Synthesis of dolastatin 10
First Claim
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1. The method of synthesizing dolastatin 10 comprising the steps of forming a solution of Z-(S,S)-isoleucine and methyl iodide in tetrahydrofuran;
- cooling said solution to about 0°
C.;
stirring said cooled solution under argon;
adding sodium hydride to said stirred cooled solution to form a suspension;
stirring said suspension at room temperature;
adding ethyl acetate and ice water to said stirred suspension to form an aqueous layer;
washing aqueous layer with ether;
acidifying said washed aqueous layer with acid at 0°
C.;
extracting said acidified aqueous layer with ethyl acetate; and
washing said extract;
removing said solvent from said extract to provide N-Z-N-methyl- (S,S)- isoleucine;
dissolving said N-Z-N-methyl-(S,S)- isoleucine in tetrahydrofuran at 0°
C. under argon;
adding borane-tetrahydrofuran complex to said solution with stirring;
extracting the product from said solution with ethyl acetate;
evaporating the solvent from extracted product to form an oil;
filtering said oil through a column of silica gel;
eluting said column with hexane-acetone (7;
3) to form N-Z-N-methyl-(S,S)-isoleucinol;
admixing said N-Z-N-methyl-(S,S)-isoleucinol with triethylamine in dimethylsulfoxide at room temperature;
cooling the mixed solution to 0°
C.;
adding sulfur trioxide-pyridine complex to said solution under argon;
extracting the aldehyde from said solution with ether;
washing said ethereal solution successively with citric acid, water, and sodium bicarbonate to yield chromotographically pure N-Z-N-methyl- (S,S)-isoleucinal;
preparing a solution of lithium diisopropylamide from n-butyllithium and diisopropylamine in tetrahydrofuran at -78°
C.;
warming said solution to -20°
C.;
recooling said solution to -78°
C.;
adding tert-butyl acetate to said recooled solution;
stirring said solution while rewarming said solution to -20°
C.;
recooling said solution to -78°
C. and adding said chromatographically pure N-Z-N-methyl-(S,S)-isoleucinal thereto;
treating the resulting mixture with ice water;
extracting the mixture with ether;
drying said extract;
solvent evaporating said dry extract to yield a viscous oil;
chromatographing and eluting said viscous oil with hexane-acetone (47;
3) to yield tert-butyl(3S,4S, 5S)-3-hydroxy-4-(N-Z-N-methyl)-amino-5-methyl-heptanoate and tert-butyl (3R,4S,5S)-3-hydroxy-4-(N-Z-N-methyl)-amino-5-methyl-heptanoate;
adding boron trifluoride etherate to a cooled and stirred solution of tert-butyl (3R,4S,5S)-3-hydroxy-4-(N-Z-N-methyl) -amino-5-methyl-heptanoate in dichloromethane under argon;
thereafter adding an anhydrous solution of diazomethane in dichloromethane to said solution;
filtering the polymethylene side products from said solution to form a filtrate;
concentrating said filtrate;
chromatographing said concentrated filtrate on a silica gel column;
eluting said column with hexane-acetone (97;
3) to yield tert-butyl (3R,4S,5S)-3-methoxy-4-(N-Z-N-methyl) -amino-5-methyl-heptanoate;
admixing trifluoroacetic anhydride in dichloromethane into a cooled -78°
C. solution of dimethylsulfoxide in dichloromethane with stirring;
adding N-Boc-S-prolinol in dichloromethane to said cool stirred mixture and continue stirring for about an hour;
adding triethylamine to said solution;
warming said solution to -20°
C.;
extracting said solution with ether to form an ethereal solution;
washing and concentrating said ethereal solution to form an oil;
dissolving said oil in acetone;
filtering said oil-acetone solution through a silica-gel column;
eluting said column with hexane-acetone (93;
