HK1114101B - METHOD FOR PREPARING 4β-AMINO-4'-DEMETHYL-4-DESOXYPODOPHYLLOTOXIN - Google Patents

Description

Method for preparing 4 beta-amino-4' -demethyl-4-deoxypodophyllotoxin

Technical Field

The present invention relates to a process for preparing 4 β -amino-4 '-demethyl-4-deoxypodophyllotoxin of formula 1 from 4 β -haloacetamido-4' -demethyl-4-deoxypodophyllotoxin of formula 3 (X ═ Cl, Br or I) by cleavage in the presence of thiourea and an acid. Specifically, the present invention relates to a method for preparing 4 β -amino-4 ' -demethyl-4-deoxypodophyllotoxin of formula 1 from 4' -demethylepipodophyllotoxin of formula 2 via 4 β -haloacetamido-4 ' -demethyl-4-deoxypodophyllotoxin of formula 3 (X ═ Cl, Br or I).

Formula 1 formula 2

Formula 3 formula 4

Background

4 beta-amino-4' -demethyl-4-deoxypodophyllotoxin is a synthetic intermediate useful in the preparation of anticancer compounds (French patent application No. 0404053).

The strategy for the preparation of this intermediate is based on the conversion of 4 '-demethylepipodophyllotoxin (formula 2) into 4 β -azido-4' -demethyl-4-deoxypodophyllotoxin of formula 4 followed by the conversion of this azide derivative into the amino derivative of formula 1 by catalytic reduction. The problem with this transformation is the lack of stereoselectivity of the transformation of the active derivative at the 4 position (benzyl position) to give a mixture of azides alpha and beta of formula 4. In j.med.chem.1991, 34, 3346, the problem has been partially solved by using sodium azide and trifluoroacetic acid. It has proven necessary to purify the azido intermediate of formula 4 as well as the catalytic reduction product (i.e., the amino compound of formula 1) by chromatography. Another method is described in Chinese Chemical Letters 1993, 4(4) 289. These authors used the azide method, but at BF at-10 to-15 ℃₃Reacting azothydric acid with HN in the presence of an etherate₃Reaction (in situ preparation). The results obtained by these authors show good stereoselectivity of the conversion and a yield at least equal to 80%. Methods for converting the azide compound of formula 4 to the amino compound of formula 1 are also described in tet.let.1999, 40, 1967 and tet.let.2000, 41, 7743. These authors used samarium iodide or FeSO in t-BuOH and THF₄.7H₂O/NH₃Coupling compound (couple). Recently, bioorg.med.chem.2003, 11, 5135 demonstrated the necessity for chromatographic purification. This gave the amino compound of formula 1 in a yield of 70%.

However, these methods still present two problems. 1) The use of dangerous potentially explosive azide derivatives, especially in processes for the industrial preparation of drugs on a large scale, and 2) the necessity to pass through one or even 2 chromatographic stages to provide amino compounds of formula 1 with good quality for the subsequent preparation of the finished product, i.e. anticancer drugs, which entails steps that are difficult to handle on an industrial scale.

The object of the present invention is to solve both problems without the use of dangerous or explosive compounds and without the need for chromatographic purification stages.

The intermediate 4 β -haloacetamido-4' -demethyl-4-deoxypodophyllotoxin of formula 3 is a known compound (French patent application No.040453, WO 2004/073375). Similarly, the route from the compound of formula 2 to the compound of formula 3 is known (French patent application No. 0404053). Accordingly, an object of the present invention is a process for the synthesis of a compound of formula 1 from a compound of formula 3.

In classical organic Synthesis, cleavage of chloroacetamide to give an amine is carried out by treating the chloroacetamido derivative of the tertiary amide with thiourea in ethanol in the presence of acetic acid in an optimal ratio of 5: 1 (a. jirgensons et al, Synthesis 2000, 1709). In this reaction, ethanol and acetic acid used contained no water. This method has never been continuously used for podophyllotoxin and is not suitable. In fact, in the case of the compound of formula 3, the process taught leads to less than 10% conversion of the starting material used (compound of formula 3) after 10 hours of reflux, and the reaction intermediate (S-isothiourea in the form of X ═ chlorideSalt) no longer reacted (see comparative example). Longer reaction times are disadvantageous with regard to purity and by-products occur.

