CERTAIN CHEMICAL ENTITIES, COMPOSITIONS, AND METHODS

Abstract

Chemical entities that are bufalin derivatives, pharmaceutical compositions and methods of treatment of cancer are described.

Claims

1. At least one chemical entity chosen from compounds of Formula I ##STR00023## and pharmaceutically acceptable salts thereof, wherein Z is chosen from OR.sub.9 and NR.sub.10R.sub.11; where R.sub.9 is chosen from optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted heterocycloalkyl, optionally substituted aryl, and optionally substituted heteroaryl; R.sub.10 is chosen from hydrogen, optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted heterocycloalkyl, optionally substituted aryl, and optionally substituted heteroaryl; R.sub.11 is chosen from optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted heterocycloalkyl, optionally substituted aryl, and optionally substituted heteroaryl; or R.sub.10 and R.sub.11 may optionally be joined together with any intervening atoms to form an optionally substituted heterocycloalkyl ring.

2. At least one chemical entity of claim 1 wherein Z is OR.sub.9.

3. At least one chemical entity of claim 2 wherein R.sub.9 is chosen from optionally substituted alkyl, optionally substituted cycloalkyl, and optionally substituted heterocycloalkyl.

4. At least one chemical entity of claim 1 wherein Z is NR.sub.10R.sub.11.

5. At least one chemical entity of claim 4 wherein R.sub.10 is chosen from hydrogen, optionally substituted alkyl, optionally substituted cycloalkyl, and optionally substituted heterocycloalkyl, and R.sub.11 is chosen from optionally substituted alkyl, optionally substituted cycloalkyl, and optionally substituted heterocycloalkyl.

6. At least one chemical entity of claim 5 wherein R.sub.10 is hydrogen and R.sub.11 is chosen from optionally substituted alkyl.

7. At least one chemical entity of claim 4 wherein R.sub.10 and R.sub.11 are joined together to form a 5- to 7-membered heterocycloalkyl ring.

8. At least one chemical entity chosen from compounds I-a-I-f and pharmaceutically acceptable salts thereof.

9. At least one chemical entity chosen from compounds of Formula II ##STR00024## and pharmaceutically acceptable salts thereof, wherein R.sub.1 and R.sub.2 are independently chosen from hydrogen, optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted heterocycloalkyl, optionally substituted aryl, and optionally substituted heteroaryl; or R.sub.1 and R.sub.2 may optionally be joined together with any intervening atoms to form an optionally substituted heterocycloalkyl ring; for each occurrence, R.sub.3 and R.sub.4 are independently chosen from hydrogen, optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted heterocycloalkyl, optionally substituted aryl, and optionally substituted heteroaryl; or R.sub.3 and R.sub.4 may optionally be joined together with any intervening atoms to form an optionally substituted cycloalkyl ring or optionally substituted heterocycloalkyl ring; or R.sub.1 and one occurrence of R.sub.3 may optionally be joined together with any intervening atoms to form an optionally substituted heterocycloalkyl ring; and n is selected from 1, 2, 3, 4, 5 and 6.

10. At least one chemical entity of claim 9 wherein R.sub.1 and R.sub.2 are each independently chosen from hydrogen and optionally substituted lower alkyl.

11. At least one chemical entity of claim 10 wherein R.sub.1 and R.sub.2 are both hydrogen.

12. At least one chemical entity of claim 9 wherein R.sub.1 and R.sub.2 are joined together to form a 5- to 7-membered heterocycloalkyl ring.

13. At least one chemical entity of any one of claims 9 to 12 wherein R.sub.3 and R.sub.4 are each independently chosen from hydrogen and optionally substituted lower alkyl.

14. At least one chemical entity of any one of claims 9 to 13 wherein n is chosen from 1, 2, and 3.

15. At least one chemical entity of claim 9 wherein n is 1, and R.sub.1 and R.sub.3 are joined together to form a 5- to 7-membered heterocycloalkyl ring.

