HK1245798B - Methods for preparing anti-viral nucleotide analogs - Google Patents

Description

Methods for preparing antiviral nucleotide analogs

This application is a divisional application of Chinese invention patent application filed on October 3, 2012, with application number 201280048965.7 and entitled "Method for preparing antiviral nucleotide analogues".

Cross-referencing related applications

This application claims priority to U.S. Provisional Patent Application No. 61/544,950, filed on October 7, 2011, the entire contents of which are incorporated herein by reference.

Background Technology

U.S. Patent Nos. 7,390,791 and 7,803,788 (the entire contents of each patent are incorporated herein by reference) describe certain phosphonate nucleotide analog prodrugs that can be used in therapies. One such prodrug is 9-{(R)-2-[((S)-{[(S)-1-(isopropoxycarbonyl)ethyl]amino}phenoxyphosphonyl)methoxy]propyl}adenine (compound 16):

This compound is also named by Chemical Abstracts as N-[(S)-[[(1R)-2-(6-amino-9H-purin-9-yl)-1-methylethoxy]methyl]phenoxyphosphonyl]-L-alanine 1-methylethyl ester. U.S. Patents 7,390,791 and 7,803,788 also disclose the monofumaric acid form of this compound and its preparation method (see, for example, Example 4).

Compounds 12, 13 (where X is a halogen group), and 15:

It is a synthetic intermediate that can be used to prepare compound 16. Compound 15 is described as a mixture of diastereomers at the phosphorus center. The two diastereomers constituting the mixture of compound 15 are shown here as compounds 15a and 15b. Isomer 15a is structurally identical to compound 16.

Currently, there is a need in the industry for improved methods to prepare compounds 12, 13, 15, and 16. Specifically, there is a need for improved methods to prepare compounds 13, 15, and 16 with high diastereomeric purity. Such improved methods should offer higher yields, be easier to perform, or use reagents that are less expensive or less toxic than current methods.

Summary of the Invention

This invention describes an improved method for separating 9-{(R)-2-[((S)-{[(S)-1-(isopropoxycarbonyl)ethyl]amino}phenoxyphosphonyl)methoxy]propyl}adenine (compound 16) using crystallization-induced dynamic resolution; an improved method for preparing compounds 13 and 15 with high diastereomeric purity; and an improved method for preparing compound 12.

Therefore, in one embodiment, a method is provided comprising subjecting a solution comprising the following conditions for selective crystallization of 9-{(R)-2-[((S)-{[(S)-1-(isopropoxycarbonyl)ethyl]amino}phenoxyphosphine)methoxy]propyl}adenine: a) a suitable solvent; b) a suitable base; c) a diastereomer mixture of 9-{(R)-2-[((R,S)-{[(S)-1-(isopropoxycarbonyl)ethyl]amino}phenoxyphosphine)methoxy]propyl}adenine; and optionally, d) one or more seed crystals of 9-{(R)-2-[((S)-{[(S)-1-(isopropoxycarbonyl)ethyl]amino}phenoxyphosphine)methoxy]propyl}adenine.

In another embodiment, a method is provided for preparing compound 13 to be at least about 90% diastereomeric purity by treating a toluene solution of compound 12 with thionyl chloride:

To provide compound 13, where X = Cl.

In another embodiment, a method is provided for preparing 9-{(R)-2-[((R,S)-{[(S)-1-(isopropoxycarbonyl)ethyl]amino}phenoxyphosphonyl)methoxy]propyl}adenine (compound 15) of compound 16 as at least about 90% diastereomeric purity, said method comprising preparing compound 13 as at least about 90% diastereomeric purity:

(where X is a halogen group); treated with amine 11 under conditions where compound 16 (i.e., isomer 15a) is provided to be at least about 90% diastereomeric pure:

In another embodiment, a method for preparing compound 12 is provided:

It includes PMPA treated with triphenyl phosphite in the presence of a suitable base:

To provide compound 12.

This invention also provides novel methods and intermediates disclosed herein.

Detailed Implementation

The specific values listed below for groups, substituents, and ranges are for illustrative purposes only; they do not exclude other defined values or other values within the ranges defined for the groups and substituents mentioned.

Compound 16 was prepared by crystallization-induced dynamic resolution.