It is necessary to adjust and modify the mode of operation to obtain the preferred conversion. Surprisingly, the present inventors have determined a method for synthesizing a compound of formula 1 from a compound of formula 3 such that the compound of formula 1 has good purity without the need for additional purification steps (especially chromatography).

Disclosure of Invention

Accordingly, an object of the present invention is a process for synthesizing 4 β -amino-4' -demethyl-4-deoxypodophyllotoxin of formula 1,

formula 1

Characterized in that the method comprises the following successive steps:

a) reacting thiourea with 4 beta-haloacetamido-4' -demethyl-4-deoxypodophyllotoxin of formula 3 in a pure weak acid free of other solvents at a temperature higher than ambient temperature,

formula 3

Wherein X represents a halogen atom selected from chlorine, bromine and iodine, advantageously chlorine;

b) recovering 4 beta-amino-4' -demethyl-4-deoxypodophyllotoxin.

It has been found that the operation can be carried out in a pure weak acid, i.e. without water or other organic solvents, compared to the chloroacetamide cleavage methods described in the prior art (a. jirgensons et al, Synthesis 2000, 1709). According to the invention, the term "acid" is used with reference to the Bronsted definition, in particular capable of providing H⁺The chemical type of the proton. Weak acids are acids that do not completely dissociate in water, as opposed to strong acids.

The weak acid advantageously has a pKa value of 4 to 6 at 25 ℃. In particular, said weak acid is advantageously a carboxylic acid of formula 5R-COOH, wherein R represents hydrogen or C₁-C₂Alkyl of (2). Heavier acids can no longer be used as solvents or do not have suitable olfactive characteristics (especially butyric acid). More particularly, the weak acid is selected from formic acid, acetic acid or propionic acid, preferably acetic acid. In the following description, a given ratio between different compounds corresponds to the ratio of the amounts of these compounds involved, unless otherwise indicated.

In the context of the present invention, the expression "pure weak acid" means that the acid is ice-like (glacial), i.e. contains no water. The expression "free of other solvents" means that the reaction medium of step a) comprises only pure weak acid, the compound of formula 3 and thiourea, and accordingly does not comprise water or any other solvent, such as an alcohol or an organic solvent.

In step a), the reaction medium is advantageously heated to a temperature higher than 60 ℃, more advantageously to 60 to 100 ℃. Another feature of the present invention is the use of pure weak acids as reaction solvents.

The molar ratio of 4 β -haloacetamido-4' -demethyl-4-deoxypodophyllotoxin and said weak acid is at least 0.5. The molar ratio of 4 β -haloacetamido-4' -demethyl-4-deoxypodophyllotoxin and thiourea is advantageously between 0.5 and 1. According to one advantageous variant of the invention, in step a), the 4 β -haloacetamido-4' -demethyl-4-deoxypodophyllotoxin is contacted with the weak acid prior to addition of the thiourea. According to an even more advantageous variant, the 4 β -haloacetamido-4 '-demethyl-4-deoxypodophyllotoxin is contacted with said pure weak acid, the 4 β -haloacetamido-4' -demethyl-4-deoxypodophyllotoxin is advantageously suspended in the pure weak acid, and the reaction medium is heated to the desired temperature, at which the thiourea is then added.

The reaction time of step a) is advantageously from 1 to 3 hours. In the case of pure acetic acid, the reaction time of step a) is about 2 hours.

After step a), the final product of formula 1 is precipitated in the reaction medium. The product is recovered in step b) by any technique known to the person skilled in the art, wherein in particular a simple filtration and drying according to standard methods is sufficient.