16. At least one chemical entity chosen from compounds II-a-II-h and pharmaceutically acceptable salts thereof.

17. At least one chemical entity chosen from compounds of Formula III ##STR00025## and pharmaceutically acceptable salts thereof, wherein R.sub.5 is chosen from hydrogen, optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted heterocycloalkyl, optionally substituted aryl, and optionally substituted heteroaryl; R.sub.6 is chosen from optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted heterocycloalkyl, optionally substituted aryl, optionally substituted heteroaryl, optionally substituted acyl, optionally substituted alkoxycarbonyl, and —P(═O)(OR.sub.7)(OR.sub.8), where R.sub.7 and R.sub.8 are independently chosen from hydrogen and optionally substituted alkyl.

18. At least one chemical entity of claim 17 wherein R.sub.5 is chosen from hydrogen and optionally substituted lower alkyl.

19. At least one chemical entity of claim 18 wherein R.sub.5 is chosen from hydrogen and methyl.

20. At least one chemical entity of any one of claims 17 to 19 wherein R.sub.6 is chosen from optionally substituted alkyl.

21. At least one chemical entity of any one of claims 17 to 19 wherein R.sub.6 is chosen from optionally substituted acyl.

22. At least one chemical entity of claim 21 wherein R.sub.6 is chosen from acetyl, propionyl, isobutyryl, and pivaloyl.

23. At least one chemical entity of any one of claims 17 to 19 wherein R.sub.6 is chosen from optionally substituted alkoxycarbonyl.

24. At least one chemical entity of claim 23 wherein R.sub.6 is chosen from optionally substituted methoxycarbonyl, ethoxycarbonyl, and isopropoxycarbonyl,

25. At least one chemical entity of any one of claims 17 to 19 wherein R.sub.6 is chosen from —P(═O)(OR.sub.7)(OR.sub.8), where R.sub.7 and R.sub.8 are independently chosen from hydrogen and optionally substituted alkyl.

26. At least one chemical entity of claim 25 wherein R.sub.6 is —P(═O)(OH)(OH).

27. At least one chemical entity chosen from compounds III-a-III-f and pharmaceutically acceptable salts thereof.

28. A pharmaceutical composition comprising a pharmaceutically acceptable carrier and at least one chemical entity of any one of claims 1 to 27.

29. A pharmaceutical composition of claim 28 wherein the composition is formulated in a form chosen from tablets, capsules, powders, liquids, suspensions, suppositories, and aerosols.

30. A packaged pharmaceutical composition comprising a pharmaceutical composition of claim 28 or 29 and instructions for using the composition to treat a subject suffering from cancer.

31. A method of treating cancer in a subject which comprises administering to a subject in need thereof a therapeutically effective amount of at least one chemical entity of any one of claims 1 to 27.

Description

EXAMPLES

[0247] The following examples serve to more fully describe the manner of using the invention. These examples are presented for illustrative purposes and should not serve to limit the true scope of the invention.

[0248] In carrying out the procedures of the methods described herein, it is of course to be understood that reference to particular buffers, media, reagents, cells, culture conditions and the like are not intended to be limiting, but are to be read so as to include all related materials that one of ordinary skill in the art would recognize as being of interest or value in the particular context in which that discussion is presented. For example, it is often possible to substitute one buffer system or culture medium for another and still achieve similar, if not identical, results. Those of skill in the art will have sufficient knowledge of such systems and methodologies so as to be able, without undue experimentation, to make such substitutions as will optimally serve their purposes in using the methods and procedures disclosed herein.

