HK1155148A - Method for preparing combretastatin - Google Patents

Description

Process for preparing combretastatin

Technical Field

The present application relates to a process for the preparation of combretastatin (A) in base form or in acid addition salt form

Background

US 6759555 describes a process for the preparation of combretastatin having the formula

Wherein X represents-NH₂Or one of the following two groups:

PG represents a group protecting an amino functional group.

Bioorg.med.chem.2000, 8, 2417-.

J.Pept.Res.1999, 54(1), 54-65 compared the acid activators that form peptide bonds, which resulted in TDBTU being optimal.

Bioorg.Med.chem.2006, 14, 3231-3244 describes the preparation of combretastatin having the formula (A) wherein HOBt-H is coupled using DCC as acid activator₂O (step e, Compound 10).

Chem.commun.1999, 1847-1848 describes T3P in the preparation of amide bonds; however, T3P was described as producing more epimerization, resulting in poorer yields than HAPyU (see table 3).

These documents neither describe nor suggest the method which is the subject of claim 1. Similarly, neither enrichment of the amide salt using benzyl alcohol and acetonitrile nor coupling using T3P is described.

Technical problem

Combretastatin or stilbene (stilbene) derivatives exhibit strong cytotoxic activity and as a result can be used as anticancer agents. However, the (Z) isomer showed the strongest cytotoxic activity. These compounds are described in particular in US 5731353, US 5561122 or US 6759555. The present application improves the process for the preparation of combretastatin (a).

Disclosure of Invention

The present invention relates to a process for the preparation of combretastatin (a) in base form or in acid addition salt form:

the method comprises the following steps: in the presence of a base and T3P having the following formula (III):

reacting a (Z) -amino compoundOr salts of (Z) -amino compoundsAnd has the formulaCoupling the double protected L-serine derivative of (a) to (b) to give a compound having the formula (Z) - (Ib):

wherein B is^-Represents a counter anion (counter anion), PG represents a group protecting the amino function; then, in the presence of an acid, deprotection and ring opening of (Z) - (Ib) are carried out to obtain a salt (-NH)₃ ⁺) Combretastatin (a) in form; and optionally, adding a base to obtain a base (-NH)₂) Combretastatin (A) in a form,

the salt of the (Z) -amino compound is obtained by enriching the salt of the amino compound having the following formula in the form of the (Z) isomer:

wherein B is^-Represents a counter anion, said enrichment comprising:

to a suspension of the mixture of the salt of the (Z) -amino compound and the salt of the (E) -amino compound in acetonitrile, benzyl alcohol is added, followed by

Mechanical separation of the salt of the amino compound enriched in the (Z) isomeric form.

The invention also relates to a process for the enrichment of the salt of an amino compound having the formula

Wherein B is^-Represents a counter anion, the method comprising:

to a suspension of the mixture of the salt of the (Z) -amino compound and the salt of the (E) -amino compound in acetonitrile is added benzyl alcohol, and

mechanical separation of the salt of the amino compound enriched in the (Z) isomeric form.

The invention also relates to the use of T3P having formula (III),

the T3P having formula (III) is used to couple a (Z) -amino compound or a salt of a (Z) -amino compound with a di-protected L-serine derivative in the presence of a base.

The ratio of acetonitrile/(Z) -and (E) -amino compound salt is 5 to 17 by weight, preferably 10 to 12 by weight. The temperature at which the enrichment is carried out is preferably from 20 to 70 ℃. The ratio of benzyl alcohol/(Z) -and (E) -amino compound salts is 1 to 4, preferably 2 to 3, by weight.