Once filtered and dried according to conventional methods, the compound of formula 1 can be obtained in the form of the hydrochloride, hydrobromide or hydroiodide salt, with an average molar yield of said compound of formula 1 of more than 85%, advantageously more than 90%, based on the molar amount of the compound of formula 3 used. In the case of pure acetic acid, the compound of formula 1 is obtained in the form of the hydrochloride, hydrobromide or hydroiodide salt in an average molar yield of 93%, based on the molar amount of the compound of formula 3 used.

Advantageously, the compound of formula 1 is obtained in a purity greater than 90%, more advantageously greater than or equal to 95%.

The resulting compound of formula 1 in the form of the hydrochloride, hydrobromide or hydroiodide salt is pure and does not require additional chromatographic purification steps. It can be used directly in the subsequent synthetic steps, presenting major advantages from the point of view of preparation on an economic and industrial scale.

Also, an object of the present invention is a method for synthesizing 4 β -amino-4' -demethyl-4-deoxypodophyllotoxin of formula 1,

formula 1

Characterized in that the method comprises the following successive steps:

i) reacting thiourea with a 4 beta-haloacetamido-4' -demethyl-4-deoxypodophyllotoxin of formula 3 in a mixture of an acid, water and an organic solvent at a temperature above ambient temperature,

formula 3

Wherein X represents a halogen atom selected from chlorine, bromine and iodine, advantageously chlorine;

ii) recovering the 4 beta-amino-4' -demethyl-4-deoxypodophyllotoxin.

With respect to the cleavage of chloroacetamides described in the prior art (a. jirgensons et al Synthesis 2000, 1709), it has been found that the addition of water to the reaction medium facilitates the reaction by completely consuming the starting material and does not show degradation products.

The reaction medium is advantageously free of other solvents or reagents. In step i), the reaction medium is advantageously heated to a temperature higher than 60 ℃, more advantageously to 60 to 100 ℃. The molar ratio between 4 β -haloacetamido-4' -demethyl-4-deoxypodophyllotoxin and thiourea is advantageously between 0.5 and 1. In step i), the 4 β -haloacetamido-4' -demethyl-4-deoxypodophyllotoxin is advantageously contacted with a mixture of an acid, water and an organic solvent prior to addition of thiourea. Even more advantageously, the 4 β -haloacetamido-4 '-demethyl-4-deoxypodophyllotoxin is contacted with a mixture of an acid, water and an organic solvent, the 4 β -haloacetamido-4' -demethyl-4-deoxypodophyllotoxin is advantageously suspended in said mixture, and the reaction medium is heated to the desired temperature, at which the thiourea is then added.

In the second process according to the invention, the organic solvent used is advantageously a water-soluble organic solvent, more advantageously selected from cyclic ethers (in particular dioxane), alcohols (in particular methanol, ethanol, propanol and isopropanol) and also N, N-Dimethylacetamide (DMA), Dimethylformamide (DMF) and N-methylpyrrolidone (NMP).

Thus, with respect to the chloroacetamide cleavage process described in prior art 1 (a. jirgensons et al, Synthesis 2000, 1709), it has also been found that the operation can be carried out in the presence of water in the presence of an organic solvent (e.g. dioxane or DMA) instead of ethanol.

According to a first advantageous variant of the second process of the invention, the organic solvent is an alcohol, advantageously ethanol.

Within the scope of this first variant, the acid is advantageously a strong acid, in particular a strong acid selected from hydrochloric acid, sulfuric acid and phosphoric acid. The volume ratio of alcohol/(water + strong acid) is advantageously 2 to 5/0.5 to 2, more advantageously 2.5/1, and the strong acid is at one or two times the equivalent concentration (equivalent concentration is 1 to 2). Advantageously, a molar yield of greater than 80%, more advantageously greater than 85%, advantageously equal to 90%, of the compound of formula 1 is obtained. The reaction time is advantageously greater than 8 hours but less than 10 hours, even more advantageously about 9 hours.

Likewise, the compound of formula 1 is obtained in a purity of greater than 90%, advantageously 95%.

