AU724760B2 - Substituted guanine compounds - Google Patents

Description

i

AUSTRALIA

PATENTS ACT 1990 DIVISIONAL APPLICATION NAME OF APPLICANT(S): Medivir AB ADDRESS FOR SERVICE: *DAVIES COLLISON CAVE Patent Attorneys 1 Little Collins Street Melbourne, 3000.

INVENTION TITLE: Substituted guanine compounds The following statement is a full description of this invention, including the best method of performing it known to us: Q:\OPER\DCD2222546.DIV 8/10/99 1 'II

IA

Acyclic Nucleoside Derivatives Technical Field This invention relates to the field of antivirals and in particular to derivatives of acyclic nucleosides useful against herpes and retroviral infections. The invention provides novel intermediates towards the compounds of AU 715062.

Background to the invention AU 715062 discloses diester derivatives ofH2G bearing specific combinations of an amino acid ester and a fatty acid ester that are able to provide significantly improved oral bioavailability relative to the parent compound (H2G). These compounds have formula I 2 where a) R is -C(O)CH(CHCH 3 2 )N1 2 or S. substituted alkyl; or

OR

2 2 15 where a) R, is -C(0)CH(CH(CH3)2)NH2 or -C(0)CH(CH(CH3)CH2CH3)NH2 and R2 is -C(0)C3-C2, saturated or monounsaturated, optionally substituted alkyl; or b) R, is -C(O)C 3

-C

2 1 saturated or monounsaturated, optionally substituted alkyl and R 2 is -C(O)CH(CH(CH 3 2

)NH

2 or

-C(O)CH(CH(CH

3

)CH

2

CH

3

)NH

2 and

R

3 is OH or H; and pharmaceutically acceptable salts thereof The present invention provides novel intermediates useful for preparing the compounds of Formula I and having the Formula II:

R

9

NN

H

2 N N

N

OH

-OR

7

OR

6 wherein R 6 and R 7 are lower alkyl or benzyl or R 6 and R7 taken together are

-CH

2

CH

2 or -CH 2

CH

2

CH

2 or -CH 2

CH

2

CH

2

CH

2 and R, is H or an alcohol protecting group.

The term "lower alkyl" as used herein refers to straight or branched chain alkyl radicals containing from 1 to 7 carbon atoms including, but not limited to, methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, t-butyl, n-pentyl, .i 1-methylbutyl, 2,2-dimethylbutyl, 2-methylpentyl, 2,2-dimethylpropyl, n-hexyl and the like.

Preferably R6 and R 7 are each ethyl.

Alcohol protecting groups include conventional groups such as benzyl.

The compounds of the invention can be used in a process as shown in Scheme C: SCHEME C

OR

7

R

6 0

X

R

4 0 2

CO

2

R

5

R

4 0 2

C

HO

OH

R

7 0 6P lipase cI

NNK

NN

H

2 N N 8 7 HO

OC(O)R

8

R

7 06 O R 6 x 2

OC(O)R

8

R

7 0 7 0OR 6 *9*9 9 9.

9999 H O-7 N N 0 R 6

H

2 N N 12Ri R 7 0

HO

OH

N

N N

N

NI\> N<N\>

H

2 N N N 0 2N 14Ri 13 Ri 0

OH

'INHPI

FORMULA I Ril Referring to Scheme C, malonate 1 (R 4 and R 5 are lower alkyl or benzyl or the like) is alkylated by reaction with from about 0.5 to about 2.0 molar equivalents of acetal 2 (R 6 and R 7 are lower alkyl or benzyl and the like or R 6 and R 7 taken together are -CH 2

CH

2 or

-CH

2

CH

2

CH

2 or -CH 2

CH

2

CH

2

CH

2 -and X 1 is a leaving group (for example, Cl, Br or I, or a sulfonate such as methanesulfonate, triflate, p-toluenesulfonate, benzenesulfonate and the like)) in the presence of from about 0.5 to about 2.0 molar equivalents of a base (for example, potassium t-butoxide or sodium ethoxide or NaH or KH and the like) in an inert solvent (for example, DMF or THF or dioxane or dioxolane or N-methylpyrrolidone and the like) at a temperature of from about -40 0 C to about 190 0 C to provide alkylated malonate 3.