In one embodiment, a method is provided for crystallization-induced dynamic resolution of 9-{(R)-2-[((R,S)-{[(S)-1-(isopropoxycarbonyl)ethyl]amino}phenoxyphosphine)methoxy]propyl}adenine (compound 15) to provide 9-{(R)-2-[((S)-{[(S)-1-(isopropoxycarbonyl)ethyl]amino}phenoxyphosphine)methoxy]propyl}adenine (compound 16).

The method comprises subjecting a solution containing the following conditions for epimerization to provide a phosphorus center, under conditions that also provide selective crystallization of 9-{(R)-2-[((S)-{[(S)-1-(isopropoxycarbonyl)ethyl]amino}phenoxyphosphine)methoxy]propyl}adenine: a) a suitable solvent; b) a suitable base; c) 9-{(R)-2-[((R,S)-{[(S)-1-(isopropoxycarbonyl)ethyl]amino}phenoxyphosphine)methoxy]propyl}adenine; and optionally, d) one or more seed crystals of 9-{(R)-2-[((S)-{[(S)-1-(isopropoxycarbonyl)ethyl]amino}phenoxyphosphine)methoxy]propyl}adenine.

Crystallization can be carried out in any suitable solvent. For example, it can be carried out in or in mixtures of aprotic organic solvents. For example, aprotic organic solvents may include ethyl acetate, methyl acetate, propyl acetate, isopropyl acetate, diethyl ether, diisopropyl ether, tetrahydrofuran, dichloromethane, acetone, methyl ethyl ketone, methyl tert-butyl ether, toluene, or acetonitrile, or mixtures thereof. In one embodiment, the solvent comprises acetonitrile.

Resolution can be carried out in the presence of any suitable base. For example, resolution can be carried out in the presence of a base selected from the following: 1,5-diazobicyclo[4.3.0]non-5-ene (DBN), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD), tetramethylguanidine, verkade bases (e.g., 2,8,9-triisopropyl-2,5,8,9-tetraaza-1-phosphabicyclo[3.3.3]undecane and 2,8,9-triisobutyl-2,5,8,9-tetraaza-1-phosphabicyclo[3.3.3]undecane), metal carbonates ₍ e.g., _MXCO3 ), metal phenolates (M ⁺ -OPh), and PhOTMS with a fluoride ion source (e.g., _R4N ^+- F, combinations and mixtures thereof of TASF (tris(dimethylamino)sulfonium difluorotrimethylsilicate) or TBAT (tetrabutylammonium triphenyldifluorosilicate) (M), wherein each M is a suitable metal, such as an alkali metal or an alkaline earth metal, and each R is, for example, an ( _C1 - _C6 ) alkyl group. In one particular embodiment, the base is DBU.

The splitting can also be performed at any suitable temperature (e.g., in the range of about 0°C to about 50°C). In one particular embodiment, the splitting is performed at a temperature of about 20°C.

In one particular embodiment, the splitting is carried out in the presence of phenol.

The percentage of compound 16 in the starting diastereomer mixture can be any value ranging from about 0% to about 99%. In one embodiment of the invention, the percentage of compound 16 in the starting diastereomer mixture is in the range of about 0% to about 20%. In one embodiment, the percentage of compound 16 in the starting diastereomer mixture is in the range of about 20% to about 99%. In one embodiment, the percentage of compound 16 in the starting diastereomer mixture is in the range of about 50% to about 99%. In one embodiment, the final compound 16 is at least about 90%, about 95%, about 97%, or about 99% diastereomerically pure. In one embodiment, the final compound 16 contains less than 1% of any diastereomer impurities. In one embodiment, the final compound 16 is free of any detectable diastereomer impurities.

Preparation of compound 13 with high diastereomeric purity

Compound 13 (where X is a halogen group) of at least about 90% diastereomeric purity can be prepared by treating compound 12 with a suitable halogenating agent. For example, compound 13 can be prepared by treating compound ₁₂ with a halogenating agent (e.g., thionyl chloride ( _SOCl₂ ), _{oxalyl chloride (C₂O₂Cl₂ )} , phosphorus trichloride ( _PCl₃ ), trichlorophenylphosphine salt, thionyl bromide ( _SOBr₂ ), oxalyl bromide ( _{C₂O₂Br₂} ), phosphorus _tribromide ( _PBr₃ ), or trichlorophenylphosphine salt). The reaction can be carried out at a suitable temperature (e.g., in a _temperature range of about -20°C to about 100°C) in a suitable organic solvent. Suitable solvents include tetrahydrofuran, 2-methyltetrahydrofuran, dichloromethane, acetonitrile, toluene, chlorobenzene, 1,2-dichloroethane, 1,4-dioxane, sulfolane, and trichloroethylene and mixtures thereof.