Alternatively, within the scope of this first variant, the acid is advantageously a weak acid, in particular a carboxylic acid of formula 5R-COOH, wherein R represents hydrogen or C₁-C₂Alkyl group of (1). Heavier acids can no longer be used as solvents or do not have suitable olfactive characteristics (especially butyric acid). More particularly, the weak acid is selected from formic acid, acetic acid or propionic acid, preferably acetic acid. The volume ratio of alcohol/water/weak acid is advantageously from 2 to 10/0.5 to 2/0.5 to 2, more particularly 5/1/1. More particularly, the volume ratio ethanol/water/acetic acid is advantageously 5/1/1. Advantageously, a molar yield of greater than 55%, advantageously equal to 60%, of the compound of formula 1 is obtained. The reaction time is advantageously greater than 8 hours but less than 11 hours, even more advantageously about 10 hours.

Advantageously, the compound of formula 1 is obtained in a purity of greater than 90%, advantageously 95%.

According to a second advantageous variant of the second process according to the invention, the organic solvent is a cyclic ether (in particular dioxane), and DMA, DMF or NMP.

The volume ratio of cyclic ether (dioxane) or DMA, DMF, NMP/water/weak acid (acetic acid) is advantageously from 2 to 10/0.5 to 2//0.5 to 2, more particularly 5/1/1. The volume ratio of dioxane or DMA, DMF, NMP/water/acetic acid is advantageously 5/1/1.

Advantageously, a molar yield of greater than 60%, more advantageously greater than 65%, advantageously equal to 70%, of the compound of formula 1 is obtained. The reaction time is advantageously greater than 4 hours, but less than 10 hours, even more advantageously about 5 to 6 hours.

Thus, the compound of formula 1 is advantageously obtained in a purity of greater than 90%, advantageously 95%.

In the case studied, the final product precipitates in the reaction medium. The product is recovered in step b) by any technique known to the person skilled in the art, wherein in particular a simple filtration and drying according to conventional methods is sufficient.

The resulting compound of formula 1 in the form of the hydrochloride, hydrobromide or hydroiodide salt is pure and does not require additional chromatographic purification steps. It can be used directly in the subsequent synthetic steps, presenting major advantages from the point of view of preparation on an economic and industrial scale.

Within the scope of the first or second process according to the invention, 4' -demethylepipodophyllotoxin of formula 2 is prepared by reacting in an acidic medium

Formula 2

And X-CH of formula 6₂Reaction of a haloacetonitrile of-C.ident.N advantageously gives a 4 β -haloacetamido-4' -demethyl-4-deoxypodophyllotoxin of formula 3, in which X represents a halogen atom selected from chlorine, bromine and iodine. The Ritter reaction ensures that 4 β -chloroacetamido-4' -demethyl-4-deoxypodophyllotoxin is provided directly by crystallization at the completion of the reaction, with a yield advantageously greater than 80%, even more advantageously greater than 90%, at the completion of the reaction.

This intermediate has exclusively beta stereochemistry at the 4-carbon. The stereochemistry problem is solved at this step. The intermediate is of such purity that it can be used in a cleavage step without subsequent purification to provide 4 β -amino-4' -demethyl-4-deoxypodophyllotoxin of formula 1.

The 4' -demethylepipodophyllotoxin of formula 2 (prepared according to the method described in patent FR 2742439) is advantageously treated with sulfuric acid by means of the common inexpensive reagent chloroacetonitrile. Then, 4 β -chloroacetylamino-4' -demethyl-4-deoxypodophyllotoxin was advantageously obtained in a yield of 93%.

Once filtered and dried according to standard methods, the compound of formula 1 can be obtained in the form of its hydrochloride, hydrobromide or hydroiodide salt, in an average molar yield of 86% based on the molar amount of 4' -demethylepipodophyllotoxin (formula 2) used, i.e. in 2 steps (from compound of formula 2 to compound of formula 3, then from compound of formula 3 to compound of formula 1), within the scope of using pure glacial acetic acid (neither aqueous nor any other organic solvent, according to the first method of the present invention).

Detailed Description

The following examples show the operating techniques used.

Example 1: preparation of 4 beta-chloroacetylamino-4' -demethyl-4-deoxypodophyllotoxin (formula 3).