Reduction of 3 with from about 0.5 to about 4.0 molar equivalents of an ester to alcohol S 15 reducing agent (for example, LiBH 4 or Ca(BH,) 2 or NaBH 4 or LiAlH 4 and the like) in an inert solvent (for example, THF or methyl t-butyl ether or t-BuOH and the like) at a temperature of from about -20 0 C to about 100°C provides diol 4. Enzymatic esterification of 4 by reaction with from about 1.0 to about 20.0 molar equivalents of a vinyl ester 5 (R 8 is C 3

-C

2 1 saturated or monounsaturated, optionally substituted alkyl) in the presence of a 0 20 lipase (for example, Lipase PS-30 or Lipase PPL or Lipase CCL and the like) or a phospholipase (for example phospholipase D and the like) provides the desired Sstereoisomer of ester 6. This reaction can be carried out in the absence of solvent or in the S* presence of an inert solvent (for example, methyl t-butyl ether or toluene or hexane and the like). The reaction is carried out at a temperature of from about -20 0 C to about 80 0

C.

The alcohol substituent of 6 is converted to a leaving group (for example, a halogen or a sulfonate) by reaction with a halogenating agent (for example NBS/P(Ph) 3 or NCS/P(Ph) 3 or POC1 3 or NCS/P(Ph) 3 /Nal in acetone and like) in an inert solvent (for example, methylene chloride or toluene or ethylacetate and the like) or by reaction with from about 0.8 molar equivalents to about 2.0 molar equivalents of a sulfonyl halide (for example, benzenesulfonylchloride, toluenesulfonylchloride or methane sulfonylchloride and the 6a like) in the presence of from about 1.0 to about 4.0 molar equivalents of a base (for fl' example, triethylamine or potassium carbonate or pyridine or dimethylaminopyridine or ethyldiisopropylamine and the like) in an inert solvent (for example methylene chloride or toluene or ethylacetate or pyridine or methyl t-butyl ether and the like) at a temperature of from about -25 0 C to about 100 0 C to provide ester 7. (X 2 is a halogen or sulfonate leaving group).

Reaction of 7 with from about 0.9 to about 2.0 molar equivalents of 2-amino-4chloropurine 8 in the presence of from about 1.0 to about 6.0 molar equivalents of a base (for example, potassium carbonate or NaH or KH or NaOH or KOH or lithium diisopropylamide and the like) in an inert solvent (for example, DMF or THF or acetonitrile or N-methylpyrrolidone or ethanol and the like) at a temperature of from about °C to about 140 0 C provides substituted purine 9.

S. Alternatively Mitsunobu coupling (for example P(Ph) 3 /diethyl azidocarboxylate) of 15 alcohol 6 with 2-amino-4-chloropurine 8 provides 9.

Reaction of 9 with from about 2.0 to about 20 molar equivalents of an alcohol R 9 0H (R 9 is an alcohol protecting group such as benzyl and the like) in the presence of from about 1.0 to about 6.0 molar equivalents of a base (for example, potassium t-butoxide or 20 potassium carbonate or NaH or KH or lithium diisopropylamide and the like) in an inert solvent (for example, THF or DMF and the like) at a temperature of from about -25 0 C to about 150°C provides alcohol Removal of the alcohol protecting group R 9 of 10 (for example, by catalytic hydrogenation in an inert solvent such as ethanol or benzyl alcohol or methanol or THF and the like in the presence of an hydrogenation catalyst such as Pd/C or Pd(OH) 2 and the like) provides substitued guanine 11.

