WO2003080613A1

WO2003080613A1 - Process for the preparation of intermediates in the synthesis of 2- (purin-9-yl) - tetrahydrofuran-3,4-diol derivatives

Info

Publication number: WO2003080613A1
Application number: PCT/EP2003/003027
Authority: WO
Inventors: Philip Blatcher
Original assignee: Glaxo Group Limited
Priority date: 2002-03-21
Filing date: 2003-03-19
Publication date: 2003-10-02
Also published as: AU2003212376A1; GB0206655D0

Abstract

A process for preparing a compound of formula (II) Which comprises reacting a compound of formula (IV) wherein P1 represents a protecting group which is a cyclic ether connected to the purine ring nitrogen in the 2-position, or a salt thereof, with a compound of formula (V) R2NH2 (V) followed by deprotection and optional salt conversion to yield the compound of formula (II) or a salt thereof.

Description

PROCESS FOR THE PREPARATION OF INTERMEDIATES IN THE SYNTHESIS OF 2- (PURIN-9-YL) -TETRAHYDROFURAN-3 , 4-DIOL DERIVATIVES

2-(Purin-9-yl)-tetrahydrofuran-3,4-diol derivatives are described in patent cases WO98/28319, WO99/67265, WO99/67264, WO99/41267 and WO99/38877 (Glaxo Group) as being useful as agonists of the adenosine 2a receptor and therefore are expected to have anti-inflammatory properties.

These patent applications describe compounds having general formula (I)

wherein R¹ and R² independently represent a group selected from:

(ϋ) hydrogen;

(iϋ) aryl₂CHCH₂-;

(iv) C^cycloalkylC^alkyl-;

(v) C_1-8alkyl-;

(vi) arylC_1-6alkyl-;

(vϋ) R⁴R⁵N-C_1-6alkyl-;

(viii) C_1-6alkyl-CH(CH₂OH)-;

(ix) arylC₁.₅alkyl-CH(CH₂OH)-;

(x) arylC₁.₅alkyl-C(CH₂OH)₂-;

(xi) C₃.₈cycloalkyl independently substituted by one or more (e.g. 1 2 or 3)

(CH₂)_pR^β groups;

(xii) H₂NC(=NH)NHC^alkyl-;

(xiii) a group of formula

or such a group in which one methylene carbon atom adjacent to X, or both if such exist, is substituted by methyl;

(xiv) -C_1-6alkyl-OH;

(xv) -C_1-8haloalkyl;

(xvi) a group of formula

(xvii) aryl; and

(xviii) -(CH₂)_fSO₂NH_g(C₁^ alkyl-)_2-g or -(CH.J_fSO.NH^arylC^alkyl-)^; A represents a moiety selected from the following groups (a) to (h):

N—

O^^ (^h)

R³ represents C_1-3alkyl, cyclopropyl or -CH₂OH; a and b independently represent an integer 0 to 4 provided that a + b is in the range 3 to

5; c, d and e independently represent an integer 0 to 3 provided that c + d + e is in the range 2 to 3; f represents 2 or 3 and g represents an integer 0 to 2; p represents 0 or 1 ;

R⁴ and R⁵ independently represent hydrogen, C_1-6alkyl, aryl, arylC_1-6alkyl- or NR⁴R⁵ together may represent pyrrolidinyl, piperidinyl, morpholinyl, azetidinyl, azepinyl, piperazinyl or N-C_1-6alkylpiperazinyl.

R⁶ represents OH, NH_2l NHCOCH₃ or halogen; R⁷ represents hydrogen, C_1-ealkyl, C^ealkylaryl or -COC_1-6alkyl ;

X represents NR⁷, O, S, SO or SO₂; aryl represents phenyl optionally substituted by one or more C_1-6alkyl or halogen groups; and salts and solvates thereof.

References to C_1-6alkyl include references to an aliphatic hydrocarbon grouping containing 1 to 6 carbon atoms which may be straight chain or branched and may be saturated or unsaturated although will be preferably saturated. References to C_1-4alkyl, C_1-5alkyl, C^alkyl and C^alkyl may be interpreted similarly.

Preferably R³ represents ethyl.

