or 1,2-phenylene, R ¹ = OH base, NR ² R ³ , OR ³ , SR ³ , OCH ₂ CONR ⁴ R ⁵ , or OH

R ² = hydrogen, methyl R ³ = (CH ₂ ) _n NR ⁶ R ⁷ ; (CH ₂ ) _n KPR ⁶ R ⁷ R ⁸ X ⁶ n = 1 to 3

R ⁴ = hydrogen, lower alkyl containing 1 to 4 carbons

R ⁵ = hydrogen, lower alkyl containing 1 to 4 carbons, benzyl, hydroxyethyl, CH ₂ C0 ₂ H, dimethylaminoethyl R ⁶ R ⁷ = lower alkyl containing 1 or 2 carbons, benzyl or R ⁶ and

R ⁷ together with the nitrogen atom of NR ⁶ R ⁷ form the following rings

R ⁸ = lower alkyl containing 1 or 2 carbons, benzyl

X ⁶ = halide base = NH ₃ , (HOC ₂ H ₄ ) ₃ N, N(CH ₃ ) ₃ , CH ₃ N(C ₂ H ₄ OH) ₂ ,

NH ₂ (CH ₂ ) ₆ NH ₂ , N-methylglucamine, NaOH, KOH. The preparation of compounds in which X _x or X ₂ is -COGCOR ¹ is set forth in Hangwitz U.S. Patent 4,942,184 which is incorporated herein by reference.

The following examples illustrate the invention.

EXAMPLE 1

Preparation of N-debenzoyl-N- (furoyl)-3'- desphenyl-3'- (4-nitrophenyl) taxol.

To a solution of 7-triethylsilyl baccatin III (200 mg, 0.286 mmol) in 2 mL of THF at -45 °c was added dropwise 0.174 mL of a 1.63M solution of nBuLi in hexane. After 0.5 h at -45 °C, a solution of cis-1- (furoyl) -3-tri- ethylsilyloxy-4-(4-nitrophenyl)azetidin-2-one (596 mg, 1.43 mmol) in 2 mL of THF was added dropwise to the mixture. The solution was warmed to 0 °C and kept at that

temperature for 1 h before 1 mL of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 ₃ and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave a residue which was purified by filtration through silica gel to give 320 mg of a mixture containing (2 'R, 3 ' S ) -2 ' ,7- (bis) triethylsilyl- N-debenzoyl-N- (furoyl) -3 ' -desphenyl-3 ' - (4-nitrophenyl) taxol and a small amount of the (2'S,3'R) isomer.

To a solution of 320 mg (0.286 mmol) of the mixture obtained from the previous reaction in 18 mL of acetonitrile and 0.93 mL of pyridine at 0 °C was added 2.8 mL of 48% aqueous HF. The mixture was stirred at 0 °C for 3 h, then at 25 °C for 13 h, and partitioned between saturated aqueous sodium bicarbonate and ethyl acetate. Evaporation of the ethyl acetate solution gave 254 mg of material which was purified by flash chromatography to give 187 mg (74%)N-debenzoyl-N- (furoyl) -3 '-desphenyl- 3 '- (4-nitrophenyl) taxol, which was recrystallized from methanol/water. m.p.184-185 oc; [α] ²⁵ _Na -60.0° (c 0.006, CHC1 ₃ ) .

^X H NMR (CDC1 ₃ , 300 MHz) δ 8.26 (d, J = 8.79 Hz, 2H, Ar-N0 ₂ ) , 8.12 (d, J=7.2 Hz, 2H, benzoate ortho) , 7.68 (d, J=8.8 Hz 2H, benzamide ortho) , 7.7-7.47 ( , 6 H, aromatic), 7.3 (d, J = 9.3 Hz, IH, NH) , 7.02 (d, J=3.3 Hz, IH, furyl), 6.48(dd, J=3.3 Hz, 1.65 Hz, IH, furyl) , 6.27

(s, IH Hz, H10), 6.26 (dd, J = 8.5, 8.5 Hz, IH, H13), 5.87 (dd, J = 8.8, 1.65 Hz, IH, H3 ' ) , 5.65 (d, J = 6.6 Hz, IH, H2β), 4.93 (d, J = 8.2 Hz, IH, H5), 4.79 (dd, J = 2.7, 1.4 Hz, IH, H2'), 4.38 (m, IH, H7) , 4.29 (d, J = 8.4 Hz, IH, H20α), 4.18 (d, J = 8.4 Hz, IH, H20β) , 3.97 (d, J=3.3 Hz, IH, 2'OH), 3.79 (d, J = 6.6 Hz, IH, H3) , 2.5 ( , IH, H6α) , 2.4(m, IH, 70H) , 2.38 (s, 3H, 4Ac) , 2.27 (m, 2H, H14), 2.22 (s, 3H, lOAc) , 1.88 (m, IH, H6β) , 1.81 (br s, 3H, Mel8), 1.78 (s, IH, 10H) , 1.68 (s, 3H, Mel9) , 1.21 (s, 3H, Mel7), 1.13 (s, 3H, Mel6) .