Detailed Description

Scheme 1 below describes the reaction steps (i) to (iv) of the process for the preparation of combretastatin (a):

scheme 1

Step (i): carrying out a Wittig reaction (Witting reaction) between nitromethoxybenzaldehyde and trimethoxybenzylphosphonium bromide or trimethoxybenzylphosphonium chloride in the presence of a base to give a salt of the nitro compound which is 2-methoxy-5- [2- (3, 4, 5-trimethoxyphenyl) vinyl]A mixture of two (Z) and (E) isomers of nitrobenzene ((Z) -nitro and (E) -nitro);

step (ii): reducing the mixture to obtain a mixture of (Z) -amino compound and (E) -amino compound, wherein the (Z) -amino compound and the (E) -amino compound are converted into the salt (B)^-Represents a counter anion, e.g. Cl^-Or SO₄ ^2-) Followed by a step of isolating the (Z) -amino compound;

step (iii): coupling a salt of the (Z) -amino compound with an L-serine derivative (compound having formula (II)) that is double protected at-OH and amino functional groups to give compounds (Z) - (Ib);

PG represents a group protecting an amino functional group: it may, for example, be tert-Butoxycarbonyl (BOC), benzyloxycarbonyl (CBZ) or 9-Fluorenylmethoxycarbonyl (FMOC);

steps (iv) and (v): deprotection and opening of the ring is carried out to give combretastatin (a) in salt or non-salt form.

Step (i) is described in US 5731353 and Bioorg. Med. chem.2000, 8, 2417-. The reaction is carried out in an organic solvent, such as an aromatic solvent (e.g. toluene), in the presence of a base, preferably a strong base, such as MeONa or NaH. The ratio (Z)/(E) is of the order of 75/25.

The reduction step (ii) described in US 6759555 is carried out in the presence of an excess of iron (greater than 2 equivalents relative to (Ia)). The reduction can also be carried out in the presence of zinc as described in US 5525632 (example 2, step 2), but the reduction is incomplete (yield 49.3%), which moreover leads to the formation of a large amount of "azo" by-products. The (Z) -amino compound is subsequently obtained in sufficient purity by one or more complex separations. The separation after the reduction is carried out by continuous crystallization (fractional crystallization). The (E) -amino compound can be removed by a first crystallization and then the (Z) -amino compound can be isolated by a second crystallization (see, US 6759555, example 1).

The coupling step (iii) is advantageously carried out in the presence of an acid activating agent, such as EDCI (1- (3-dimethylaminopropyl) -3-ethylcarbodiimide chloride), DCC (dicyclohexylcarbodiimide), TOTU (O- [ ethoxycarbonyl ] cyanomethyleneamino) -N, N, N ', N' -tetramethyluronium tetrafluoroborate), HBTU (O-benzotriazol-1-yl-N, N, N ', N' -tetramethyluronium hexafluorophosphate), PivCl (pivaloyl chloride) or N, N-carbonyldiimidazole (carbondiazole). The term "acid activator" ("coupling agent") is used to indicate a compound whose function is to activate the acid function-COOH in order to promote the formation of peptide bonds. For a more detailed description of acid activators, reference may be made to the reviews ChemFiles Vol.7, No.2, page 3 (published by Aldrich Chemical Co.) or to Tetrahedron report No.672, 2004, 60, 2447-2467, "Recent level of peptide linking reagents in organic synthesis". Review Tetrahedron 2005, 61, 10827 and 10852 discloses that a number of acid activators are available.

Step (iv) is carried out in the presence of an acid in order to promote ring opening andobtaining the salt (-NH)₃ ⁺) Combretastatin (a) in form (a). It involves deprotection/ring opening. In the presence of BOC, hydrochloric acid (for example in the form of a methanol solution) is advantageously used to obtain the hydrochloride. Combretastatin (a) is obtained in base form by neutralizing the salt with a base such as sodium hydroxide (see e.g. example 1-step (iii)).

Method of the invention

The process of the present invention repeats the same steps of scheme 1, but improves steps (ii) and (iii). Indeed, in the present invention, during step (ii), the (Z) isomer of the salt of the amino compound is obtained by a process comprising:

to a suspension of the mixture of the salt of the (Z) -amino compound and the salt of the (E) -amino compound in acetonitrile is added benzyl alcohol, and

mechanical separation of the salt of the amino compound enriched in the (Z) isomeric form.