A number of processes for preparing such 2-(purin-9-yl)-tetrahydrofuran-3,4-diol derivatives have been described however one particularly convenient convergent route comprises reacting a compound of formula (II)

or a salt thereof with a compound of formula (III)

wherein L represents a leaving group (eg acetyloxy) or a protected derivative thereof (eg a derivative in which the two hydroxy groups are protected eg as acetonide or more preferably by acetyloxy).

We have now invented a novel and improved process for preparing compounds of formula (II).

Thus according to the invention we provide a process for preparing a compound of formula (II), or a salt thereof, which comprises reacting a compound of formula (IV)

wherein P¹ represents a protecting group which is a cyclic ether connected to the purine ring nitrogen in the 2-position, or a salt thereof, with a compound of formula (V)

R²NH₂ (V) followed by deprotection and optional salt conversion to yield the compound of formula (II) or a salt thereof. Examples of protecting groups P¹ include 5- and 6- membered ring cyclic ethers eg tetrahydro-2H-furan-2-yl and tetrahydro-2H-pyran-2-yl (THP), especially THP.

Use of the protected compound of formula (IV) is advantageous since it permits the reaction to be performed a lower temperatures than in the case of unprotected compound. For example we have found that in the case that P¹ represents THP and R¹ represents hydrogen, the reaction may be performed at a temperature 50°C lower than that possible without the use of a protecting group. The reaction is also advantageous in that it produces a cleaner product with less propensity to produce dimeric by-products. Compounds of formula (IV) may also be more soluble in organic solvents and more crystalline in solid form than the unprotected derivatives.

The reaction of compounds of formula (IV) and (V) will typically take place in the presence of a high boiling polar organic solvent, especially a high boiling alcohol such as ethylene glycol at elevated temperature eg 100-130 °C, especially 115-120 °C.

Deprotection may be performed by conventional means, for example as described in T W Greene "Protective Groups in Organic Synthesis" (J Wiley and Sons, 1991). For example when P¹ represents THP, this may be removed by treatment with acetyl chloride in a polar organic protic solvent such as methanol. The use of acetyl chloride is sometimes advantageous since it results in production of the hydrochloride salt of the product directly.

Salt conversion may be performed by conventional means. For example, an acid salt may be converted to the free base by treatment with base eg potassium carbonate. The free base may be converted to an acid salt by treatment with the acid.

Compounds of formula (IV) may be prepared by reacting a compound of formula (VI)

with a compound of formula (VII)

R¹NH₂ (VII)

This reaction may be performed by conventional means eg combination of the ingredients in a polar organic solvent eg methanol or isopropanol at elevated temperature eg up to 85 °C.

Compounds of formula (VI) may readily be prepared by protection of 2,6-dichloropurine. For example when P¹ represents THP, the compound of formula (VI) may be prepared by treating 2,6-dichloropurine with 2,3- ihydropyran together with paratoluenesulphonic acid in the presence of a polar organic solvent eg ethyl acetate at elevated temperature eg 50-60 °C.

In a first set of preferred compounds, preferably R¹ represents hydrogen. Preferably R² represents 4-amino-cyclohexyl, (1-methyl-1H-imidazol-4-yl)-CH₂CH₂-, cyclopentyl, pyrrolidin-3-yl or 2-(pyridin-2-ylamino)CH₂CH₂-, or a group of formula arylC_1-5 alkyl- CH(CH₂OH)-, particularly phenylalaninyl (especially L-phenylalaninyl ((1S)-benzyl-2- hydroxyethyl)). In the compound of formula (I) which may be produced, preferably A represents moiety (a) and R³ represents ethyl.

In a second set of preferred compounds, preferably R¹ represents 2,2-diphenylethyl, 2- cyclohexylethyl or pent-3-yl, particularly pent-3-yl. Preferably R² represents represent plperidin-1 -ylethyl, morpholin-1-ylethyl, -(CH₂)₂OH, 2-(1-methyl-1 H-imidazol-4-yl)ethyl, H₂NC(=NH)NHethyl, pyridin-2-ylethyl, (1S)-benzyl-2-hydroxyethyl, pyridin-2-yl- NH(CH₂)₂-, 4-(H₂NSO₂)-phenylethyl, trans-4-aminocyclohexyl, trans-4-(CH₃CONH)- cyclohexyl, pyrrolidin-3-yl, 3,4-dimethoxyphenylethyl, N-benzyl-pyrrolidin-3-yl-, pyrrolidin-1 -ylethyl, aminoethyl or ethyl, more preferably is piperidin-1 -ylethyl or 2-(1- methyl-1H-imidazol-4-yl)ethyl especially 2-(1-methyl-1 H-imidazol-4-yl)ethyl. In the compound of formula (I) which may be produced, preferably A represents moiety (c) and R³ represents ethyl.