7) to yield N-Boc-S-prolinal;
adding 2-S-Propionyloxy-1,1,2-triphenylethanol to a solution of lithium diisopropylamide in tetrahydrofuran at -78°
C. under argon to form a reaction mixture;
permitting said reaction mixture to warm to room temperature over two hours to form a yellow solution;
cooling the yellow solution to - 95°
C.;
adding freshly synthesized magnesium bromide to said cooled yellow solution;
thereafter adding a solution of Boc-S-prolinal in tetrahydrofuran to said yellow solution and allowing the reaction therebetween to proceed for two hours at -95°
C. under methanol-liquid nitrogen;
terminating said reaction with saturated aqueous ammonium chloride;
warming said mixture to 0°
C.;
adding ether to said mixture to form an ethereal solution;
washing, drying and solvent evaporating said ethereal solution to provide a glassy solid;
dissolving said glassy solid to form a solution;
adsorbing said solution on silica gel;
chromatographing said adsorbed silica gel; and
eluting said chromatographed silica gel to provide N-Boc-2S-3'"'"'-[2"ethoy-(1"hydroxy-1",1",2"-triphenyl) 2'"'"'S-methyl-3'"'"'R-hydroxy- propionate]-pyrrolidine;
methylating said N-Boc-2S-3, propionate-pyrrolidine in dichloromethane with boron trifluoride etherate and diazomethane in anhydrous dichloromethane;
eluting said methylated pyrrolidine with hexane-acetone (9;
1) to provide N-Boc-2S-3'"'"'-[2"-ethoxy(1"-hydroxy-1",1",2"-triphenyl) 2'"'"'S-methyl-3'"'"'R-methoxy-propionate]-pyrrolidine;
adding potassium tert-butoxide to a solution of said (2'"'"'S,3'"'"'R) ester in tetrahydrofuran with stirring until the solution turns bright yellow;
warming the bright yellow solution to -15°
C. and stopping the epimerization thereof by the addition of sufficient saturated aqueous citric acid thereto to dilute said solution;
extracting said solution with dichloromethane to form a combined extract;
washing said extract and removing the solvent therefrom to provide a clear oil;
chromatographing said yellow oil on silica gel;
eluting said silica gel to provide N-Boc-2S-3'"'"'-[2"ethoxy(1"hydroxy- 1",1", 2"-triphenyl) 2'"'"'S- methyl-3'"'"'R-methoxy-propionate]-pyrrolidine;
forming a solution of N-Boc-S-phenylalaninol in anhydrous dimethylsulfoxide-triethylam;
ine;
oxidizing said solution with sulfur trioxide pyridine complex;
adding water to said oxidized solution to precipitate N-Boc-S-phenylalaninal;
forming a solution of N-Boc-S-phenylalaninal and 2-aminoethanethiol in anhydrous benzene;
stirring said solution under argon for four hours;
removing the solvents and excess reagents from said stirred solution by filtration through a silica gel pad to form a residue;
crystallizing said residue to form 2-(N-Boc-1'"'"'S-amino-2'"'"'-phenyl-ethyl)-2-(R,S)-thiazolidine [N-Boc-2(3),4(5)-tetrahydro-dolaphenine];
forming a suspension of battery grade manganese dioxide in anhydrous benzene;
adding 1'"'"'-ethyl (N-Boc-1'"'"'S-amino-2'"'"'-phenyl)-2(R,S)-thiazolidine [N-Boc-2(3),4(5)-tetrahydro-dolaphenine] in benzene to said suspension to form a mixture;
stirring said mixture under argon at 55°
C. for 24 hours;
adding additional manganese dioxide with continued stirring;
filtering said stirred solution through silica gel;
washing said silica gel sequentially with benzene, ethyl acetate, chloroform and chloroform acetone (1;
1) to form a combined eluant;
evaporating said combined eluant to form a residue;
chromatographing said residue on a silica gel column;
eluting said column with ethyl acetate-hexane; and
crystallizing from said eluant granules consisting of 2-(1'"'"'S-Boc-amino-2'"'"'-phenyl-ethyl)-2-thiazole[N-Boc-S-dolaphenine].