Thus, the (Z) isomer is obtained by "enrichment", which term means that at the end of the two steps of the above process the ratio of the (Z) isomer with respect to the (E) isomer increases; mention may also be made of processes for separating the (Z) isomer from mixtures of the (Z) isomer and the (E) isomer. The advantage of enrichment over (re) crystallization is that,direct connectionAnd isSimple and easyIs carried out. This amino compound can be obtained enriched in the (Z) isomer form with a low content of residual (E) isomer (which can be < 1 mol%; see example 1 where the purity of the product is 99.93% for the (Z) isomer and 0.07% for the (E) isomer). The mechanical separation may be, for example, filtration or centrifugation. At the end of the mechanical separation, the salt of the (Z) isomer may optionally be washed and dried.

The suspension preferably has a ratio of acetonitrile/(Z) -and (E) -amino compound salt of 5 to 17, preferably 10 to 12 by weight (i.e. the weight of acetonitrile in the suspension is 5 to 17 times the weight of (Z) -and (E) -amino compounds).

The amount of benzyl alcohol added is preferably such that the ratio of benzyl alcohol/(Z) -and (E) -amino compound salt is 1 to 4, preferably 2 to 3 by weight (i.e., the weight of benzyl alcohol added is 1 to 4 times the weight of (Z) -and (E) -amino compound). This ratio can maintain a high (Z)/(E) ratio for the final product. The function of the benzyl alcohol is to preferentially dissolve the salt of the (E) -amino compound.

The temperature at which the enrichment is carried out is preferably from 20 to 70 ℃, advantageously from 30 to 70 ℃, preferably from 35 to 65 ℃. Above 70 ℃, the amino compound starts to decompose slowly.

Preferred methods of preparing the suspension are described below. Sodium dithionite (Na) is used in the solvent₂S₂O₄) To reduce the (Z) -and (E) -nitro compounds, the solvent may be a mixture of water and an alcohol, for example a water/methanol mixture. After reduction, a strong acid (e.g., HCl or H) is introduced into the reaction medium₂SO₄) The acid reacts with the reaction intermediates and also reacts with dithionite and disulfite (disulphite) residues. Then, a mixture of salts (e.g., hydrochloride or sulfate) of the (Z) -and (E) -amino compounds is obtained. Then, a strong base is added to obtain the free baseIt can be extracted with an organic solvent, for example a chlorinated solvent such as Dichloromethane (DCM). An alcoholic solution of a strong acid is added to the organic phase, and the alcohol is then displaced with acetonitrile, giving a suspension of the salts of the (Z) -and (E) -amino compounds in acetonitrile. The strong acid may be HCl or H₂SO₄(B^-Cl or SO₄ ^-). This solvent displacement can be carried out by adding acetonitrile after more or less complete removal of the alcohol under vacuum. The addition of acetonitrile may be accompanied by removal of the alcohol under vacuum. The alcohol is preferably a light alcohol (light alcohol), such as methanol or ethanol.

For step (iii), the coupling between the salt of the (Z) -amino compound and the doubly protected L-serine derivative having formula (II) is performed in an organic solvent in the presence of a base using propanephosphonic anhydride (T3P) as an acid activator. The function of the base is to trap the acid species, moving the salt towards the free base. The amount of base added is 2 to 3 equivalents relative to the salt of the (Z) -amino compound (see example 1, where 2.7 equivalents are used). It is also possible to couple the (Z) -amino compound directly with the compound of formula (II) in the presence of T3P and a base; in this case, the amount of base added is small, ranging from 1 to 2 equivalents (approximately less than 1 equivalent when starting from the salt).

The base may be a tertiary amine, such as Triethylamine (TEA), Diisopropylethylamine (DIEA), N-methylmorpholine (NMM) or methylpiperidine. The organic solvent may be Dichloromethane (DCM), toluene, methyl isobutyl ketone (MIBK), ethyl acetate, acetonitrile, Tetrahydrofuran (THF), Me-tetrahydrofuran (Me-THF), or cyclopentyl methyl ether.