The advantages of the process include the fact that it involves more facile chemistry, produced higher yields, generates fewer byproducts and that more favourable reaction conditions (eg lower reaction temperatures) may be employed. Preferably the compound of formula (II) is prepared as a salt, especially a salt of a hydrohalic acid especially the hydrochloride salt. The hydrochloride salt of the compound of formula (II) when R¹ represents hydrogen and R² represents L- phenylalaninyl is new and forms an aspect of the invention. This salt is more readily isolated than the free base and its use improves the efficiency of the reaction with compounds of formula (III) relative to the free base.

We also provide a process for preparing a compound of formula (I) which comprises preparing a compound of formula (II) as just described and reacting it with a compound of formula (III). This reaction will generally be performed in the presence of suitable reagents eg trimethylsilyltrifluoromethanesulphonate (TMSOTf), optionally in the presence of N,O-bistrimethylsilylacetamide (BSA) or 1 ,8-diazabicyclo[5.4.0]undec-7-ene (DBU) at a suitable temperature, eg 60°C. This process will generally be followed by a deprotection step which typically comprises the use of a suitable base, eg. potassium carbonate in the presence of a suitable solvent, eg. methanol at a suitable temperature, eg. room temperature.

A first preferred compound of formula (I) is(2R,3R,4S,5R)-2-[6-Amino-2-{[(1S)-1-benzyl- 2-hydroxyethyl]amino}-9H-purin-9-yl]-5-(2-ethyl-2H-tetrazol-5-yl)-tetrahydrofuran-3,4- diol or a salt thereof (eg the maleate salt).

A second preferred compound of formula (I) is (2S,3S,4R,5R)-2-(3-Ethyl-isoxazol-5-yl)- 5-{6-(1-ethyl-propylamino)-2-[2-(1-methyl-1 H-imidazol-4-yl)-ethylamino]-purin-9-yl}- tetrahydro-furan-3,4-diol or a salt thereof.

Other compounds of interest are:

(2S,3S,4R,5R)-2-(3-Ethyl-isoxazol-5-yl)-5-[6-(1-ethyl-propylamino)-2-(2-piperidin-1-yl- ethylamino)-purin-9-yl]-tetrahydro-furan-3,4-diol, (2R,3R,4S,5S)-2-[6-(1 -Ethyl-propylamino)-2-(2-piperidin-1 -yl-ethylamino)-purin-9-yl]-5-

(3-methyl-isoxazol-5-yl)-tetrahydro-furan-3,4-diol,

N-(4-{6-(2,2-Diphenyl-ethylamino)-9-[5S-(3-ethyl-isoxazol-5-yl)-3R,4S-dihydroxy- tetrahydro-furan-2R-yl]-9H-purin-2-ylamino}-cyclohexyl)-acetamide,

(2R,3R,4S,5S)-2-{6-(2,2-Diphenyl-ethylamino)-2-[2-(pyridin-2-ylamino)-ethylamino]- purin-9-yl}-5-(3-ethyl-isoxazol-5-yl)-tetrahydro-furan-3,4-diol, (2R,3R,4S,5S)-2-{6-(3,3-Dimethyl-butylamino)-2-[2-(1-methyl-1 H-imidazol-4-yl)- ethylamino]-purin-9-yl}-5-(3-ethyl-isoxazol-5-yl)-tetrahydro-furan-3,4-diol, (2R,3R,4S,5S)-2-[6-(1-Ethyl-propylamino)-2-(2-piperidin-1-yl-ethylamino)-purin-9-yl]-5- (3-hyd roxymethy l-isoxazol-5-y I )-tetra hyd ro-f u ran-3 ,4-d iol , (2f?,3f?,4S,5R)-2-{2-{[(1 S)-1 -benzyl-2-hydroxyethyl]amino}-6-[(2,2-diphenylethyl)amino]-