Example I

Preparation of (R)-(3S,5R,8R,9S,10S,13R,14S,17R)-14-hydroxy-10,13-dimethyl-17-(2-oxo-2H-pyran-5-yl)hexadecahydro-1H-cyclopenta[a]phenanthren-3-yl 2-aminopropanoate

[0249] ##STR00014## ##STR00015##

[0250] To a solution of Boc-amino acid (11.3 mg, 0.06 mmol, 1.2 eq), HOBT (9.7 mg, 0.072 mmol. 1.44 eq), EDC (13.8 mg, 0.072 mmol, 1.44 eq) and DMAP (16.8 mg, 0.15 mmol, 3 eq) in CH.sub.2Cl.sub.2 was added bufalin (20 mg, 0.05 mmol). The mixture was stirred at 37° C. for 16 h and then purified via preparative TLC (PE/EA=1:1) to afford (R)-(3S,5R,8R,9S,10S,13R,14S,17R)-14-hydroxy-10,13-dimethyl-17-(2-oxo-2H-pyran-5-yl)hexadecahydro-1H-cyclopenta[a]phenanthren-3-yl 2-((tert-butoxycarbonyl)amino)propanoate (23 mg, 79.8%).

##STR00016##

[0251] To a solution of (R)-(3S,5R,8R,9S,10S,13R,14S,17R)-14-hydroxy-10,13-dimethyl-17-(2-oxo-2H-pyran-5-yl)hexadecahydro-1H-cyclopenta[a]phenanthren-3-yl 2-((tert-butoxycarbonyl)amino)propanoate in EtOAc (3 mL) was added HCl (4 M in EtOAc, 3 mL) in drops at 0° C. The resulting mixture was warmed to rt after 30 min and stirred for 2 h. The mixture was quenched with saturated NaHCO.sub.3 solution and extracted with EtOAc (20 mL×3). The organic layer was washed with H.sub.2O (10 mL×4) and then dried over anhydrous Na.sub.2SO.sub.4, concentrated under reduced pressure. The crude product was then purified via Prep-TLC (CH.sub.2Cl.sub.2:MeOH=10:1) to afford the (R)-(3S,5R,8R,9S,10S,13R,14S,17R)-14-hydroxy-10,13-dimethyl-17-(2-oxo-2H-pyran-5-yl) hexadecahydro-1H-cyclopenta[a]phenanthren-3-yl 2-aminopropanoate (8 mg, 43% yield) as a white solid. LRMS (M+H.sup.+) m/z 458.5. .sup.1H NMR (CD.sub.3OD, 400 MHz) δ 7.89 (dd, J=9.6, 2.4 Hz, 1H), 7.33 (m, 1H), 6.17 (d, J=9.6 Hz, 1H), 5.02 (m, 1H), 3.54 (m, 1H), 2.43-2.48 (m, 1H), 1.08-2.15 (m, 24H), 0.88 (s, 3H), 0.62 (s, 3H).

Example II

Preparation of (3S,5R,8R,9S,10S,13R,14S,17R)-14-hydroxy-10,13-dimethyl-17-(2-oxo-2H-pyran-5-yl)hexadecahydro-1H-cyclopenta[a]phenanthren-3-yl (2-(pyrrolidin-1-yl)ethyl) carbonate

[0252] ##STR00017##

[0253] To a solution of 1 (60 mg, 0.15 mmol), and DMAP (16.8 mg, 0.15 mmol) in CH.sub.2Cl.sub.2 (10 mL) was added DIEA (77.4 mg, 0.6 mmol) and 4-nitrophenyl carbonochloridate (60.6 mg, 0.3 mmol). The mixture was stirred at 37° C. for 16 h and then purified via preparative TLC (PE/EA=1:1) to afford (3S,5R,8R,9S,10S,13R,14S,17R)-14-hydroxy-10,13-dimethyl-17-(2-oxo-2H-pyran-5-yl)hexadecahydro-1H-cyclopenta[a]phenanthren-3-yl 4-nitrophenyl carbonate as a white solid (72 mg, 87.1%).