T3P has the formula:

the advantage of using T3P instead of another acid activator is that the by-product of T3P (both are soluble in water) can be easily removed and it is an inexpensive activator. Furthermore, the reaction can be carried out in the presence of the (Z) -amino compound (in salt or base form) and the compound (II), brought together according to the "one-pot method": in the presence of T3P and a base, the (Z) -amino compound (in salt or base form) and compound (II) are thus reacted together in the same vessel. This is not the case for all coupling agents, since some coupling agents, such as PivCl (pivaloyl chloride), require a prior activation of the acid function of compound (II) for the same reaction before being able to add the salt of the (Z) -amino compound.

Finally, we noticed that T3P did not cause epimerisation of the asymmetric center, thus combretastatin (a) could be obtained in good purity and good yield. It has also been noted that T3P can give good yields in terms of the coupled product (see table III).

The coupling reaction is typically carried out at a temperature of 5 ℃ to 70 ℃, for example, under reflux of DCM. The proportion of T3P relative to the (Z) -amino compound is 1 to 2 equivalents, preferably 1.5 to 1.8 equivalents.

Examples

Example 1 (according to the invention)

Step (i):

sodium methoxide solution (5.66kg, 29.34mol) was flowed into a mixture comprising toluene (91.1 l), trimethoxybenzylphosphonium bromide (15.35kg, 29.33mol) and 4-methoxy-3-nitrobenzaldehyde (5.06kg, 27.93mol) at a temperature of 5-10 ℃. At the end of the reaction, 0.32 l (5.59mol) of acetic acid was fed in. After the medium was held at 20 ℃, it was filtered. The filter cake was washed with toluene (11.1 l). The filtrate was washed several times with water (20.2 l) and then concentrated under vacuum. Isopropanol (87.6 liters) was then introduced, the medium was concentrated and then cooled. The suspension was then filtered at 10 ℃. The isolated product was dried under vacuum (6.46kg, 52.2%). The purity of the isolated product is of the order of 78% for (Z) and 22% for (E).

Step (ii):

water (80ml) was passed at 50 ℃ into a medium comprising methanol (100ml), the (Z) -and (E) -nitro compounds to be reduced (20g, 0.058mol) and sodium dithionite (36.8g, 0.179mol, 3.1 equiv). Once the reaction was complete (hold time at 50 ℃ C. for 1 h), hydrochloric acid (36.3ml, 0.406mol) was added. The work-up was carried out by adding water (70ml) and DCM (80ml) followed by sodium hydroxide (30.5% base, 10N) to pH 7. After re-extraction with DCM (20ml) the aqueous phase was removed and the DCM phase was concentrated in vacuo (about 200mbar, 35 ℃) and replaced with acetonitrile (160 ml); the solvent change from DCM to acetonitrile was carried out under reduced pressure to maintain the reaction volume at about 200 ml. A solution of hydrogen chloride in methanol (27ml, 0,081mol) was flowed in and the solvent was evaporated under reduced pressure (90mbar) and a solvent change from methanol-acetonitrile to acetonitrile was carried out at a constant volume of about 233 ml. At the end of the solvent change, the total volume (solvent + organic compound) was adjusted to 280 ml.

The suspension was then obtained as a white broth (white broth). Benzyl alcohol (46ml) was then added to the suspension at 45. + -. 3 ℃. After cooling to 25 ℃, the medium was then filtered, washed with acetonitrile (30ml) and benzyl alcohol (3.3 ml). The isolated product was then dried under vacuum (11.7g, 74.4%). The purity of the product, determined by HPLC, was 99.93% for (Z) and 0.07% for (E). At the end of step (ii), a salt of the (Z) -amino compound of good purity is thus obtained simply and directly.

