PROCESS FOR THE PREPARATION OF 4-DEMETHOXYDAUNOMYCINONE, THE AGLYCONE OF 4-DEMETHOXY-DAUNORUBICIN

Abstract: 4-Demethoxy-daunomycinone I: the known aglycone of 4-demethoxy-daunorubicin, is prepared by protecting the 13-keto group of 4-demethyl-daunomycinone, sulfonylating the 4-hydroxy group, reacting the sulfonylated compound with an amine, removing the amino protecting group from the resultant 4-demethyl-4-(protected amino)-13-­ dioxolanyl-daunomycinone, diazotising the thus-freed 4-amino group and reducing under mild conditions the resulting diazonium compound.

Description: The present invention relates to a process for preparing 4-demethoxydaunomycinone which has the formula I: 4-Demethoxydaunorubicin, which is an analogue of the known antibiotic daunorubicin, is a glycoside formed from a tetracyclic aglycone (+) 4-demethoxydaunomycinone (I) and the amino sugar daunosamine. Its utility as a potent antitumor compound is described in Cancer Treatment Report 60 (7): 829-834 (1976) and ibidem 61 (5): 893-894 (1977). A synthesis of (+) 4-demethoxydaunomycinone is described in US-A-4046878. Another synthesis is based on the preparation of racemic 1,4-dimethoxy-6-hydroxy-6-acetyl-tetraline, its optical resolution, condensation of the (-) enantiomer with phthalic anhydride and stereoselective introduction of the OH group in position 7 (see US-A-4077988 and US-A-4132721). According to the present invention, there is provided a process for the preparation of 4-demethoxy-daunomycinone of formula (I): which process comprises: (a) protecting the 13-keto group of 4-demethyl-daunomycinone of formula (2): by treatment with ethylene glycol; (b) reacting the resultant 4-demethyl-13-dioxolanyl-daunomycinone of formula (3): with a sulfonyl chloride of formula II: R-SO₂Cl (II) wherein R represents an alkyl group of from 1 to 10 carbon atoms optionally substituted by one or more halogen atoms or an aryl group optionally substituted by halogen, alkyl, alkoxy or nitro, in the presence of N,N-diisopropylethylamine and a catalytic amount of 4-dimethylamino-pyridine; (c) reacting the resultant sulfonated 4-demethyl-13-dioxolanyl-daunomycinone of formula (4): wherein R is as defined above, with an amine of formula III: R¹(R²)CH-NH₂ (III) wherein R¹ and R² each independently represents a hydrogen atom or a phenyl group bearing one or more alkoxy groups; (d) removing the amino protecting group from the resultant 4-demethyl-4-(protected amino)-13-dioxolanyl-daunomycinone of formula (5): wherein R¹ and R² are as defined above; (e) diazotising the 4-amino group of the resultant 4-demethoxy-4-amino-daunomycinone of formula (6): and (f) reducing the resultant diazo-derivative of formula (7): under mild conditions, thereby to obtain 4-demethoxy-daunomycinone of formula I. The 4-demethyl-daunomycinone of formula (2) may be prepared by demethylation of daunomycinone of formula (1): It is therefore possible to provide a process, which may start from the naturally-occurring (+) daunomycinone, which is more efficient and requires less steps than the total chemical synthesis. Moreover the process does not require either optical resolution or chemical purification steps. The intermediates of formulae (3) to (5) are novel and are included in the invention. The present process is illustrated by the following reaction scheme (Scheme 1). The starting material for the process may be (+) daunomycinone (1). This can be prepared by a suitable hydrolysis of daunorubicin, in its turn obtained by fermentation as described in US-A-4012284. Daunomycinone can be demethylated by treatement with AlCl₃ in an inert organic solvent such as nitrobenzene at the reflux temperature to give 4-demethyldaunomycinone which is called also carminomycinone (2). Such a process is described in US-A-4188377. Step (a) may be effected by treatment with ethylene glycol in the presence of p-toluenesulfonic acid at the reflux temperature. The resultant compound (3) is sulfonated in step (b) at position C4-OH to give compound (4), without any protection of the remaining OH groups. The sulfonating agent is a sulfonyl chloride of formula II: R-SO₂Cl (II) wherein R represents an alkyl group having from 1 to 10 carbon atoms, a halo or polyhalo such alkyl group or an aryl group, such as phenyl, optionally substituted by at least one, for example from one to three, substitutents