Process for the preparation of fosamprenavir calcium

1. A process for the preparation of fosamprenavir calcium, wherein the process comprises

a) treating (3S)-tetrahydrofuran-3-yl[(2S,3R)-4-{(2-methylpropyl)[(4-nitrophenyl)sulfonyl]amino}-1-phenyl-3-(phosphonooxy)butan-2-yl]carbamate of Formula II

or a starting salt of (3S)-tetrahydrofuran-3-yl[(2S,3R)-4-{(2-methylpropyl)[(4-nitrophenyl)sulfonyl]amino}-1-phenyl-3-(phosphonooxy)butan-2-yl]carbamate of Formula II, with a source of calcium ions, to obtain a calcium salt of the compound (3S)-tetrahydrofuran-3-yl[(2S,3R)-4-{(2-methylpropyl)[(4-nitrophenyl)sulfonyl]amino}-1-phenyl-3-(phosphonooxy)butan-2-yl]carbamate of Formula II, wherein the starting salt is selected from lithium, sodium, potassium, magnesium, and ammonium;

b) isolating the solid calcium salt of the compound (3S)-tetrahydrofuran-3-y1[(2S,3R)-4-{(2-methylpropyl)[(4-nitrophenyl)sulfonyl]amino}-1-phenyl-3-(phosphonooxy)butan-2-yl]carbamate of Formula II from the reaction mixture thereof;

c) reducing the nitro group of the calcium salt of the compound (3S)-tetrahydrofuran-3-yl[(2S,3R)-4-{(2-methylpropyl)[(4-nitrophenyl)sulfonyl]amino}-1-phenyl-3-(phosphonooxy)butan-2-yl]carbamate of Formula II to an amino group; and

d) isolating fosamprenavir calcium from the reaction mixture thereof.

2. The process according to claim 1 , wherein the reduction is carried out using a reducing agent which does not use hydrogen gas or which uses hydrogen gas and a hydrogenation catalyst.

3. The process according to claim 1 , wherein the reduction is carried out in the presence of a solvent.

4. The process according to claim 3 , wherein the solvent is C 1-3 alkanol, ethyl acetate, water, acetone, denaturated or industrial methylated spirit or a mixture thereof.

5. The process according to claim 1 , wherein step a) is carried out in the presence of a solvent system comprising an organic solvent, water or a mixture thereof.

6. The process according to claim 5 , wherein the organic solvent is a water miscible organic solvent.

7. The process according to claim 6 , wherein the water miscible organic solvent is a C 1-3 alkanol.

8. The process according to claim 1 , wherein the source of calcium ions is calcium acetate, calcium chloride or calcium hydroxide.

9. The process according to claim 1 wherein the starting salt used in step a) is a sodium or potassium salt.