G-quadruplex binding assays and compounds therefor

A G-quadruplex analog polynucleotide comprising the structure:

• (5′-(L1)q(L2)r(L3)s(L4)t(L5)u(L6)v)x
• wherein:
• each L1, L2, L3, L4, L5 and L6 is independently selected from the group consisting of a nucleotide, a nucleotide analog, and a nucleotide comprising a 6-methyl-isoxanthopterin nucleobase;
• q, r, s, t, u and v are each independently 0, 1 or 2, provided that the sum of q+r+s+t+u+v is at least 3;
• and
• x is 1 to 8;
• provided that:
• said sequence 5′-(L1)q(L2)r(L3)s(L4)t(L5)u(L6)v is an analog of a telomeric repeat sequence;
• said polynucleotide contains at least one nucleotide comprising a 6-methyl-isoxanthopterin nucleobase;
• said G-quadruplex analog polynucleotide forms or is capable of forming a G-quadruplex structure;
• each 6-methyl-isoxanthopterin nucleobase is located within said G-quadruplex structure;
• the G1 position of said G-quadruplex analog comprises a 6-methyl-isoxanthopterin nucleobase;
• and
• the 6-methyl-isoxanthopterin at said G1 position shows an increase or enhancement in fluorescence upon G-quadruplex formation.