In one embodiment, compound 12 is treated with thionyl chloride in toluene at a temperature of about 22°C to about 110°C to provide compound 13a:

The compound 13a is at least about 90% diastereomer purity. In one embodiment, the final compound 13a is at least about 90%, about 95%, about 97%, or about 99% diastereomer purity. In one embodiment, the final compound 13a contains less than 1% of any diastereomer impurities. In one embodiment, the final compound 13a is free of any detectable diastereomer impurities.

Compound 15 was prepared with high diastereomeric purity.

Compound 15 can be prepared by treating compound 13 (where X is a halogen group) with amine 11 under the conditions provided for compound 15 to obtain a specific isomer 15a with at least about 90% diastereomeric purity, also referred to herein as compound 16. For example, compound 15 can be prepared by treating compound 13 with amine 11 in a suitable organic solvent at a suitable temperature (e.g., in the range of about -78°C to about 25°C). Suitable solvents include organic solvents such as tetrahydrofuran, 2-methyltetrahydrofuran, dichloromethane, 1,2-dichloroethane, trichloroethylene, 1,4-dioxane, acetonitrile, toluene, chlorobenzene, sulfolane, and isopropyl acetate and mixtures thereof. The reaction can be conveniently carried out in the presence _{of a suitable base, such as triethylamine ((C₂H₅)₃N ) ,} N,N-diisopropylethylamine ([( _CH₃ ) _₂CH ] _₂NC₂H₅ ), or _1,8 -bis(dimethylamino)-naphthalene ( _proton sponge, _{C₁₄H₁₈N₂ )} . After the reaction, the resulting material can be washed with an aqueous solution containing a suitable washing agent, such as sodium dihydrogen phosphate ( _NaH₂PO₄ ), potassium _bicarbonate ( _KHCO₃ ), citric acid ( _C₆H₈O₇ ), or sodium _bicarbonate ( _NaHCO₃ ). The resulting organic solution can be dried with a suitable drying agent ( _e.g. , sodium sulfate, magnesium sulfate, or calcium _chloride ) to provide compound 15, which is compound 16 at least about 90% diastereomeric pure.

In one embodiment, compound 13 (where X is chlorine) is treated with amine 11 in dichloromethane in the presence of triethylamine at a temperature of -25°C to 25°C to obtain a compound with at least about 90% diastereomeric purity. The resulting reaction mixture is then washed with an aqueous solution containing _sodium dihydrogen phosphate ( _NaH₂PO₄ ) and potassium bicarbonate ( _KHCO₃ ) and dried over sodium sulfate to provide compound 15, which is compound 16 with at least about 90% diastereomeric purity. In one embodiment, the starting compound 13 and the resulting compound 15 are at least about 95% or 97% diastereomeric pure. In one embodiment, the final compound 15 contains at least about 90%, about 95%, about 97%, or about 99% diastereomeric purity of compound 16. In one embodiment, the final compound 15 contains less than 1% of any diastereomeric impurities.

Preparation of compound 12

Compound 12 may be prepared as described, for example, in U.S. Patent No. 7,390,791, or as described herein. In one embodiment, a method for preparing compound 12 is provided, comprising treating PMPA with triphenyl phosphite in the presence of a suitable base to provide compound 12. The reaction may be readily carried out in a suitable solvent, such as acetonitrile, N-methylpyrrolidone (NMP), dichloroethane, pyridine, alkyl acetate (e.g., ethyl acetate), or dialkyl ether (e.g., diethyl ether), or mixtures thereof. The reaction may also be readily carried out in the presence of a suitable base, such as trialkylamine (e.g., triethylamine), 2-methylimidazole, dimethylaminopyridine (DMAP), 1,5-diazobicyclo[4.3.0]non-5-ene (DBN), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), or pyridine, or mixtures thereof. The reaction can also be conveniently carried out at suitable temperatures (e.g., from about 20°C to about 120°C (e.g., from about 20°C to about 82°C)). In one particular embodiment, PMPA is treated with triphenyl phosphite in acetonitrile at about 80°C in the presence of triethylamine and dimethylaminopyridine to provide compound 12.

The following are non-restrictive illustrative examples.