9ry-purin-9-yl}-5-(5-ethyl-4H-1 ,2,4-triazol-3-yl)tetrahydrofuran-3,4-diol, (2R,3R,4S,5R)-2-{6-(2,2-Diphenyl-ethylamino)-2-[2-(1-methyl-1 H-imidazol-4-yl)- ethylamino]-purin-9-yl}-5-(5-ethyl-[1_>2,4]oxadiazol-3-yl)-tetrahydro-furan-3,4-diol, (2R,3R,4S,5S)-2-(6-[(2-cyclohexylethyl)amino]-2-{[2-(1-methyl-1H-imidazol-4- yl)ethyl]amino}-9H-purin-9-yl)-5-(3-ethylisoxazol-5-yl)tetrahydrofuran-3,4-diol or a salt of any one thereof.

Compounds of formula (III) may be prepared following methods described in WO98/28319, WO99/67265, WO99/67264, WO99/41267 and WO99/38877 (Glaxo Group).

Preferably in the compound of formula (III) L represents acetyloxy. Preferably the two hydroxy groups are protected as acetyloxy.

Throughout the specification and the claims which follow, unless the context requires otherwise, the word 'comprise', and variations such as 'comprises' and 'comprising', will be understood to imply the inclusion of a stated integer or step or group of integers but not to the exclusion of any other integer or step or group of integers or steps.

Abbreviations

BSA N,O-bistrimethylsilylacetamide

TMSOTf Trimethylsilyltrifluoromethanesulphonate

THP tetrahydro-2H-pyran-2-yl

DBU 1 ,8-diazabicyclo[5.4.0]undec-7-ene

The invention will be illustrated by reference to the following examples: Intermediates

Intermediate 1 : 2,6-dichloro-9-tetrahydro-2H-pyran-2-yl-9A7-purine 2,6-dichloropurine (1wt) and p-toluenesulphonic acid (0.01 wt, 0.01 eq) were suspended in ethyl acetate (2 vol). Dihydropyran (0.63 vol, 1.3eq) was added to the suspension and the reaction mixture heated to 50 °C. The reaction was held at 50 °C for 15 mins during which crystallisation occurred. N-Hexane (8 vol) was then added to the suspension over 15 mins whilst maintaining the vessel at 50 °C. Once the addition was complete, the slurry was cooled to 0 °C for 1 hr. The product was then filtered, washed with cold (0-5 °C) ethyl acetate/n-hexane (2x3 vols, 1:4) and dried in vacuo at 50°C to give the title compound, (yield 88%th) as a white solid.

Intermediate 2: 2-chloro-9-tetrahydro-2/-/-pyran-2-yl-9H-purin-6-amine Intermediate 1 (1wt) was suspended in 2M ammonia in isopropanol (10 vol, 5.5eq) and the reaction mixture heated to 48 °C. The reaction was seeded at 1 hr and held at 48°C for a further 5 hrs. The slurry was then cooled to 20°C for 1 hr, filtered then washed with isopropanol (2x3 vol). The product was then dried in vacuo at 50°C. to give the title compound, (yield 103.6%th^*) as a white solid. ^{* 1}H nmr shows the presence of 9.5%w/w isopropanol, the corrected yield is 93.6%th.

Intermediate 3: 2-chloro-Λ/-(1 -ethylpropyl)-9-tetrahydro-2H-pyran-2-yl-9H-purin-6-amine

3-Pentylamine (97ml) was added over 5 minutes to a stirred slurry of Intermediate 1 (90.7g, 0.33mol) in IPA (272ml) at 25°C. Once the exotherm had subsided the mixture was heated to 50°C for 1 hour. Water (315 ml) was added over 12mins, the mixture was warmed to 55°C and then allowed to cool to 15°C. The slurry was filtered and the cake was washed with cold isopropanol-water (1:2, 2 x 200ml) and sucked dry. The solid was dried in vacuo at 50°C to give the title compound (93.2g, 0.29mol, 87%th) as white prisms.

Intermediate 4: (2ft,3/?,4fl)-4,5-bis(acetyloxy)-2-(2-ethyl-2H-tetrazol-5- yl)tetrahydrofuran-3-yl acetate

This compound was prepared according to the method of WO99/67265, Intermediate K.