##STR00018##

[0254] To a solution of (3S,5R,8R,9S,10S,13R,14S,17R)-14-hydroxy-10,13-dimethyl-17-(2-oxo-2H-pyran-5-yl)hexadecahydro-1H-cyclopenta[a]phenanthren-3-yl 4-nitrophenyl carbonate (24 mg, 0.044 mmol) in CH.sub.2Cl.sub.2 was added 2-(pyrrolidin-1-yl)ethanol (50.6 mg, 0.44 mmol, 10 eq), DIEA (22.7 mg, 0.176 mmol, 4 eq) and DMAP (19.7 mg, 0.176 mmol, 4 eq). The resultant mixture was stirred at 40° C. for 16 h and then purified via preparative TLC to afford (3S,5R,8R,9S,10S,13R,14S,17R)-14-hydroxy-10,13-dimethyl-17-(2-oxo-2H-pyran-5-yl)hexadecahydro-1H-cyclopenta[a]phenanthren-3-yl 2-(pyrrolidin-1-yl)ethyl carbonate (20 mg, 87.0%) as a white solid. LRMS (M+H.sup.+) m/z 528.4. .sup.1H NMR (CD.sub.3OD, 400 MHz) δ 8.01 (dd, J=10.0, 2.4 Hz, 1H), 7.44 (m, 1H), 6.29 (d, J=10.0 Hz, 1H), 5.00 (m, 1H), 4.35 (t, J=5.4 Hz, 2H), 3.12 (m, 2H), 2.96 (m, 4H), 2.55-2.60 (m, 1H), 1.08-2.15 (m, 25H), 0.99 (s, 3H), 0.73 (s, 3H).

Example III

Preparation of 4-(((((3S,5R,8R,9S,10S,13R,14S,17R)-14-hydroxy-10,13-dimethyl-17-(2-oxo-2H-pyran-5-yl)hexadecahydro-1H-cyclopenta[a]phenanthren-3-yl)oxy)carbonyl)amino)butanoic acid

[0255] ##STR00019##

[0256] To a solution of (3S,5R,8R,9S,10S,13R,14S,17R)-14-hydroxy-1 0,13-dimethyl-17-(2-oxo-2H-pyran-5-yl)hexadecahydro-1H-cyclopenta[a]phenanthren-3-yl 4-nitrophenyl carbonate (20 mg, 0.036 mmol) in CH.sub.2Cl.sub.2 was added 4-aminobutanoic acid (37.1 mg, 0.36 mmol, 10 eq), DIEA (18.6 mg, 0.144 mmol, 4 eq) and DMAP (16.1 mg, 0.144 mmol, 4 eq). The resultant mixture was stirred at 40° C. for 16 h and then purified via preparative TLC to afford 4-(((3S,5R,8R,9S,10S,13R,14S,17R)-14-hydroxy-10,13-dimethyl-17-(2-oxo-2H-pyran-5-yl)hexadecahydro-1H-cyclopenta[a]phenanthren-3-yloxy)carbonylamino)butanoic acid (10 mg, 53.5%) as a white solid. LRMS (M−H.sup.+) m/z 514.4. .sup.1H NMR (CD.sub.3OD, 400 MHz) δ 7.89 (dd, J=9.6, 2.4 Hz, 1H), 7.33 (m, 1H), 6.18 (d, J=9.6 Hz, 1H), 4.82 (m, 1H), 3.03 (m, 2H), 2.44-2.48 (m, 1H), 1.08-2.15 (m, 25H), 0.87 (s, 3H), 0.62 (s, 3H).

Example IV

Preparation of (3S,5R,8R,9S,10S,13R,14S,17R)-14-hydroxy-10,13-dimethyl-17-(2-oxo-2H-pyran-5-yl)hexadecahydro-1H-cyclopenta[a]phenanthren-3-yl (2-(pyrrolidin-1-yl)ethyl)carbamate