EXAMPLE 2

Preparation of N-debenzoyl-N- (2 -furoyl ) taxol

To a solution of 7-triethylsilyl baccatin III (200 mg, 0.286 mmol) in 2 mL of THF at -45 °C was added dropwise 0.174 mL of a 1.63M solution of nBuLi in hexane. After 0.5 h at -45 ©C, a solution of cis-1- (2-furoyl) -3- triethylsilyloxy-4-phenylazetidin-2-one (531 mg, 1.43 mmol) in 2 mL of THF was added dropwise to the mixture. The solution was warmed to 0 °C and kept at that temperature for 1 h before 1 mL of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 ₃ and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave a residue which was purified by filtration through silica gel to give 306 mg of a mixture containing (2'R,3'S) -2' ,7- (bis)triethylsilyl- N-debenzoyl-N-(2-furoyl) taxol and a small amount of the (2'S,3'R) isomer.

To a solution of 306 mg (0.286 mmol) of the mixture obtained from the previous reaction in 18 mL of acetonitrile and 0.93 mL of pyridine at 0 °C was added 2.8 mL of 48% aqueous HF. The mixture was stirred at 0 °C for 3 h, then at 25 °C for 13 h, and partitioned between saturated aqueous sodium bicarbonate and ethyl acetate. Evaporation of the ethyl acetate solution gave 240 mg of material which was purified by flash chromatography to give 192 mg (80%) of N-debenzoyl-N-(2-furoyl) taxol, which was recrystallized from methanol/water.

m.p.172-174 oC; [α] ²⁵ _Na -49.6° (c 0.0103, CHC1 ₃ ).

^α H NMR (CDC1 ₃ , 300 MHz) δ 8.12 (d, J = 7.1 Hz, 2H, benzoate ortho), 7.64-7.33 (m, 9H, aromatic), 7.19 (d, J = 8.8 Hz, IH, NH) , 7.01 (d,J= 3.3 Hz, IH, furyl), 6.45 (dd,lH, furyl) ,6.26(s, IH, H10), 6.21 (dd, J = 8.8, 8.8 Hz, IH, H13), 5.72 (dd, J = 8.8, 1.7 Hz, IH, H3' ) , 5.66 (d, J = 7.1 Hz, IH, H2β) , 4.92 (d, J = 8.2 Hz, IH, H5) , 4.75 (br S,1H, H2'), 4.40 (m, IH, H7) , 4.28 (d, J = 8.2 Hz, IH, H20α), 4.18 (d, J = 8.2 Hz, IH, H20β) , 3.78 (d, J = 6.6 Hz, IH, H3), 3.69 (d,J = 3.8 Hz,lH, 2OH) , 2.53 (m, IH,

H6α) , 2.47 (br S,1H, 70H) , 2.36 (s, 3H, 4Ac) , 2.32 ( , 2H, H14), 2.22 (s, 3H, lOAc) , 1.84 (m, IH, H6β) , 1.79 (br s, 3H, Mel8), 1.67 (s, 3H, Mel9), 1.22 (s, 3H, Mel7), 1.13 (s, 3H, Mel6) .

EXAMPLE 3

Preparation of N-debenzoyl-N-(2-thienoyl) taxol.

To a solution of 7-triethylsilyl baccatin III (200 mg, 0.286 mmol) in 2 mL of THF at -45 °C was added dropwise 0.174 mL of a 1.63M solution of nBuLi in hexane. After 0.5 h at -45 OC, a solution of cis-1- (2-thienoyl) -3- triethylsilyloxy-4-phenylazetidin-2-one (554 mg, 1.43 mmol) in 2 mL of THF was added dropwise to the mixture. The solution was warmed to 0 °C and kept at that temperature for 1 h before 1 mL of a 10% solution of AcOH in THF was added. The mixture was partitioned between

saturated aqueous NaHC0 ₃ and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave a residue which was purified by filtration through silica gel to give 311 mg of a mixture containing (2'R,3 'S) -2' ,7-(bis)triethylsilyl- N-debenzoyl-N- (2-thienoyl) taxol and a small amount of the (2'S,3'R) iso er.

