A compound of formula (I), wherein: R2 and R3 are independently selected from H, R, OH, OR, =O, =CH-R, =CH2, CH2-CO2R, CH2-CO2H, CH<2>-SO2R, O-SO2R, CO2R, COR and CN, and there is optionally a
double bond between C1 and C2 or C2 and C3; R6, R7, R8 and R9 are independently selected from H, R, OH, OR, halo, nitro, amino, Me3Sn; R11 is either H or R; Q is S, O or NH; L is a linking group, or a
single bond; O is a
solid support; or where one or more of R2, R3, R6, R7 and R8 are independently: H-(T)n-X-Y-A- where: X is CO, NH, S or O; T is a combinatorial unit; Y is a
divalent group such that HY=R; A is O, S, NH, or a
single bond and n is a positive integer