[0257] ##STR00020##

[0258] To a solution of (3S,5R,8R,9S,10S,13R,14S,17R)-14-hydroxy-10,13-dimethyl-17-(2-oxo-2H-pyran-5-yl)hexadecahydro-1H-cyclopenta[a]phenanthren-3-yl 4-nitrophenyl carbonate (29 mg, 0.054 mmol) in CH.sub.2Cl.sub.2 was added 2-(pyrrolidin-1-yl)ethanamine (61.6 mg, 0.54 mmol). The resultant mixture was stirred at rt for 16 h and then purified via preparative TLC to afford (3S,5R,8R,9S,10S,13R,14S,17R)-14-hydroxy-10,13-dimethyl-17-(2-oxo-2H-pyran-5-yl)hexadecahydro-1H-cyclopenta[a]phenanthren-3-yl (2-(pyrrolidin-1-yl)ethyl)carbamate (21 mg, 75%) as a white solid. LRMS (M+H.sup.+) m/z 527.5. .sup.1H NMR (CD.sub.3OD, 400 MHz) δ 7.89 (dd, J=9.6, 2.4 Hz, 1H), 7.33 (m, 1H), 6.18 (d, J=9.6 Hz, 1H), 4.88 (m, 1H), 3.35 (m, 2H), 3.12 (m, 2H), 2.46 (m, 1H), 1.08-2.15 (m, 29H), 0.87 (s, 3H), 0.62 (s, 3H).

Example V

Preparation of (3S,5R,8R,9S,10S,13R,14S,17R)-14-hydroxy-10,13-dimethyl-17-(2-oxo-2H-pyran-5-yl)hexadecahydro-1H-cyclopenta[a]phenanthren-3-yl piperazine-1-carboxylate

[0259] ##STR00021##

[0260] To a solution of (3S,5R,8R,9S,10S,13R,14S,17R)-14-hydroxy-10,13-dimethyl-17-(2-oxo-2H-pyran-5-yl)hexadecahydro-1H-cyclopenta[a]phenanthren-3-yl 4-nitrophenyl carbonate (29 mg, 0.054 mmol) in CH.sub.2Cl.sub.2was added piperazine (46.4 mg, 0.54 mmol). The resultant mixture was stirred at rt for 16 h and then purified via preparative TLC to afford (3S,5R,8R,9S,10S,13R,14S,17R)-14-hydroxy-10,13-dimethyl-17-(2-oxo-2H-pyran-5-yl)hexadecahydro-1H-cyclopenta[a]phenanthren-3-yl piperazine-1-carboxylate (18.6 mg, 69.2%) as a white solid. LRMS (M+H.sup.+) m/z 499.5. .sup.1H NMR (CD.sub.3OD, 400 MHz) δ 7.90 (dd, J=9.6, 2.4 Hz, 1H), 7.33 (m, 1H), 6.18 (d, J=9.6 Hz, 1H), 4.89 (m, 1H), 3.41 (m, 4H), 2.77-2.80 (m, 4H), 2.44-2.48 (m, 1H), 1.08-2.15 (m, 21H), 0.88 (s, 3H), 0.62 (s, 3H).

Example VI

Preparation of (3S,5R,8R,9S,10S,13R,14S,17R)-14-hydroxy-10,13-dimethyl-17-(2-oxo-2H-pyran-5-yl)hexadecahydro-1H-cyclopenta[a]phenanthren-3-yl (2-morpholinoethyl)carbamate

[0261] ##STR00022##

[0262] To a solution of (3S,5R,8R,9S,10S,13R,14S,17R)-14-hydroxy-10,13-dimethyl-17-(2-oxo-2H-pyran-5-yl)hexadecahydro-1H-cyclopenta[a]phenanthren-3-yl 4-nitrophenyl carbonate (29 mg, 0.054 mmol) in CH.sub.2Cl.sub.2 was added 2-morpholinoethanamine (70.2 mg, 0.54 mmol). The resultant mixture was stirred at rt for 16 h and then purified via preparative TLC to afford (3S,5R,8R,9S,10S,13R,14S,17R)-14-hydroxy-10,13-dimethyl-17-(2-oxo-2H-pyran-5-yl)hexadecahydro-1H-cyclopenta[a]phenanthren-3-yl (2-morpholinoethyl)carbamate (18 mg, 61.4%) as a white solid. LRMS (M+H.sup.+) m/z 543.4. .sup.1H NMR (CD.sub.3OD, 400 MHz) δ 7.89 (dd, J=9.6, 2.4 Hz, 1H), 7.33 (m, 1H), 6.18 (d, J=9.6 Hz, 1H), 4.82 (m, 1H), 3.59 (m, 4H), 3.16 (m, 2H), 2.46 (m, 2H), 2.41 (m, 5H), 1.08-2.15 (m, 21H), 0.87 (s, 3H), 0.61 (s, 3H).