Esterification of 11 by reaction with a) from about 0.8 to about 2.0 molar equivalents of RioCOOH and a coupling agent (for example DCC/DMAP) and the like in an inert solvent (for example THF or DMF and the like) or b) from about 0.8 to about 2.0 molar equivalents of an activated derivative of R 10 COOH (for example, the acid chloride or N-hydroxysuccinimide ester or RioC(0)OC(0)Rio and the like) in the presence of from about 0 to about 3.0 molar equivalents of a base (for example, pyridine or triethylamine or ethyldiisopropylamine or DBU or potassium carbonate and the like) in an inert solvent (for example, methylene chloride or THF or pyridine or acetonitrile or DMF and the like) at a temperature of from about -25 0 C to about 100 0 C provides ester 12.

The acetal substituent of 12 is deprotected and the resulting aldehyde is reduced by first reacting 12 with from about 0.1 to about 10.0 molar equivalents of an acid (for example, triflic acid or HC1 or acetic acid or sulfuric acid and the like) in an inert solvent (for example, THF/H 2 0 or methylene chloride/H 2 0 or ethylacetate/H 2 O or ethanol/H 2 0 or and the like) at a temperature of from about -25 oC to about 100 0 C. To the crude reaction mixture is added from about 0.1 to about 10.0 molar equivalents of a base (for example, sodium bicarbonate or potassium carbonate or triethylamine or pyridine or KOH and the like), additional inert solvent (for example, THF and or methylene chloride 15 or ethylacetate or methyl t-butyl ether or isopropoanol and the like) and from about 0.3 to about 5.0 molar equivalents of an aldehyde reducing agent (for example, sodium borohydride or RaNi/H 2 and the like) at a temperature of from about -25 °C to about 100 0 C to provide alcohol 13.

20 Reaction of 13 with from about 0.8 to about 3.0 molar equivalents of N-protected amino acid P 1

NHCH(R

1 1 )COOH or an activated derivative thereof (P 1 is an N-protecting group and R 11 is isopropyl or isobutyl) in an inert solvent (for example, THF or dioxane or dioxolane or DMF or methylene chloride and the like) at a temperature of from about to about 100 0 C provides alcohol 14. N-deprotection of 14 provides the compound of the invention of formula I wherein R 3 is -OH.

Alternatively compound 13 can be reacted with the symmetrical anhydride derived from PINHCH(R,,)COOH (i.e.PNHCH(R, to provide 1 wherein R3 is OH.

The process of Schemes C is characterized by the fact that each of the hydroxyl groups of the acyclic side chain is differentiated by the use of different hydroxy protecting groups or precursor groups. This allows the selective acylation of each of the hydroxy groups with either an amino acid or a fatty acid group.

Detailed Description of the Invention The invention will now be illustrated by way of example only with reference to the following non-limiting Examples.

EXAMPLE 1 Preparation of (R)-9-[4-Hvdroxv-2-(stearoyloxymethyl)butyl guanine a) Preparation of ethyl 4,4-diethoxy-2-ethoxycarbonyl-butyrate .EtO 2

C..CO

2 Et -OEt ,OEt Potassium tert-butoxide (141.8g, 1.11 equiv.) was dissolved in dry DMF (1 L).

Diethyl malonate (266 mL, 1.54 equiv.) was added over 5 minutes.

Bromoacetaldehyde diethylacetal (172 mL, 1.14 mole) was added over 5 minutes.

The mixture was heated to 1200 C (internal temperature), and stirred at 1200 C for hours. The mixture was allowed to cool to room temperature, poured into water and extracted with methyl tert-butyl ether (MTBE, 3 x 600 mL). The organic solution was dried over MgSO 4 filtered, concentrated, and distilled (0.5 mm, 1400 C) to yield the desired diester (244 g, 78%) as a colorless oil.

