Enhanced triple-helix and double-helix formation with oligomers containing modified purines

An oligomer of the formula (5);

• ##STR13## wherein each R.sup.1 is independently H, PO.sub.3.sup.-2, or a blocking group;
• each R.sup.3 is independently selected from the group consisting of H, OH, F, NH.sub.2, OCH.sub.3, OC.sub.2 H.sub.5, OC.sub.3 H.sub.7, SCH.sub.3, SC.sub.2 H.sub.5, SC.sub.3 H.sub.7, OC.sub.3 H.sub.5, and SC.sub.3 H.sub.5 ;
• each X.sup.1 is independently selected from the group consisting of --P(S)(O)--, --P(S)(S)--, --P(O)(O)--, --P(CH.sub.3)(O)-- and --P(CH.sub.3)(S)--;
• n is an integer from 0 to 98;
• and
• B is a base, provided that at least one B is of formula (1) or (2):
• ##STR14## wherein Pr is H or a monovalent or divalent protecting group;
• W is N or CH;
• R.sup.2 is aryl, heteroaryl or 1-alkynylheteroaryl;
• R.sup.8 is OH, SH, a NPr or NH.sub.2 ;
• R.sup.9 is H, OH, SH, NPr, NHPr or NH.sub.2 ;
• R.sup.10 is independently H, OH, CN, halogen (F, Cl, Br, I), alkyl (C1-12), alkenyl (C2-12), alkynyl (C2-12), aryl (C6-9), heteroaryl (C4-9), or both R.sup.10, taken together with the carbon atoms to which they are linked at positions 11 and 12, form
• (a) a 5 or 6 membered carbocyclic ring or,
• (b) a 5 or 6 membered heterocyclic ring comprising 1-3 N, O or S ring atoms, provided that no 2 adjacent ring atoms are O--O, S--S, O--S or S--O,
• and wherein any unsaturated C atom of the carbocyclic or heterocyclic ring is substituted by R.sup.11 and any saturated carbons contain 2 R.sup.11 substituents, wherein;
• R.sup.11 is independently H, alkyl (C1-4), alkenyl (C2-4), alkynyl (C2-4), OR.sup.12, SR.sup.12, or N(R.sup.12).sub.2 or halogen provided that there are no more than four halogens per 5 or 6 member ring;
• and
• R.sup.12 is independently H, or alkyl (C1-4).

A nucleomonomer having the structural formula (3) or (4):

• ##STR16## wherein each R.sup.1 is independently H or a blocking group;
• R.sup.2 is aryl, heteroaryl or 1-alkynylheteroaryl;
• R.sup.3 is selected from the group consisting of H, OH, F, NH.sub.2, OCH.sub.3, OC.sub.2 H.sub.5, OC.sub.3 H.sub.7, SCH.sub.3, SC.sub.2 H.sub.5, SC.sub.3 H.sub.7, OC.sub.3 H.sub.5, and SC.sub.3 H.sub.5 ;
• R.sup.8 is OH, SH, NPr, NHPr or NH.sub.2 ;
• R.sup.9 is H, OH, SH, NPr, NHPr or NH.sub.2 ;
• R.sup.10 is independently H, OH, CN, halogen (F, Cl, Br, I), alkyl (C1-2), alkenyl (C2-12), alkynyl (C2-12), aryl (C6-9), heteroaryl (C4-9), or both R.sup.10, taken together with the carbon atoms to which they are linked at positions 11 and 12, form
• (a) a 5 or 6 membered carbocyclic ring or,
• (b) a 5 or 6 membered heterocyclic ring comprising 1-3 N, O or S ring atoms, provided that no 2 adjacent ring atoms are O--O, S--S, O--S or S--O,
• and wherein any unsaturated C atom of the carbocyclic or heterocyclic ring is substituted by R.sup.11 and any saturated carbons contain 2 R.sup.11 substituents, wherein;
• R.sup.11 is independently H, alkyl (C1-4), alkenyl (C2-4), alkynyl (C2-4), OR.sup.12, SR.sup.12, or N(R.sup.12).sub.2 or halogen provided that there are no more than four halogens per 5 or 6 member ring;
• R.sup.12 is independently H, or alkyl (C1-4);
• W is CH or N;
• and
• Pr is H or a monovalent or divalent protecting group.

An oligomer comprising from 2 to 30 nucleomonomers wherein at least one of said nucleomonomers comprises a base having the formula:

• ##STR18## wherein Pr is H or a monovalent or divalent protecting group;
• R.sup.2 is 1-propynyl;
• R.sup.8 is OH, SH, NPr, NHPr or NH.sub.2 ;
• R.sup.9 is H, OH, SH, NPr, NHPr or NH.sub.2 ;
• and
• W is N or CH and salts thereof.

An oligomer of the formula (5):

• ##STR19## wherein each R.sup.1 is independently H, PO.sub.3.sup.-2, or a blocking group;
• each R.sup.3 is independently selected from the group consisting of H, OH, F, NH.sub.2, OCH.sub.3, OC.sub.2 H.sub.5, OC.sub.3 H.sub.7, SCH.sub.3, SC.sub.2 H.sub.5, SC.sub.3 H.sub.7, OC.sub.3 H.sub.5, and SC.sub.3 H.sub.5 ;
• each X.sup.1 is independently selected from the group consisting of --P(S)(O)--, --P(S)(S)--, --P(O)(O)--, --P(CH.sub.3)(O)-- and --P(CH.sub.3)(S)--;
• n is an integer from 0 to 98;
• and
• B is a base, provided that at least one B is of formula:
• ##STR20## wherein R.sup.2 is 1-propynyl;
• R.sup.8 is OH or SH;
• R.sup.9 is NPr, NHPr or NH.sub.2 ;
• Pr is H or a monovalent or divalent protecting group;
• and
• W is N or CH.