WO1995009855A1

WO1995009855A1 - Amino acids esters of penciclovir and brl 44385

Info

Publication number: WO1995009855A1
Application number: PCT/EP1994/003219
Authority: WO
Inventors: Michael Raymond Harnden; Stuart Bailey
Original assignee: Smithkline Beecham P.L.C.
Priority date: 1993-10-01
Filing date: 1994-09-26
Publication date: 1995-04-13
Also published as: GB9320316D0

Abstract

Amino acid esters of penciclovir and BRL 44385.

Description

AMINO ACID ESTERS OF PENCICLOVIR AND BRL 44385

The present invention relates to novel compounds which are of potential use as antiviral agents, to a process for their preparation and to their use as pharmaceuticals.

EP-A-141927 and EP-A-182024 (Beecham Group p. I.e.), disclose 9-(4-hydroxy-3-hydroxymethylbut-l-yl)guanine, penciclovir, and its oral form, 2-amino-9-(4-acetoxy-3-acetoxymethylbut-l-yl)purine, famciclovir. EP-A-242482 (Beecham Group p. I.e.), discloses 9-(3-hydroxyprop-l-oxy)guanine, BRL 44385. EP-A-308065 (The Wellcome Foundation Limited) discloses certain amino acid esters of the purine nucleoside, acyclovir including the compound, 2-[2-amino- l,6-dihydro-6-oxo-9H-purin-9-yl)methoxy]ethyl L-valinate, valaciclovir, as having improved oral bioavailabilty as compared with the alanine and glycine esters of acyclovir, disclosed in EP-A-99493. It has now been discovered that mono- and di- amino acid esters of penciclovir, in particular the mono- and di- valinate derivatives and the amino acid esters of BRL 44385, in particular, the valinate, are potentially useful prodrugs therefor, by the oral route of administration or possibly by another route such as the topical route of administration. Oral administration of the valinate esters to mice (0.2 mmol/kg) led to a substantial increase in oral bioavailability relative to the parent compounds.

Accordingly, the present invention comprises amino acid esters of penciclovir and BRL 44385, hereinafter referred to as compounds of formula (I). Suitable examples of amino acids are as described in EP-A-99493 and especially in EP-A-308065.

Examples include penciclovir di-O- valinate, BRL 44385 O- valinate, and penciclovir O- valinate.

Examples of pharmaceutically acceptable salts of the compound of formula (I) are acid addition salts formed with a pharmaceutically acceptable acid such as hydrochloric acid, orthophosphoric acid and sulphuric acid.

It will be appreciated that some of the compounds of formula (I), often have an asymmetric centre, and therefore are capable of existing in more than one stereoisomeric form (D and L forms of the amino acid). The invention extends to each of these forms individually and to mixtures thereof, including racemates. The isomers may be separated conventionally by chromatographic methods or using a resolving agent. Alternatively, the individual isomers may be prepared by asymmetric synthesis using chiral intermediates.

The compounds of formula (I) including their pharmaceutically acceptable salts may form solvates such as hydrates and these are included wherever a compound of formula (I) or a salt thereof is herein referred to.

The first two compounds are prepared by acylation of the parent acyclonucleoside with Cbz-L-valine in N,N-dimethylformamide in the presence of dicyclohexylcarbodiimide and dimethylamino pyridine, followed by deprotection of the purified product by hydrogenolysis in the presence of hydrochloric acid (Beauchamp et al, Antiviral Chem. Chemother. 3, 157-164). The last compound was prepared similarly from the N,O-bis(methoxytrityl) derivative of penciclovir (Harnden et al, J. Med. Chem. 30, 1636 -1642), the trityl protecting groups being removed by acidic treatment prior to hydrogenolysis.

Pharmaceutically acceptable salts may be prepared in conventional manner, for example, in the case of acid addition salts, by reaction with the appropriate organic or inorganic acid.

The compounds of the invention are of potential use in the treatment of infections caused by viruses, in particular DNA viruses and Hepatitis B virus.

Examples of DNA viruses include herpesviruses such as herpes simplex types 1 and 2, varicella-zoster virus, Epstein-Barr virus and cytomegalovirus.

Compounds of the invention may be formulated for use in a pharmaceutical composition. Accordingly, in a further aspect of the invention, there is provided a pharmaceutical composition which comprises a compound of formula (I) or pharmaceutically acceptable salt thereof together with a pharmaceutically acceptable carrier or excipient.

A composition which may be administered by the oral route to humans may be compounded in the form of a syrup, tablet or capsule. When the composition is in the form of a tablet, any pharmaceutical carrier suitable for formulating such solid compositions may be used, for example magnesium stearate, starch, lactose, glucose, rice, flour and chalk. The composition may also be in the form of an ingestible capsule, for example of gelatin, to contain the compound, or in the form of a syrup, a solution or a suspension. Suitable liquid pharmaceutical carriers include ethyl alcohol, glycerine, saline and water to which flavouring or colouring agents may be added to form syrups. The compounds may also be presented with a sterile liquid carrier for injection.