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Abstract
A complicated but extremely important scheme of synthesis has been developed for synthesizing, dolaisoleuine, dolaproine, dolaphenine and dolavaline from readily available starting materials such as Z-(S,S)isoleucine, S-phenylalaline, S-phenylalaninol, S-prolinol, S-mandelate, and S-valine. The requisite amino acids have been combined using several peptide coupling procedures to create pharmaceutically pure dolastatin 10.
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Citations
24 Claims
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1. The method of synthesizing dolastatin 10 comprising the steps of forming a solution of Z-(S,S)-isoleucine and methyl iodide in tetrahydrofuran;
- cooling said solution to about 0°
C.;
stirring said cooled solution under argon;
adding sodium hydride to said stirred cooled solution to form a suspension;
stirring said suspension at room temperature;
adding ethyl acetate and ice water to said stirred suspension to form an aqueous layer;
washing aqueous layer with ether;
acidifying said washed aqueous layer with acid at 0°
C.;
extracting said acidified aqueous layer with ethyl acetate; and
washing said extract;
removing said solvent from said extract to provide N-Z-N-methyl- (S,S)- isoleucine;
dissolving said N-Z-N-methyl-(S,S)- isoleucine in tetrahydrofuran at 0°
C. under argon;
adding borane-tetrahydrofuran complex to said solution with stirring;
extracting the product from said solution with ethyl acetate;
evaporating the solvent from extracted product to form an oil;
filtering said oil through a column of silica gel;
eluting said column with hexane-acetone (7;
3) to form N-Z-N-methyl-(S,S)-isoleucinol;
admixing said N-Z-N-methyl-(S,S)-isoleucinol with triethylamine in dimethylsulfoxide at room temperature;
cooling the mixed solution to 0°
C.;
adding sulfur trioxide-pyridine complex to said solution under argon;
extracting the aldehyde from said solution with ether;
washing said ethereal solution successively with citric acid, water, and sodium bicarbonate to yield chromotographically pure N-Z-N-methyl- (S,S)-isoleucinal;
preparing a solution of lithium diisopropylamide from n-butyllithium and diisopropylamine in tetrahydrofuran at -78°
C.;
warming said solution to -20°
C.;
recooling said solution to -78°
C.;
adding tert-butyl acetate to said recooled solution;
stirring said solution while rewarming said solution to -20°
C.;
recooling said solution to -78°
C. and adding said chromatographically pure N-Z-N-methyl-(S,S)-isoleucinal thereto;
treating the resulting mixture with ice water;
extracting the mixture with ether;
drying said extract;
solvent evaporating said dry extract to yield a viscous oil;
chromatographing and eluting said viscous oil with hexane-acetone (47;
3) to yield tert-butyl(3S,4S, 5S)-3-hydroxy-4-(N-Z-N-methyl)-amino-5-methyl-heptanoate and tert-butyl (3R,4S,5S)-3-hydroxy-4-(N-Z-N-methyl)-amino-5-methyl-heptanoate;
adding boron trifluoride etherate to a cooled and stirred solution of tert-butyl (3R,4S,5S)-3-hydroxy-4-(N-Z-N-methyl) -amino-5-methyl-heptanoate in dichloromethane under argon;
thereafter adding an anhydrous solution of diazomethane in dichloromethane to said solution;
filtering the polymethylene side products from said solution to form a filtrate;
concentrating said filtrate;
chromatographing said concentrated filtrate on a silica gel column;
eluting said column with hexane-acetone (97;
3) to yield tert-butyl (3R,4S,5S)-3-methoxy-4-(N-Z-N-methyl) -amino-5-methyl-heptanoate;
admixing trifluoroacetic anhydride in dichloromethane into a cooled -78°
C. solution of dimethylsulfoxide in dichloromethane with stirring;