'H NMR (CDC13) 6 1.19 6H), 1.28 6H), 2.22 (dd, 2H), 3.49 2H), 3.51 (t, 1H), 3.65 2H) 4.20 (qd, 4H), 4.54 1H).

b) Preparation of 4,4-diethoxy-2-(hydroxymethyl)-butanol HO OH K OEt SOEt \1T LiBH4 (purchased solution, 2M in THF, 22.5 mL) and the product of Example 14 step a) (5 g in 15 mL of THF, 18.1 mmol) were combined and warmed to 600 C and stirred at 600 C for 4 hours. The reaction mixture was allowed to cool to room temperature and the reaction vessel was placed in a cool water bath. Then triethanolamine (5.97 mL, 1 equiv.) was added at such a rate that the temperature of the reaction mixture was maintained between 20-25 oC. Brine (17.5 mL) was added at a rate such that gas evolution was controlled and the mixture was stirred for minutes at room temperature. The layers were separated, the organic layer was washed with brine (2 x 15 mL). The combined brine washes were extracted with MTBE (methyl tert-butyl ether, 3 x 20 mL). The combined organic extracts were evaporated and the residue was dissolved in MTBE (50 mL) and washed with brine mL). The brine layer was back-extracted with MTBE (3 x 25 mL). The combined organic extracts were dried over Na 2

SO

4 filtered, and concentrated to yield the desired diol (3.36g, 15.5 mmol, 97%) as a colorless oil.

'H NMR (CDC13) 6 1.22 6H), 1.73 (dd, 2H), 1.92 1H), 2.67 (bs, 2H), 3.52 2H), 3.69 2H), 3.72 4H), 4.62 1H).

S

c) Preparation of (2R)-2-acetoxymethyl-4,4-diethoxy-butanol HO HO OAc EtO OEt Into a 10 ml 1 neck round bottom flask was charged the product of Example 14 step b) (3.84 g, 20 mmol), followed by addition of vinyl acetate (2.6 g, 30 mmol) and finally Lipase PS 30 (69 mg, purchased from (Amano, Lombard, Illinois). The mixture was allowed to stir at ambient temperature for 16 hours. Progress of the reaction was closely monitored by TLC (2/1 hexane EtOAc; stained with Ce 2

(SO

4 3 and charred on hot plate; r.f. of diol is 0.1, monoacetate is 0.3, bis acetate is 0.75). The reaction mixture was diluted with CH 2 C1 2 and filtered through a '30 micron filter. The filter was washed with additional CH 2 C1 2 I The filtrate was then concentrated in vacuo to afford the desired product.

"M IT d) Preparation of (2S)-2-acetoxymethyl-4,4-diethoxybutyl toluenesulfonate TsO" OAc EtO OEt Into a 100 mL 1-neck round bottom flask, equipped with a magnetic stir bar and septum under N2 was charged the crude product of Example 14 step c) (4.62 g, 19 mmol), dry CH 2 Cl 2 (20 mL) and Et 3 N (5.62 mL, 40 mmol). To this solution was added tosyl chloride (4.76 g, 25 mmol). The resulting mixture was stirred at ambient temperature for 4 hours. Charged H 2 0 (0.27 g, 15 mmol) and stirred vigorously for 4 hours. The reaction mixture was diluted with 80 mL EtOAc and mL H20 and the aqueous layer was separated. To the organic layer was added ml of a 5 aq. solution of KH2PO 4 After mixing and separation of the layers, the aqueous layer was removed. The organic layer was washed with 50 mL of saturated 15 NaHCO 3 solution, dried over Na 2

SO

4 filtered and concentrated in vacuo to a constant weight of 7.40 g of the desired product.

'H NMR (CDCl 3 8 1.17 6H); 1.62 2H); 1.94 3H); 2.19 1H); 2.45 (s, 0* 3H); 3.42 2H); 3.6 2H); 4.03 4H); 4.51 1H); 7.36 2H); 7.79 (d, 2H).

e) Preparation of OAc EtO-( OEt Into a 50 mL 1 neck round bottom flask was charged the product of Example 14 step d) (3.88 g, 10 mmol), anhydrous DMF (20 mL), 2-amino-4-chloro-purine S(2.125 g, 12.5 mmol) and K 2