Intermediate 5: (2 ,3ff,4f?,5R)-4-(acetyloxy)-2-(6-amino-2-{[(1 S)-1-benzyl-2- hydroxyethyl]-amino}-9ry-purin-9-yl)-5-(2-ethyl-2r/-tetraazol-5-yl)tetrahydrofuran-3-yl acetate

Example 1 (15.0g, 0.94eq) was suspended in ethyl acetate (102ml) and BSA (17.4ml, 1.7eq) was added. After 30min TMSOTf (18.1ml, 2eq) was added. The mixture was heated to 60°C and a solution of Intermediate 4 (17.05g, 1eq) in ethyl acetate (32ml) was added over 45 minutes. The solution was stirred at 60°C for 1.5 hours, cooled to 15°C and quenched by the slow addition of water (85ml). Ethyl acetate (35ml) was added and the phases were separated. The aqueous phase was re-extracted with ethyl acetate (51ml). The organic extracts were combined and washed with 10% potassium bicarbonate solution (85ml, then 2 x 35ml). The solvent was removed in vacuo to give the title compound as a dry foamed residue.

Intermediate 6: Dimethyl 2,3-O-(1-methylethylidene)-beta-D-ribofuranosiduronate

Concentrated H₂SO₄ (5 mL) was added dropwise over 3 minutes to a solution of methyl

2,3-O-(1-methylethylidene)-β-D-ribofuranosiduronic acid (50 g, 230 mmol) in MeOH (500 mL). The colourless solution was stirred at room temperature for 3 hours then poured into saturated NaHCO_{3 (aq)} (200 mL), resulting in a slight exotherm and the evolution of gas. The resulting white emulsion was then concentrated under reduced pressure to -300 mL, diluted with water (100 mL) and extracted with EtOAc (3 x 400 mL). The combined organic layers were then washed with brine (200 mL), dried (MgSO₄) and solvent removed under reduced pressure to yield the impure title compound as a colourless oil. Purification of the impure title compound was achieved via Biotage chromatography (800 g cartridge), eluting with 1:1 EtOAc/cyclohexane yielded the title compound as a colourless oil (35.0 g, 0.15 mmol, 66%).

Intermediate 7: 5-[(3aS,4S,6R,6aR)-6-methoxy-2,2-dimethyltetrahydrofuro[3,4- d][1 ,3]dioxol-4-yl]-3-ethyl-4,5-dihydroisoxazol-5-ol

"BuLi (161 mL, 1.6 M in hexane) was added dropwise to a 0-5 °C solution of 2-butanone oxime (12.2 mL, 0.129 mmol) in THF (240 mL) over 1 % hours, initially resulting in a white precipitate, which became a cloudy light yellow solution after the addition was complete. An exotherm was observed during the addition ofⁿBuLi, therefore the addition was carried out at a rate which maintained the internal temperature below 5 °C. The exotherm was greater during the addition of the first equivalent of "BuLi.

The reaction mixture was stirred at 0-5 °C for 1 hour then a solution of Intermediate 6 (20 g, 86.1 mmol) in THF (160 mL) was added over 20 minutes, maintaining the internal temperature below 5 °C. The cloudy light yellow solution was then removed from the cooling bath and allowed to warm to room temperature. After 4 hours 1M HCI_<aq) (180 mL) was added to the light brown/orange opaque reaction mixture, resulting in an increase in internal temperature to 32 °C. The yellow mixture was stirred for 5 min, poured into saturated NaHCO_{3 (aq)} (60 mL) and extracted with EtOAc (1 x 200 mL & 2 x

300 mL). The combined organic layers were washed with saturated brine (300 mL) and concentrated under reduced pressure to yield the impure title compound (25.8 g). Biotage chromatography of the impure title compound (800 g cartridge), eluting with 1:1 EtOAc/cyclohexane yielded the impure title compound as an amorphous white solid (12.6 g). This impure title compound was dissolved in EtOAc (40 mL) then cyclohexane

(130 mL) was added and the light yellow solution stirred at room temperature, after 2 minutes fine needle like crystals began to form in the solution. The mixture was stirred for 2 % hours then the solid was isolated via filtration to yield the title compound as a white fine needle like solid (2.24 g). During the filtration more solid crystallised out of the filtrate, this was isolated via filtration to give the title compound as a fine needle like white solid (1.55 g). The filtrate was concentrated under reduced pressure to yield the title compound as a light brown oil which was dissolved in EtOAc (10 mL), followed by the addition of cyclohexane (50 mL). The solution was then cooled to 0-5 °C and stirred at this temperature for 1 hour. The resulting mixture was then filtered to yield the title compound as a fine needle like white solid (1.20 g). Total yield: 4.99 g, 17.0 mmol, 20%.