selected from halogen atom(s) and alkyl such as C₁-C₄ alkyl, alkoxy such as C₁-C₄ alkoxy and nitro groups. Preferred groups which R may represent are: 4-fluorophenyl and 4-tolyl. Preferably the reaction is carried out in pyridine. It should be stressed that this selective sulfonylation does not affect either the phenolic C6-OH and C11-OH or the benzylic C7-OH only under the conditions of the invention, namely reacting the 4-demethyl-daunomycinone derivative (3) with the sulfonyl chloride in the presence of N,N-diisopropylethlamine and a catalytic amount of 4-dimethylamino pyridine. The compound (4) thus formed is directly treated in solution in step (c) with an appropriate amine of formula III: wherein R¹ and R² may each independently represent a hydrogen atom or a phenyl group bearing one or more, for example from 1 to 3, alkoxy groups. The alkoxy group(s) may have from 1 to 4 carbon atoms. Preferred amines of formula III are 4-methoxybenzylamine and 3,4-dimethoxybenzylamine. The protected amine of formula (5) can be treated in step (d) with trifluoroacetic acid, for example for three hours at room temperature, in order to liberate the 4-amino derivative (6). Diazotisation in the next step (e) can be effected using sodium nitrite, for example using an aqueous solution of sodium nitrite at from 0° to 5°C. Thus, the acidic solution from step (d), to which water and methylene chloride have been added, can be treated with sodium nitrite to give the diazonium salt (7) which may be extracted in the aqueous phase. Treatment of the aqueous solution with hypophosphorous acid, for example with 50% hypophosphorous acid, affords in step (f) the desired 4-demethoxy-daunomycinone (I) of high optical and chemical purity. 4-Demethoxy-daunomycinone is the aglycone moiety of the useful antitumor drug 4-demethoxy-daunorubicin. Accordingly, the present invention further provides a process for preparing 4-demethoxy-daunorubicin of formula IV or a pharmaceutically acceptable salt thereof, which process comprises reacting 4-demethoxy-daunomycinone of formula I which has been prepared by the process of the invention with an appropriate sugar derivative and, if desired, converting the 4-demethoxy-daunorubicin thus-obtained into a pharmaceutically acceptable salt thereof. The sugar derivative may have the formula wherein Hal represents a halogen atom, R⁴ represents a protected hydroxy groups and R⁵ represents a protected amino group. The protecting groups are removed after reaction with the 4-demethoxy-daunomycinone. Preferably Hal is a chlorine atom. The hydroxy group may be protected by a trifluoroacetyl group. The amino group may be protected by as trifluoroacetyl group also. The resulting 4-demethoxy-daunorubicin or pharmaceutically acceptable salt thereof may be formulated, for example for use as an antibiotic or an an antitumor agent, as a pharmaceutical composition comprising a pharmaceutically acceptable carrier or diluent. The following Examples illustrate the invention. Example 1. 4-Demethyldaunomycinone (2) To a solution of 15.04 g (37.8 mmol) of daunomycinone (1) in 1.4 L of methylene chloride under stirring, in a nitrogen atmosphere, 52.8 g (396.4 mmol) of anhydrous aluminium chloride were added portionwise over a period of 1.5 hour. The reaction mixture was refluxed for one hour, then the solvent was distilled off. A solution of 22.8 g (25.4mmol) of oxalic acid in 200 mL of water cooled at 0°C was carefully added to the residue and the mixture stirred for two hours at room temperature. The solid was recovered by filtration and washed with water. The product was no further purified and showed, on HPLC analysis, to be of 83% purity. TLC on Kieselgel plate F 254 (Merck) using Chloroform/Acetone (8:2 by volume) Rf=0.58 Example 2. 4-Demethyl-13-dioxolanyl-daunomycinone (3) To a suspension in benzene (400 mL) of the crude 4-demethyldaunomycinone (2), obtained as described in example 1, 30 mL of ethylene glycol and 0.3 g of p.toluene sulfonic acid were added. The reaction mixture was refluxed with azeotropic removal of water for ca. 6 hours. After cooling to room temperature the solid was recovered by filtration and washed with water and ethanol to give, after drying 11,3 g of (3) (HPLC: 98,3 %, conditions as described in example 1). Overall yield from (1): 70% ¹H-NMR 300 MHz (in CDCl₃ ): δ = 1.42 (3H,s), 1.94 (1H,dd), 2.42 (1H,dt), 2.75 (1H,d), 3.18 (1H,dd), 4.04 (4H,s), 5.20 (1H,dd), 7.25 (1H,d), 7.65 (1H,t), 7.84 (1H,d), 12.18 (1H,s), 12.92 (1H,s), 13.52 (1H,s). M.S. : m/z = 428 (M⁺ , base peak). TLC on Kieselgel plate F 254 (Merck) using Chloroform/Acetone (8:2 by volume) Rf=0.52 Example 3. 