Example VII

Additional Compounds

[0263] Using methods similar to those described above, the following compounds were also prepared.

TABLE-US-00001 Observed Chemical Name Ion m/z (R)-(3S,5R,8R,9S,10S,13R,14S,17R)-14- M + H.sup.+ 486.5 hydroxy-10,13-dimethyl-17-(2-oxo-2H-pyran-5-yl) hexadecahydro-1H-cyclopenta[a]phenanthren-3-yl 2-amino-3-methylbutanoate (R)-(3S,5R,8R,9S,10S,13R,14S,17R)-14- M + H.sup.+ 500.6 hydroxy-10,13-dimethyl-17-(2-oxo-2H-pyran-5-yl) hexadecahydro-1H-cyclopenta[a]phenanthren-3-yl 2-amino-4-methylpentanoate (S)-(3S,5R,8R,9S,10S,13R,14S,17R)-14- M + H.sup.+ 500.5 hydroxy-10,13-dimethyl-17-(2-oxo-2H-pyran-5-yl) hexadecahydro-1H-cyclopenta[a]phenanthren-3-yl 2-amino-4-methylpentanoate (3S,5R,8R,9S,10S,13R,14S,17R)-14- M + H.sup.+ 544.5 hydroxy-10,13-dimethyl-17-(2-oxo-2H-pyran-5-yl) hexadecahydro-1H-cyclopenta[a]phenanthren-3-yl (2-morpholinoethyl) carbonate (S)-(3S,5R,8R,9S,10S,13R,14S,17R)-14- M + H.sup.+ 458.5 hydroxy-10,13-dimethyl-17-(2-oxo-2H-pyran-5- yl)hexadecahydro-1H-cyclopenta[a]phenanthren-3-yl 2-aminopropanoate (S)-(3S,5R,8R,9S,10S,13R,14S,17R)-14- M + H.sup.+ 486.5 hydroxy-10,13-dimethyl-17-(2-oxo-2H-pyran-5- yl)hexadecahydro-1H-cyclopenta[a]phenanthren-3-yl 2-amino-3-methylbutanoate (3S,5R,8R,9S,10S,13R,14S,17R)-14-hydroxy- M + H.sup.+ 500.4 10,13-dimethyl-17-(2-oxo-2H-pyran-5-yl)hexa- decahydro-1H-cyclopenta[a]phenanthren-3-yl morpholine-4-carboxylate

Example VIII

Measurement of Equilibrium Solubility

[0264] The equilibrium solubility of compounds is measured in aqueous buffer. Excess amount of solid compound is added into buffer solution and the sample is briefly sonicated and then shaken at rt for 24 h. The sample is filtered and the concentration is analyzed by HPLC UV. A standard solution at 0.2 mg/mL was prepared in methanol for each compound and used as an external standard for quantification. Data for bufalin and four of the compounds specifically described herein in NaOAc/AcOH buffer (100 mM, pH 5.0) is shown below.