Intermediate 7: 5-[(3aS,4S,6R,6aR)-6-methoxy-2,2-dimethyltetrahydrofuro[3,4- d][1 ,3]dioxol-4-yl]-3-ethyl-4,5-dihydroisoxazol-5-ol (alternative method)

2-butanone oxime (6ml, 1.8eq) was taken into THF (100ml) and the solution was cooled to ca. -10°C. nBuLi (25ml, 1.8eq, 2.5M in hexanes) was added at such a rate as to maintain the reaction temperature at ca. -10°C. The resulting milky suspension was allowed to warm to 0°C and a further aliquot of nBuLi (25ml, 1.8eq, 2.5M in hexanes) was added at such a rate as to maintain the reaction at 0°C. The resulting bright yellow solution was cooled to -10°C and a solution of Intermediate 8 (10g, 35mmol) in THF (25ml) was added whilst maintaining the reaction at -10°C. The solution was allowed to warm to 0°C and 5M HCI (33ml) was slowly added keeping the reaction at 0°C. The mixture was allowed to warm to room temperature and the phases separated. The organics were washed with water (2 x 30ml) and then concentrated to ca. 30ml at atmospheric pressure. Isooctane (100ml) was added and the mixture was seeded and stirred at 65°C for 1 hour. The suspension was then cooled to 20°C and stirred overnight. The product is filtered, washed with THF:isooctane (2 x 20ml, 1 :4) and dried in vacuo at 50°C to give the title compound as a white solid (6.0g, 60%th).

Intermediate 8: 4-[1-O-methyl-2,3-O-(1-methylethylidene)-β-D- ribofuranuronoyljmorpholine

Pyridine (3.7ml, 0.05eq) was added to suspension of methyl 2,3-O-(1- methylethylidene)-β-D-ribofuranosiduronic acid (200g, 0.92mol) in dichloromethane (1.7L). The mixture was then heated to reflux and oxalyl chloride (80ml, 1.0eq) was added over ca.1 hour. The solution is stirred at reflux for 3 hours before being cooled to 0°C. Morpholine (240ml) was added over ca.1 hour keeping the temperature below 5°C. The mixture was warmed to 20°C and the layers separated. The organics are washed with 2.5M HCI (667ml), 10% KHCO₃ (667ml) and then water (667ml). The organics were concentrated under reduced pressure to yield a orange/yellow oil, which solidified on standing and was dried in vacuo @50°C to give the title compound as a pale yellow solid (234g, 89%th).

Intermediate 9: (2S,3f?,4ff)-4,5-bis(acetyloxy)-2-(3-ethylisoxazol-5-yl)tetrahydrofuran-3- yl acetate

Intermediate 7 (10g, 35mmol) and p-toluene sulphonic acid (0.66g, 0.1 eq) are taken into MeOH (100ml). Solvent was distilled off at atmospheric pressure and replaced with MeOH (4 x 20ml). The remaining solvent was removed in vacuo to give an oil which was dissolved in acetic acid (30ml) and warmed to 35°C. Acetic anhydride (11.5ml, 3.5 eq) was added and the solution was stirred at 35°C for 2 hours. The solution was then heated to 60°C and cone, sulphuric acid (1 drop) was added. The mixture was heated at 60°C for 2h, cooled to RT and water (100ml) was added. The mixture was extracted with ethyl acetate (100ml). The layers are separated and the aqueous phase was re- extracted with ethyl acetate (50ml). The organic extracts were combined, washed with saturated NaHCO₃ (2 x 50ml) and then concentrated in vacuo to give the title compound as a brown oil (11.2g, 84%th). Intermediate 10: (2 ?,3R,4f?,5S)-4-(acetyloxy )-5-(3-ethylisoxazol-5-yl)-2-(6-r(1 - ethylpropyl)amino]-2-{[2-(1-methyl-1H-imidazol-4-yl)ethyl]amino}-9 - -purin-9- yl)tetrahydrofuran-3-yl acetate