Step (iii):

TEA (53.4ml, 0.383mol) was then poured into a medium at 20 ℃ containing DCM (500ml), the hydrochloride form of the (Z) -amino compound (50g, 0.142mol) and doubly protected L-serine of formula (II) (L-serine-N-BOC-acetonide, 41.8g, 0.170mol) PG ═ BOC, followed by a DCM solution of T3P (154g, 0.242 mol). The medium was refluxed and then water (500ml) was added. After separation by settling and concentration, a solution of hydrogen chloride in methanol (189.5ml, 1.136mol) and methanol (189.5ml) were added. Water (300ml) was added to the medium and the phases were separated by sedimentation. Isopropyl acetate (650ml) was added to the aqueous phase followed by sodium hydroxide (115ml, 1.150mol) influx at 20 ℃. The organic phase separated and washed by settling was concentrated in vacuo and then heated to 65 ℃. Methanol (35ml) and a solution of hydrogen chloride in methanol (47.4ml, 0.142mol) were added at this temperature. After cooling and filtration, the product was isolated (49.6g, 79.5%). The purity of the final product was 99.2%.

Example 2 (according to the invention)

A1.6 l jacketed reactor was charged with the hydrochloride form of (Z) -amino compound-Z-aminostilbene HCl (Z-aminostil, HCl, 50.0g), N-BOC-acetonide (41.8g) and 500ml DCM. 53.4ml of triethylamine (2.7 equiv.) were then passed at 22. + -. 3 ℃ followed by a 50% solution of T3P in DCM (1.7 equiv.). The mixture was stirred under DCM reflux for 1 hour. The mixture was then cooled to 22. + -. 3 ℃ and 500ml of demineralised water added. The mixture was separated by settling and the phases were separated. The DCM phase is washed with 500ml of a 6% by weight aqueous solution of sodium hydrogen phosphate (30g) and then with 500ml of demineralized water. The DCM phase is concentrated at about 40-50 ℃ under reduced pressure of 360 to 150 mbar. Then 3mol/l HCl in methanol (379ml, 8 equivalents) was flowed in followed by 300ml of demineralized water. The mixture was separated by settling and the phases were separated. The DCM/methanol phase was washed with demineralized water (200ml) and the phases were separated. 650ml of isopropyl acetate are added, followed by 115ml of 30% sodium hydroxide solution (8.1 equiv). The mixture was separated by settling and the organic phase was washed with 400ml of demineralized water. The mixture was separated by settling and the phases were separated. The organic phase was then concentrated under reduced pressure of 160 to 60mbar until 300-350ml were obtained, and solvent exchange from DCM to isopropyl acetate was carried out. The mixture was then heated at 62 ℃ and 35ml of methanol were added and a 3mol/l solution of hydrogen chloride in methanol (47.4ml, 1 eq.) was poured in. The resulting product was then cooled to ambient temperature and the white broth filtered. The final solid was washed.

In examples 3-6, step (ii) was repeated at the beginning with different amounts of (Z) -and (E) -nitro compounds. The ratio of acetonitrile/(Z) -and (E) -amino compound salt was fixed at 10.8, and the ratio of benzyl alcohol/(Z) -and (E) -amino compound salt was varied in part.

Example 3 (according to the invention)

Water (60ml) was passed at 50 ℃ into a medium containing methanol (50ml), the (Z) -and (E) -nitro compounds to be reduced (15g, 0.043mol) and sodium dithionite (27.2g, 0.133 mol). Once the reaction was complete, hydrochloric acid (26.2ml, 0.314mol) was added. Work-up was performed by adding water and DCM, followed by sodium hydroxide to pH 7. To the DCM phase was added a solution of hydrogen chloride in methanol (18.9ml, 0.0586mol), followed by replacement of the solvent with acetonitrile. A broth is then obtained. Benzyl alcohol (31ml) was then added to the suspension at 50 ℃ and held at 65 ℃ for 2 hours. After cooling, the medium is then filtered and washed. The isolated product was then dried under vacuum.

Examples 4 to 6:the same as in example 3, except that the amount of benzyl alcohol was different.