Example 1: Preparation of the diastereomeric mixture 9-{(R)-2-[((R,S)-{[(S)-1-(isopropoxycarbonyl)ethyl]amino}phenoxyphosphino)methoxy]propyl}adenine (compound 15)

a. Preparation of Compound 11. L-alanine isopropyl hydrochloride (Compound 10) (1 kg, 5.97 mol, 1.0 equivalent) and potassium bicarbonate (1.45 kg, 14.5 mol, 2.43 equivalent) were stirred at maximum agitation in a DCM (4 kg) for 10 to 14 hours, maintaining the tank temperature between 19°C and 25°C. The mixture was then filtered and further washed with DCM (2 kg). The filtrate was dried on a molecular sieve bed until the water content of the solution was ≤0.05%. The resulting mother liquor containing Compound 11 was then cooled to a tank temperature of -20°C and held for further use.

b. Preparation of Compound 13a. Compound 12 (1 kg, 2.75 mol, 1.00 equivalent) was added in 10 equal portions to a solution of thionyl chloride (0.72 kg, 6.02 mol, 2.19 equivalent) in acetonitrile (5.5 kg) at 60 °C for 2 hours. The tank temperature was then adjusted to 70 °C and stirred for 1 to 3 hours until the reaction was considered complete. The tank temperature was then adjusted to 40 °C and a vacuum was applied. The mixture was distilled to dryness, with the maximum jacket temperature maintained at 40 °C. The dried residue was then absorbed into dichloromethane (30 kg) and the tank temperature was adjusted to 19 °C to 25 °C. The resulting slurry containing Compound 13a was retained for further use.

c. Preparation of Compound 15. A slurry containing Compound 13a (1.0 equivalent) was added to the mother liquor of L-alanine isopropyl ester 11 (4.82 equivalents) at -25°C for a maximum of 2 hours, while maintaining the tank temperature at ≤-10°C. The mixture was then kept at ≤-10°C for at least 30 minutes, followed by pH checking using water-wetted pH paper. If pH < 4, it was adjusted to pH 4-7 with triethylamine. The tank temperature was then adjusted to room temperature (19°C to 25°C). A solution of sodium dihydrogen phosphate (2.2 kg, 18 mol, 6.90 equivalents) in water (16 kg) was prepared in a separate container. Half of the sodium dihydrogen phosphate solution was loaded into a phosphonamidate reactor and stirred vigorously. The layers were allowed to settle and separate. The organic layers were washed again with the remaining half of the sodium dihydrogen phosphate solution. In a separate container, a solution of potassium bicarbonate (1.1 kg, 11 mol, 4.22 equivalents) in water (5.5 kg) was prepared. Half of the potassium bicarbonate solution was added to the organic phase and stirred vigorously. The layers were allowed to settle and separate. The organic layer was washed again with the remaining half of the potassium bicarbonate solution, followed by a final wash with water (3.3 kg). The organic phase was then retained and distilled to a volume of about 6 L. The water content of the resulting solution was analyzed. If the water content was >1.0%, it was loaded into a distillate container and distilled again to about 6 L. When the water content of the solution was less than 1.0% or about 1.0%, the container temperature was adjusted to 19°C to 25°C, and the mother liquor in the distillate container was drained to provide a diastereomeric mixture of 9-{(R)-2-[((R,S)-{[(S)-1-(isopropoxycarbonyl)ethyl]amino}phenoxyphosphonyl)methoxy]propyl}adenine (compound 15). ¹ HNMR (400MHz, CDCl ₃ ): δ1.20-1.33(m,12H),3.62-3.74(m,1H),3.86-4.22(m,5H),4.30-4.44(m,1H),4.83-5.10(m,1H),6.02(br s, 3H), 7.18-7.34 (m, 5H), 7.98-8.02 (m, 1H), 8.32-8.36 (m, 1H); ³¹ P NMR (162MHz, CDCb): δ.21.5, 22.9.