Trimethylsilylthfluoromethanesulfonate (1.78g, 2.5eq) was added to a stirred suspension of Example 2 (1.06g, 1eq) and Intermediate 9 (1.2g, 1.1 eq) in ethyl acetate (8.5ml) at 0-

5°C. The mixture was heated at 55-60°C for 5.5 hours, cooled to 0-5°C and saturated sodium bicarbonate solution (9 ml) was added at <10°C. The layers were separated and the organic phase was washed with saturated sodium bicarbonate solution (2ml) and water (2 x 2ml) and evaporated to dryness to give the title compound as a pale orange foam (2.5g, quant.)

Examples

Examples 1 and 2 illustrate preparations of compounds of formula (II). Examples 3 and

4 illustrate preparations of compounds of formula (I).

Example 1 (2S)-2-[(6-amino-9H-purin-2-yl)amino]-3-phenylpropan-1-ol hydrochloride

Intermediate 2 (1wt) and L-phenylalaninol (2.38wt, 4eq) were suspended in ethylene glycol (2 vol) and the reaction mixture placed in a pre-heated oil bath (135°C) and the contents stirred heated to 120 °C for 40 hours. The reaction mixture was then cooled to

20 °C and ethyl acetate (6 vol) was added and then stirred for 1 hr. The suspension was filtered through glass fibre and water (8 vol) was added to the filtrate and the aqueous phase adjusted to pH7 with 5M HCI. The layers were separated and the aqueous phase back extracted with ethyl acetate (6 vol). The organic layers were combined and seeded. A solution of hydrogen chloride in methanol was prepared by adding acetyl chloride (0.31vol, 1.1eq) to methanol (1vol) whilst keeping the temp at 20±5°C. This solution was then added to the extract over ca.30min, maintaining the temperature at 50±5°C. The suspension was cooled to 20±5°C and stirred at this temp for at least 1 h, filtered and washed with ethyl acetate (2x3vol). The product was dried/n vacuo at 50°C to give the title compound (48.3%th) as a white/off-white solid.

Example 2: /^-(l-ethylpropyQ-A^-^l-methyl-IH-imidazol^-y ethyll-gH-purine^.e- diamine A slurry of Intermediate 3 (10g, 0.31 mol) and 1-methylhistamine (9.7g, 2.5eq) in ethylene glycol (15ml) was heated at 109°C for 71 hours and then allowed to cool to 30°C. The mixture was diluted with water (45ml), extracted with 3-pentanone (2 x 50ml) and then the combined organic extracts were extracted with 2M HCI (50ml). The aqueous layer was washed with 3-pentanone (40ml), basified to ca.pH11 with 5M NaOH and extracted with 3-pentanone (230ml) at ca.45°C. The organic layer was washed with water (2 x 40ml) and then ca. 3vols of solvent were removed by distillation. The solution (at 55°C) was seeded and then allowed to cool to 10°C. The mixture was filtered and then the cake was washed with cold 3-pentanone (2 x 30ml) and sucked dry. The solid was dried in vacuo at 55°C to give the title compound (7.9g, 0.24mol, 74%th) as white crystals.

Example 3: (2R,3R,4S,5R)-2-[6-Amino-2-{[(1 S)-1 -benzyl-2-hydroxyethyl]amino}-9H- purin-9-yl]-5-(2-ethyl-2H-tetrazol-5-yl)-tetrahydrofuran-3,4-diol maleate Intermediate 5 (500mg) and potassium carbonate (20mg) were dissolved in methanol

(1ml) and stirred at ambient temperature for 2 hours. A solution of maleic acid (116mg) in methanol (1.2ml) was added and the mixture was stirred at ambient temperature overnight. Methanol (1ml) was then added and the mixture was filtered. The filter cake was washed with methanol (3 x 0.5ml) and dried in vacuo at 30°C to give the title compound (354mg, 72%th from the product of step (a)) as a white solid.