TABLE I

acetonitrile/Z + E amino compound salt ratio 10.8

In examples 5 and 7 to 9, the ratio of benzyl alcohol/(Z) -and (E) -amino compound salt was fixed at 2.25, and the ratio of acetonitrile/(Z) -and (E) -amino compound salt was varied.

TABLE II

Benzyl alcohol/salt of Z + E amino compound ratio 2.25

Examples 10-14 describe the results of coupling (step (iii)) using a coupling agent other than T3P.

Example 10 (comparative): using TOTU

The conditions of step (iii) were repeated but in the presence of TOTU as acid activator (1 equivalent of TOTU +5 equivalents of TEA). Then, the final yield was only 71%.

Example 11 (comparative): using TOTU

TEA (0.71g, 7.0mmol) was run at 5 ℃ followed by TOTU (0.46g, 1.4mmol) into a medium containing DCM (10ml), the (Z) -amino compound as the hydrochloride salt (0.50g, 1.4mmol) and the doubly protected L-serine of formula (II) (L-serine-N-BOC-propanone compound; 0.35g, 1.4mmol) of PG ═ BOC. The medium was kept at 5 ℃ for 24 hours, then water (5ml) was added. After separation by settling, the organic phase was analyzed by HPLC. The quantitative yield of the coupled product was 50.1% and its purity was 69.3%.

Example 12 (comparative): using BOP-Cl (bis (2-oxo-3-oxazolidinyl) phosphonyl chloride (bis(2-oxo-3-oxazolidinyl)phosphinic chloride))

NMM (0.42g, 4.2mmol) and then BOP-Cl (0.72g, 2.8mmol) were flowed at 5 ℃ into a medium containing DCM (5ml), (Z) -amino compound (0.50g, 1.4mmol) and PG ═ BOC, doubly protected L-serine of formula (II) (L-serine-N-BOC-acetonide; 0.35g, 1.4 mmol). The medium was kept at 5 ℃ for 24 hours, then water (5ml) was added. After separation by settling, the organic phase was analyzed by HPLC. The quantitative yield of the coupled product was 29.1% and its purity was 91.6%.

Example 13 (comparative): using PyClOP (chlorotris pyrrolidino phosphonium hexafluorophosphate) (chlorotripyrrolidinophosphonium hexafluorophosphate))

NMM (0.42g, 4.2mmol) and then PyClOP (1.2g, 2.8mmol) were flowed at 5 ℃ into a medium containing ethyl acetate (10ml), (Z) -amino compound (0.50g, 1.4mmol) and PG ═ BOC, double protected L-serine of formula (II) (L-serine-N-BOC-acetonide; 0.70g, 2.8 mmol). The medium was kept at 5 ℃ for 24 hours, then water (5ml) was added. After separation by settling, the organic phase was analyzed by HPLC. The quantitative yield of the coupled product was 53.3% and its purity was 83.9%.

Example 14 (comparative): using PyBROP (bromotripyrrolidinophosphonium hexafluorophosphate)

NMM (0.42g, 4.2mmol) and then PyBROP (0.65g, 1.4mmol) were flowed at 25 ℃ into a medium containing Me-CN (5ml), (Z) -amino compound (0.50g, 1.4mmol) and PG ═ BOC of doubly protected L-serine of formula (II) (L-serine-N-BOC-propanone compound; 0.35g, 1.4 mmol). The medium was kept at 25 ℃ for 24 hours, then water (5ml) was added. After separation by settling, the organic phase was analyzed by HPLC. The quantitative yield of the coupled product was 24.9% and its purity was 75.4%.

TABLE III

It was noted that T3P gave better yields than TOTU, BOP-Cl, PyClOP or PyBROP in coupling the product.