0.5mL of concentrated sulfuric acid was added dropwise to a suspension of 30g (0.075 mole) of 4' -demethylepipodophyllotoxin in 47.5mL (0.75 mole) of chloroacetonitrile at ambient temperature. It was stirred at this temperature for 1h, dissolved and then re-precipitation was observed. 300mL of 2-propanol was added. The precipitate was filtered and washed with 200mL of 2-propanol and water to return to pH 7. The resulting white solid was dried under vacuum at 40 ℃ to give 32.9g of the chloroacetamido compound of formula 3, or 93% molar yield.

Melting point F240 ℃.

NMR analysis of protons:¹H RMN(DMSO)δ8,65(d，1H，J＝7Hz，NH)，8,26(s，1H，4′-OH)，6,78(s，1H，H₅)，6,54(s，1H，H₈)，6,24(s，2H，H_2′，H_6′)，5,99(d，2H，J＝11.3Hz，OCH₂o), 5,17(dd, 1H, J ═ 4,56, and 7Hz, H)₄)，4,51(d，1H，J＝5,2Hz，H₁)，4,29(t，1H，J＝8Hz，H_11a)，4,10(s，2H，CH₂Cl)，3,97(m，1H，H₃) 3,78(dd, 1H, J ═ 8Hz and 10Hz, H_11b)，3,63(s，6H，2xOCH₃) 3,15(dd, 1H, J ═ 5,2 and 14Hz, H₂).

Similarly, by using bromoacetonitrile or iodoacetonitrile, other haloacetamides (X ═ Br, I) are obtained.

Comparative example: preparation of 4-amino-4' -demethyl-4-deoxypodophyllotoxin (formula 1) -using ethanol: method with acetic acid 5: 1 (according to Synthesis 2000, 1709)

Table 1: number 1.

A suspension of 0.5g (1.05mmol) of 4 β -chloroacetylamino-4' -demethyl-4-deoxypodophyllotoxin obtained in example 1 in a mixture of 2.5mL of ethanol and 0.5mL of glacial acetic acid is warmed to 80 ℃ with stirring. 0.12g (1.57mmol) of thiourea was added in one portion. It was stirred at this temperature for 10 hours. Analysis of the reaction medium by thin layer chromatography (CCM) showed that only less than 10% of the desired product, 4 β -amino-4' -demethylepipodophyllotoxin (formula 1), was present as an unreactive intermediate, isothioureaSalts (X ═ S-isothiourea)Salt) and degradation products.

Example 2: preparation of 4 beta-amino-4' -demethyl-4-deoxypodophyllotoxin (formula 1) -method using pure glacial acetic acid-first method according to the present invention

Table 1: and (4) numbering 2.

A suspension of 17g (0.0358mol) of 4 β -chloroacetylamino-4' -demethyl-4-deoxypodophyllotoxin obtained in example 1 in 75mL of glacial acetic acid is warmed to 80 ℃ with stirring. 4.2g (0.0537mol) of thiourea were added in one portion. It was stirred at this temperature for 1 hour 30 minutes, dissolved, and then reprecipitation was observed. The reaction medium was filtered hot and rinsed with 75mL of glacial acetic acid and diisopropyl ether. The resulting white solid was dried under vacuum at 40 ℃ to give 14.6g of the compound of formula 1 as the hydrochloride salt, corresponding to a molar yield of 93%.

The melting point F is more than 260 ℃.

NMR analysis of protons:¹H RMN(DMSO)δ8,63(m，2H)，8,32(m，1H)，7,23(s，1H，H₅)，6,60(s，1H，H₈)，6,18(s，2H，H_2′，H_6′)，6,05(d，2H，J＝2,1Hz，OCH₂O)，4,73(d，1H，J＝4,5Hz，H₄)，4,56(d，1H，J＝5,2Hz，H₁)，4,34(m，2H，H_11aand H_11b)，3,65(dd，1H，J＝5,2Hz，H₂)，3,62(s，6H，2xOCH₃)，3,06(m，1H，H₃).

