Synthesis of protected 3′-amino nucleoside monomers
Orthogonally protected 3′-amino nucleoside monomers and efficient methods for their synthesis are described. The methods employ selective protection of the 3′-amino group in the presence of the unprotected nucleoside base.
1. A method of preparing an adenosine, guanosine or cytidine monomer having a protected nucleoside base and a protected 3′-amino group, wherein said base and said 3′-amino group are orthogonally protected, the method comprising:
(a) providing a 3′-amino-3′-deoxy adenosine, cytidine, or guanosine monomer in which the 5′-hydroxyl group, nucleoside base, and 3′-amino group are unprotected;
(b) selectively reacting said 3′-amino group with a first protecting group consisting of a triarylmethyl group or fluoroenylmethoxycarbonyl group;
(c) reacting said 5′-hydroxyl group of the compound from step (b) with a second protecting group consisting of acyl, base-labile trialkyl silyl ether, or fluoride-labile silyl ether; and
(d) reacting said nucleoside base of the compound from step (c) with a third protecting group consisting of an acyl group or a formamidinyl group;
wherein said first protecting group can be removed from said 3′-amino group, under conditions which do not deprotect said nucleoside base, and said second protecting group can be removed from said 5′-hydroxyl group under conditions which do not deprotect said nucleoside base or said 3′-amino group.
2. The method of claim 1 , further comprising the step of (e) removing said second protecting group from said 5′-hydroxyl group, under conditions which do not deprotect said nucleoside base or said 3′-amino group.
3. The method of claim 1 , wherein said first protecting group is acid labile.
4. The method of claim 3 , wherein said first protecting group is triarylmethyl.
5. The method of claim 4 , wherein said first protecting group is triphenylmethyl (trityl).
6. The method of claim 1 , wherein said monomer is an adenosine or guanosine monomer.
7. The method of claim 1 wherein said second and third protecting groups are both acyl groups.
8. The method of claim 7 , wherein said second and third protecting groups are both benzoyl groups.
9. The method of claim 1 , wherein said second protecting group is a base labile trialkyl silyl ether, and said third protecting group is an acyl group.
10. The method of claim 1 , wherein said second protecting group is a fluoride labile silyl ether, and said third protecting group is an acyl group.
11. The method of claim 1 , wherein said monomer comprises a 2′group selected from hydrogen, hydroxy, lower alkoxy, lower alkyl, and fluoro.
12. The method of claim 11 , wherein said monomer is a 2′,3′-dideoxy monomer, such that said 2′group is hydrogen.
13. A method of preparing an adenosine, guanosine or cytidine monomer having a free 5′-hydroxyl group, a protected nucleoside base, and a protected 3′-amino group, wherein said base and said 3′-amino group are orthogonally protected, the method comprising:
(a) providing a 3′-amino-3′-deoxy adenosine, cytidine, or guanosine monomer in which the 5′-hydroxyl group, nucleoside base, and 3′-amino group are unprotected;
(b) selectively reacting said 3′-amino group with a first protecting group consisting of a triarylmethyl group or fluoroenylmethoxycarbonyl group; and
(c) selectively reacting said nucleoside base of the compound from step (b) with a further protecting group consisting of a formamidinyl group or an acyl group;
wherein said first protecting group can be removed from said 3′-amino group under conditions which do not deprotect said nucleoside base.
14. The method of claim 13 , wherein said monomer is a cytidine monomer and said further protecting group is an acyl group.
15. The method of claim 14 , wherein said reacting with a further protecting group comprises reaction with an acyl anhydride.
16. The method of claim 13 , wherein said monomer is an adenosine or guanosine monomer, and said further protecting group is a dialkylformamidinyl, di(cycloalkyl)formamidinyl, or di(aralkyl)-formamidinyl group.
17. The method of claim 13 , wherein said first protecting group is triarylmethyl.
18. The method of claim 17 , wherein said first protecting group is triphenylmethyl (trityl).
19. The method of claim 1 , wherein said third protecting group is a dialkyl-, di(cycloalkyl)-, or di(aralkyl)- formamidinyl group.
20. The method of claim 19 , wherein alkyl is C 1 -C 4 alkyl and cycloalkyl is C 5 -C 6 cycloalkyl.
21. The method of claim 19 , wherein said third protecting group is a dimethylformamidinyl group or a dibenzylformamidinyl group.
22. The method of claim 21 , wherein said third protecting group is a dimethylformamidinyl group.
23. The method of claim 19 , wherein said monomer is an adenosine or a guanosine monomer.