TABLE-US-00002 Solubility Chemical Name (mg/mL) Bufalin 0.041 (S)-(3S,5R,8R,9S,10S,13R,14S,17R)-14- 0.12 hydroxy-10,13-dimethyl-17-(2-oxo-2H- pyran-5-yl)hexadecahydro-1H- cyclopenta[a]phenanthren-3-yl 2-amino-3-methylbutanoate (3S,5R,8R,9S,10S,13R,14S,17R)-14- 0.71 hydroxy-10,13-dimethyl-17-(2-oxo-2H- pyran-5-yl)hexadecahydro-1H- cyclopenta[a]phenanthren-3-yl (2-(pyrrolidin-1-yl)ethyl) carbonate (3S,5R,8R,9S,10S,13R,14S,17R)-14- 1.04 hydroxy-10,13-dimethyl-17-(2-oxo-2H- pyran-5-yl)hexadecahydro-1H- cyclopenta[a]phenanthren-3-yl (2-(pyrrolidin-1-yl)ethyl)carbamate (3S,5R,8R,9S,10S,13R,14S,17R)-14- 0.84 hydroxy-10,13-dimethyl-17-(2-oxo-2H- pyran-5-yl)hexadecahydro-1H- cyclopenta[a]phenanthren-3-yl piperazine-1-carboxylate

Example IX

Inhibition of Cell Proliferation in Tumor Cell Lines

[0265] Tumor cells were plated in 96-well plates at densities from 4000 cells/well of a 96-well plate and allowed to adhere/grow for 24 h. They were then treated with various concentrations of drug for 72 h. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT, Sigma) was used to determine the number of viable cells at the time of compound addition and the number of cells remaining after 72 h compound exposure. The number of cells remaining after 72 h was compared to the number of viable cells at the time of compound addition by measuring the absorbance at 570 nm, allowing for calculation of growth inhibition. Taxol (Sigma) was used positive control.

[0266] All concentrations of compounds are tested in triplicate and controls are averaged over 4 wells. IC.sub.50 was calculated by plotting the concentration of compound vs the percentage of inhibition in treated wells using GraphPad Prism 5. Data for bufalin and representative compounds are shown below.

TABLE-US-00003 TABLE I Inhibitory activity of representative compounds in A549 cells. A549 cell Chemical Name IC.sub.50 (nM) Bufalin 4.4 (R)-(3S,5R,8R,9S,10S,13R,14S,17R)-14- 3.4 hydroxy-10,13-dimethyl-17-(2-oxo-2H- pyran-5-yl)hexadecahydro-1H- cyclopenta[a]phenanthren-3-yl 2-aminopropanoate (R)-(3S,5R,8R,9S,10S,13R,14S,17R)-14- 147.1 hydroxy-10,13-dimethyl-17-(2-oxo-2H- pyran-5-yl)hexadecahydro-1H- cyclopenta[a]phenanthren-3-yl 2-amino-3-methylbutanoate (R)-(3S,5R,8R,9S,10S,13R,14S,17R)-14- 58.8 hydroxy-10,13-dimethyl-17-(2-oxo-2H- pyran-5-yl)hexadecahydro-1H- cyclopenta[a]phenanthren-3-yl 2-amino-4-methylpentanoate (S)-(3S,5R,8R,9S,10S,13R,14S,17R)-14- 15.1 hydroxy-10,13-dimethyl-17-(2-oxo-2H- pyran-5-yl)hexadecahydro-1H- cyclopenta[a]phenanthren-3-yl 2-amino-4-methylpentanoate (3S,5R,8R,9S,10S,13R,14S,17R)-14- 12.2 hydroxy-10,13-dimethyl-17-(2-oxo-2H- pyran-5-yl)hexadecahydro-1H- cyclopenta[a]phenanthren-3-yl (2-morpholinoethyl) carbonate (3S,5R,8R,9S,10S,13R,14S,17R)-14- 2.8 hydroxy-10,13-dimethyl-17-(2-oxo-2H- pyran-5-yl)hexadecahydro-1H- cyclopenta[a]phenanthren-3-yl (2-(pyrrolidin-1-yl)ethyl)carbamate (3S,5R,8R,9S,10S,13R,14S,17R)-14- 7.4 hydroxy-10,13-dimethyl-17-(2-oxo-2H- pyran-5-yl)hexadeca-hydro-1H- cyclopenta[a]phenanthren-3- yl(2-morpholino-ethyl)-carbamate (3S,5R,8R,9S,10S,13R,14S,17R)-14- 1.8 hydroxy-10,13-dimethyl-17-(2-oxo-2H- pyran-5-yl)hexadeca-hydro-1H- cyclopenta[a]phenanthren-3- yl piperazine-1-carboxylate 4-(((((3S,5R,8R,9S,10S,13R,14S,17R)- 60.0 14-hydroxy-10,13-dimethyl-17-(2-oxo- 2H-pyran-5-yl)-hexadecahydro-1H- cyclopenta[a]phenanthren-3-yl)- oxy)carbonyl)amino)butanoic acid