Example 3: preparation of 4 β -amino-4' -demethyl-4-deoxypodophyllotoxin (formula 1) -process using ethanol and 1N hydrochloric acid-first alternative to the first variant of the second process according to the present invention.

Table 1: and (4) number 3.

A suspension of 0.5g (1.05mmol) of 4 β -chloroacetylamino-4' -demethyl-4-deoxypodophyllotoxin obtained in example 1 in a mixture of 2.5mL of ethanol and 1mL of 1N hydrochloric acid is warmed to 80 ℃ with stirring. 0.12g (1.57mmol) of thiourea was added in one portion. It was stirred at this temperature for 9 hours, dissolved, and then reprecipitation was observed. The cooled reaction medium is filtered and washed with ethanol and diisopropyl ether. The resulting white solid was dried under vacuum at 40 ℃ to give 0.4g of the compound of formula 1 as the hydrochloride salt, corresponding to a molar yield of 90%.

The melting point F is more than 260 ℃.

Example 4: preparation of 4 β -amino-4' -demethyl-4-deoxypodophyllotoxin (formula 1) -method using ethanol: water: acetic acid (5: 1) -second alternative to the first variant of the second method according to the present invention.

Table 1: and 4, numbering.

A suspension of 0.5g (1.05mmol) of 4 β -chloroacetylamino-4' -demethyl-4-deoxypodophyllotoxin obtained in example 1 in a mixture of 2.5mL of ethanol, 0.5mL of water and 0.5mL of glacial acetic acid is warmed to 80 ℃ with stirring. 0.12g (1.57mmol) of thiourea was added in one portion. It was stirred at this temperature for 10 hours, dissolved, and then reprecipitation was observed. The cooled reaction medium is filtered and washed with ethanol and diisopropyl ether. The resulting white solid was dried under vacuum at 40 ℃ to give 0.27g of the compound of formula 1 as the hydrochloride salt, corresponding to a molar yield of 60%.

The melting point F is more than 260 ℃.

Example 5: preparation of 4 β -amino-4' -demethyl-4-deoxypodophyllotoxin (formula 1) -process using solvent (DMA, dioxane)/water/acetic acid-second variant of the second process according to the present invention.

Table 1: number 5.

A suspension of 0.5g (1.05mmol) of 4 β -chloroacetylamino-4' -demethyl-4-deoxypodophyllotoxin obtained in example 1 in a mixture of 2.5mL of dioxane or DMA, 0.5mL of water and 0.5mL of glacial acetic acid is warmed to 80 ℃ with stirring. 0.12g (1.57mmol) of thiourea was added in one portion. This was stirred at this temperature for 5 to 6 hours, dissolved, and then reprecipitation was observed. The cooled reaction medium is filtered and washed with 2-propanol and diisopropyl ether. The resulting white solid was dried under vacuum at 40 ℃ to give 0.31g of the compound of formula 1 as the hydrochloride salt, corresponding to a molar yield of 70%.

The melting point F is more than 260 ℃.

The analytical results for the comparative examples and examples 2 to 5 are summarized in the following Table 1:

numbering	Condition	Reaction time	Compound 1 yield	Purity of
					1	Ethanol/acetic acid (5/1)	10h	< 10% evaluation of non-separated CCM	Presence of starting materials, reaction intermediates, degradation products
2	Pure glacial acetic acid at 80 DEG C	2h	93％	＞95％
					3	ethanol/1N hydrochloric acid	9h	90％	95％
4	Ethanol/water/acetic acid (5/1/1)	10h	60％	95％
					5	Solvent: dioxane or DMA/acetic acid/water (5/1/1)	5-6h	70％	95％

Table 1 shows the main advantage of using pure glacial acetic acid at 80 ℃ providing the desired product with a short reaction time of 2h, with excellent yields in a highly satisfactory state of purity for the subsequent synthesis of anticancer compounds.