adding N-Boc-S-prolinol in dichloromethane to said cool stirred mixture and continue stirring for about an hour;
adding triethylamine to said solution;
warming said solution to -20°
C.;
extracting said solution with ether to form an ethereal solution;
washing and concentrating said ethereal solution to form an oil;
dissolving said oil in acetone;
filtering said oil-acetone solution through a silica-gel column;
eluting said column with hexane-acetone (93;
7) to yield N-Boc-S-prolinal;
adding 2-S-Propionyloxy-1,1,2-triphenylethanol to a solution of lithium diisopropylamide in tetrahydrofuran at -78°
C. under argon to form a reaction mixture;
permitting said reaction mixture to warm to room temperature over two hours to form a yellow solution;
cooling the yellow solution to - 95°
C.;
adding freshly synthesized magnesium bromide to said cooled yellow solution;
thereafter adding a solution of Boc-S-prolinal in tetrahydrofuran to said yellow solution and allowing the reaction therebetween to proceed for two hours at -95°
C. under methanol-liquid nitrogen;
terminating said reaction with saturated aqueous ammonium chloride;
warming said mixture to 0°
C.;
adding ether to said mixture to form an ethereal solution;
washing, drying and solvent evaporating said ethereal solution to provide a glassy solid;
dissolving said glassy solid to form a solution;
adsorbing said solution on silica gel;
chromatographing said adsorbed silica gel; and
eluting said chromatographed silica gel to provide N-Boc-2S-3'"'"'-[2"ethoy-(1"hydroxy-1",1",2"-triphenyl) 2'"'"'S-methyl-3'"'"'R-hydroxy- propionate]-pyrrolidine;
methylating said N-Boc-2S-3, propionate-pyrrolidine in dichloromethane with boron trifluoride etherate and diazomethane in anhydrous dichloromethane;
eluting said methylated pyrrolidine with hexane-acetone (9;
1) to provide N-Boc-2S-3'"'"'-[2"-ethoxy(1"-hydroxy-1",1",2"-triphenyl) 2'"'"'S-methyl-3'"'"'R-methoxy-propionate]-pyrrolidine;
adding potassium tert-butoxide to a solution of said (2'"'"'S,3'"'"'R) ester in tetrahydrofuran with stirring until the solution turns bright yellow;
warming the bright yellow solution to -15°
C. and stopping the epimerization thereof by the addition of sufficient saturated aqueous citric acid thereto to dilute said solution;
extracting said solution with dichloromethane to form a combined extract;
washing said extract and removing the solvent therefrom to provide a clear oil;
chromatographing said yellow oil on silica gel;
eluting said silica gel to provide N-Boc-2S-3'"'"'-[2"ethoxy(1"hydroxy- 1",1", 2"-triphenyl) 2'"'"'S- methyl-3'"'"'R-methoxy-propionate]-pyrrolidine;
forming a solution of N-Boc-S-phenylalaninol in anhydrous dimethylsulfoxide-triethylam;
ine;
oxidizing said solution with sulfur trioxide pyridine complex;
adding water to said oxidized solution to precipitate N-Boc-S-phenylalaninal;
forming a solution of N-Boc-S-phenylalaninal and 2-aminoethanethiol in anhydrous benzene;
stirring said solution under argon for four hours;
removing the solvents and excess reagents from said stirred solution by filtration through a silica gel pad to form a residue;
crystallizing said residue to form 2-(N-Boc-1'"'"'S-amino-2'"'"'-phenyl-ethyl)-2-(R,S)-thiazolidine [N-Boc-2(3),4(5)-tetrahydro-dolaphenine];
forming a suspension of battery grade manganese dioxide in anhydrous benzene;
adding 1'"'"'-ethyl (N-Boc-1'"'"'S-amino-2'"'"'-phenyl)-2(R,S)-thiazolidine [N-Boc-2(3),4(5)-tetrahydro-dolaphenine] in benzene to said suspension to form a mixture;
stirring said mixture under argon at 55°
C. for 24 hours;
adding additional manganese dioxide with continued stirring;
filtering said stirred solution through silica gel;
washing said silica gel sequentially with benzene, ethyl acetate, chloroform and chloroform acetone (1;