TABLE-US-00004 TABLE II Inhibitory activity of representative compounds in Bcap-37 cells. Bcap-37 cell Chemical Name IC50 (nM) Bufalin 14.0 (S)-(3S,5R,8R,9S,10S,13R,14S,17R)-14- 15.9 hydroxy-10,13-dimethyl-17-(2-oxo-2H- pyran-5-yl)hexadecahydro-1H- cyclopenta[a]phenanthren-3-yl 2-aminopropanoate (S)-(3S,5R,8R,9S,10S,13R,14S,17R)-14- 48.9 hydroxy-10,13-dimethyl-17-(2-oxo-2H- pyran-5-yl)hexadecahydro-1H- cyclopenta[a]phenanthren-3-yl 2-amino-3-methylbutanoate (3S,5R,8R,9S,10S,13R,14S,17R)-14- 10.6 hydroxy-10,13-dimethyl-17-(2-oxo-2H- pyran-5-yl)-hexadecahydro-1H- cyclopenta[a]phenanthren-3-yl (2-(pyrrolidin-1-yl)ethyl) carbonate (3S,5R,8R,9S,10S,13R,14S,17R)-14- 5.3 hydroxy-10,13-dimethyl-17-(2-oxo-2H- pyran-5-yl)hexa-decahydro-1H- cyclopenta[a]phenanthren-3-yl (2-(pyrrolidin-1-yl)ethyl)carbamate (3S,5R,8R,9S,10S,13R,14S,17R)-14- 223.0 hydroxy-10,13-dimethyl-17-(2-oxo-2H- pyran-5-yl)hexa-decahydro-1H- cyclopenta[a]phenanthren-3-yl morpholine-4-carboxylate

Example X

Inhibition of Tumor Growth in Xenograft Model.

[0267] Cells were implanted in BALB/c female nude mice and grown as tumor xenografts. When tumors achieved 150-200 mm.sup.3, mice were assigned into treatment and control groups using randomized block design based upon their tumor volumes. Each group contained 10 tumor-bearing mice. Tumors were measured twice weekly in two dimensions using a caliper, and the tumor volume was calculated from two-dimensional measurements using the equation V=0.5×a×b.sup.2 where a and b are the long and short diameters of the tumor, respectively. The tumor volume was then used for calculations of T/C values. The T/C value was an indication of antitumor effectiveness; T and C were the mean volume of the treated and control groups, respectively, on a given day. Data for one of the compounds specifically described in Example IX is shown below.

TABLE-US-00005 Tumor Tumor Volume Volume Pre- Post- Dose treatment treatment (mg/kg) Schedule Route (mm.sup.3) (mm.sup.3) T/C Vehicle — QDX10 i.v. 151 ± 12 524 ± 53 — Compound  3 QDX10 i.v. 151 ± 12 261 ± 26 49.8% Paclitaxel 10 Q4DX3 i.v. 152 ± 13 391 ± 43 74.6%

[0268] While some embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. For example, for claim construction purposes, it is not intended that the claims set forth hereinafter be construed in any way narrower than the literal language thereof, and it is thus not intended that exemplary embodiments from the specification be read into the claims. Accordingly, it is to be understood that the present invention has been described by way of illustration and not limitations on the scope of the claims.