Example 2: Crystallization-induced dynamic resolution of the diastereomer mixture 9-{(R)-2-[((R,S)-{[(S)-1-(isopropoxycarbonyl)ethyl]amino}phenoxyphosphinyl)methoxy]propyl}adenine (compound 15) to provide 9-{(R)-2-[((R,S)-{[(S)-1-(isopropoxycarbonyl)ethyl]amino}phenoxyphosphinyl)methoxy]propyl}adenine (compound 16)

A 22 wt% solution (2.3 kg solution, 0.51 kg compound 15, 1.1 mol, 1 equivalent) of 9-{(R)-2-[((R,S)-{[(S)-1-(isopropoxycarbonyl)ethyl]amino}phenoxyphosphonyl)methoxy]propyl}adenine (compound 15) in acetonitrile was loaded into a container equipped with a top stirrer, distillation apparatus, and nitrogen inlet. The mixture was concentrated to a final concentration of 30 wt% to 35 wt% by distillation at 100 mbar to 300 mbar in a temperature range of 45°C to 55°C. The distillation apparatus was then removed and the solution was cooled to 20°C. Seeds were added to the solution using 2.0% compound 16 and the mixture was stirred at 20°C for 1 hour. Phenol (9.9 g, 0.11 mol, 0.1 equivalent) and DBU (16 g, 0.11 mol, 0.1 equivalent) were added, and the mixture was stirred for another 24 hours, or until the weight percentage of compound 16 remaining in the solution was less than 12%. The slurry was then cooled to 0 °C and stirred at 0 °C for another 18 hours. The slurry was filtered at 0 °C and washed with a 1:1 solution of isopropyl acetate:acetonitrile (1.5 L). The solid was dried in a vacuum furnace at 50 °C to give 0.40 kg of compound 16 as a white solid (80% yield). ¹ H NMR (400MHz, CDCl ₃ ): δ1.21(m,9H),1.28(d,J＝7.0Hz,3H),3.65(dd,J＝13.1,10.7,1H)4.00(m,4H),4.33(dd,J＝14.4,3. 1Hz,1H),5.00(m,1H)6.00(bs,2H),6.99(m,2H),7.07(m,1H),7.19(m,2H),7.97(s,1H),8.33(s,1H). ^31P NMR (162MHz, CDCl ₃ ): δ.20.8.

Example 3: Preparation of compound 13a with high diastereomeric purity

Thionyl chloride (3.0 mL, 41 mmol, 1.5 equivalent) was added to a slurry of compound 12 (10.0 g, 27.5 mmol, 1.00 equivalent) in toluene (60 mL) at ambient temperature. The slurry was heated to 70 °C and stirred for 48 to 96 hours until the reaction and diastereomeric enrichment were considered complete by HPLC (target: conversion of compound 12 to compound 13a >97.0% and diastereomeric ratio of compound 13a >90:10). The mixture was concentrated and dried by vacuum distillation, and the dried residue was absorbed into toluene (50 mL). The resulting slurry containing compound 13a was kept at ambient temperature for further use.

Example 4: Preparation of 9-{(R)-2-[((R,S)-{[(S)-1-(isopropoxycarbonyl)ethyl]amino}phenoxyphosphine)methoxy]propyl}adenine (Compound 15) with high diastereomeric purity

Add a slurry containing at least 90% diastereomeric purity of compound 13a (1.00 equivalent) in toluene (50 mL) to a solution of L-alanine isopropyl ester 11 (4.50 equivalents) in DCM (80 mL) for at least 45 minutes at -25°C, while maintaining the internal temperature at ≤-20°C. Then, maintain the mixture at ≤-20°C for at least 30 minutes and check the pH using water-wetted pH paper. If the pH < 4, adjust it to pH 4 to 7 with triethylamine. Adjust the tank temperature to room temperature (19°C to 25°C). Transfer the mixture to a separatory funnel and wash sequentially with 10% w/v sodium dihydrogen phosphate aqueous solution (2 × 50 mL), 15% w/v potassium bicarbonate aqueous solution (2 × 20 mL), and water (50 mL). Dry the final organic layer with anhydrous sodium sulfate, filter, and concentrate under vacuum to a viscous amber oil. The oily substance was dissolved in toluene/acetonitrile (4:1) (50 mL), and seed crystals were added to the solution using 9-{(R)-2-[((R,S)-{[(S)-1-(isopropoxycarbonyl)ethyl]amino}phenoxyphosphonyl)methoxy]propyl}adenine (approximately 1 mg, 99:1 diastereomer ratio) and stirred at ambient temperature for 2 hours. The resulting slurry was filtered, and the filter cake was washed with toluene/acetonitrile (4:1) (15 mL) and dried in a vacuum oven at 40 °C for 16 hours to give the product 9-{(R)-2-[((R,S)-{[(S)-1-(isopropoxycarbonyl)ethyl]amino}phenoxyphosphonyl)methoxy]propyl}adenine (compound 15) (10.0 g, 76.4%, 97.5:2.5 diastereomer ratio, favoring compound 16) as a white solid. ¹ HNMR (400MHz, CDCl ₃ ): δ1.20-1.33(m,12H),3.62-3.74(m,1H),3.86-4.22(m,5H),4.30-4.44(m,1H),4.83-5.10(m,1H),6.02(br s, 3H), 7.18-7.34 (m, 5H), 7.98-8.02 (m, 1H), 8.32-8.36 (m, 1H); ³¹ PNMR (162MHz, CDCl ₃ ): δ.21.5, 22.9.

