Nucleotide analogues as precursor molecules for antivirals

1. A purine phosphonate compound of formula (I) as follows:

or pharmaceutically acceptable salt thereof; wherein:

B is a base selected from the group consisting of adenine, xanthine, hypoxanthine, guanine, 8-bromoguanine, 8-chloroguanine, 8-aminoguanine, 8-hydrazinoguanine, 8-hydroxyguanine, 8-methylguanine, 8-thioguanine, 2-aminopurine, and 2,6-diaminopurine;

R 1 is selected from the group consisting of a hydrogen atom, and a methyl, ethyl, hydroxymethyl, hydroxyethyl and C 1-6 haloalkyl group;

R 3 is selected from the group consisting of a hydroxyl group or alkaline metal salt thereof, —OR 3A , a prodrug moiety, a linear or branched C 1-8 alkyl, C 2-8 alkenyl, C 2-8 alkynyl, C 1-8 heteroalkyl, C 2-8 heteroalkenyl or C 2-8 heteroalkenyl group, an amino acid residue, and an amine group R″HN, wherein R 3A represents C 1-8 alkyl, C 2-8 alkenyl, C 2-8 alkynyl, C 1-8 heteroalkyl, C 2-8 heteroalkenyl, C 2-8 heteroalkynyl, —P(═O)(OH) 2 or alkaline metal salt thereof, or —P(═O)(OH)OP(═O)(OH) 2 or alkaline metal salt thereof, and R″ is a linear or branched C 1-8 alkyl, C 2-8 alkenyl, C 2-8 alkynyl, C 1-8 heteroalkyl, C 2-8 heteroalkenyl, C 2-8 heteroalkynyl, or C 6-10 aryl group; and

(a) X is selected from the group consisting of a selenium atom and a sulphur atom, and R 2 is selected from the group consisting of a fluorine atom, a hydroxyl group or alkaline metal salt thereof, —OR 2A , a prodrug moiety, BH 3 − , a linear or branched C 1-8 alkyl, C 2-8 alkenyl, C 2-8 alkynyl, C 1-8 heteroalkyl, C 2-8 heteroalkenyl or C 2-8 heteroalkynyl group, an amino acid residue, and an amine group R′HN wherein R 2A represents C 1-8 alkyl, C 2-8 alkenyl, C 2-8 alkenyl, C 1-8 heteroalkyl, C 2-8 heteroalkenyl, C 2-8 heteroalkenyl, —P(═O)(OH) 2 or alkaline metal salt thereof, —P(═O)(OH)OP(═O)(OH) 2 , or alkaline metal salt thereof, and R′ is a linear or branched C 1-8 heteroalkyl, C 2-8 heteroalkenyl, C 2-8 heteroalkynyl, or C 6-10 aryl; or

(b) X represents an oxygen atom, and R 2 is selected from the group consisting of a fluorine atom and a BH 3 − group.

2. A compound as claimed in claim 1 , wherein B is a base selected from the group consisting of adenine and guanine.

3. A compound as claimed in claim 1 wherein R 1 is selected from the group consisting of a hydrogen atom, a methyl group, a hydroxymethyl and a fluoromethyl group.

4. A compound as claimed in claim 1 , wherein the compound has the following structure:

wherein R 4A and R 5A are independently a hydrogen atom or an alkaline metal cation.

5. A compound as claimed in claim 1 , wherein the compound has the following structure:

wherein R 4A , R 4B , and R 5B are independently a hydrogen atom or an alkaline metal cation.

6. A compound as claimed in claim 1 , wherein the compound has the following structure:

wherein R 4A , R 4B , R 4C , and R 5C are independently a hydrogen atom or an alkaline metal cation.

7. A compound as claimed in claim 1 , wherein the compound has one of the following structures:

wherein

R 4A is an enzyme-labile group selected from the group consisting of —CH 2 OC(═O)CH(CH 3 ) 2 , —CH 2 OC(═O)C(CH 3 ) 3 , —CH 2 CH 2 SC(═O)C(CH 3 ) 3 and —CH 2 CH 2 SC(═O) CH 3 ;

R 4 is selected from the group consisting of an amino acid residue selected from the group consisting of alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine and valine, and an amine group —NHR′, wherein R′ is a linear or branched C 1-8 alkyl, C 1-8 heteroalkyl or C 6-10 aryl; and

R 5A is a hydrogen atom or an alkaline metal cation.

8. A compound as claimed in claim 1 , wherein the compound has one of the following structures:

wherein

R 4 is selected from the group consisting of —OR 4A , an amino acid residue selected from the group consisting of alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, and valine, and an amine group —NHR′;

R 5 is selected from the group consisting of —OR 5A , an amino acid residue selected from the group consisting of alanine, argnine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, and valine and an amine group —NHR″;

wherein R 4A and R 5A are independently an enzyme-labile group selected from the group consisting of —CH 2 OC(═O)OCH(CH 3 ) 2 , —CH 2 OC(═O)C(CH 3 ) 3 , —CH 2 CH 2 SC(═O)C(CH 3 ) 3 and —CH 2 CH 2 SC(═O)CH 3 ; and

R′ and R″ are independently a linear or branched C 1-8 alkyl, C 1-8 heteroalkyl or C 6-10 aryl group.

9. A compound as claimed in claim 1 , wherein the compound has the following structure:

wherein

R 4A is a hydrogen atom, an alkaline metal cation or C 1-8 alkyl;

R i is a hydrogen atom or an amino acid side chain; and

R ii is a hydrogen atom, an alkaline metal cation or C 1-8 alkyl.

10. A compound as claimed in any one of claims 4 to 9 , wherein B is adenine.

11. A compound as claimed in any one of claims 4 to 9 , wherein R 1 is hydrogen.

12. A compound as claimed in any one of claims 4 to 9 , wherein R 1 is methyl or ethyl and the carbon atom bearing R 1 has an R-configuration.

13. A compound as claimed in any one of claims 4 to 9 , wherein R 1 is hydroxymethyl or hydroxyethyl and the carbon atom bearing R 1 has an S-configuration.

14. A compound as claimed in any one of claims 4 to 9 , wherein R 1 is —CH 2 F and the carbon atom bearing R 1 has an R- or S-configuration.

15. A compound as claimed in claim having one of the following structures:

16. A pharmaceutical composition comprising a carrier and a purine phosphonate compound as claimed in claim 1 .

17. A medicament comprising a carrier and a purine phosphonate compound as claimed in claim 1 .