Carbocyclic nucleosides and their pharmaceutical use and compositions

A compound of the formula

• wherein R1 and R2 are independently selected from hydrogen, CO2C1-C4 alkyl, C1-C6 alkyl, C2-C6 alkenyl and C2-C6 alkynyl, wherein the alkyl moieties of said alkyl, alkenyl, and alkynyl groups may be linear, branched chain or a combination of linear and branched chain
• where n is 0 to 3,
• where n is 1 to 2, C3-C7 cycloalkyl, a three to twelve membered heterocyclic ring containing up to 3-heteroatoms where the heteroatoms are independently selected from N, O and S and where each heterocyclic ring may be optionally substituted at one or more carbon atoms by from 1 to 3 substituents independently selected from C1-C6 alkoxy, and O—C1-C6 alkyl;
• R3 and R4 are independently selected from hydrogen and C1-C6 alkyl;
• R5 and R6 are independently selected from hydrogen and —CO2C4H9;
• A is selected from a covalent bond, O, S, Se, C1-C6 alkyl, and (CH2)nO, where n is an integer from 0 to 3;
• X is selected from a covalent bond, O, S and Se;
• B is selected from a covalent bond, —CH2, —CH2—CH2—, —CH2—CH2—CH2—, trans-CH═CH—,
• cis-CH═CH—, —C≡C—, —CHR7—CHR8—, cis or trans-CR7═CR8—, wherein R7 and R8 are independently selected from C1-C6 alkyl, C2-C6 alkenyl, C2-C6 alkynyl, and C3-C7 cycloalkyl;
• and
• Y is selected from of OH, SH, OR9 wherein R9 is C1-C6 alkyl, C2-C6 alkenyl and C2-C6 alkynyl, C3-C7 cycloalkyl, and (CH2)nOH, wherein n is an integer from 1 to 6 and NR9R10 wherein R9 and R10 are independently selected from C1-C6 alkyl and C3-C7 cycloalkyl;
• or a pharmaceutically acceptable salt thereof.