4-Demethyl-4-p.toluenesulfonyl-13-dioxalanyl-daunomycinone (4) To a suspension in pyridine (330 mL) of 11,3 g (26.4 mmol) of (3), 22.6 mL (132 mmol) of diisopropylethylamine and 0.65 g of (5.3 mmol) of 4-dimethylaminopyridine, a solution of 5.54 g (29 mmol) of p.toluene sulfonyl chloride in 25 mL of pyridine was added dropwise over a 5 minutes period. After stirring for 15 minutes at room temperature the reaction was completed. The crude product was directly used in the next step. ¹H-NMR 300 MHz (in CDCl₃ ): δ = 1.45 (3H,s), 1.92 (1H,dd), 2.18 (1H,s), 2.40 (3H,s), 2.34-2.52 (1H,m), 2.70 (1H,d), 3.15 (1H,dd), 4.06 (4H,m), 5.18 (1H, d), 7.28 (2H,d), 7.53 (1H,d), 7.74 (1H,t), 7.82 (2H,d), 8.28 (1H,d), 13.15 (1H,s), 13.48 (1H,s) M.S : m/z = 582 (M⁺ , base peak). TLC on Kieselgel plate F 254 (Merck) using Chloroform/Acetone (8:2 by volume) Rf=0.62 Example 4. 4-Demethyl-4-p.methoxybenzylamino-13-dioxolanyl-daunomycinone (5) To the solution obtained in example 3, maintained at 35 °C, 101 mL (792 mmol) of p.methoxybenzylamine were added. The reaction mixture was stirred at 35 °C for 16 hours then cooled to 0°C and added with 4 L of methylene chloride and 2 L of 10% hydrochloric acid. After separation, the organic phase was washed with water, saturated NaHCO₃ and water. The solution was dried over sodium sulfate and the solvent evaporated under reduced pressure. The residue was directly used in the next step. ¹H-NMR 300 MHz (in CDCl₃ ) : δ = 1.50 (3H,s), 1.95 (1H,dd), 2.45 (1H,dt), 2.78 (1H,d), 3.20 (1H,bs), 3.23 (1H,dd), 3.80 (1H,bs), 3.84 (3H,s), 4.08 (4H,s) 4.53 (2H,d), 5.24 (1H,bs), 6.93 (2H,d), 7.03 (1H,d), 7.31 (2H,d), 7.48 (1H,t), 7.63 (1H,dd), 9.80 (1H,t), 13.47 (1H,s), 13.72 (1H,s). TLC on Kieselgel plate F 254 (Merck) using Chloroform/Acetone (8:2 by volume) Rf=0.70 M.S. : m/z = 547 (M⁺ ,base peak) Example 5. 4-Demethoxydaunomycinone (I) The crude product obtained as described in example 4 was dissolved in 100 mL of trifluoroacetic acid and stirred for 3 hours at room temperature. The reaction mixture, after neutralization was purified by column chromatography to give (6). ¹H-NMR 300 MHz (CDCL₃ ) : δ = 2.14 (dd, J=4.8,15 Hz, 1H, 8 ax. H), 2.35 (ddd, J=2.0, 2.0, 15.0 Hz, 1H, 8 eq. H), 2.45 (s,3H, CDCH₃ ), 2.92 (d, J=19 Hz, 1H, 10 ax. H), 3.17 (dd, J=2.0, 19.0 Hz, 1H, 10 eq. H), 3.74 (d, J=4.8 Hz, 1H, 7-OH), 4.54 (s, 1H, 9-OH), 5.32 (ddd, J=2.0, 4.8, 4.8 Hz, 1H, 7-H), 6.80 (broad, 2H, 4-NH₂ ), 6.93 (d, J=8.0 Hz, 1H, 3-H), 7.46 (t, J=8.0 Hz, 1H, 2-H), 7.64 (d, J=8.0 Hz, 1H, 1-H), 13.52 (s, 1H, 11-OH), 14.00 (s, 1H, 6-OH). M.S. : m/z = 383 (M⁺ ,base peak). TLC on Kieselgel plate F 254 (Merck) using Chloroform/Acetone (8:2 by volume) Rf=0.50 To the solution of (6) in trifluoroacetic acid were added 2L of methylene chloride and 700 mL of water, then, after cooling to 0°C, 0.93 g (13.5 mmol) of sodium nitrite were added. After stirring for 10 min. the aqueous phase was separated, washed once with 100 mL of methylene chloride and added with 300 mL of 50% hypophosphorous acid and 300 mL of methylene chloride. The reaction mixture was stirred at room temperature for one hour and then the phases were separated. The organic phase was washed with water, saturated NaHCO₃ and water, dried over sodium sulfate and the solvent evaporated "in vacuo" to give 1.61 g (4.37 mmol) of 4-demethoxydaunomycinone (I) (HPLC 92%). Overall yield from daunomycinone 11.5%. ¹H-NMR 300 MHz (CDCl₃ ) : δ = 2.19 (dd, J=4.8, 14.5 Hz, 1H, 8 ax. H), 2.37 (ddd, J=2.0, 2.0, 14.5 Hz, 1H, 8eq. H), 2.43 (s, 3H, COCH₃ ), 2.95 (d, J=18.6, 1H, 10 ax. H), 3.20 (dd, J=2.0, 18.6 Hz, 1H, 10 eq. H), 3.83 (d, J=4.8 Hz, 1H, 7-OH), 4.55 (s, 1H, 9-OH), 5.32 (ddd, J=2.0, 4.8, 4.8 Hz, 1H, 7-H), 7.84-7.86 (m, 2H, 2,3-H), 8.33-8.36 (m, 2H, 1,4-H), 13.30 (s, 1H, 6-OH), 13.60 (s, 1H, 11-OH). U.V. spectrum (in EtOH): λ = 208, 252, 257, 285, 480, 500, 514 nm., λ max = 252 nm I.R. spectrum (KBr pellet) ν - 3450, 1715, 1625, 1585 cm⁻¹ . [α] 20 / D (C = 0.1 in dioxane) = + 156° M.S. : m/z = 368 (M⁺ ,base peak) TLC on Kieselgel plate F 254 (Merck) using Chloroform/Acetone (8:2 by volume) Rf=0.70.