C

3 (4.83 The resulting suspension was stirred at

S^Y

EtO- 1 L) °C under a N 2 blanket for 20 hours. The mixture was concentrated to remove most of the DMF on a rotary evaporator. The residue was diluted with EtOAc mL) and H20 (50 mL). The reaction mixture was transferred to a separatory funnel, shaken and the aqueous layer was separated. The aqueous layer was extracted with EtOAc (25 mL). The organic layers were combined and washed with 5 KH 2

PO

4 mL). The organic layer was separated and washed with H 2 0 (75 mL), brine mL), dried over Na 2

SO

4 filtered and concentrated in vacuo to afford 3.95 g of crude product. The crude product was slurried with 40 mL of methyl-t-butyl ether. This mixture was stirred overnight at 4°C and the mixture was filtered. The filtrate was concentrated to afford 3.35 g of the product as an oil (containing 2.6 g of the desired product based upon HPLC analysis).

300 MHz 'H NMR (CDC1 3 8 1.19 6H); 1.69 1.79 1H); 2.03 3H); 2.52 1H); 3.48 2H); 3.62 2H); 4.04 2H); 4.16 2H); 4.61 (t,lH); 15 5.12 (bs, 2H); 7.81 1H).

f) Preparation of Bn o oL 1 N HN N N

OH

SEtO- OEt (Bn=benzyl) .i 20 Into a 500 mL 1 neck round bottom flask was charged benzyl alcohol (136 mL), cooled to 0 followed by portionwise addition of KO-t-Bu (36 g, 321 mmol).

The temperature was allowed to warm to 40 0 C, and the mixture was stirred minutes. To this mixture was added at 0 oC the crude product of Example 14 step e) (24.7 g, 64.2 mmol) dissolved in 25 mL anhydrous THF and benzyl alcohol mL). The temperature was allowed to slowly warm to 8 OC over 2 hours. The reaction mixture was poured into 500 mL ice and was extracted with 500 mL MTBE. The organic layer was washed with 250 mL of brine, dried over Na 2

SO

4 i- filtered and concentrated in vacuo to afford 193 g of a benzyl alcohol solution of the desired product. HPLC analysis indicated that the solution contained 25.96 g of the desired product.

300 MHz 'H NMR (CDC1 3 5 1.22 1.55 2.18 1H); 3.15 1H); 3.40 1H); 3.51 2H); 3.70 2H); 4.25 2H); 4.63 4.90 (bs, 2H); 5.25 1H); 5.58 2H); 7.35 3H); 7.51 2H); 7.72 1H).

MS (M 416 (CI).

g) Preparation of

H

N

H2N N N

OH

EtO-- OEt Into a 100 mL 1 neck round bottom flask was charged the crude product of Example 14 step f) (9.65 g of the benzyl alcohol solution, containing 1.30 g, 3.13 mmol of the product of Example 14, step f) dissolved in absolute EtOH (20 mL). To this was Sadded 0.45 g of 10 Pd/C slurried in 5 mL absolute EtOH. The reaction flask was evacuated and charged with H 2 three times with a balloon of H 2 The reaction flask o was pressurized with 1 atm. H 2 and the reaction mixture was stirred overnight. The reaction mixture was filtered through a pad of diatomaceous earth to remove Pd/ C.

The volatiles were removed in vacuo. The residue was mixed with 25 mL of isopropyl acetate and then concentrated in vacuo. The residue was diluted with 20 EtOAc (10 mL), seeded with the desired product, heated to reflux and then CH 3

CN

(2 mL) and MTBE (35 ml) were added. The mixture was stirred for 30 minutes.

The precipitate was filtered and dried to a constant weight of 600 mg of the desired product.