Example 5: Preparation of Compound 12

PMPA (100.0 g, 0.35 mol, 1 equivalent) was loaded into a container equipped with a top stirrer, reflux condenser, and nitrogen inlet, followed by acetonitrile (800 mL). Triethylamine (71.0 g, 0.70 mol, 2 equivalents) was added to the container, followed by DMAP (42.6 g, 0.35 mol, 1 equivalent) and triphenyl phosphite (162.1 g, 0.52 mol, 1.5 equivalents). The mixture was heated to 80 °C and stirred at 80 °C for ≥48 hours or until the reaction was confirmed to be complete by ³¹ P NMR. (A sample was taken directly from the reaction and an _insert containing 10% _H3PO2 present in _D2O was added. The intermediate formed was PMPA anhydride at 7 ppm to 8 ppm; the product was 12.3 ppm to 12.6 ppm. The reaction was considered complete when less than 5% anhydride was present.) The reaction mixture was distilled to about 1.5 volumes of acetonitrile and diluted with ethyl acetate (200 mL) and water (300 mL). The aqueous layer was separated and washed twice with ethyl acetate (200 mL). The aqueous layer was returned to the container and the pH was adjusted to pH 3 using 12.1 M HCl (21.0 mL). Seed crystals of 0.05% compound 12 were then added to the reaction mixture and stirred at 25 °C. An additional 12.1 M HCl (7.0 mL) was added over 20 minutes until pH 2 was achieved. Crystallization was stirred at ambient temperature for 30 minutes and then cooled to 10 °C over 2 hours. Once 10 °C was reached, crystallization was stirred at 10 °C for 2.5 hours. The slurry was filtered and washed with water (200 g) at pH 1.5. After drying in a vacuum oven, 102.2 g of compound 12 as a white solid was obtained (81% yield). ¹ HNMR(400MHZ,D ₂ O): δ1.31(d,J＝6.1Hz,3H),3.59(dd,J＝14.0,9.0Hz,1H),3.85(dd,J＝14.0,9.0Hz,1H),4.1(m,1H),4.3(dd,J＝15.0,9,0H z, 1H), 4.5 (dd, J = 15.0, 2Hz, 1H), 6.75 (d, J = 7Hz, 2H), 7.15 (t, J = 7Hz, 1H), 7.25 (t, J = 7Hz, 2H), 8.26 (s, 1H), 8.35 (s, 1H). ³¹ PNMR (162MHz, D ₂ O): δ.14.8.

All publications, patents, and patent documents are incorporated herein by reference as individually incorporated. The invention has been described with reference to specific and preferred embodiments and techniques. However, it should be understood that many changes and modifications can be made while remaining within the spirit and scope of the invention.

Claims (4)

1. A method for selectively crystallizing 9-{(R)-2-[((S)-{[(S)-1-(isopropoxycarbonyl)ethyl]amino}phenoxyphosphino)methoxy]propyl}adenine, comprising the following steps: Treat solutions containing the following using alkali: a) Suitable solvents; and b) Phenol; c) One or more seed crystals of 9-{(R)-2-[((S)-{[(S)-1-(isopropoxycarbonyl)ethyl]amino}phenoxyphosphino)methoxy]propyl}adenine d)9-{(R)-2-[((R,S)-{[(S)-1-(isopropoxycarbonyl)ethyl]amino}phenoxyphosphonyl)methoxy]propyl}adenine; The base thereon is 1,8-diazabicyclo[5.4.0]undec-7-ene. 2. The method according to claim 1, wherein the solvent comprises an aprotic organic solvent. 3. The method according to claim 1 or 2, wherein the solvent comprises ethyl acetate, methyl acetate, propyl acetate, isopropyl acetate, diethyl ether, diisopropyl ether, tetrahydrofuran, dichloromethane, acetone, methyl ethyl ketone, methyl tert-butyl ether, toluene, or acetonitrile or a mixture thereof. 4. The method of claim 3, wherein the solvent comprises acetonitrile.