Claims: A process for the preparation of 4-demethoxy-daunomycinone of formula (I): which process comprises: (a) protecting the 13-keto group of 4-demthyl-daunomycinone of formula (2): by treatment with ethylene glycol; (b) reacting the resultant 4-demethyl-13-dioxolanyl-daunomycinone of formula (3): with a sulfonyl chloride of formula II: R-SO₂Cl (II) wherein R represents an alkyl group of from 1 to 10 carbon atoms optionally substituted by one or more halogen atoms or an aryl group optionally substituted by halogen, alkyl, alkoxy or nitro, in the presence of N,N-diisopropylethylamine and a catalytic amount of 4-dimethylamino-pyridine. (c) reacting the resultant sulfonated 4-demethyl-13-dioxolanyl-daunomycinone of formula (4): wherein R is as defined above, with an amine of formula III: R¹(R²)CH-NH₂ (III) wherein R¹ and R² each independently represents a hydrogen atom or a phenyl group bearing one or more alkoxy groups; (d) removing the amino protecting group from the resultant 4-demethyl-4-(protected amino)-13-dioxolanyl-daunomycinone of formula (5): wherein R¹ and R² are as defined above; (e) diazotising the 4-amino group of the resultant 4-demethoxy-4-amino-daunomycinone of formula (6): and (f) reducing the resultant diazo-derivative of formula (7): under mild conditions, thereby to obtain 4-demethoxy-daunomycinone of formula I. A process according to claim 1, wherein the 4-demethyl-daunomycinone of formula (2) has been prepared by demethlylation of daunomycinone of formula (1): A process according to claim 2, wherein demethylation is effected by reflux with aluminium chloride in an inert organic solvent. A process according to any one of the preceding claims, wherein step (a) is effected by treatment with ethylene glycol in the presence of p-toluenesulfonic acid at the reflux temperature. A process according to any one of the preceding claims, wherein the sulfonyl chloride of formula (II) in step (b) is p-toluenesulfonyl chloride or 4-fluorophenyl-sulfonyl chloride. A process according to any one of the preceding claims, wherein the amine of formula (III) in step (c) is 4-methoxybenzylamine or 3,4-dimethoxybenzylamine. A process according to any one of the preceding claims, wherein step (d) is effected by reaction with trifluoroacetic acid. A process according to any one of the preceding claims, wherein step (e) is effected using sodium nitrite. A process according to any one of the preceding claims, wherein step (f) is effected using hypophosphorous acid. A process for preparing 4-demethoxy-daunorubicin of formula IV or a pharmaceutically acceptable salt thereof, which process comprises reacting 4-demethoxy-daunomycinone of formula I which has been prepared by a process according to any one of the preceding claims with a sugar derivative of the formula V: wherein Hal represents a halogen atom, R⁴ represents a protected hydroxy group and R⁵ represents a protected amino group, and the protecting groups are removed after reaction with the 4-demethoxy-daunomycinone; and, if desired, converting the 4-demethoxy-daunorubicin thus-obtained into a pharmaceutically acceptable salt thereof. A pharmaceutical composition comprising a pharmaceutically acceptable carrier or diluent and, as active ingredient, 4-demethoxy-daunorubicin or a pharmaceutically acceptable salt thereof which has been prepared by a process as claimed in claim 10. A compound of formula (4) as defined in claim 1. A compound of formula (5) as defined in claim 1.

Inventors: CABRI, WALTER, DE BERNARDINIS, SILVIA, FRANCALANCI, FRANCO, MARTINENGO, TIZIANO
Applicants: FARMITALIA CARLO ERBA S.R.L.
Application year: 1989
Main classification: C07C50
IPC codes: C07D317, C07C225, C07C45, C07C241, C07C46, C07H15, C07C245, C07C67, C07C50