The composition may possibly also be formulated for topical application to the skin or eyes. For topical application to the skin, the composition may be in the form of a cream, lotion or ointment. These formulations may be conventional formulations well known in the art, for example, as described in standard books of pharmaceutics and cosmetics, such as Harry's Cosmeticology published by Leonard Hill Books and the British Pharmacopaeia.

The composition for application to the eyes may be a conventional eye-drop composition well known in the art, or an ointment composition.

Preferably, the composition of this invention is in unit dosage form or in some other form that may be administered in a single dose. A suitable dosage unit might contain from 50 mg to 1 g of active ingredient, for example 100 to 500 mg. Such doses may be administered 1 to 4 times a day or more usually 2 or 3 times a day. The effective dose of compound will in general be in the range of from 1.0 to 20 mg/kg of body weight per day or more usually 2.0 to 10 mg/kg per day. No unacceptable toxicological effects are indicated at the above described dosage levels.

The invention also provides a method of treating viral infections in a human or non-human animal, which comprises administering to the animal an effective, non-toxic amount of a compound of formula (I) or a pharmaceutically acceptable salt thereof.

The invention also provides a compound of formula (I) or a pharmaceutically acceptable salt thereof for use as an active therapeutic substance, in particular for the treatment of viral infections.

The compounds of the invention are also believed to exhibit a synergistic antiherpes virus effect in conjunction with interferons; and combination products comprising these two components for sequential or concomitant administration, by the same or different routes, are therefore within the ambit of the present invention. The following examples illustrate the invention.

Example 1

Penciclovir di-0-valinate a) To a stirred suspension of penciclovir (0.95 g, 3.75 mmol) in N,N- dimethylformamide at 60°C were added N-benzyloxycarbonyl-L-valine (2.87 g, 11.42 mmol), N,N-dimethylaminopyridine (0.13 g, 1.05 mmol) and dicyclohexylcarbodiimide (2.71 g, 13.1 mmol). The mixture was allowed to cool to room temperature and after two days identical amounts of the reagents were again added and the mixture stirred for a further 2 days. The solution was filtered, the solvent evaporated under reduced pressure, and the residue purified by column chromatography on silica gel eluting with chloroform to afford penciclovir bis-O- (N-benzyloxycarbonyl-L-valinate) (2.76g, 98%); δ (d6-DMSO) 0.8 (12H, 4 x

CH₃), 1.8 (2H, 2'-H), 2.0 (3H, 2 x CHMe₂ and 3'-H), 4.0 (8H, l'-H, 3'-(CH₂)2, and 2 x CHCO), 5.0 (4H, 2 x PhCH₂), 6.4 (2H, D₂O exchangeable, NH₂), 7.3 (10H, 2 x C6H₅), 7.7 (3H, 8-H and 2 x NH), and 10.6 (1H, D₂O exchangeable, 1-

H). b) A mixture of penciclovir bw-0-(N-benzyloxycarbonyl-L-valinate) (1.35 g, 1.88 mmol), 10% palladium on charcoal (0.46 g), 2M hydrochloric acid (3.3 ml) and methanol (41.5 ml) was stirred under an atmosphere of hydrogen for 5 hours. The solution was filtered and the solvent evaporated under reduced pressure to afford penciclovir di-O-valinate as its bis hydrochloride salt (0.99 g, 100%). A portion of this material (0.25 g) was dissolved in water, neutralised with concentrated aqueous ammonia and freeze dried. The residue was taken up in water, passed down a column of Cig-reverse phase silica gel, and the product fractions evaporated under reduced pressure (0.12 g); δ (d6-DMSO) 1.0 (12H, 4 x CH₃), 2.15 (5H, 2'-H, 3'-H and 2 x CHMe₂), 3.8 (2H, 2 x CHCO), 4.5 (6H, I'¬ ll and 3'-(CH₂)₂ ), 7.4 (2H, D₂O exchangeable, NH₂), 8.5 (6H, D₂O exchangeable, 2 x NH₃), 9.4 (1H, 8-H) and 11.9 (1H, D₂O exchangeable, 1-H).