1) to form a combined eluant;
evaporating said combined eluant to form a residue;
chromatographing said residue on a silica gel column;
eluting said column with ethyl acetate-hexane; and
crystallizing from said eluant granules consisting of 2-(1'"'"'S-Boc-amino-2'"'"'-phenyl-ethyl)-2-thiazole[N-Boc-S-dolaphenine]. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 16, 17, 18)
- cooling said solution to about 0°
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14. The method of synthesizing dolastatin 10 comprising the steps of:
- forming a cooled first solution (0°
C.) of 2-(N-Boc-1'"'"'S-amino-2'"'"'-phenyl-ethyl)-2-thiazole (N-Boc-S- dolaphenine), in dichloromethane;
adding trifluoroacetic acid to said first solution to form a second solution;
stirring said second solution at 0°
C. for one hour and at room temperature for one hour;
evaporating the solvent from said second solution in a stream of nitrogen to leave a residue;
triturating said residue with hexane;
drying said triturated residue in a high vacuum over phosphorous pentoxide for 24 hours to form the trifluoroacetate salt of dolaphenine as a gum;
mixing said trifluoroacetate salt of dolaphenine in dimethoxyethane and Boc-(2S,2'"'"'R,3'"'"'R)-Dap to form a first mixture;
cooling said mixture to 0°
C.;
treating said cooled first mixture with triethylamine followed by diethylphosphorocyanidate to form a second mixture;
stirring said second mixture under argon for three hours at 0°
C.;
evaporating the solvent from said second mixture;
chromatographing said second mixture successfully on SEPHADEX®
LH-20 in hexane-methanol-dichloromethane (2;
2.5;
7.5) and on silica gel with hexane-acetone (9;
1) to yield Boc-(2S,2'"'"'R,3'"'"'R)-Dap-Doe;
concurrently therewith, forming a third solution of S-Dov-S-Val-(3R,4S,5S)-Dil-OBut in dichloromethane;
cooling said third solution to 0°
C.;
adding trifluoracetic acid to said cooled third solution;
holding said cooled third solution under argon for two hours;
evaporating said third solution with a stream of nitrogen;
adding carbon tetrachloride to said evaporated third solution;
evaporating said carbon tetrachloride from said third solution to provide a tripeptide [S-Dov-S-Val-(3R,4S,5S)-Dil-OH] trifluoroacetic acid salt;
drying said tripeptide trifluoroacetic acid salt;
adding trifluoracetic acid to said Boc-(2S,2'"'"'R,3'"'"'R)-Dap-S-Doe in dichloromethane at 0°
C. to form a fourth solution;
holding said fourth solution under argon for one hour;
evaporating said fourth solution with a stream of nitrogen;
adding carbon tetrachloride to said evaporated fourth solution;
evaporating said carbon tetrachloride from said fourth solution to form a dipeptide trifluoroacetic acid salt;
forming a fifth solution of said dipeptide [(2S,2'"'"'R,3'"'"'R)-Dap-S-Doe] trifluoroacetic acid salt and a trifluoroacetic acid salt of S-Dov-S-Val-(3R,4S,5S)-Dil in dimethoxyethane;
cooling said fifth solution under argon to 0°
C.;
adding triethylamine and diethylphosphorocyanidate to said cooled fifth solution;
stirring said fifth solution at 0°
C. for one hour and then at room temperature for two hours to complete the peptide bond formation;
evaporating the solvent from said fifth solution with a stream of nitrogen to form a crude mixture;
chromatographing said crude mixture successfully on a column of SEPHADEX®
LH-20 in hexane-dichloromethane- methanol (2;
7.5;
2.5) and on a column of silica gel;
eluting said silica gel column with dichloromethane to dichloromethane-methanol gradient of from one to five percent to yield dolastatin 10 as an amorphous powder. - View Dependent Claims (15, 19, 20, 21, 22, 23, 24)
- forming a cooled first solution (0°
Specification