Claims (17)

1. Process for the preparation of combretastatin (a) in base form or in acid addition salt form:

the method comprises the following steps:

in the presence of a base and T3P having the formula (III),

reacting a (Z) -amino compoundOr salts of (Z) -amino compoundsAnd has the formulaCoupling the double protected L-serine derivative of (a) to (b) to give a compound having the formula (Z) - (Ib):

wherein B is^-Represents a counter anion, PG represents a group protecting the amino function;

then in the presence of an acid, performing deprotection and opening of the rings of (Z) - (Ib) to obtain combretastatin having formula (a) in salt form;

and optionally, adding a base, thereby obtaining combretastatin having formula (A) in base form,

the salt of the (Z) -amino compound is obtained by enriching the salt of the amino compound having the following formula in the form of the (Z) isomer:

wherein B is^-Represents a counter anion, said enrichment comprising:

to a suspension of the mixture of the salt of the (Z) -amino compound and the salt of the (E) -amino compound in acetonitrile, benzyl alcohol is added, followed by

Mechanical separation of the salt of the amino compound enriched in the (Z) isomeric form.

2. Process for enriching the salt of an amino compound having the formula

Wherein B is^-Represents a counter anion, the method comprising:

to a suspension of the mixture of the salt of the (Z) -amino compound and the salt of the (E) -amino compound in acetonitrile is added benzyl alcohol, and

mechanical separation of the salt of the amino compound enriched in the (Z) isomeric form.

3. The method according to claim 1 or 2, wherein the mechanical separation is filtration.

4. Process for the preparation of combretastatin (a) in base form or in acid addition salt form:

the method comprises the following steps:

reacting a (Z) -amino compound in the presence of a base and T3POr salts of (Z) -amino compoundsAnd has the formulaCoupling the double protected L-serine derivative of (a) to (b) to give a compound having the formula (Z) - (Ib):

wherein B is^-Represents a counter anion, PG represents a group protecting the amino function;

then deprotecting and opening the rings of (Z) - (Ib) in the presence of an acid to give combretastatin (a) in salt form;

and optionally, adding a base, thereby obtaining the base form of the bestatin (a).

5. A method according to any one of claims 1 to 4, wherein PG represents BOC, CBZ or FMOC.

6. The process according to any one of claims 1 to 5, wherein B^-Represents Cl^-Or SO₄ ^2-。

7. A method according to any one of claims 1 to 6 wherein PG represents BOC, B^-Represents Cl^-。

8. A process according to any one of claims 1 to 7, wherein the base is a tertiary amine.

9. The process according to claim 8, wherein the base is Triethylamine (TEA), Diisopropylethylamine (DIEA), N-methylmorpholine (NMM) or methylpiperidine.

10. The process according to any one of claims 1 to 9, wherein the (Z) -amino compound or the salt of the (Z) -amino compound and the compound of formula (II) are reacted together in the presence of T3P and a base in the same vessel.

11. The process according to any one of claims 1 to 10, wherein the ratio of acetonitrile to the salt of the (Z) -amino compound and the salt of the (E) -amino compound is from 5 to 17, preferably from 10 to 12, by weight.

12. The method according to any one of claims 1 to 11, wherein the enrichment is carried out at a temperature of 20 to 70 ℃.

13. The process according to any one of claims 1 to 12, wherein the ratio of benzyl alcohol to the salt of the (Z) -amino compound and the salt of the (E) -amino compound is from 1 to 4, preferably from 2 to 3, by weight.

14. Use of T3P having formula (III),

the T3P having the formula (III) is used for preparing a compound having the formulaOr (Z) -amino compounds of the formulaAnd salts of (Z) -amino compounds of the formulaIs coupled with a doubly protected L-serine derivative of (1), wherein B^-Represents a counter anion, and PG represents a group protecting an amino functional group.

15. Use according to claim 14, wherein PG represents BOC, CBZ or FMOC, and/or B^-Represents Cl^-Or SO₄ ^2-。

16. Use according to claim 14 or 15, wherein the base is a tertiary amine.

17. Use according to any one of claims 14 to 16, wherein the (Z) -amino compound or the salt of the (Z) -amino compound and the compound of formula (II) are reacted together in the presence of T3P and a base in the same vessel.