Symmetric, monofunctionalised polymethine dyes labelling reagents

A symmetric cyanine of the formula:

• wherein:
• X is C(CH3)2;
• W represents non-metal atoms required to form a benzo-condensed or a naphto-condensed ring;
• R1 is selected from the group consisting of(CH2)nCH3, (CH2)nSO3− and (CH2)nSO3H, wherein n is an integer selected from 0 to 6 when R1 is (CH2)nCH3, and n is an integer selected from 3 to 6 when R1 is (CH2)nSO331 or (CH2)nSO3H;
• R2 and R3 are independently selected from the group consisting of H, a sulphonic moiety and a sulphonate moiety;
• Q is selected from the group consisting of:
• wherein q is 0 or 1 and D is selected from the group consisting of:
• wherein
• G is a nucleophile moiety selected from the group consisting of (CH2)mNH2, (CH2)mSH, (CH2)mY(CH2)pOH, (CH2)mY(CH2)pNH2 and (CH2)mY(CH2)pSH, wherein Y is selected from the group consisting of —NH—, —CONH—, —O— and —S—, m is an integer selected from 0 to 6 and p is an integer selected from 1 to 6;
• or wherein G is a moiety capable of reacting with N, O or S nucleophiles, and is selected from the group consisting of (CH2)mCOOH, (CH2)mglycidyl, (CH2)mmaleimide, (CH2)mCO—NHS, (CH2)mCO-imidazole, (CH2)mSO2CH═CH2, (CH2)mCONHNH2, (CH2)mCHO, (CH2)mY(CH2)pCOOH, (CH2)mY(CH2)pglycidyl, (CH2)mY(CH2)pmaleimide, (CH2)mY(CH2)pCO—NHS, (CH2)mY(CH2)pCO-imidazole, CH2(CH2)mO—PAM, (CH2)mY(CH2)pSO2CH═CH2, (CH2)mY(CH2)pCONHNH2, (CH2)mY(CH2)pCHO and (CH2)mY(CH2)pO—PAM, wherein Y, m and p have the meanings indicated above.