Claims (23)

1. A method for synthesizing 4 beta-amino-4' -demethyl-4-deoxypodophyllotoxin of formula 1,

formula 1

Characterized in that the method comprises the following successive steps:

a) reacting thiourea with 4 beta-haloacetamido-4' -demethyl-4-deoxypodophyllotoxin of formula 3 in a pure weak acid without other solvents at a temperature above ambient temperature,

formula 3

Wherein X represents a halogen atom selected from chlorine, bromine and iodine;

b) recovering 4 beta-amino-4' -demethyl-4-deoxypodophyllotoxin.

2. The process according to claim 1, characterized in that said X is chlorine.

3. A process according to claim 1, characterised in that the pure weak acid is a carboxylic acid of formula 5R-COOH, wherein R represents hydrogen or C₁-C₂Alkyl group of (1).

4. The method according to claim 1, characterized in that said pure weak acid is acetic acid.

5. The process according to any one of claims 1 to 4, characterized in that in step a), the reaction medium is heated to a temperature of 60 to 100 ℃.

6. The process according to any one of claims 1 to 4, characterized in that in step a) the 4 β -haloacetamido-4' -demethyl-4-deoxypodophyllotoxin is contacted with said pure weak acid prior to addition of thiourea.

7. The process according to any one of claims 1 to 4, characterized in that the reaction time of step a) is 1 to 3 hours.

8. A method for synthesizing 4 beta-amino-4' -demethyl-4-deoxypodophyllotoxin of formula 1,

formula 1

Characterized in that the method comprises the following successive steps:

i) reacting thiourea with a 4 beta-haloacetamido-4' -demethyl-4-deoxypodophyllotoxin of formula 3 in a mixture of an acid, water and an organic solvent at a temperature above ambient temperature,

formula 3

Wherein X represents a halogen atom selected from chlorine, bromine and iodine;

ii) recovering the 4 beta-amino-4' -demethylepipodophyllotoxin.

9. The process according to claim 8, characterized in that said X is chlorine.

10. The process according to claim 8, characterized in that in step i), the reaction medium is heated to a temperature of 60 to 100 ℃.

11. A process according to any one of claims 8 to 10, characterized in that in step i) the 4 β -haloacetamido-4' -demethyl-4-deoxypodophyllotoxin is contacted with a mixture of acid, water and organic solvent prior to addition of thiourea.

12. A process according to any one of claims 8 to 10, characterised in that the organic solvent is a water-soluble organic solvent.

13. Process according to any one of claims 8 to 10, characterized in that the organic solvent is selected from cyclic ethers, alcohols and N, N-dimethylacetamide, dimethylformamide, N-methylpyrrolidone.

14. The process according to any one of claims 8 to 10, characterized in that the organic solvent is dioxane.

15. Process according to any one of claims 8 to 10, characterized in that the solvent is ethanol.

16. The process of claim 15, characterized in that the acid is a strong acid.

17. The method of claim 15, characterized in that the acid is selected from the group consisting of hydrochloric acid, sulfuric acid and phosphoric acid.

18. A process according to any one of claims 8 to 10, characterised in that the acid is a weak acid.

19. The process according to claim 18, characterized in that the acid is a carboxylic acid of formula 5R-COOH, wherein R represents hydrogen, C₁-C₂Alkyl group of (1).

20. The process of claim 18, characterized in that the acid is acetic acid.

21. Process according to claim 20, characterized in that the volume ratio organic solvent/water/acetic acid is 5/1/1, wherein the organic solvent is selected from ethanol or dioxane or N, N-dimethylacetamide, dimethylformamide, N-methylpyrrolidone.

22. Process according to any one of claims 1 to 4 and 8 to 10, characterized in that the molar ratio between the 4 β -haloacetamido-4' -demethyl-4-deoxypodophyllotoxin and the thiourea is comprised between 0.5 and 1.

23. The process according to any one of claims 1 to 4 and 8 to 10, characterized in that 4' -demethylepipodophyllotoxin of formula 2 is obtained by reacting in an acid medium

Formula 2

And X-CH of formula 6₂-C.ident.N haloacetonitrile to give a 4 β -haloacetamido-4' -demethyl-4-deoxypodophyllotoxin of formula 3 wherein X represents a halogen atom selected from chlorine, bromine and iodine.