Example 2 Penciclovir 0-valinate a) To a stirred suspension of N2,0-bis(monomethoxytrityl)penciclovir (M. R. Harnden, R.L. Jarvest, T.H. Bacon, and M.R. Boyd, J. Med. Chem., 1987, 30, 1636; 0.74 g, 1.94 mmol) in N,N-dimethylformamide at 60°C were added N- benzyloxycarbonyl-L-valine (0.74 g, 2.95 mmol), Ν,Ν-dimethylaminopyridine (0.03 g, 0.27 mmol) and dicyclohexylcarbodiimide (0.70g, 3.4 mmol). The mixture was allowed to cool to room temperature and after two days identical amounts of the reagents were again added and the mixture stirred for a further 2 days. The solution was filtered,^' the solvent evaporated under reduced pressure and the residue purified by column chromatography on silica gel eluting with chloroform-methanol (15: 1) and again with ethyl acetate to afford N-^,0- bis(monomethoxytrityl)penciclovir 0-(N-benzyloxycarbonyl-L-valinate) (1.15 g, 59%); δ (d₆-DMSO) 0.78 (6H, C(CH₃)₂), 1.55 (2H, 2'-H), 1.7 (1H, 3'-H), 1.94 (1H, CHMe₂), 2.8 (2H, CH₂O), 3.35 (2H, l'-H), 3.65 (3H, CH₃O), 3.74 (3H, CH₃O), 3.85 (3H, CH₂OCO and CHCO), 5.0 (2H, PhCH₂), 7.25 (36H, 5 x C6H5, 2 x C₆H₄, 8-H, and NH₂), and 10.51 (1H, D₂O exchangeable, 1-H). b) A solution of N2,0-bis(monomethoxytrityl)penciclovir 0-(N- benzyloxycarbonyl-L-valinate) (1.15 g, 1.14 mmol) in 80% acetic acid (12 ml) was heated at 70 °C for 3 hours, the solvent evaporated under reduced pressure, and the residue purified by column chromatography on silica gel eluting with chloroform- methanol (10:1) to afford penciclovir 0-(N-benzyloxycarbonyl-L-valinate) (0.35 g, 62%); δ (d₆-DMSO) 0.8 (6H, C(CH₃)₂), 1.75 (3H, 2'-H and 3'-H), 2.0 (1H, CHMe₂), 2.8 (2H, CH₂O), 3.4 (2H, CH₂OH), 4.0 (5H, CH₂OCO, l'-H, and CHCO), 4.65 (1H, D₂O exchangeable, OH), 5.0 (2H, PhCH₂), 6.4 (2H, D₂O exchangeable, ΝH₂), 7.3 (5H, C₆H₅), 7.7 (2H, 8-H and NH), and 10.5 (1H, D₂O exchangeable, 1-H). c) A mixture of penciclovir 0-(N-beπzyloxycarbonyl-L-valinate) (0.35 g, 0.71 mmol), 10% palladium on charcoal (0.06 g), 2M hydrochloric acid (0.42 ml) and methanol (5.3 ml) was stirred under an atmosphere of hydrogen for 4 hours. The solution was filtered, washed through with hot methanol, and the solvent evaporated under reduced pressure. The residue was suspended in ethanol and the solid collected by centrifugation to afford penciclovir O- valinate as its hydrochloride salt (0.08 g, 30%).; δ (d₆-DMSO) 0.94 (6H, C(CH₃)₂), 1.84 (3H, 2'-H, and 3'-H), 2.15 (1H, CHMe₂), 3.45 (2H, CH₂OH), 3.86 (1H, CHCO), 4.15 (4H, l'-H and CH₂OCO), 6.94 (2H, D₂O exchangeable, NH₂), and 8.53 (4H, 8-H and NH₃).

Example 3 9-(3-Hydroxypropoxy)guanine 0-valinate

9-(3-Hydroxypropoxy)guanine O- valinate was prepared in a similar manner to penciclovir di-O-valinate and was obtained as its hydrochloride salt by recrystallisation from methanol-ethanol; δ (dg-DMSO) 0.97 (6H, C(CH₃) ), 2.05 (2H, CCH₂C), 2.15 (1H, CHMe₂), 3.89 (2H, CHCO), 4.38 (4H, 2 x CH₂O), 6.80 (2H, D₂O exchangeable, NH₂), 8.15 (1H, 8-H), 8.54 (3H, D₂O exchangeable, NH₃), and 11.9 (1H, D O exchangeable, 1-H)

Claims

1. Amino acid esters of penciclovir and BRL -44385.

2. Valinate esters of penciclovir and BRL 44385.

3. Penciclovir di-O- valinate .

4. BRL 44385 O-valinate.

5. Penciclovir O- valinate.

6. A compound as described herein with reference to any one of the Examples.

7. A pharmaceutical composition comprising a compound according to any one of claims 1 to 6, and a pharmaceutically acceptable carrier.

8. A compound according to any one of claims 1 to 6 for use as an active therapeutic substance.

9. A compound according to any one of claims 1 to 6 for use in treating viral diseases.

10. Use of a compound according to any one of claims 1 to 6 in the manufacture of a medicament for use in the treatment of viral diseases.

11. A method of treatment of viral diseases in mammals, which comprises the administration to mammal in need of such treatment, an effective amount of a compound according to any one of claims 1 to 6.

12. A compound, use or method according to any one of claims 9, 10 or 11 wherein the viral infection is a herpesvirus infection.