300 MHz 'H NMR (d6-DMSO) 6 1.16 1.45 1H); 1.61 1H); 2.16 1H); 3.45 2H); 3.40 1H); 3.62 2H); 4.02 (m,2 4.53 1H); 4.85 1H); 6.55 (bs, 1H); 7.75 1H). MS (M 416 (CI).

h) Preparation of

OH

o K- O 1

(CH

2

)CH

3 EtO- OEt Into a 25 mL 1 neck round bottom flask was charged the product of Example 14 step g) (0.650 g, 2.0 mmol), pyridine (4 mL) and CH 2 Cl 2 (2 mL), DMAP The mixture was cooled to -5 OC and stearoyl chloride (790 mg, 2.6 mmol) dissolved in CH 2

CI

2 (0.5 mL) was added over 5 minutes. The resulting mixture was stirred 16 hours at -5 Absolute EtOH (0.138 g, 3.0 mmol) was added and the mixture was stirred an additional 1 hour. The reaction mixture was concentrated in vacuo. Toluene (30 mL) was added to the residue and then the mixture was 10 concentrated in vacuo. Again, toluene (30 mL) was added to the residue and then the mixture was concentrated in vacuo. To the residue was added 1 KH 2

PO

4 mL) and this mixture was extracted with CH 2 Cl 2 (60 mL). The organic layer was separated and was dried over Na 2

SO

4 filtered and concentrated in vacuo to a constant weight of 1.65 g. The crude product was chromatographed on 40 g of 15 SiO 2 eluting with 95/5 CH 2 C12 EtOH, affording 367 mg of the desired product.

S

300 MHz 'H NMR (CDC13) 6 0.89 3H); 1.26 30 1.65 (m,3 2.32 (m, 1H); 3.45 1 3.60 2H); 4.08 2H); 4.60 1 6.0 (bs, 2H); 7.53 1 H).

i) Preparation of

OH

NA

N

H

2 NN N

O

(CH

2 1 6

CH

HO-/

Into a 25 mL 1 neck round bottom flask was charged the product of Example 14, step h) (0.234 g, 0.394 mmol) dissolved in THF (1.7 mL). To this solution was 5 added triflic acid (0.108 g) in H 2 0 180 mg. The mixture was stirred overnight at to

^VT^

13 room temperature. To the reaction mixture was added saturated NaHCO 3 solution mL), THF (5mL), CH 2 C1 2 (2 mL) and NaBH 4 (0.10 This mixture was stirred for 30 minutes. To the reaction mixture was added a 5 solution of KH2PO 4 mL). This mixture was extracted with 2 x 15 ml of CH 2 C1. The organic layers were combined and dried over Na 2 SO4, filtered and concentrated in vacuo to a constant weight of 207 mg. This material was recrystallized from EtOAc (8 mL) and CH 3 CN (0.5 mL) affording 173 mg of the desired product.

300 MHz 'H NMR (d6-DMSO) 6 0.82 3H); 1.19 30H); 1.41 4H); 2.19 2H); 2.32 1H); 3.40 2H); 3.9 4H); 4.49 1H); 6.4 (bs, 2H); 7.61 1.5H); 9.55 4 e e The product of step i) is esterified with an appropriately N-protected amino acid as 15 described in AU 715062 (WO 97/30051) to result in the end product of formula I.

.o

G.

9 4 *9 9 Ik j* .ft 'T C>-

Claims (4)

1. A compound of the Formula II R9 N N NII H 2 N N OH -OR 7 OR 6 0*000 0 0 S S 00 0 @060 *00 0 S S. .00.S a s 0 @000 S 0 S @0 S 0 wherein R 6 and R 7 are lower alkyl or benzyl or R 6 and R 7 taken together are -CH 2 CH 2 or -CH 2 CH 2 CH 2 or -CH 2 CH 2 CH 2 CH 2 and R 9 is H or an alcohol protecting group.

2. A compound according to claim 1, wherein R, is H.

3. A compound according to claim 1, wherein the alcohol protecting group is benzyl.

4. A compound according to claim 1, 2 or 3 wherein R 6 and R 7 are each ethyl. A compound according to claim 1, substantially as hereinbefore described with reference to the Examples. DATED this 21st day of July, 2000 MEDIVIR AB by its Patent Attorneys DAVIES COLLISON CAVE J*X \^rr Y