Synthesis of estetrol via estrone derived steroids
A process is provided for the making of estetrol starting from a 3-A-oxy-estra-1,3,5(10),15-tetraen-17-one, wherein A is an C 1 -C 5 alkyl group, preferably a methyl group, or a C 7 -C 12 benzylic group, preferably a benzyl group. This process is particularly suitable to industry.
1. A process for the preparation of estra-1,3,5(10)-trien-3,15α,16α,17β-tetraol, comprising:
(a) converting estrone into 3-A-oxy-estra-1,3,5(10),15-tetraen-17-one, wherein A is a protecting group;
(b) reducing the 17-keto group of 3-A-oxy-estra-1,3,5(10),15-tetraen-17-one to 3-A-oxy-estra-1,3,5(10),15-tetraen-17β-ol;
(c) protecting the 17-OH group of 3-A-oxy-estra-1,3,5(10),15-tetraen-17β-ol to 3-A-oxy-17-Cp-oxy-estra-1,3,5(10),15-tetraene, wherein Cp is a protecting group;
(d) oxidizing the carbon-carbon double bond of ring D of 3-A-oxy-17-Cp-oxy-estra-1,3,5(10), 15-tetraene to protected estetrol; and
(e) removing the protecting groups;
wherein the protecting group A is selected from an C 1 -C 5 alkyl group or a C 7 -C 12 benzylic group and the protecting group Cp is selected from the group consisting of C 1 -C 5 carboxylates.
2. The process according to claim 1 , wherein the protecting group A is a C 7 -C 12 benzylic group.
3. The process according to claim 1 , wherein the the protecting group Cp is acetyl.
4. The process according to claim 1 , wherein the reduction of the carbonyl group is carried out using a reducing agent selected from the group of metal hydride compounds.
5. The process according to claim 4 , wherein the metal hydride compound is selected from the group consisting of LiAlH 4 , NaBH 4 , NaBH(OAc) 3 , ZnBH 4 , and NaBH 4 /CeCl 3 .
6. The process according to claim 5 , wherein the metal hydride compound is NaBH 4 in combination with CeCl 3 hydrate.
7. The process according to claim 1 , wherein the oxidation of the carbon-carbon double bond in ring D is carried out with an oxidizing agent comprising osmium tetroxide.
8. The process according to claim 7 , wherein the oxidizing agent is osmium tetroxide immobilized on poly-4-vinylpyridine.
9. The process according to claim 1 , wherein the oxidation of the carbon-carbon double bond in ring D is carried out with a catalytic amount of osmium tetroxide immobilized on poly-4-vinylpyridine.
10. The process according to claim 9 , wherein the osmium tetroxide immobilized on poly-4-vinylpyridine is used in combination with a co-oxidant.
11. The process according to claim 10 , wherein the co-oxidant is selected from the group consisting of trimethylamine-N-oxide, N-methyl morpholine-N-oxide or hydrogen peroxide.
12. The process according to claim 11 , wherein the co-oxidant is trimethylamine-N-oxide.
13. The process according to claim 1 , wherein the protective C 7 -C 12 benzylic group is removed by catalytic hydrogenation conditions.
14. The process according to claim 13 , wherein the catalytic hydrogenation conditions comprise a hydrogenation reaction using Pd on activated carbon under a hydrogen atmosphere.
15. The process according to claim 1 , wherein the protective C 1 -C 5 alkyl group is removed by using BBr 3 .
16. The process according to claim 1 , wherein protecting group A is removed first to form 17-OCp protected estetrol and subsequently protecting group Cp is removed to form estetrol.
17. The process according to claim 2 , wherein the C 7 -C 12 benzylic group is a benzyl group.