To a solution of 311 mg (0.286 mmol) of the mixture obtained from the previous reaction in 18 mL of acetonitrile and 0.93 mL of pyridine at 0 °C was added 2.8 mL of 48% aqueous HF. The mixture was stirred at 0 °C for 3 h, then at 25 °C for 13 h, and partitioned between saturated aqueous sodium bicarbonate and ethyl acetate. Evaporation of the ethyl acetate solution gave 246 mg of material which was purified by flash chromatography to give 195 mg (80%) of N-debenzoyl-N-(2-thienoyl) taxol, which was recrystallized from methanol/water. m.p.218-219 >C [α] ²⁵ _Na -47.6° (c 0.0103, CHC1 ₃ ) .

^α H NMR (CDC1 _3/ 300 MHz) δ 8.12 (d, J = 7.1 Hz, 2H, benzoate ortho), 7.64-7.31 (m, 10H, aromatic), 7.05 (dd, IH, thienyl ring), 6.86 (d, J = 9.3 Hz, IH, NH) , 6.23 (s, IH, H10), 6.21 (dd, J = 8.8, 8.8 Hz, IH, H13), 5.75 (dd, J = 8.8, 2.2 Hz, IH, H3' ) , 5.66 (d, J = 7.1 Hz, IH, H2β) , 4.93 (dd, J = 9.3, 1.65 Hz, IH, H5) , 4.78 (dd,J = 5.0, 2.7 Hz,lH, H2'), 4.41 (m, IH, H7), 4.28 (d, J = 8.2 Hz, IH, H20α), 4.18 (d, J = 8.2 Hz, IH, H20β) , 3.78 (d, J = 6.6 Hz, IH, H3), 3.63 (d, J = 4.9 Hz,lH, 2'OH), 2.53 (m, IH, H60C) , 2.48 (d, J = 4.4 Hz,lH, 70H) , 2.36 (s, 3H, 4Ac) , 2.30 (m, 2H, H14), 2.23 (s, 3H, lOAc) , 1.85 (m, IH, H6β) , 1.78 (br s, 3H, Mel8) , 1.68 (s, 3H, Mel9), 1.23 (s, 3H, Mel7), 1.13 (s, 3H, Mel6) .

EXAMPLE 4 Tubulin binding assays were .performed using compounds (4), (5), (6) and substantially as set forth in Parness et al. , J. Cell Biology 91: 479-487 (1981) and

compared to taxol and taxotere. The results are presented in Table 1.

EXAMPLE 5 Taxanes 4, 5 and 6 was evaluated in .in vitro cytotoxicity activity against human colon carcinoma cells HCT-116 and HCT-116/VM46. The HCT116/VM cells are cells that have been selected for teniposide resistance and express the multidrug resistance phenotype, including resistance to taxol. Cytotoxicity was assessed in HCT116 and HCT VM46 human colon carcinoma cells by XTT (2,3-bis (2-methoxy-4-nitro-5-sulfophenyl) -5-[ (phenyl- a ino)carbonyl] -2H-t etrazolium hydroxide) assay (Scudiero et al, "Evaluation of a soluble tetrazolium/formazan assay for cell growth and drug sensitivity in culture using human and other tumor cell lines", Cancer Res. 48:4827-4833, 1988). Cells were plated at 4000 cells/well in 96 well microtiter plates and 24 hours later drugs were added and serial diluted. The cells were incubated at 37°c for 72 hours at which time the tetrazolium dye, XTT, was added. A dehydrogenase enzyme in live cells reduces the XTT to a form that absorbs light at 450 nm which can be quantitated spectrophotometrically. The greater the absorbance the greater the number of live cells. The results are expressed as an IC ₅₀ which is the drug

concentration required to inhibit cell proliferation (i.e. absorbance at 450 nm) to 50% of that of untreated control cells. The results are presented in Table 2. Lower numbers indicate greater activity.

In view of the above, it will be seen that the several objects of the invention are achieved.

As various changes could be made in the above compositions without departing from the scope of the invention, it is intended that all matter contained in the above description be interpreted as illustrative and not in a limiting sense.