Example 4: (2S,3S,4R,5R)-2-(3-Ethylisoxazol-5-yl)-5-{6-(1 -ethyl-propylamino)-2-[2-(1 - methyl-1H-imidazol-4-yl)ethyl]amino]-9H-purin-9-yl}-tetrahydro-furan-3,4-diol

Crude Intermediate 10 (2.5g) was dissolved in a mixture of methanol (5.3ml) and ethyl acetate (5.3ml) and potassium carbonate (250mg) was added. The mixture was heated at 40-45° for ca.1 hour. The solvent was evaporated off in vacuo and the residue was dissolved in ethyl acetate (20ml) and water (10ml). The layers were separated and the organic phase was washed with 10% brine. The organic phase was treated with charcoal which was removed by filtration through celite. The filtrate was evaporated in vacuo to give the title compound as a pale orange foam (1.6g, 82%th from Example 2).

The application of which this description and claims forms part may be used as a basis for priority in respect of any subsequent application. The claims of such subsequent application may be directed to any feature or combination of features described herein. They may take the form of product, composition, process, or use claims and may include, by way of example and without limitation, the following claims.

The above mentioned patents and patent applications are herein incorporated by reference

Claims

1. A process for preparing a compound of formula (II)

wherein R¹ and R² independently represent a group selected from:

(i) C^cycloalkyl-;

(ii) hydrogen;

(iii) aryl₂CHCH₂-;

(iv) Ca^cycloalkylC^alkyl-; (v) C^alkyl-;

(vi) arylC_1-6alkyl-;

(vii) R R⁵N-C^alkyl-;

(viii) C^alkyl-CH(CH₂OH)-;

(ix) arylC_1-5alkyl-CH(CH₂OH)-; (x) arylC_1-5alkyl-C(CH₂OH)₂-;

(xi) C^cycloalkyl independently substituted by one or more (e.g. 1 , 2 or 3)

(CH₂)_pR^β groups;

(xii) H₂NC(=NH)NHC^alkyl-;

(xiii) a group of formula

or such a group in which one methylene carbon atom adjacent to X, or both if such exist, is substituted by methyl; (xiv) -C^alkyl-OH; (xv) -C^haloalkyl;

(xvi) a group of formula

(xvii) aryl; and

(xviii) -(CH₂)_fSO₂NH_g(C_1-4 alkyl-)_2-g or -(CH₂)_fSO₂NH_g(arylC₁^alkyl-)₂-_g; a and b independently represent an integer 0 to 4 provided that a + b is in the range 3 to

R⁴ and R⁵ independently represent hydrogen, C_1-6alkyl, aryl, arylC^alkyl- or NR⁴R⁵ together may represent pyrrolidinyl, piperidinyl, morpholinyl, azetidinyl, azepinyl, piperazinyl or N-C^alkylpiperazinyl.

R⁶ represents OH, NH₂₎ NHCOCH₃ or halogen;

R⁷ represents hydrogen, C_1-6alkyl, C_1-6alkylaryl or -COC_1-6alkyl ;

X represents NR⁷, O, S, SO or SO₂; aryl represents phenyl optionally substituted by one or more C_1-6alkyl or halogen groups; or a salt thereof, which comprises reacting a compound of formula (IV)

R²NH₂ (V) followed by deprotection and optional salt conversion to yield the compound of formula (II) or a salt thereof.

2. A process according to claim 1 wherein P¹ represents tetrahydro-2H-pyran-2-yl.

3. A process according to claim 1 or claim 2 wherein R¹ represents hydrogen.

4. A process according to any one of claims 1 to 3 wherein R² represents 4-amino- cyclohexyl, (1-methyl-1 H-imidazol-4-yl)-CH₂CH₂-, cyclopentyl, pyrrolidin-3-yl or 2- (pyridin-2-ylamino)CH₂CH₂-, or a group of formula arylC^ alkyl-CH(CH₂OH)-.

5. A process according to claim 4 wherein R² represents L-phenylalaninyl.

6. A compound of formula (II)

wherein R¹ represents hydrogen and R² represents L-phenylalaninyl, in the form of a hydrochloride salt.

7. A process according to any one of the proceding claims further comprising the steps of (a) reacting the compound of formula (II), or a salt thereof, with a compound of formula (III)

wherein L represents a leaving group, or a protected derivative thereof, and A represents a moiety selected from the following groups (a) to (h):

or a protected derivative thereof, and

(b) if necessary deprotecting the product of step (a), to yield a compound of formula (I)

or a salt thereof.

8. A process according to claim 7 wherein A represents moiety (a).

9. A process according to claim 7 or 8 wherein R³ represents ethyl.